Pituitary Adenoma
A benign neoplasm arising from adenohypophyseal cells that may cause hormonal hypersecretion or hyposecretion and mass effects such as visual field deficits due to optic chiasm compression.
Pituitary Adenoma
A pituitary adenoma is a benign neoplasm arising from the epithelial cells of the anterior pituitary gland (adenohypophysis). The name breaks down as: "pituitary" = relating to the pituitary gland (Latin pituita = phlegm/mucus, a historical misnomer), "adeno-" = gland (Greek aden), "-oma" = tumour/swelling (Greek). So literally, a "glandular tumour of the pituitary."
These tumours are overwhelmingly benign — they do not metastasise (if they do, they are reclassified as pituitary carcinoma, which is exceedingly rare). However, "benign" does not mean "harmless." Even a benign tumour in the sella turcica — a tiny bony fossa at the skull base — can wreak havoc through:
- Hormonal hypersecretion — the tumour autonomously produces one or more anterior pituitary hormones
- Hormonal hyposecretion (hypopituitarism) — the growing mass compresses and destroys surrounding normal pituitary tissue
- Mass effect — compression of adjacent structures (optic chiasm, cavernous sinus, hypothalamus, third ventricle)
- Acute catastrophe (pituitary apoplexy) — haemorrhagic infarction of the adenoma [1][2][3]
Key concept: A pituitary adenoma can present with too much hormone, too little hormone, visual loss, headache, or be found completely by accident. Your job is to figure out which combination is at play.
2. Epidemiology
- Pituitary adenomas account for 10–15% of all primary intracranial neoplasms [1][3][4]
- Found in 12–22% of autopsy series — meaning many are clinically silent "incidentalomas" [2][3]
- 20–25% at autopsy per neurosurgical lecture data [4]
- Up to 10% of normal middle-aged individuals have pituitary abnormalities on MRI — hence MRI pituitary should NOT be performed without clinical indication [2]
- Most common cause of sellar mass from the 3rd decade onwards [5]
- Clinically significant pituitary adenomas have an estimated prevalence of ~80–100 per 100,000 population
| Adenoma Type | Peak Age | Sex Predominance |
|---|---|---|
| Prolactinoma | 20–40 years | F > > M |
| GH-secreting (acromegaly) | 30–50 years | M ≈ F |
| ACTH-secreting (Cushing's disease) | 25–45 years | F > > M (1:3–8) |
| Non-functioning | 40–60 years | M ≈ F (slight M predominance) |
| TSH-secreting | Any age | M ≈ F |
Descending order of frequency [2][5]:
- Prolactinoma (most common overall, ~40–45% of all functioning adenomas)
- Non-functioning adenoma (25–35%)
- Somatotroph (GH-secreting) adenoma (~12%)
- Corticotroph (ACTH-secreting) adenoma (~5–10%)
- Thyrotroph (TSH-secreting) adenoma (~1%, very rare)
- Gonadotroph adenoma — technically the most common non-functioning macroadenoma (70–90% of "non-functioning" adenomas are gonadotroph in origin), but classified as non-functioning because they don't produce a clinical hormonal syndrome [5]
3. Anatomy and Function of the Pituitary Gland
Understanding pituitary adenoma requires a solid grasp of the anatomy. Let's build this from first principles.
The pituitary gland sits in the sella turcica (Latin: "Turkish saddle" — because the bony depression in the sphenoid bone looks like a saddle). It is normally < 0.8 cm deep [2].
Key anatomical relations — these explain every symptom of pituitary adenomas:
| Direction | Structure | Clinical Consequence of Compression |
|---|---|---|
| Superior | Diaphragma sellae (dural fold), then optic chiasm | Bitemporal hemianopia (classic), visual loss |
| Lateral | Cavernous sinus (containing CN III, IV, V1, V2, VI, and the internal carotid artery) | Diplopia, CN palsies (uncommon unless invasive) |
| Inferior | Sphenoid sinus (an air-filled paranasal sinus) | Surgical corridor for transsphenoidal approach; rarely CSF rhinorrhoea if tumour erodes floor |
| Anterosuperior | Optic chiasm specifically | Visual field defects |
| Posterosuperior | Third ventricle | Hydrocephalus (only with very large/giant adenomas) |
3.2 Structure of the Pituitary
The pituitary has two functionally distinct lobes:
- Derived embryologically from Rathke's pouch (an ectodermal outpouching of the oral cavity/stomodeum)
- Connected to the hypothalamus via the hypothalamic-hypophyseal portal system — a specialised venous portal system carrying releasing and inhibiting hormones from the median eminence of the hypothalamus to the anterior pituitary
- Produces six major hormones from five cell types:
| Cell Type | Hormone(s) | Hypothalamic Regulator | Target |
|---|---|---|---|
| Lactotroph | Prolactin (PRL) | Dopamine (inhibitory) — this is KEY | Breast (milk production) |
| Somatotroph | Growth Hormone (GH) | GHRH (+), Somatostatin (−) | Liver (IGF-1), bones, soft tissue |
| Corticotroph | ACTH | CRH (+) | Adrenal cortex (cortisol) |
| Thyrotroph | TSH | TRH (+), T3/T4 (−) | Thyroid gland |
| Gonadotroph | FSH, LH | GnRH (+) | Gonads |
Why Prolactin is Special
Prolactin is the only anterior pituitary hormone under tonic inhibition by the hypothalamus (via dopamine). All other hormones are under tonic stimulation. This means:
- If you cut the pituitary stalk → all hormones ↓ EXCEPT prolactin, which ↑ (because you've removed the dopamine "brake")
- This is the basis of the "stalk effect" — any mass compressing the stalk can cause mild hyperprolactinaemia (usually < 100 ng/mL, and almost always < 200 ng/mL)
- Derived from a downward extension of the hypothalamus (neural tissue)
- Stores and releases oxytocin and ADH (vasopressin), which are actually synthesised in the hypothalamic supraoptic and paraventricular nuclei and transported down axons through the stalk
- Normally appears bright on T1 MRI due to ADH neurosecretory granules [2]
- Loss of this "bright spot" suggests posterior pituitary dysfunction (e.g., diabetes insipidus)
Connects the hypothalamus to the pituitary. Contains:
- Portal vessels carrying hypothalamic releasing/inhibiting hormones to the anterior lobe
- Nerve fibres from hypothalamus to the posterior lobe
Compression or transection of the stalk (by tumour, surgery, or trauma) leads to:
- Hypopituitarism (loss of stimulatory signals to anterior pituitary)
- Hyperprolactinaemia (loss of inhibitory dopamine → "stalk effect")
- Diabetes insipidus (loss of ADH transport to posterior pituitary)
A paired venous sinus lateral to the sella. Contains:
- Cranial nerve III (oculomotor) — most medial, hence most vulnerable to lateral tumour extension
- Cranial nerve IV (trochlear)
- Cranial nerve V1 (ophthalmic division of trigeminal)
- Cranial nerve V2 (maxillary division of trigeminal)
- Cranial nerve VI (abducens) — runs within the sinus itself, close to the ICA
- Internal carotid artery (ICA)
Invasion of the cavernous sinus by an aggressive/invasive adenoma can produce CN palsies and is a critical consideration for surgical planning (cavernous sinus invasion = incomplete surgical resection likely) [2][5].
4. Etiology
4.1 Pathogenesis — Why Do Pituitary Adenomas Form?
The pathogenesis is predominantly monoclonal — most pituitary adenomas arise from a single mutated cell that gains a growth advantage.
| Mechanism | Details |
|---|---|
| Somatic mutations | Most pituitary adenomas are sporadic, driven by acquired somatic mutations |
| GNAS1 mutation (Gsα activating mutation) | Found in ~40% of GH-secreting adenomas → constitutive activation of the Gs-cAMP-PKA pathway → unregulated GH secretion and cell proliferation |
| USP8 mutation | Found in ~40–60% of corticotroph adenomas (Cushing's disease), particularly in women → enhances EGFR signalling → ACTH hypersecretion |
| Loss of tumour suppressors | Loss of p27 (CDKN1B), Rb, p16; epigenetic silencing of GADD45γ, MEG3 |
| Oncogene activation | PTTG (pituitary tumour-transforming gene) overexpression — promotes chromosomal instability |
About 5% of pituitary adenomas occur in the context of inherited syndromes:
| Syndrome | Gene | Pituitary Tumour Type | Other Features |
|---|---|---|---|
| MEN1 | MEN1 (encoding menin) at 11q13 | Pituitary adenoma (15–42%), most commonly prolactinoma; 85% are macroadenomas | Parathyroid hyperplasia (100%), pancreatic NETs (gastrinoma, insulinoma) |
| MEN4 | CDKN1B (p27) | Pituitary adenomas (similar to MEN1) | Parathyroid adenomas, other NETs |
| Carney complex | PRKAR1A | GH-secreting or PRL-secreting adenomas | Cardiac myxomas, skin pigmentation, adrenal nodular hyperplasia |
| McCune-Albright syndrome | GNAS1 (postzygotic mosaic) | GH-secreting adenoma | Polyostotic fibrous dysplasia, café-au-lait spots, precocious puberty |
| Familial isolated pituitary adenoma (FIPA) | AIP (aryl hydrocarbon receptor-interacting protein) in ~20% | GH-secreting or prolactinoma, often in young patients | No other endocrine tumours |
MEN1 and Pituitary Adenomas
- No clearly established modifiable risk factors for sporadic pituitary adenomas
- High-dose ionising radiation is the only proven environmental risk factor for brain tumours including meningiomas and gliomas; its role in pituitary adenomas is less clear but prior cranial irradiation may increase risk [7]
- Familial syndromes as above (MEN1, Carney complex, FIPA, McCune-Albright)
- Longstanding end-organ failure can cause pituitary hyperplasia (which may be mistaken for adenoma):
- Longstanding primary hypothyroidism → thyrotroph hyperplasia (due to loss of T4 negative feedback → chronic TSH stimulation → hyperplasia)
- Longstanding primary hypogonadism → gonadotroph hyperplasia
- Pregnancy → lactotroph hyperplasia (physiological)
- Ectopic GHRH secretion → somatotroph hyperplasia [5]
These hyperplastic conditions are not true adenomas but can mimic them on imaging and must be distinguished clinically.
- The distribution of pituitary adenoma types in Hong Kong follows international patterns
- Prolactinoma remains the most common functioning adenoma
- Non-functioning adenomas are frequently encountered in neurosurgical and endocrine clinics
- MEN1 screening is performed in families with identified mutations; genetic counselling services are available at major centres (Queen Mary Hospital, Prince of Wales Hospital)
- Incidental pituitary lesions are increasingly detected due to widespread MRI use in Hong Kong's public and private healthcare systems
- Traditional Chinese medicine and herbal remedies should be considered as potential causes of iatrogenic Cushing's syndrome (steroids hidden in herbal preparations) — this is particularly relevant in the Hong Kong context when evaluating ACTH-dependent vs independent causes [2]
Before assuming a sellar mass is a pituitary adenoma, consider the full differential [5]:
5.1 Comprehensive DDx of Sellar/Parasellar Masses
| Category | Examples | Distinguishing Features |
|---|---|---|
| Pituitary adenoma | Functioning or non-functioning | Most common sellar mass in adults |
| Pituitary hyperplasia | Lactotroph (pregnancy), thyrotroph (1° hypothyroidism), gonadotroph (1° hypogonadism), somatotroph (ectopic GHRH) | Diffuse enlargement, no focal lesion; correct the underlying cause and the gland shrinks |
| Craniopharyngioma | Benign, from Rathke's pouch remnants | 50% calcified (visible on XR/CT), often cystic, most common sellar mass in children, bimodal age (childhood + 50–60y) [3] |
| Meningioma | Suprasellar/parasellar | Dural tail on MRI, calcified, enhances homogeneously |
| Rathke's cleft cyst | Remnant of Rathke's pouch | Cystic, non-enhancing, between anterior and posterior lobes |
| Arachnoid cyst | CSF-filled | Follows CSF signal on MRI |
| Dermoid/epidermoid cyst | Developmental | Fat signal (dermoid) or restricted diffusion (epidermoid) |
| Pituicytoma | Rare, from pituicytes of posterior pituitary/stalk | Solid, enhancing |
| Metastases | CA lung (M), CA breast (F) most common | Usually in posterior pituitary (richer blood supply), may present with DI |
| Germ cell tumours | Germinoma, teratoma | Typically suprasellar in young patients; check β-hCG, AFP |
| Chordoma | From notochord remnants | Clival, destructive, bone erosion |
| CNS lymphoma | Primary or secondary | Homogeneous enhancement, consider in immunosuppressed |
| Pituitary carcinoma | Extremely rare | Defined by CSF or systemic metastasis |
| Lymphocytic hypophysitis | Autoimmune | Peripartum women, diffuse stalk/gland enlargement, DI common |
| Pituitary abscess | Infection | Fever, ring enhancement, may follow surgery |
| Carotid-cavernous fistula | Vascular | Pulsatile proptosis, chemosis, bruit |
| Aneurysm | ICA aneurysm can mimic sellar mass | "Cerebral aneurysm mimicking a sellar tumour" — must exclude before surgery! [4] |
Do NOT Miss This
A cerebral aneurysm can mimic a sellar tumour on imaging [4]. Always consider vascular pathology before proceeding to transsphenoidal surgery — operating on an aneurysm thinking it's a pituitary adenoma would be catastrophic. MRI with MR angiography or CT angiography can help distinguish.
6. Classification of Pituitary Adenomas
| Category | Size | Notes |
|---|---|---|
| Microadenoma | < 1 cm | More likely to be discovered incidentally or via hormonal symptoms; less likely to cause mass effect |
| Macroadenoma | > 1 cm (most commonly 1–4 cm) | More likely to cause visual field defects, hypopituitarism, headache |
| Giant adenoma | > 4 cm | Significant mass effect, may obstruct third ventricle causing hydrocephalus [4] |
| Category | Proportion | Explanation |
|---|---|---|
| Functioning adenomas | ~70–80% of surgically resected adenomas (but includes prolactinomas managed medically) | Autonomously secrete one or more hormones → clinical syndrome |
| Non-functioning adenomas | ~25–35% clinically; but ~50% of macroadenomas | Do not produce a clinically recognisable hormonal syndrome; 70–90% are gonadotroph adenomas that secrete inefficiently [5] |
The 2017/2022 WHO classification shifted from purely functional to transcription factor–based classification, recognising that each pituitary cell lineage is driven by specific transcription factors:
| Lineage | Transcription Factor | Cell Type | Hormone(s) | Clinical Syndrome |
|---|---|---|---|---|
| PIT-1 lineage | PIT-1 | Somatotroph | GH | Acromegaly/gigantism |
| PIT-1 | Lactotroph | Prolactin | Hyperprolactinaemia (galactorrhoea, hypogonadism) | |
| PIT-1 | Thyrotroph | TSH | Secondary hyperthyroidism | |
| PIT-1 | Mixed somatotroph-lactotroph | GH + PRL | Acromegaly + hyperprolactinaemia | |
| T-PIT lineage | T-PIT | Corticotroph | ACTH | Cushing's disease |
| SF-1 lineage | SF-1 | Gonadotroph | FSH, LH, α-subunit | Usually non-functioning |
| Null cell | None identified | Null cell adenoma | None | Non-functioning |
| Plurihormonal | Variable | Mixed | Multiple | Variable |
WHO 2022 Terminology Update
The WHO 2022 classification now uses the term "pituitary neuroendocrine tumour (PitNET)" instead of "pituitary adenoma" to better reflect the neoplastic nature of these lesions and bring nomenclature in line with other neuroendocrine tumours. However, "pituitary adenoma" remains widely used clinically and in exams. Know both terms.
- Enclosed adenomas: confined within the sella
- Invasive adenomas: extend into cavernous sinus (Knosp grade), sphenoid sinus, or suprasellar region
- Knosp classification (grades 0–4): based on relationship to the intracavernous ICA on coronal MRI
- Grade 0–2: medial to ICA tangent lines → potentially resectable
- Grade 3–4: lateral to or encasing ICA → cavernous sinus invasion → unlikely complete surgical resection
Certain subtypes are recognised as "aggressive" or "high-risk" and are more likely to recur or resist treatment:
- Sparsely granulated somatotroph adenoma (responds poorly to somatostatin analogues)
- Silent corticotroph adenoma (often invasive)
- Crooke's cell adenoma (aggressive corticotroph variant)
- Male prolactinoma (often larger and more invasive than in women)
- Plurihormonal PIT-1 positive adenoma (previously "silent subtype 3")
7. Pathophysiology
7.1 Hormonal Hypersecretion — How Each Adenoma Type Produces Disease
Mechanism of hyperprolactinaemia:
- Autonomous PRL secretion by tumour cells, independent of dopamine inhibition
- PRL acts on the breast → galactorrhoea
- PRL inhibits GnRH pulsatility at the hypothalamus → hypogonadotropic hypogonadism → amenorrhoea (F), erectile dysfunction/infertility (M), decreased libido, osteoporosis
Why do women present earlier?
- Menstrual irregularity is noticed quickly → diagnosed at the microadenoma stage
- Men often ignore decreased libido → present late with macroadenomas and visual field defects
Stalk effect vs. true prolactinoma — a critical distinction:
| Feature | Stalk Effect | True Prolactinoma |
|---|---|---|
| Mechanism | Mass compresses stalk → blocks dopamine delivery → mild ↑PRL | Tumour autonomously produces PRL |
| PRL level | Usually < 100–200 ng/mL | Usually > 200 ng/mL (often > 10× ULN) |
| Response to dopamine agonist | PRL normalises but tumour doesn't shrink | PRL normalises AND tumour shrinks |
The Hook Effect
In giant prolactinomas with extremely high PRL levels (> 10,000 ng/mL), the immunoassay can paradoxically report a falsely normal or mildly elevated PRL due to antibody saturation. This is the "hook effect." Always request serial dilutions of the PRL sample if you have a large macroadenoma with only mildly elevated PRL — it could be a giant prolactinoma masquerading as a non-functioning adenoma.
Mechanism:
- Autonomous GH secretion → GH acts on liver to produce IGF-1 (insulin-like growth factor 1)
- IGF-1 mediates most of GH's anabolic effects: soft tissue growth, bone growth, metabolic effects
- In adults (closed epiphyses) → acromegaly ("acro-" = extremities, "-megaly" = enlargement)
- In children (open epiphyses) → gigantism (linear bone growth at growth plates)
Why is acromegaly insidious?
- Changes occur over years → patient and family don't notice gradual coarsening of features
- Average delay to diagnosis is 7–10 years
~30% co-secrete prolactin because somatotrophs and lactotrophs share the PIT-1 transcription factor lineage [2]
Mechanism:
- Autonomous ACTH secretion → stimulates adrenal cortex → excess cortisol
- Cushing's disease specifically refers to Cushing's syndrome caused by a pituitary ACTH-secreting adenoma
- These are usually microadenomas (often < 5 mm) → frequently difficult to see on MRI
- Cushing's disease typically affects women 25–45 years with M:F ratio 1:3–8 [2]
Mechanism:
- Autonomous TSH secretion → stimulates thyroid → secondary (central) hyperthyroidism
- Very rare (~1% of pituitary adenomas) [2]
- Key distinguishing feature: elevated fT4 with non-suppressed (elevated or normal) TSH — the opposite of Graves' disease where TSH is suppressed
- May secrete only α- or β-subunits → clinically non-functioning [5]
Mechanism:
- Most common pituitary macroadenoma subtype (~70–90% of non-functioning adenomas) [5]
- Although technically secrete FSH, LH, or their subunits (most commonly FSH > FSH-β > α-subunit > LH > LH-β), they are:
- Poorly differentiated and inefficient secretors → rarely produce supranormal hormone levels [5]
- α-subunit is not biologically active → no clinical syndrome from its secretion
- In rare cases: precocious puberty (children), ovarian hyperstimulation (women)
- Because they are functionally silent, they grow large before detection → present as macroadenomas with mass effect and hypopituitarism
- Lactotroph/somatotroph adenoma (~10%) — well-recognised, produces clinical syndromes of both GH excess and hyperprolactinaemia [5]
- Plurihormonal PIT-1 positive adenomas can secrete GH, PRL, and TSH in various combinations
When a growing adenoma compresses the surrounding normal pituitary tissue, hormone deficiencies develop in a predictable sequential order:
Classical order of hormone loss [2][3]:
GH → FSH/LH → ACTH → TSH (→ Prolactin last, if ever)
Mnemonic: "Go Look For ACTH and TSH" — or simply remember that GH is the most sensitive and TSH the most resistant.
Why this order?
- GH-secreting cells (somatotrophs) are the most numerous (~50% of anterior pituitary cells) and are located laterally — vulnerable to compression
- Gonadotrophs are scattered throughout — vulnerable to even moderate compression
- Corticotrophs and thyrotrophs are more centrally located and fewer in number, but their pathways are more robust
- Prolactin is under tonic inhibition, so compression of the stalk actually increases PRL (stalk effect) rather than decreasing it — PRL deficiency is exceedingly rare and essentially only occurs after complete destruction of the gland
7.3 Mass Effect — Compression of Adjacent Structures
The classic visual field defect is bitemporal hemianopia [3][4]:
Why bitemporal hemianopia?
- The optic chiasm sits just above the pituitary
- In the chiasm, fibres from the nasal retina (which see the temporal visual field) cross to the opposite side
- A mass pushing up from below compresses the crossing nasal fibres → loss of temporal visual fields bilaterally
- This produces the classic pattern: the patient cannot see objects in their peripheral (temporal) fields on both sides
But the visual field defect is not always bitemporal hemianopia:
Due to stretching of the diaphragma sellae [3] — the dural fold that covers the sella. The dura is pain-sensitive (innervated by the trigeminal nerve). As the tumour expands within or beyond the sella, it stretches this structure → headache. Headache can also occur from dural invasion.
- Hydrocephalus — only with large/giant adenomas that extend superiorly enough to obstruct the foramen of Monro or compress the third ventricle [4]
- Leads to raised ICP → headache, nausea/vomiting, papilloedema
- CSF rhinorrhoea (rare)
- This downward expansion is actually exploited surgically — the transsphenoidal approach accesses the pituitary through the sphenoid sinus via the nose
Pituitary apoplexy is a neurosurgical emergency [2][3][4]:
Definition: Sudden haemorrhagic infarction of a pituitary adenoma (or rarely, of the normal gland).
Pathophysiology:
- Pituitary adenomas can outgrow their blood supply → ischaemic necrosis ± secondary haemorrhage
- The sudden swelling within the confined bony sella turcica → rapid compression of adjacent structures
Presentation (sudden or subacute over 1–2 days) [3]:
- Excruciating headache (stretching/rupture of sella)
- Diplopia (pressure on CN III — the most medial nerve in the cavernous sinus)
- Hypopituitarism, especially adrenal crisis (acute cortisol deficiency = life-threatening)
- ± Visual field defects (acute chiasmal compression)
- ± Altered consciousness, vertigo [3]
- May mimic subarachnoid haemorrhage (blood can leak into CSF)
Imaging: hyperdensity (acute blood) in pituitary on CT; MRI shows haemorrhage [3][4]
Management: steroid cover (hydrocortisone) + urgent surgical decompression if [2][3]:
- Signs of raised ICP
- Change in conscious state
- Evidence of compression on neighbouring structures
Pituitary Apoplexy — Don't Forget Steroids First!
Before ANY surgical intervention for pituitary apoplexy, give IV hydrocortisone (100 mg stat then 50 mg Q6–8H). The patient is likely acutely cortisol-deficient, and surgical stress without cortisol replacement is fatal.
8. Clinical Features
8.1 Symptoms
Clinical features can be organised into four domains: local/mass effect, hormonal hypersecretion, hormonal hyposecretion, and acute presentation (apoplexy).
| Symptom | Pathophysiological Basis |
|---|---|
| Headache | Stretching of the dura (diaphragma sellae) by the expanding tumour; dura is innervated by trigeminal nerve branches |
| Visual field loss (typically bitemporal hemianopia, but variable) | Suprasellar extension compresses optic chiasm — crossing nasal retinal fibres subserve temporal visual fields |
| Decreased visual acuity | Direct optic nerve compression (especially with prefixed chiasm) |
| Diplopia | Lateral extension into cavernous sinus compresses CN III (most common), IV, or VI → ocular misalignment |
| Facial numbness/pain | Cavernous sinus invasion compressing CN V1/V2 |
| Nausea, vomiting, drowsiness | Very large tumour obstructs third ventricle → obstructive hydrocephalus → raised ICP |
| CSF rhinorrhoea | Inferior erosion through the sphenoid sinus floor (rare) |
a) Prolactinoma symptoms:
| Symptom | Mechanism |
|---|---|
| Galactorrhoea | PRL stimulates mammary gland ductal epithelium to produce milk |
| Amenorrhoea (F) | PRL inhibits GnRH → ↓FSH/LH → anovulation |
| Infertility (F) | Anovulation from hypogonadotropic hypogonadism |
| Erectile dysfunction, decreased libido (M) | Hypogonadotropic hypogonadism → ↓testosterone |
| Gynaecomastia (M, rare) | PRL effects on breast tissue in males |
| Osteoporosis | Chronic hypogonadism → ↓oestrogen/testosterone → ↓bone density |
b) GH-secreting adenoma symptoms (Acromegaly):
| Symptom | Mechanism |
|---|---|
| Enlarging hands/feet (increased ring/shoe size) | GH/IGF-1–driven acral soft tissue and periosteal bone overgrowth |
| Coarsening of facial features | Soft tissue and bony hypertrophy: prominent supraorbital ridges, enlarged nose, prognathism |
| Thickened lips, macroglossia, interdental separation | Soft tissue overgrowth in oral structures |
| Deepening of voice | Laryngeal cartilage and soft tissue hypertrophy |
| Carpal tunnel syndrome (~50%) | Median nerve compression from soft tissue swelling in the carpal tunnel |
| Obstructive sleep apnoea (~50%) | Macroglossia + pharyngeal soft tissue hypertrophy → upper airway narrowing |
| Excessive sweating (hyperhidrosis, > 80%) | GH stimulates sweat glands directly |
| Joint pain/arthropathy | Cartilage and synovial tissue hypertrophy → hypertrophic arthropathy, pseudogout |
| Snoring | Upper airway narrowing (same mechanism as OSA) |
| Headache | Both mass effect and direct GH/IGF-1 effects on intracranial structures |
c) ACTH-secreting adenoma symptoms (Cushing's disease): — see Cushing's syndrome notes for full detail
- Central obesity, moon face, buffalo hump (cortisol → visceral fat redistribution)
- Purple striae (cortisol → collagen breakdown → skin thinning → dermal vessels visible)
- Proximal myopathy (cortisol → protein catabolism in muscle)
- Easy bruising, poor wound healing (cortisol → collagen/connective tissue breakdown)
- Hirsutism, acne (adrenal androgen co-secretion)
- Emotional lability, depression, psychosis
- Hypertension (cortisol has mineralocorticoid activity at high levels)
- Hyperglycaemia/DM (cortisol → gluconeogenesis, insulin resistance)
- Osteoporosis (cortisol → ↓osteoblast activity)
d) TSH-secreting adenoma symptoms:
- Symptoms of hyperthyroidism: weight loss, tremor, heat intolerance, palpitations, tachycardia, diarrhoea
- Often also has features of mass effect (since these are typically macroadenomas)
- May present with diffuse goitre (TSH-driven thyroid stimulation)
When normal pituitary tissue is compressed by the expanding adenoma:
| Hormone Deficient | Symptoms | Mechanism |
|---|---|---|
| GH (first to be lost) | Fatigue, decreased muscle mass, increased visceral fat, decreased quality of life; growth failure in children | Loss of GH anabolic effects |
| FSH/LH (second) | Amenorrhoea (F), erectile dysfunction/decreased libido (M), infertility, loss of secondary sexual characteristics, osteoporosis | Loss of gonadal stimulation → ↓oestrogen/testosterone |
| ACTH (third) | Fatigue, weakness, weight loss, postural hypotension, nausea; life-threatening in acute illness (adrenal crisis) | Loss of cortisol; NB: aldosterone is preserved (RAAS-dependent, not ACTH-dependent) → no hyperkalaemia (unlike primary adrenal insufficiency) |
| TSH (fourth) | Fatigue, cold intolerance, constipation, weight gain, dry skin, bradycardia | Central hypothyroidism (low fT4 with inappropriately normal/low TSH) |
| Prolactin (rarely lost) | Failure of lactation postpartum | Only with complete gland destruction (e.g., Sheehan's syndrome) |
| ADH (posterior pituitary — rarely affected by adenomas, more common with stalk lesions, craniopharyngiomas, or surgery) | Polyuria, polydipsia, nocturia | Central diabetes insipidus — loss of ADH → inability to concentrate urine |
Secondary vs Primary Adrenal Insufficiency
In hypopituitarism, the adrenal insufficiency is secondary (ACTH-dependent). Unlike primary adrenal insufficiency (Addison's disease):
- No hyperpigmentation (ACTH is low, not high → no melanocyte stimulation)
- No hyperkalaemia (aldosterone is preserved — it's regulated by RAAS, not ACTH)
- Hyponatraemia can still occur (cortisol deficiency → impaired free water excretion + ↑ADH)
- Sudden excruciating headache (thunderclap type)
- Acute visual loss (bilateral or unilateral)
- Diplopia (CN III palsy)
- Nausea, vomiting, meningism (blood in subarachnoid space)
- Collapse, altered consciousness (adrenal crisis + raised ICP)
8.2 Signs
| Sign | Condition | Mechanism |
|---|---|---|
| Acromegaloid facies: prominent brow, large nose, prognathism, thick lips, macroglossia | Acromegaly | GH/IGF-1–driven bony and soft tissue overgrowth |
| Large, spade-like hands with sweaty palms | Acromegaly | Acral overgrowth + hyperhidrosis |
| Skin tags | Acromegaly | GH promotes epidermal growth |
| Cushingoid habitus: central obesity, moon face, buffalo hump, thin limbs, purple striae | Cushing's disease | Cortisol-driven fat redistribution + protein catabolism |
| Galactorrhoea (expressible on breast examination) | Prolactinoma | PRL → breast milk production |
| Gynaecomastia (M) | Prolactinoma | PRL effect + hypogonadism |
| Signs of hypogonadism: sparse body hair, testicular atrophy (M), breast atrophy (F) | Hypogonadotropic hypogonadism (any large adenoma or prolactinoma) | ↓FSH/LH → ↓sex hormones |
| Pallor | Hypopituitarism | ACTH deficiency → ↓cortisol, also ↓MSH (POMC product) → "alabaster pallor"; also normocytic anaemia |
| Dry, coarse skin; loss of lateral eyebrows | Central hypothyroidism | ↓TSH → ↓T4 → hypothyroid features |
| Postural hypotension | ACTH deficiency | ↓cortisol → impaired vascular tone + impaired free water excretion |
| Sign | Test | Mechanism |
|---|---|---|
| Bitemporal hemianopia | Confrontation visual field testing; formal perimetry (Humphrey/Goldmann) | Optic chiasm compression — crossing nasal retinal fibres |
| Upper temporal quadrantanopia (early) | Perimetry | Chiasm compressed from below → inferior crossing fibres (from superior nasal retina = inferior temporal field) affected first |
| Optic atrophy (pale disc on fundoscopy) | Direct ophthalmoscopy | Chronic compression → axonal degeneration in optic nerve/chiasm |
| Decreased visual acuity | Snellen chart | Optic nerve or chiasmal fibre damage |
| CN III palsy (ptosis, "down and out" eye, fixed dilated pupil) | Ocular motility testing | Cavernous sinus invasion (adenoma) or acute swelling (apoplexy) compressing CN III |
| CN IV, VI palsy | Ocular motility | Less common; lateral cavernous sinus involvement |
| Papilloedema | Fundoscopy | Raised ICP from hydrocephalus (giant adenoma obstructing 3rd ventricle) |
| Relative afferent pupillary defect (RAPD) | Swinging flashlight test | Asymmetric optic nerve involvement |
A full pituitary examination should systematically assess for both excess and deficiency:
Acromegaly-specific signs:
- Thick heel pads (> 22 mm) — can be measured on lateral foot X-ray
- Prognathism with malocclusion
- Increased interdental separation
- Coarse, oily skin with skin tags
- Bitemporal field defect (if macroadenoma)
- Goitre (GH/IGF-1 → thyroid enlargement; usually non-toxic but can be toxic) [2]
- Carpal tunnel signs (Tinel's, Phalen's)
- Hypertension
- Signs of heart failure (cardiomyopathy)
Cushing's disease-specific signs:
- Central obesity with thin extremities
- Moon face with plethora
- Dorsocervical fat pad (buffalo hump)
- Supraclavicular fat pads
- Purple striae > 1 cm wide (especially on abdomen, thighs, axillae)
- Proximal myopathy (cannot rise from chair without using hands)
- Easy bruising
- Hirsutism, acne
- Hypertension
Clinical Pearl: If you see a patient with both acromegaloid features AND galactorrhoea, think of a mixed somatotroph-lactotroph adenoma (PIT-1 lineage) or consider stalk effect from a large GH-secreting macroadenoma.
When you encounter a suspected pituitary lesion, the clinical approach follows a systematic algorithm:
The approach to pituitary hormonal assessment depends on the mode of secretion [2]:
| Secretion Pattern | Hormones | Assessment Method |
|---|---|---|
| Pulsatile secretion | GH, ACTH | Requires dynamic (stimulation/suppression) tests — a single random level is often uninterpretable |
| Constant secretion | Prolactin, TSH, LH/FSH | Direct measurement of basal serum level is sufficient |
High Yield Summary
Pituitary Adenoma — Key Points for Exams:
- Most common sellar mass in adults; 10–15% of intracranial neoplasms; found in 20–25% at autopsy [4]
- Classification: Microadenoma ( < 1 cm) vs Macroadenoma ( > 1 cm) vs Giant ( > 4 cm); Functioning vs Non-functioning
- Prolactinoma is the most common functioning adenoma; non-functioning adenomas are the most common macroadenoma (usually gonadotroph origin)
- Bitemporal hemianopia is the classic visual field defect (optic chiasm compression from below)
- Stalk effect: any mass compressing the pituitary stalk → mild hyperprolactinaemia ( < 100–200 ng/mL) by blocking dopamine delivery; PRL > 200 ng/mL almost always = true prolactinoma
- Order of hormone loss in hypopituitarism: GH → FSH/LH → ACTH → TSH
- Pituitary apoplexy = neurosurgical emergency: sudden headache + diplopia (CN III) + hypopituitarism (adrenal crisis); manage with IV hydrocortisone + urgent surgery if compressive signs
- Treatment paradigm: Prolactinoma → dopamine agonist first; GH/ACTH/TSH-secreting → surgery first; Non-functioning microadenoma → observe [4]
- MEN1 = Parathyroid + Pancreatic NETs + Pituitary adenoma (prolactinoma most common)
- Always exclude aneurysm before operating on a "sellar mass" [4]
- MRI pituitary (with gadolinium contrast) is the imaging modality of choice; CT is better for calcification (craniopharyngioma, meningioma) [2]
Active Recall - Pituitary Adenoma (Definition, Epidemiology, Anatomy, Etiology, Classification, Clinical Features)
[1] Senior notes: Ryan Ho Neurology.pdf (Section: Pituitary Adenoma, p. 166) [2] Senior notes: Ryan Ho Endocrine.pdf (Section 5: Pituitary Gland, pp. 104–132) [3] Senior notes: Ryan Ho Fundamentals.pdf (Section 3.8.4: Presenting Problems in Pituitary Gland, pp. 441–444) [4] Lecture slides: GC 108. A mass in the brain brain tumours.pdf (pp. 3–4, 11–12, 17–18, 41–42, 47–48) [5] Senior notes: felixlai.md (Pituitary adenoma section) [6] Senior notes: Ryan Ho Endocrine.pdf (Section 6.3: Multiple Endocrine Neoplasia, p. 132) [7] Senior notes: maxim.md (Brain tumours section, p. 771)
Differential Diagnosis of Pituitary Adenoma
When a patient presents with a sellar/parasellar mass, the reflexive assumption is "pituitary adenoma" — and statistically you'd be right most of the time in an adult. But assuming = missing, and the sellar region is a crossroads of many pathologies. The differential diagnosis must be systematically considered across three clinical axes:
- What else can cause a sellar mass? (Structural DDx)
- What else can cause the hormonal syndrome? (Functional DDx — i.e., DDx of hyperprolactinaemia, acromegaly, Cushing's syndrome, etc.)
- What else can cause the presenting symptom? (Symptom-based DDx — bitemporal hemianopia, headache, CN palsy, etc.)
Let's work through each systematically from first principles.
1. Structural Differential Diagnosis: "What Else Can Sit in or Around the Sella?"
This is the most critical DDx because the management is completely different for each entity. You cannot just biopsy a sellar mass — it could be an aneurysm, and sticking a needle in it would be lethal.
| Differential | Key Distinguishing Features | Why It Matters |
|---|---|---|
| Pituitary adenoma | Most common sellar mass in adults; enhances less than normal pituitary on gadolinium MRI; can be micro or macro; hormonal hypersecretion or hyposecretion | Commonest diagnosis — but don't stop here |
| Craniopharyngioma | 50% calcified (seen on CT/XR); often cystic with a "motor oil" appearance of cyst fluid; arises from Rathke's pouch remnants; most common sellar mass in children; bimodal age peak (childhood + 50–60y); commonly causes cranial DI (stalk involvement) and growth retardation (GH deficiency) [3] | Unlike adenoma: frequently calcified, cystic, suprasellar, and causes DI. CT is better for detecting calcification [2][3] |
| Meningioma | Arises from meninges (dura); classically shows homogeneous enhancement with a "dural tail" on MRI; often calcified; displaces the pituitary rather than arising from it; suprasellar/parasellar location | May mimic non-functioning macroadenoma clinically; CT better for calcification [2] |
| Rathke's cleft cyst | Benign cystic remnant of Rathke's pouch; sits between anterior and posterior lobes; non-enhancing on MRI; variable signal depending on cyst contents (mucoid = T1 bright, serous = T1 dark) | Usually incidental; can compress stalk → mild hyperprolactinaemia + DI |
| Pituicytoma | Rare, solid, enhancing tumour of pituicytes (glial cells of the posterior pituitary/stalk); suprasellar | Very vascular — important to know pre-operatively |
| Metastases | Most commonly from CA lung (males) and CA breast (females); preferentially involves posterior pituitary (richer blood supply via inferior hypophyseal arteries); may present with diabetes insipidus (unlike adenoma, which rarely causes DI) [5] | DI as the first pituitary symptom in an older patient with weight loss → think metastasis, not adenoma |
| Germ cell tumours (germinoma, teratoma) | Young patients; suprasellar; may secrete β-hCG or AFP (tumour markers); often associated with DI and visual loss | Check serum and CSF β-hCG and AFP in young patients with suprasellar mass |
| Chordoma | Arises from notochord remnants at the clivus; destructive, bone-eroding mass on CT; midline; often extends to involve the sella | Clival destruction on CT is the giveaway |
| CNS lymphoma | Homogeneous enhancement; may be periventricular; consider in immunosuppressed patients (HIV, post-transplant) | Biopsy-proven; treat with chemo ± RT, not surgery |
| Pituitary carcinoma | Extremely rare; defined by the presence of craniospinal or systemic metastases (not by histological features alone) | Cannot be diagnosed on histology of the primary tumour — need to demonstrate metastasis |
| Lymphocytic hypophysitis | Autoimmune inflammation of the pituitary; classically in peripartum women; diffuse enlargement of gland and stalk (not a focal mass); often presents with DI + hypopituitarism ± headache | May mimic adenoma on MRI; history of recent pregnancy is the clue; responds to steroids |
| Pituitary abscess | Rare; may follow surgery or haematogenous seeding; ring enhancement on MRI with restricted diffusion centrally; fever, meningism | Neurosurgical emergency |
| ICA aneurysm | A cerebral aneurysm can mimic a sellar tumour [4]; signal void on MRI (flowing blood); pulsatile mass; may present with CN III palsy from posterior communicating artery aneurysm or with SAH | MUST exclude before transsphenoidal surgery — operating on an aneurysm = catastrophic haemorrhage [4] |
| Carotid-cavernous fistula | Pulsatile proptosis, chemosis (conjunctival oedema), orbital bruit, arterialized conjunctival vessels | Vascular, not neoplastic |
| Pituitary hyperplasia | Diffuse symmetric enlargement (no focal lesion); occurs in specific physiological/pathological contexts: pregnancy (lactotroph), longstanding primary hypothyroidism (thyrotroph), longstanding primary hypogonadism (gonadotroph), ectopic GHRH (somatotroph) [5] | Treat the underlying cause → gland shrinks back; no surgery needed |
The Three Masses That Must Not Be Biopsied/Operated Without Specific Workup
- ICA aneurysm — must be excluded by CTA/MRA before any surgery on a "sellar mass" [4][8]
- Germ cell tumour — check β-hCG and AFP first; may be treated with chemo + RT without surgery
- CNS lymphoma — steroids before biopsy can cause temporary regression and render biopsy non-diagnostic; discuss with team before giving dexamethasone
| Feature on MRI | Think of... | Why |
|---|---|---|
| Focal lesion within the sella, enhances less than surrounding normal pituitary [5] | Pituitary adenoma | Adenoma tissue has a different vascular pattern and takes up gadolinium more slowly than normal pituitary [5] |
| Calcification (better on CT) | Craniopharyngioma > Meningioma | Craniopharyngiomas are 50% calcified; meningiomas frequently calcify [2] |
| Cystic/mixed solid-cystic suprasellar mass | Craniopharyngioma, Rathke's cleft cyst | Craniopharyngiomas are often cystic; Rathke's cleft cysts are purely cystic |
| Homogeneous enhancement + dural tail | Meningioma | Classic meningioma sign |
| Ring enhancement with restricted diffusion | Pituitary abscess | Abscess cavity |
| Diffuse gland + stalk enlargement (no focal mass) | Lymphocytic hypophysitis, pituitary hyperplasia | Diffuse process, not focal |
| Posterior pituitary bright spot absent | DI (central); stalk lesion; metastasis | ADH granules lost |
| T1 bright signal in the sella | Haemorrhage (apoplexy), lipid-rich cyst (Rathke's), proteinaceous content | Methaemoglobin (blood) or fat/mucoid material |
| Signal void ("flow void") in the sella | ICA aneurysm | Flowing blood produces no signal on standard MRI |
| Separate from normal pituitary gland on MRI | NOT a pituitary adenoma — consider other sellar pathology [5] | A true adenoma arises within the gland; a lesion clearly separate from the gland is something else (craniopharyngioma, meningioma, etc.) |
2. Functional Differential Diagnosis: "What Else Can Cause This Hormonal Syndrome?"
When a pituitary adenoma is functioning, it produces a clinical syndrome. But other conditions can mimic those syndromes. This is crucial because treatment differs dramatically.
This is the most important functional DDx because mild hyperprolactinaemia has a vast differential, and mistaking a non-functioning macroadenoma with stalk effect for a prolactinoma (and treating with dopamine agonist alone) would be a critical error.
| Category | Causes | Mechanism | PRL Level |
|---|---|---|---|
| Physiological | Pregnancy, breastfeeding, nipple stimulation, stress, sleep, coitus | Normal regulatory increase in PRL | Mild–moderate |
| Pharmacological | Antipsychotics (D2 blockers — haloperidol, risperidone), metoclopramide, domperidone, methyldopa, oestrogens, SSRIs | Block dopamine D2 receptors on lactotrophs → remove inhibition → ↑PRL | Usually < 100 ng/mL |
| Stalk effect ("disconnection") | Any sellar/suprasellar mass (non-functioning adenoma, craniopharyngioma, meningioma), stalk transection, post-surgery, granulomatous disease | Interrupts dopamine delivery from hypothalamus to lactotrophs | Usually < 100–200 ng/mL |
| True prolactinoma | Lactotroph adenoma | Autonomous PRL secretion by tumour cells | Usually > 200 ng/mL (often > 10× ULN) [2][3] |
| Hypothyroidism | Primary hypothyroidism | ↑TRH (which also stimulates lactotrophs) | Mild |
| Chronic kidney disease | Renal failure | ↓PRL clearance by kidney | Mild–moderate |
| Chest wall irritation | Thoracotomy, herpes zoster, chest wall trauma | Afferent neural stimulation mimics suckling reflex → hypothalamic PRL release | Mild |
The Critical Distinction: Stalk Effect vs. Prolactinoma
A 3 cm sellar mass with PRL of 80 ng/mL is almost certainly a non-functioning macroadenoma causing stalk effect — NOT a prolactinoma. A true prolactinoma of that size would produce PRL > 1,000–10,000 ng/mL. This distinction changes management entirely: the non-functioning adenoma needs surgery, while a prolactinoma needs dopamine agonist. The "degree of PRL elevation should be proportional to tumour size" — if it's not, suspect stalk effect or hook effect [2][5].
| Cause | Proportion | Mechanism |
|---|---|---|
| GH-secreting pituitary adenoma | Vast majority (> 95%) [2][3] | Autonomous GH secretion |
| GHRH-secreting hypothalamic tumours | Rare | Ectopic GHRH → pituitary somatotroph hyperplasia → GH excess |
| Ectopic GHRH secretion | < 1% | Neuroendocrine tumours (carcinoid, pancreatic NET, SCLC) secrete GHRH → somatotroph hyperplasia |
| Ectopic GH secretion | Exceedingly rare | Lymphoma or pancreatic islet cell tumour secreting GH directly |
| McCune-Albright syndrome | Very rare | Activating GNAS1 mutation → constitutive GH secretion |
The key differentiator: if the pituitary is diffusely enlarged (hyperplasia) rather than showing a focal adenoma, suspect ectopic GHRH secretion. Measure serum GHRH levels [2].
This is a well-structured DDx covered in detail in Cushing's syndrome notes, but here is the pituitary-relevant summary:
| Category | Cause | % of Endogenous CS | Key Distinguishing Feature |
|---|---|---|---|
| ACTH-dependent | Cushing's disease (pituitary corticotroph adenoma) | 65–70% | Elevated ACTH; pituitary MRI may show microadenoma (often small, < 5 mm); high-dose dexamethasone suppression test → usually suppressible [2][9] |
| ACTH-dependent | Ectopic ACTH syndrome | 10–15% | SCLC, bronchial carcinoid, thymic carcinoid, pancreatic NET; often severe/rapid onset with very high ACTH; non-suppressible on HDDST; consider in older men > 50y [2] |
| Non-ACTH-dependent | Adrenal adenoma / carcinoma | 15–20% | Suppressed ACTH; adrenal mass on imaging |
| Iatrogenic | Exogenous glucocorticoids (most common overall) | N/A | Must r/o any herbal medicine, "OTC drugs for arthritis" (especially relevant in Hong Kong) [2] |
Pseudo-Cushing's
Several conditions can cause mild cortisol elevation that mimics Cushing's syndrome biochemically: depression, alcoholism, obesity, pregnancy, severe illness. These are termed "pseudo-Cushing's" states. The insulin tolerance test (ITT) can help differentiate: in true Cushing's, cortisol response to hypoglycaemia is blunted; in pseudo-Cushing's, cortisol responds normally [9].
When you find elevated fT4 with non-suppressed TSH (i.e., TSH is normal or elevated when it should be suppressed):
| Diagnosis | Mechanism | How to Distinguish |
|---|---|---|
| TSH-secreting pituitary adenoma | Autonomous TSH production → thyroid stimulation | MRI pituitary shows adenoma; elevated α-subunit; usually macroadenoma |
| Thyroid hormone resistance | Mutation in thyroid hormone receptor → tissues (including pituitary) are resistant to T3/T4 → pituitary continues TSH secretion despite high T4 | No pituitary mass; often familial (autosomal dominant); elevated T4 with normal/elevated TSH but patient is clinically euthyroid (tissues are resistant) |
| Assay artefact | Heterophilic antibodies (e.g., anti-mouse antibodies from biotin supplements or HAMA) interfere with TSH immunoassay | Run the sample with heterophilic antibody blocking agent; check with different assay platform |
The critical distinction here is between a TSH-secreting adenoma and thyroid hormone resistance — both show ↑fT4 with non-suppressed TSH. α-subunit : TSH molar ratio > 1 favours TSHoma; a TRH stimulation test (blunted TSH response in TSHoma, normal in resistance) can help.
If a patient has a large sellar mass with hypopituitarism but no hormonal hypersecretion, the DDx includes:
| Diagnosis | Key Differentiators |
|---|---|
| Non-functioning pituitary adenoma (most common) | Middle-aged adult, gradual visual loss + headache + gonadal dysfunction |
| Craniopharyngioma | Calcified, cystic; children or bimodal age; DI common |
| Meningioma | Dural tail, homogeneous enhancement, calcified |
| Metastasis | Known cancer; posterior pituitary involvement; DI |
| Lymphocytic hypophysitis | Peripartum female; diffuse enlargement; DI |
| Rathke's cleft cyst | Purely cystic; non-enhancing |
| "Non-functioning" gonadotroph adenoma | 70–90% of non-functioning adenomas are gonadotroph in origin — can be confirmed by immunohistochemistry (SF-1 staining) or by detecting elevated FSH/α-subunit [5] |
3. Symptom-Based Differential Diagnosis
Bitemporal hemianopia points to the optic chiasm, but not all chiasmal lesions are pituitary adenomas:
| Cause | Notes |
|---|---|
| Pituitary macroadenoma (most common) | Compresses chiasm from below |
| Craniopharyngioma | Suprasellar mass compresses chiasm from above or below |
| Suprasellar meningioma | Compresses chiasm from above |
| Glioma of the optic chiasm | Intrinsic chiasmal tumour (more common in children, often NF1-associated) |
| ICA aneurysm | Aneurysm at ICA-ophthalmic artery junction can compress chiasm |
| Arachnoiditis | Post-inflammatory adhesions around chiasm (rare) |
| Empty sella syndrome | Herniation of arachnoid into sella → chiasmal traction |
When a patient presents with diplopia from CN III involvement near the sella:
| Cause | Distinguishing Features |
|---|---|
| Pituitary apoplexy | Sudden headache + diplopia + hypopituitarism [2][3] |
| Posterior communicating artery aneurysm | Isolated painful CN III palsy with pupil involvement — neurosurgical emergency [8] |
| Cavernous sinus thrombosis | Proptosis, chemosis, fever; multiple CN palsies (III, IV, V1, V2, VI) |
| Cavernous sinus tumour (meningioma, nasopharyngeal carcinoma, pituitary adenoma invading laterally) | Gradual onset; associated CN IV, VI, V1, V2 involvement [8] |
| Microvascular ("medical") CN III palsy | DM, HTN; pupil-sparing; self-limiting in 6–12 weeks [8] |
| Uncal herniation | Altered consciousness; fixed dilated pupil; medical emergency |
Pupil Involvement in CN III Palsy — The Key Distinction
Parasympathetic fibres run on the surface of CN III. An aneurysm or mass compresses the nerve from outside → pupil is affected early (mydriasis, absent light reflex). Microvascular ischaemia (DM, HTN) affects the deep fibres via small penetrating vessels → pupil is spared [8].
Rule of thumb: An isolated CN III palsy that is pupil-involving must be investigated urgently for aneurysm (CTA/MRA). A pupil-sparing CN III palsy in a diabetic/hypertensive patient can be observed (but still image if clinical doubt).
Pituitary apoplexy presents with sudden headache ± meningism ± visual loss. The DDx of sudden severe headache includes [3][10]:
| Diagnosis | Key Distinguishing Feature |
|---|---|
| Pituitary apoplexy | Sellar mass with haemorrhage on CT/MRI; diplopia (CN III); hypopituitarism |
| Subarachnoid haemorrhage (aneurysmal) | CT head shows blood in basal cisterns; LP shows xanthochromia if CT negative; CTA for aneurysm |
| Meningitis | Fever, meningism; LP diagnostic |
| CVST | Headache, papilloedema, seizures; MRV diagnostic |
| Carotid/vertebral dissection | Unilateral neck/face pain; Horner syndrome; CTA/MRA diagnostic |
Note: pituitary apoplexy can mimic SAH because blood from the haemorrhagic adenoma can leak into the subarachnoid space → meningism. Always check the sella on imaging in "SAH-negative" thunderclap headache presentations.
| Clinical Presentation | Most Likely DDx to Consider |
|---|---|
| Adult with sellar mass + hormonal hypersecretion | Pituitary adenoma (functioning) |
| Adult with sellar mass + hypopituitarism + visual loss | Non-functioning pituitary adenoma > craniopharyngioma > meningioma > metastasis |
| Child with sellar/suprasellar mass | Craniopharyngioma (most common) > germ cell tumour > optic glioma |
| Sellar mass + DI | Craniopharyngioma, metastasis, lymphocytic hypophysitis, germ cell tumour — pituitary adenoma rarely causes DI (think of other diagnoses first) |
| Calcified sellar mass | Craniopharyngioma (50% calcified) > meningioma |
| Sellar mass + mild PRL elevation ( < 200 ng/mL) | Stalk effect from non-functioning adenoma/craniopharyngioma/meningioma; drugs; hypothyroidism — not necessarily a prolactinoma |
| Sellar mass + PRL > 200 ng/mL | True prolactinoma (degree proportional to size) |
| Sudden headache + diplopia + hypopituitarism | Pituitary apoplexy — also exclude aneurysmal SAH |
| Peripartum woman + diffuse pituitary enlargement + DI | Lymphocytic hypophysitis |
Two Golden Rules for Sellar Mass DDx
- If the mass is separate from the normal pituitary gland on MRI → it is NOT a pituitary adenoma [5]. Think craniopharyngioma, meningioma, Rathke's cyst, or other extrinsic lesion.
- If the first presenting feature is diabetes insipidus → it is probably NOT a pituitary adenoma. Pituitary adenomas arise from the anterior pituitary and very rarely affect the posterior pituitary or stalk enough to cause DI until very late. Early DI points to stalk lesions: craniopharyngioma, metastasis, germinoma, or hypophysitis.
High Yield Summary — DDx of Pituitary Adenoma
- Structural DDx of sellar mass: Pituitary adenoma (most common in adults) > craniopharyngioma (most common in children, calcified, cystic) > meningioma (dural tail) > metastasis (posterior pituitary, DI) > Rathke's cleft cyst > germ cell tumour > ICA aneurysm > lymphocytic hypophysitis > pituitary abscess
- Always exclude ICA aneurysm before surgery (CTA/MRA) [4]
- CT is better than MRI for detecting calcification (craniopharyngioma, meningioma) [2]
- Stalk effect (PRL < 100–200) vs prolactinoma (PRL > 200, proportional to size) — this distinction dictates whether you give a dopamine agonist or operate
- Cushing's DDx: Iatrogenic (commonest overall) > Cushing's disease (65–70% of endogenous) > ectopic ACTH > adrenal tumour
- DI at presentation of a sellar mass → think non-adenoma pathology (craniopharyngioma, metastasis, germinoma, hypophysitis)
- Non-functioning adenomas: 70–90% are gonadotroph in origin [5]
Active Recall - DDx of Pituitary Adenoma
References
[2] Senior notes: Ryan Ho Endocrine.pdf (Section 5: Pituitary Gland, pp. 104–111) [3] Senior notes: Ryan Ho Fundamentals.pdf (Section 3.8.4: Presenting Problems in Pituitary Gland, pp. 441–444) [4] Lecture slides: GC 108. A mass in the brain brain tumours.pdf (pp. 4, 12, 17–18, 41–42, 48) [5] Senior notes: felixlai.md (Pituitary adenoma section — Overview, Etiology, Diagnosis) [8] Senior notes: Ryan Ho Opthalmology.pdf (Section 4.2.2: Third Nerve Palsy, pp. 82–83) [9] Senior notes: Ryan Ho Chemical Path.pdf (Section 4.1–4.3: Diagnostic Function Tests, pp. 29–33) [10] Senior notes: Ryan Ho Neurology.pdf (Headache DDx, pp. 58–60; Intracranial Tumours, pp. 161–166)
Diagnostic Approach to Pituitary Adenoma
The diagnosis of a pituitary adenoma is never based on a single test. It is a convergence of three pillars — biochemistry, imaging, and visual assessment — each answering a distinct question:
- Biochemistry: "Is this mass making too much hormone? Is it destroying the normal gland?"
- Imaging: "What is this mass? Where exactly is it? What is it compressing?"
- Visual assessment: "Is it damaging the optic pathways?"
Let me walk you through the complete diagnostic algorithm from first principles.
2. Step 1 — Biochemical Evaluation: Hormonal Hypersecretion
This is the first and most critical step. Every patient with a sellar mass needs a full hormonal evaluation — you need to determine both what the tumour is secreting and what the normal gland has stopped producing.
The approach to hormonal assessment depends on the mode of secretion [2]:
| Secretion Pattern | Hormones | Assessment Method | Why |
|---|---|---|---|
| Pulsatile secretion | GH, ACTH (cortisol) | Dynamic (stimulation/suppression) tests | A single random level is meaningless because levels fluctuate widely throughout the day; you need to challenge the axis and see if it responds appropriately |
| Constant (tonic) secretion | Prolactin, TSH, LH/FSH | Direct basal serum measurement | These hormones have relatively stable levels; a single measurement is interpretable |
2.2 Hormone-Specific Diagnostic Criteria
| Test | Method | Interpretation |
|---|---|---|
| Serum prolactin | Single fasting morning sample | PRL > 200 ng/mL (usually > 10× ULN) = diagnostic of prolactinoma [2][3][5] |
Interpretation nuances — the "degree-of-elevation" rule:
| PRL Level | Most Likely Interpretation |
|---|---|
| Normal ( < 25 ng/mL) | Non-functioning adenoma or non-PRL-secreting tumour |
| 25–100 ng/mL | Stalk effect, drugs, hypothyroidism, pregnancy, CKD — NOT prolactinoma |
| 100–200 ng/mL | Grey zone — could be stalk effect from large mass or small prolactinoma; correlate with tumour size |
| > 200 ng/mL | Virtually diagnostic of prolactinoma — degree should be proportional to tumour size |
| > 1,000–10,000 ng/mL | Giant prolactinoma |
| Large macroadenoma with PRL only 50–150 ng/mL | Think stalk effect (non-functioning adenoma) or hook effect — request serial dilutions of the sample |
The Hook Effect — A Lab Pitfall That Can Kill
In giant prolactinomas with extremely high PRL ( > 10,000 ng/mL), the standard two-site immunometric assay can be overwhelmed — excessive analyte saturates both capture and detection antibodies, preventing proper sandwich formation. The result is a falsely normal or mildly elevated PRL reading. This can lead to misdiagnosis as a non-functioning adenoma → inappropriate surgery instead of dopamine agonist therapy. Always request serial dilutions (1:100) when you have a large macroadenoma with only modestly elevated PRL.
GH is secreted in pulses, so a random GH level is useless for diagnosis. Instead, we use two complementary tests:
| Test | Method | Diagnostic Criteria | Rationale |
|---|---|---|---|
| Serum IGF-1 | Single fasting sample; compare to age- and sex-matched reference range | Elevated IGF-1 (above age-adjusted ULN) [2][3] | IGF-1 is produced by the liver in response to GH. Because IGF-1 has a long half-life (~18h) and is bound to IGFBP-3, it reflects integrated daily GH secretion rather than pulsatile spikes. It acts as a smoothed-out biomarker for chronic GH excess |
| Oral glucose tolerance test (OGTT) for GH suppression | 75g oral glucose load → serial GH measurements at 0, 30, 60, 90, 120 min | Normal: GH suppresses to < 1 ng/mL (or < 0.4 ng/mL by ultrasensitive assay) after glucose load. Acromegaly: failure of GH suppression, or paradoxical GH increase (in ~30%) [2][3] | Glucose normally suppresses GH secretion via somatostatin release. In a somatotroph adenoma, the tumour cells are autonomous and do not respond to this negative feedback. Hence GH remains elevated or paradoxically rises |
When to use OGTT vs. IGF-1?
- IGF-1 is the initial screening test — if clearly elevated and clinical features are present, diagnosis is established
- OGTT is done in equivocal cases (borderline IGF-1, no typical manifestations) [2]
Other investigations for acromegaly [2]:
- Pituitary MRI and pituitary hormone profile for tumour localisation, co-secretion (30% co-secrete PRL), and assessment of local effects
- Colonoscopy for colonic tumours (↑risk of colon polyps and carcinoma)
Diagnosing Cushing's disease is a multi-step process because cortisol, like GH, is pulsatile and stress-responsive. The approach involves: (1) confirm endogenous hypercortisolism, (2) determine ACTH-dependence, (3) localise the source.
Step C1: Confirm Hypercortisolism (Screening — need ≥ 2 abnormal tests) [9][3]:
Iatrogenic Cushing's syndrome due to exogenous glucocorticoid must be ruled out first [9].
| Screening Test | Method | Positive Result | Caveats |
|---|---|---|---|
| 24-hour urinary free cortisol (UFC) ×2 | Collect all urine over 24h; measures total free cortisol excreted (eliminates pulsatility) | Elevated above ULN (> 3–4× ULN is virtually diagnostic) [9][3] | Problems: under-/over-collection, inconvenient, affected by renal disease; does not distinguish true CS from physiological hypercortisolism (depression, obesity) [9] |
| 1 mg overnight dexamethasone suppression test (DST) | 1 mg dexamethasone PO at midnight → serum cortisol at 9 AM next morning | Cortisol > 50 nmol/L (1.8 μg/dL) = failure to suppress | Affected by oestrogen (↑CBG → falsely ↑total cortisol); enzyme inducers (↑dex metabolism → false positive) [3] |
| Late-night salivary cortisol ×2 | Saliva sample at 11 PM–midnight | Elevated (loss of circadian nadir) | Only free cortisol present in saliva; not suitable for shift workers; requires sensitive LC-MS assay [9] |
≥ 2 tests abnormal → diagnostic of endogenous Cushing's syndrome [3]
Step C2: Determine ACTH-Dependence [2][3]:
| Plasma ACTH | Interpretation |
|---|---|
| < 1.1 pmol/L ( < 5 pg/mL) | Non-ACTH-dependent → adrenal source (adrenal adenoma, carcinoma, bilateral hyperplasia) [3] |
| > 3.3 pmol/L ( > 15 pg/mL) | ACTH-dependent → pituitary (Cushing's disease) or ectopic ACTH source [3] |
| 1.1–3.3 pmol/L | Indeterminate — repeat or proceed to CRH test |
Step C3: Distinguish Pituitary from Ectopic ACTH [2][3]:
| Test | Method | Cushing's Disease | Ectopic ACTH |
|---|---|---|---|
| High-dose DST (HDDST) | 2 mg dex Q6H × 2 days → measure serum cortisol | Cortisol suppressed ( > 50% suppression from baseline) — pituitary corticotrophs retain partial feedback sensitivity to high-dose glucocorticoids | No suppression — ectopic source is autonomous, not responsive to negative feedback [2][3] |
| CRH stimulation test | 1 μg/kg CRH IV → serial ACTH and cortisol over 2h | Exaggerated rise: cortisol > 20% baseline, ACTH > 50% baseline — pituitary corticotroph adenoma cells still express CRH receptors | No significant rise — ectopic tumour cells lack CRH receptors [2][3] |
| Pituitary MRI | Gadolinium-enhanced | May show microadenoma (but 40–50% of corticotroph adenomas are too small to see, and ~10% of normal population has pituitary incidentaloma) | Normal pituitary |
| Inferior petrosal sinus sampling (IPSS) | Catheterise both inferior petrosal sinuses; measure ACTH centrally vs. peripherally before and after CRH stimulation | Central-to-peripheral ACTH ratio ≥ 2 (basal) or ≥ 3 (post-CRH) = pituitary source [2][3] | Ratio < 2 (basal) or < 3 (post-CRH) = ectopic source |
HDDST is usually done before pituitary MRI to avoid picking up a pituitary incidentaloma [2]
IPSS — The Gold Standard for Localisation
When biochemistry says "ACTH-dependent" but MRI cannot show a clear pituitary adenoma (which happens in ~40% of Cushing's disease because corticotroph adenomas are often tiny), inferior petrosal sinus sampling (IPSS) is the definitive test. It directly compares ACTH concentration in the venous drainage of the pituitary (petrosal sinuses) vs. a peripheral vein. A gradient confirms pituitary origin. It can even lateralise the adenoma (left vs. right side of the gland) to guide the surgeon [2][3].
Summary of Cushing's syndrome biochemical findings [2][3]:
| Cushing's Disease | Ectopic ACTH | Adrenal Tumour | Iatrogenic | |
|---|---|---|---|---|
| Cortisol | ↑ | ↑ | ↑ | ↓ (exogenous steroid suppresses endogenous) |
| LDDST | No suppression | No suppression | No suppression | / |
| ACTH | Normal–high | Usually high | Almost invariably undetectable | Low |
| HDDST | Usually suppressed | Usually no suppression | No suppression | / |
| CRH test | Exaggerated rise | No significant rise | / | / |
| Imaging | Pituitary adenoma on MRI | Tumour on PET/CT | Adrenal tumour on CT | +ve drug Hx |
| Test | Method | Diagnostic Criteria |
|---|---|---|
| TSH + fT4 (+ fT3) [5] | Standard thyroid function tests | Elevated fT4 with non-suppressed (normal or elevated) TSH — this is the biochemical hallmark of "inappropriate TSH secretion" |
| α-subunit | Serum measurement | Elevated in TSHoma; α-subunit:TSH molar ratio > 1 favours TSHoma over thyroid hormone resistance |
| TRH stimulation test | IV TRH → measure TSH response | Blunted TSH response in TSHoma (tumour is autonomous); normal/exaggerated response in thyroid hormone resistance |
Why is this DDx important? Because treating a TSHoma patient with antithyroid drugs or thyroidectomy (as you would for Graves' disease) would be completely wrong — it would remove the feedback brake and cause the TSHoma to grow aggressively. You need to treat the pituitary adenoma.
| Test | Method | Interpretation |
|---|---|---|
| Serum LH, FSH, and α-subunit [5] | Basal levels | Gonadotroph adenomas seldom hypersecrete clinically [2][3]; may show mildly elevated FSH or α-subunit; most commonly diagnosed as "non-functioning" on biochemistry and confirmed as gonadotroph on immunohistochemistry (SF-1 positivity) post-operatively |
α-subunit is not biologically active and does not cause clinical symptoms, but it is measured to determine if a sellar mass is pituitary in origin [5].
3. Step 2 — Imaging: Radiological Diagnosis
MRI pituitary is the single best imaging procedure for most sellar masses [5][2][3].
Protocol: Dedicated pituitary MRI with thin coronal and sagittal cuts (3 mm or less) through the sella, pre- and post-gadolinium contrast.
Key MRI findings in pituitary adenoma:
| Feature | Finding | Explanation |
|---|---|---|
| Microadenoma | Focal hypointense lesion relative to normal enhancing pituitary on early post-contrast images | Normal pituitary tissue takes up gadolinium to a greater degree than CNS tissue (high-intensity signal). Adenomas take up gadolinium to a lesser degree than normal pituitary but more than surrounding CNS [5]. On early dynamic images, the adenoma enhances more slowly → appears relatively dark against the brightly enhancing normal gland |
| Macroadenoma | Sellar mass > 1 cm; may be isointense to grey matter on T1; enhances heterogeneously; may show suprasellar extension, cavernous sinus invasion, sphenoid sinus erosion | Larger tumours often have heterogeneous signal due to cystic change, haemorrhage, or necrosis |
| Stalk deviation | Stalk pushed to one side by microadenoma | Indirect sign of a microadenoma on the opposite side |
| Suprasellar extension | Mass extends above the diaphragma sellae towards the optic chiasm | Explains visual field defects |
| Cavernous sinus invasion | Mass extends laterally beyond the intracavernous ICA (Knosp grade 3–4) | Predicts incomplete surgical resection |
| Posterior pituitary bright spot | Presence or absence on T1 | Normally bright due to ADH neurosecretory granules [2]; loss suggests DI or posterior pituitary involvement |
| Haemorrhage (apoplexy) | High signal on T1 (methaemoglobin); hyperdensity on CT | Acute blood products; pituitary apoplexy: acute blood in pituitary seen on CT/MRI [2] |
If a sellar lesion can be seen as separate from the normal pituitary gland, this indicates the mass is NOT a pituitary adenoma [5] — consider craniopharyngioma, meningioma, Rathke's cleft cyst, etc.
Gadolinium Precaution
Avoid gadolinium in patients with moderate to advanced renal failure (eGFR < 30) as it is associated with nephrogenic systemic fibrosis (NSF) — a potentially severe, debilitating fibrotic condition of the skin and internal organs [5]. In such patients, use non-contrast MRI or CT instead.
Don't MRI Without Indication
MRI pituitary should NOT be performed in healthy individuals with no clinical indication — up to 10% of normal middle-aged individuals have pituitary abnormalities on MRI [2]. Imaging incidentalomas cause unnecessary anxiety and further invasive workup.
CT is better than MRI for detecting calcification [2][3][5]:
| Finding on CT | Diagnosis Suggested |
|---|---|
| Calcification in a suprasellar mass | Craniopharyngioma (50% calcified) or meningioma |
| Bone erosion of clivus | Chordoma |
| Sellar floor erosion/remodelling | Large pituitary macroadenoma |
| Hyperdensity in the pituitary (acute) | Pituitary apoplexy (acute haemorrhage) [2] |
Seldom done nowadays due to low sensitivity and specificity [10], but classic findings include:
| Modality | Indication | What It Shows |
|---|---|---|
| CTA or MRA | Must exclude ICA aneurysm before transsphenoidal surgery [4] | Flow void = aneurysm; confirms vascular anatomy |
| CT/MRI of chest, abdomen, pelvis | Suspected ectopic ACTH or GHRH secretion | Neuroendocrine tumours (carcinoid, SCLC, pancreatic NET) |
| PET/CT (⁶⁸Ga-DOTATATE or FDG) | Ectopic ACTH source localisation when conventional imaging negative | Somatostatin-receptor-expressing NETs |
4. Step 3 — Assessment for Hypopituitarism
Every patient with a pituitary macroadenoma (and ideally every pituitary adenoma) needs a full anterior pituitary function assessment — even if the presenting problem is hormonal excess. The tumour may be simultaneously overproducing one hormone while destroying cells that produce others.
| Axis | Tests to Order | Interpretation |
|---|---|---|
| Adrenal (ACTH-cortisol) | 9 AM serum cortisol | > 500 nmol/L = likely intact; < 100 nmol/L = deficient; 100–500 = indeterminate → dynamic test needed |
| Thyroid (TSH-T4) | TSH + fT4 | Low fT4 with inappropriately normal/low TSH = central hypothyroidism |
| Gonadal (LH/FSH) | LH, FSH + testosterone (M) or oestradiol (F) | Low sex steroids with inappropriately normal/low LH/FSH = hypogonadotropic hypogonadism |
| GH (GH-IGF-1) | Serum IGF-1 | Low IGF-1 suggests GH deficiency (but can be normal in mild deficiency; dynamic testing may be needed) |
| Prolactin | Serum PRL | Elevated = functional prolactinoma or stalk effect; very low = extensive gland destruction |
| Posterior pituitary (ADH) | Serum and urine osmolality; urine specific gravity | Low urine osmolality with high serum osmolality → central DI |
Classical order of hormone loss in hypopituitarism: GH → FSH/LH → ACTH → TSH [2][3]
| Test | What It Assesses | Principle | Key Thresholds |
|---|---|---|---|
| Insulin tolerance test (ITT) | GH reserve AND ACTH/cortisol reserve simultaneously [9] | IV insulin → hypoglycaemia (glucose < 2.2 mmol/L) → this is a powerful stress stimulus that should trigger both GH and cortisol release via the hypothalamic stress response | Normal: peak cortisol > 550 nmol/L; GH rise > 20 mU/L. Blunted response = deficiency [9]. Also differentiates true Cushing's (blunted cortisol response) from pseudo-Cushing's |
| Short Synacthen test | ACTH/cortisol reserve (adrenal axis) | 250 μg synthetic ACTH (Synacthen) IV/IM → measure cortisol at 0, 30 min | Peak cortisol > 550 nmol/L = intact adrenal reserve. NB: may be falsely normal in recent pituitary damage (adrenals haven't atrophied yet) |
| Glucagon stimulation test | GH and cortisol reserve (alternative to ITT) [9] | IM glucagon → counter-regulatory GH and cortisol release | Alternative when ITT is contraindicated (epilepsy, IHD, severe hypopituitarism) |
| GHRH-arginine stimulation test | GH reserve [9] | GHRH stimulates somatotrophs; arginine suppresses somatostatin → maximal GH release | GH-dependent cut-offs (BMI-adjusted) |
| Water deprivation test | Central vs nephrogenic DI | Fluid restriction for 8h → measure urine osmolality; then give desmopressin (DDAVP) | Central DI: urine concentrates after DDAVP. Nephrogenic DI: no response to DDAVP |
ITT — Preparation and Safety
The ITT is considered the gold standard for assessing GH and cortisol reserve but carries risk of severe hypoglycaemia. Mandatory safety precautions [9]:
- Prior overnight fast
- ECG to exclude IHD (contraindicated in IHD and epilepsy)
- 50% dextrose and glucagon at bedside
- IV line in situ, resuscitation trolley on standby
- POCT glucose monitoring throughout
- ≥ 2 blood samples must be drawn during confirmed hypoglycaemia ( < 2.2 mmol/L)
Formal perimetry for visual defects due to compression on optic pathways [2] should be performed in all patients with macroadenoma or any visual complaint.
| Assessment | Method | What It Detects |
|---|---|---|
| Formal perimetry (Humphrey automated or Goldmann kinetic) | Standardised visual field mapping | Bitemporal hemianopia (classic), upper temporal quadrantanopia (early), scotomas, generalised constriction |
| Visual acuity | Snellen chart / LogMAR | Decreased acuity if optic nerve compression |
| Colour vision | Ishihara plates | Reduced colour perception (red desaturation) indicates optic nerve dysfunction |
| Fundoscopy | Direct ophthalmoscopy | Optic atrophy (pale disc) from chronic compression; papilloedema if raised ICP |
| Pupillary examination | Swinging flashlight test | Relative afferent pupillary defect (RAPD) in asymmetric optic nerve involvement |
| Ocular motility | Extraocular movements in all directions | CN III, IV, VI palsies from cavernous sinus involvement |
When indicated (young patient, family history, multifocal endocrine disease), screen for:
| Syndrome | Screen | Trigger to Screen |
|---|---|---|
| MEN1 | Serum calcium + PTH (parathyroid); fasting gastrin (gastrinoma); genetic testing for MEN1 gene | Young-onset pituitary adenoma, especially prolactinoma; concurrent hyperparathyroidism or pancreatic NET; family history [6] |
| Carney complex | Cardiac echo (myxoma); skin exam (lentigines); urinary cortisol (adrenal nodular hyperplasia); PRKAR1A gene | GH-secreting adenoma with cardiac myxoma or skin pigmentation |
| FIPA/AIP | AIP gene testing | Young-onset ( < 30y) GH-secreting or PRL-secreting adenoma, especially with family history of pituitary adenomas |
| Category | Investigations | Purpose |
|---|---|---|
| Hormonal hypersecretion | PRL, IGF-1, OGTT for GH (if acromegaly suspected), UFC/LDDST/late-night salivary cortisol (if Cushing's suspected), ACTH, TSH + fT4, LH + FSH + α-subunit | Determine if functioning or non-functioning |
| Hormonal hyposecretion | 9 AM cortisol, TSH + fT4, LH/FSH + sex steroids, IGF-1, PRL; dynamic tests (ITT, Synacthen) if equivocal | Detect hypopituitarism |
| Imaging | MRI pituitary with gadolinium (modality of choice); CT if calcification suspected (craniopharyngioma, meningioma); CTA/MRA to exclude aneurysm pre-operatively | Anatomical diagnosis, surgical planning |
| Visual assessment | Formal perimetry, visual acuity, colour vision, fundoscopy, pupillary exam, ocular motility | Assess optic pathway compression |
| Pre-operative | Full pituitary panel (above), electrolytes, renal function, coagulation, ECG, CXR; CTA/MRA for vascular anatomy | Surgical fitness and safety |
| Specific tumour workup | Colonoscopy (acromegaly); ECHO/cardiac assessment (acromegaly, Cushing's); bone density (hypogonadism, Cushing's); glucose tolerance (acromegaly) | Complication screening |
| Genetic/familial | MEN1 screen (Ca, PTH, gastrin); AIP gene; Carney complex workup as indicated | Familial syndrome exclusion |
| Intra-operative | Biopsy for histopathology and immunohistochemistry (transcription factor staining: PIT-1, T-PIT, SF-1; hormone staining; Ki-67 proliferation index) | Definitive tissue diagnosis and prognostication |
High Yield Summary — Diagnosis of Pituitary Adenoma
- Three diagnostic pillars: Biochemistry (hormonal excess + deficiency) → Imaging (MRI with gadolinium) → Visual assessment (perimetry)
- Mode of secretion determines the test: Pulsatile hormones (GH, ACTH) need dynamic tests; constant hormones (PRL, TSH, LH/FSH) need direct measurement [2]
- Prolactinoma dx: Serum PRL > 200 ng/mL (> 10× ULN); always correlate PRL level with tumour size; request serial dilutions if large mass with low PRL (hook effect) [2][3]
- Acromegaly dx: Elevated age-adjusted IGF-1 ± failure of GH suppression on OGTT (GH nadir > 1 ng/mL) [2][3]
- Cushing's disease dx: ≥ 2 screening tests abnormal (UFC, overnight DST, late-night salivary cortisol) → ACTH-dependent → HDDST suppresses / CRH test exaggerated rise → pituitary MRI ± IPSS [2][3][9]
- MRI pituitary with gadolinium = imaging modality of choice; CT better for calcification [2][3][5]
- If lesion is separate from normal pituitary on MRI → NOT a pituitary adenoma [5]
- Always exclude ICA aneurysm (CTA/MRA) before transsphenoidal surgery [4]
- ITT = gold standard for GH + cortisol reserve; normal peak cortisol > 550 nmol/L, GH > 20 mU/L [9]
- Hypopituitarism sequence: GH → FSH/LH → ACTH → TSH [2][3]
Active Recall - Diagnosis of Pituitary Adenoma
References
[2] Senior notes: Ryan Ho Endocrine.pdf (Section 5: Pituitary Gland, pp. 104–111; Section 3.3: Cushing's Syndrome, pp. 60–63) [3] Senior notes: Ryan Ho Fundamentals.pdf (Section 3.8.4: Presenting Problems in Pituitary Gland, pp. 436–437, 441–444) [4] Lecture slides: GC 108. A mass in the brain brain tumours.pdf (pp. 17–18, 41–42, 48) [5] Senior notes: felixlai.md (Pituitary adenoma section — Diagnosis) [6] Senior notes: Ryan Ho Endocrine.pdf (Section 6.3: MEN, p. 132) [9] Senior notes: Ryan Ho Chemical Path.pdf (Section 4: Diagnostic Function Tests, pp. 29–33) [10] Senior notes: Ryan Ho Neurology.pdf (Section 1.2.1: Neuroimaging — Skull X-ray, p. 32; Pituitary Adenoma, p. 166)
Management of Pituitary Adenoma
The management of pituitary adenoma is one of the few areas in medicine where the treatment algorithm is completely dictated by the hormonal subtype. A prolactinoma and a GH-secreting adenoma of identical size sitting in the same sella are treated by entirely different first-line modalities. Understanding why each subtype is treated differently comes down to understanding the unique pharmacology and biology of each cell lineage.
The management decision tree rests on two questions:
- Is the tumour functional or non-functional?
- Is there mass effect or is it a small incidental finding?
Treatment Paradigm [4]:
The Key Treatment Paradigm from Lecture Slides
Prolactinoma → Dopamine agonist (bromocriptine / cabergoline) = 1st line medical therapy [4]
GH, ACTH, TSH-secreting adenomas → Surgery first [4]
Non-functioning microadenoma → Observe [2][3]
Residual or recurrent disease → Radiosurgery or conventional RT [4]
This is the single most important management framework for exam purposes.
2. Conservative Management (Observation)
Observation is indicated for non-functional pituitary adenomas < 1 cm without mass effect or hormonal abnormality [5][2][3]
Why can we observe?
- Many microadenomas are discovered incidentally and remain stable for years or even decades
- The natural history of non-functioning microadenomas is generally benign — only ~10% enlarge over 5 years
- Unnecessary surgery carries risks (hypopituitarism, DI, CSF leak) that outweigh the benefit for a stable, asymptomatic lesion
Follow-up every 3–6 months [5] initially, then less frequently if stable:
| Timepoint | Assessment |
|---|---|
| 6 months | Repeat MRI pituitary; repeat hormonal panel |
| 1 year | Repeat MRI; repeat hormonal panel; visual field testing if close to chiasm |
| Annually for 3–5 years | If stable, extend interval to every 2–3 years |
| Indications to intervene | Tumour growth on serial MRI; new visual field defect; new hormonal deficit; symptoms develop |
3. Medical Treatment
Why does medical therapy work for prolactinoma but not for other adenomas?
This is elegant pharmacology rooted in physiology. Recall that prolactin is the only anterior pituitary hormone under tonic inhibition by dopamine from the hypothalamus. Lactotroph cells express abundant dopamine D2 receptors. When you give a dopamine agonist, it:
- Binds D2 receptors on tumour cells → directly inhibits prolactin synthesis and secretion → PRL falls within days
- Induces tumour cell shrinkage → cytoplasmic involution + perivascular fibrosis → tumour volume decreases over weeks to months (often dramatically — a 3 cm prolactinoma can shrink to nothing)
No other pituitary adenoma subtype has such a clean pharmacological target, which is why dopamine agonists are only first-line for prolactinoma.
| Drug | Dose | Efficacy | Side Effects | Notes |
|---|---|---|---|---|
| Cabergoline | Start 0.25–0.5 mg once or twice weekly; titrate monthly | 70–100% normalise PRL; > 90% tumour shrinkage [2][5] | Nausea (less than bromocriptine), postural hypotension, mental fogginess, impulse control disorders (hypersexuality, compulsive gambling/shopping — important to warn patients), cardiac valvulopathy at high doses (rare at standard prolactinoma doses) | Preferred over bromocriptine due to superior efficacy and tolerability [2][5] |
| Bromocriptine | Start 1.25 mg daily with food; titrate to 2.5–10 mg daily | ~80% normalise PRL | Nausea (more than cabergoline), orthostatic hypotension, nasal congestion, headache, dizziness | Older agent; still used especially in pregnancy (longer safety record) |
Dopamine agonists are 1st line treatment for patients with hyperprolactinaemia of any cause, including lactotroph adenoma of any size [5]
Management milestones for prolactinoma on DA therapy [2]:
| Phase | Action |
|---|---|
| Start | Begin low-dose cabergoline (0.25–0.5 mg/week); titrate monthly based on PRL level |
| Monitoring | PRL level every 1–3 months; MRI at 3–6 months (assess tumour shrinkage) |
| Target | Normalise PRL + resolve symptoms + tumour shrinkage |
| Attempt withdrawal | Consider tapering off DA if PRL normalised + no residual adenoma on MRI for ≥ 2 years [2]. Approximately 30–40% relapse after withdrawal → restart DA |
| Pregnancy | Stop DA when pregnant — no need to suppress PRL during pregnancy (hypogonadism is not an issue); PRL naturally rises in pregnancy. Resume if symptoms of tumour growth (headache, visual loss). Bromocriptine has the longest safety record in pregnancy [2] |
| Refractory | If maximum dose DA fails → surgery ± adjuvant RT [2][5][10] |
Special Scenario: Giant Prolactinoma and Pregnancy
Women with giant lactotroph adenoma > 3 cm who wish to become pregnant should be considered for surgery even if responding to DA [5]. Why? Because DA will be discontinued during pregnancy, and a 3+ cm tumour may grow rapidly without the dopamine "brake," potentially causing acute chiasmal compression before delivery.
Medical therapy for acromegaly is used when surgery is not curative (residual tumour), when surgery is contraindicated, or while awaiting the effect of radiotherapy [2]:
| Drug Class | Example | Mechanism | Efficacy | Side Effects |
|---|---|---|---|---|
| Somatostatin analogues (SSAs) | Octreotide LAR (long-acting repeatable, IM monthly); Lanreotide Autogel (SC monthly) | Bind somatostatin receptors (SST2 > SST5) on somatotroph adenoma cells → inhibit GH secretion + mild anti-proliferative effect → tumour shrinkage in ~30–50% | Normalise IGF-1 in ~55–65%; GH < 2.5 ng/mL in ~50–60% | Gallstones (SSA inhibit gallbladder contraction), GI upset (diarrhoea, steatorrhoea), hyperglycaemia (suppress insulin), injection site reactions |
| GH receptor antagonist | Pegvisomant (daily SC injection) | Modified GH molecule that binds GH receptors but blocks signal transduction → blocks GH action at the peripheral level; does NOT reduce tumour size | Normalises IGF-1 in ~90–95% (most effective agent for biochemical control) | LFT abnormalities (hepatotoxicity — monitor LFTs); does not shrink tumour; very expensive; injection site lipohypertrophy |
| Dopamine agonist | Cabergoline | Works in adenomas that co-secrete PRL (~30% of GH-secreting adenomas share PIT-1 lineage); binds D2 receptors | Normalises IGF-1 in ~30–40% (mild GH elevation only) | As above for DA |
Why is surgery first-line for acromegaly, not SSAs? Because SSAs only normalise IGF-1 in ~60% and rarely cure the disease. Transsphenoidal surgery has an 80–90% cure rate for microadenomas and can debulk large macroadenomas to improve subsequent medical efficacy [3]. The surgical "first strike" maximises the chance of biochemical remission.
Medical therapy here is not curative — it is used to:
- Control hypercortisolism pre-operatively (to reduce surgical risk) [2]
- Manage patients contraindicated for surgery or with persistent disease after surgery
- Bridge until radiotherapy takes effect (6–12 months delay)
| Drug Class | Example | Mechanism | Notes |
|---|---|---|---|
| Adrenal steroidogenesis inhibitors | Metyrapone (first-line) | Inhibits CYP11B1 (11β-hydroxylase) → blocks the final step of cortisol synthesis; short-acting, effective within 2 hours; requires BD/TDS dosing [2] | Side effects: hirsutism (shunts precursors to androgens), hypertension (↑11-deoxycorticosterone has mineralocorticoid activity), GI upset |
| Ketoconazole | Azole antifungal that also inhibits multiple adrenal steroidogenic enzymes (CYP11A1, CYP17) → ↓cortisol + ↓androgen | Hepatotoxicity (requires LFT monitoring; withdrawn in some countries as antifungal); gynaecomastia, ↓libido (anti-androgen effect) [2] | |
| Osilodrostat (newer) | CYP11B1 + CYP11B2 inhibitor; potent, oral, once daily | QTc prolongation; adrenal insufficiency if overdosed | |
| Adrenolytic agent | Mitotane | Cytotoxic to adrenal cortex ("medical adrenalectomy"); used mainly for adrenal carcinoma, occasionally severe Cushing's | Slow onset; GI side effects; teratogenic |
| Pituitary-acting agents | Pasireotide (somatostatin analogue with SST5 affinity) | Corticotroph adenoma cells express SST5; pasireotide binds SST5 → ↓ACTH secretion | Hyperglycaemia (significant — may need insulin); GI side effects |
| Cabergoline (dopamine agonist) | Some corticotroph adenomas express D2 receptors | Normalises UFC in ~25–40% of mild cases; less effective than steroidogenesis inhibitors [2] | |
| Glucocorticoid receptor antagonist | Mifepristone | Blocks cortisol at the receptor level → useful for metabolic complications (hyperglycaemia) | Does not lower cortisol levels (cannot monitor UFC); risk of adrenal insufficiency; anti-progestational (abortifacient) |
Two strategies for medical cortisol control [2]:
- Block-and-replace: Total suppression of cortisol with inhibitors + add back physiological hydrocortisone replacement. Used when cortisol production is highly variable
- Normalisation: Titrate inhibitor dose to normalise UFC without replacement. Used when cortisol production is relatively stable
- Somatostatin analogues (octreotide, lanreotide): used as adjunctive therapy post-surgery or pre-operatively; can normalise TSH and fT4 in ~80% and shrink tumour in ~40%
4. Surgical Treatment
Surgery is first-line for all functioning pituitary adenomas except prolactinoma, and for all macroadenomas with mass effect [2][3][4][10]
| Adenoma Type | Indication for Surgery |
|---|---|
| GH-secreting adenoma | First-line treatment — surgery offers the best chance of biochemical cure [2][3][4] |
| ACTH-secreting adenoma | First-line treatment — transsphenoidal surgery curative in 60–70% [2][4] |
| TSH-secreting adenoma | First-line treatment [4] |
| Prolactinoma | Second-line — only if refractory or intolerant to dopamine agonist; or giant prolactinoma in woman planning pregnancy [2][5][10] |
| Non-functioning macroadenoma | Symptomatic/large non-functioning adenoma with visual field defects, progressive growth, or hypopituitarism [2][3][10] |
| Pituitary apoplexy | Urgent surgical decompression under steroid cover if: signs of raised ICP, change in conscious state, evidence of compression on neighbouring structures [2][10] |
| Approach | Route | Indication | Rationale |
|---|---|---|---|
| Transsphenoidal (route of choice) | Through the nose (transnasal) or upper lip (sublabial) → sphenoid sinus → sellar floor → pituitary | Most pituitary adenomas — both micro- and macroadenomas | The sphenoid sinus sits directly below the sella. This approach avoids brain retraction entirely; recovery is faster; complications are lower. Two techniques: microscopic or endoscopic [10] |
| Transfrontal (transcranial) | Craniotomy → frontal lobe retraction → access from above | Very large suprasellar extension or severe chiasmal compression that cannot be safely reached from below [2] | Needed when the tumour is too large or too lateral (encasing ICA) for a transsphenoidal approach |
Why is endoscopic transsphenoidal surgery now preferred over microscopic?
- The endoscope provides a wide-angle, panoramic view of the surgical field
- Allows better visualisation of the lateral recesses (cavernous sinus margins), suprasellar extension, and diaphragma sellae descent
- Enables more complete tumour removal with lower rates of residual disease in experienced hands
- Both approaches have similar complication rates; the choice often depends on surgeon preference and expertise
| Adenoma Type | Cure Rate (Micro-) | Cure Rate (Macro-) | Notes |
|---|---|---|---|
| GH-secreting | 80–90% | < 50% [3] | Can repeat surgery if MRI detects residual tumour |
| ACTH-secreting | 60–70% curative (postop cortisol undetectable) [2] | Lower (macroadenomas rare in Cushing's disease) | Microadenomectomy if feasible; otherwise subtotal anterior hypophysectomy if no fertility wish [2] |
| Prolactinoma | ~80% (when surgery is chosen) | ~30–40% | Rarely first-line; high recurrence rates compared to continued DA |
| Non-functioning | Debulking → decompression | Complete resection rates 50–70% | NOT all adenoma tissue can be excised, particularly macroadenomas [5]; surgery tends to be conservative to minimise damage to surrounding structures [5] |
Advantages of surgery [2]:
- Rapid reduction in hormone secretion and tumour size → biochemical remission achievable in days to weeks
- Remission > 85% for microadenomas; 40–50% for macroadenomas
Disadvantages of surgery [2]:
- Residual disease or recurrence, especially with macroadenomas (2–8% recurrence rate)
- Hypopituitarism — risk of new hormone deficiencies
- Diabetes insipidus — from surgical injury to the stalk or posterior pituitary (may be transient or permanent)
This is explicitly listed as essential knowledge in the lecture slides [4]:
| Complication | Mechanism | Frequency | Management |
|---|---|---|---|
| Diabetes insipidus | Injury to posterior pituitary or infundibular stalk → loss of ADH → inability to concentrate urine → polyuria + polydipsia | 10–20% transient; 1–5% permanent | Desmopressin (DDAVP); monitor urine output and serum Na closely post-op |
| Hypopituitarism | Removal or compression of normal pituitary tissue during surgery | Variable; higher with larger tumours | Lifelong hormonal replacement as needed (hydrocortisone, levothyroxine, sex steroids, GH) |
| CSF leakage (rhinorrhoea) | Defect in the sellar floor or diaphragma sellae → CSF drains through nose | 0.5–4% [5] | Lumbar subarachnoid CSF drainage first; if unsuccessful → re-operation to repack the adenoma bed; failure to stop CSF leakage increases risk of meningitis [5] |
| Meningitis | Secondary to CSF leak; direct contamination from nasal flora | ~1–2% | Prophylactic antibiotics peri-operatively; urgent treatment with IV antibiotics if develops |
| Vision loss | Intra-operative damage to optic nerves or chiasm | Rare (< 1%) | Intra-operative visual monitoring; careful surgical technique |
| Vascular injury and CVA | Injury to internal carotid artery (runs in the cavernous sinus just lateral to the sella) | Very rare but catastrophic | Pre-operative CTA/MRA to map vascular anatomy; meticulous lateral dissection |
| Intracranial haemorrhage | Bleeding from tumour bed or vascular injury | Rare | Immediate surgical evacuation if significant |
| ENT symptoms | Nasal crusting, septal perforation, sinusitis, anosmia | Common but usually minor | Nasal care; saline irrigation |
| Mortality | All causes combined | Very rare ( < 0.5%) [10] |
Post-Operative DI — The Triphasic Response
After transsphenoidal surgery, DI can follow a classic triphasic pattern:
- Phase 1 (Days 1–3): DI due to axonal shock → polyuria, dilute urine, rising serum Na
- Phase 2 (Days 4–8): Release of stored ADH from damaged axon terminals → transient SIADH → hyponatraemia
- Phase 3 (Day 9+): Permanent DI if axons are destroyed; or recovery if axonal function resumes
Not all patients go through all three phases. Monitor urine output, urine specific gravity, serum Na, and serum/urine osmolality closely in the first 7–14 days post-op.
| Timepoint | Assessment |
|---|---|
| Immediate post-op (Days 1–7) | Urine output + fluid balance (DI screening); serum Na Q6–12h; serum cortisol (if adrenal axis at risk) |
| 4–6 weeks | Full pituitary hormone panel → assess for new hypopituitarism [2]; visual fields if macroadenoma |
| 3 months | Hormonal reassessment; repeat MRI (baseline post-op scan) |
| 6–12 months | MRI pituitary; hormonal panel |
| 1y, 2y, 5y, 10y | Post-op MRI for any recurrence [2] |
4.6 Peri-Operative Management — Specific Considerations
- Pre-operative: Control and correct HTN, DM, hypokalaemia; metyrapone to lower cortisol
- Peri-operative: Steroid cover (the contralateral normal corticotrophs are suppressed by chronic hypercortisolism → acute adrenal insufficiency after tumour removal); prophylactic antibiotics (Cushing's patients are immunosuppressed); DVT prophylaxis (hypercoagulable state)
- Post-operative: Glucocorticoid replacement (15–25 mg/d hydrocortisone); taper gradually; HPA axis may take 6–18 months to recover (some patients need lifelong replacement) [2][11]
- Pre-operative SSA may be given to improve anaesthetic safety (reduce soft tissue swelling, improve cardiac function)
- Post-op: assess GH/IGF-1 at 3 months for remission
5. Radiotherapy
Radiotherapy is usually used as adjunct to surgery [2][3], not as primary treatment (with the exception of certain macroprolactinomas and patients who are not surgical candidates).
| Modality | Technique | Advantages | Disadvantages |
|---|---|---|---|
| Conventional fractionated EBRT | 45–50.4 Gy in 25–28 fractions over 5–6 weeks | Effective; proven long-term tumour control | Delayed effect on hormone secretion (months to years) [2]; higher incidence of hypopituitarism (50–100% at 10–20 years) [2]; risk of damage to optic apparatus; rare second malignancy; cognitive effects |
| Stereotactic radiosurgery (SRS) | Gamma Knife or CyberKnife / LINAC-based; single high-dose fraction precisely targeted at tumour | More precise; shorter treatment; less collateral damage to surrounding brain | NOT used if tumour is < 5 mm from the optic chiasm [2] — the single high dose would damage the chiasm; not suitable for very large tumours with suprasellar extension |
| Fractionated stereotactic RT | Multiple fractions delivered with stereotactic precision | Can treat tumours close to the optic chiasm (fractionation allows optic apparatus to repair between fractions) | Intermediate between EBRT and SRS |
or radiosurgery [4] — the lecture slides specifically mention radiosurgery as an alternative for residual/recurrent disease.
- Adjunct to surgery for residual tumour (most common use)
- Primary therapy for patients who are not surgical candidates (elderly, comorbid)
- Macroprolactinoma refractory to dopamine agonist and surgery
- Recurrent adenoma after prior surgery
- Cushing's disease: pituitary irradiation + medical therapy if residual non-resectable disease [2]
Stereotactic radiosurgery is NOT used if the tumour is < 5 mm from the optic chiasm [2] — the optic apparatus has limited radiation tolerance (~8–10 Gy single dose), and a single high-dose radiosurgery fraction would risk optic neuropathy and blindness.
- Delayed effect on secretion — not useful for acute symptom control; maximum effect 6–12 months for hormone normalisation
- Higher incidence of hypopituitarism — progressive loss of pituitary function over years (GH first, then other axes); patients need lifelong endocrine follow-up
- Risk of damage to surrounding structures — optic nerve, temporal lobes (cognitive decline), cranial nerves
- Secondary malignancy — very rare but reported (meningioma, glioma in the irradiated field, years later)
- Cerebrovascular disease — increased stroke risk years after cranial RT
6. Management by Specific Adenoma Type — Detailed Algorithm
Transsphenoidal surgery is 1st line: 80–90% curative for micro-, < 50% for macroadenoma. Can repeat surgery if MRI detects residual tumour [3]
Risk of Nelson syndrome (8–25% in adults, > 50% in children) following bilateral adrenalectomy [2]: the removal of cortisol negative feedback causes the residual corticotroph adenoma to grow aggressively and secrete very high ACTH → skin hyperpigmentation + expanding sellar mass. This is why bilateral adrenalectomy is a last resort and patients need long-term MRI surveillance.
| Scenario | Management |
|---|---|
| Microadenoma, asymptomatic, incidental | Observe with serial MRI and hormonal panel [2][3][5] |
| Macroadenoma with mass effect (visual field defects, progressive growth, hypopituitarism) | Transsphenoidal surgery → maximal safe debulking → post-op MRI at 3–6 months |
| Residual tumour post-surgery | Radiosurgery or fractionated RT if growing on serial imaging [4] |
| Growing on surveillance (previously observed) | Surgery |
Whether caused by the tumour itself or by its treatment (surgery, RT), hypopituitarism requires systematic replacement:
| Deficient Axis | Replacement | Dose | Key Points |
|---|---|---|---|
| ACTH-cortisol | Hydrocortisone | 15–25 mg/d in divided doses (10 mg AM + 5 mg PM) | Most critical — must be replaced FIRST before thyroxine (giving T4 without cortisol can precipitate adrenal crisis by increasing cortisol metabolism). Patient needs a steroid emergency card; must double/triple dose during illness ("sick day rules") |
| TSH-T4 | Levothyroxine | 1.0–1.6 μg/kg/d | Monitor with fT4 (NOT TSH — in central hypothyroidism, TSH is unreliable). Start only AFTER cortisol replacement |
| FSH/LH → Sex steroids | Testosterone (M); Oestrogen ± progesterone (F) | Testosterone: IM, transdermal, or PO; HRT: standard regimens | Restores libido, bone density, muscle mass, secondary sexual characteristics. If fertility desired: gonadotropin injections (FSH + LH/hCG) instead of sex steroids |
| GH | Recombinant human GH | Titrated to normalise IGF-1 | Improves body composition, QoL, bone density. Contraindicated if active malignancy. Expensive. Not always available |
| ADH (if DI) | Desmopressin (DDAVP) | Intranasal, oral, or SC; titrated to urine output | Monitor serum Na to avoid hyponatraemia from over-replacement |
The Order of Replacement Matters!
Always replace cortisol BEFORE thyroxine. Thyroxine increases cortisol metabolism by inducing hepatic enzymes. If you start thyroxine in a cortisol-deficient patient, you accelerate cortisol clearance → precipitate an acute adrenal crisis. This is a classic exam pitfall.
Pituitary apoplexy is a neurosurgical emergency [2][4][10]:
| Step | Action | Rationale |
|---|---|---|
| 1. Immediate | IV hydrocortisone 100 mg stat, then 50 mg Q6–8H | Presumed acute ACTH/cortisol deficiency — life-threatening if untreated |
| 2. Assess | Neurological exam: GCS, visual fields, visual acuity, pupillary responses, CN exam | Determine severity of compression |
| 3. Image | CT head (acute blood = hyperdense) → MRI pituitary if stable | Confirm diagnosis |
| 4. Decide | Urgent surgical decompression if: signs of raised ICP; change in conscious state; evidence of compression on neighbouring structures [2][10] | Surgery decompresses the chiasm and cavernous sinus; removes haemorrhagic debris |
| 5. Conservative | If haemodynamically stable, no visual deterioration, mild symptoms → conservative management with steroids + close monitoring (some centres manage stable apoplexy conservatively) | Not all apoplexy requires surgery; ~50% improve with steroids alone |
| 6. Post-acute | Full pituitary function testing at 4–6 weeks; visual field assessment; plan for definitive management of residual adenoma | Many patients develop permanent hypopituitarism; some recover function |
All patients with treated pituitary adenomas require lifelong follow-up because:
- Recurrence can occur years later (especially with macroadenomas)
- Hypopituitarism can develop late (especially after RT)
- Hormone replacement needs monitoring and adjustment
| Component | Frequency | Purpose |
|---|---|---|
| MRI pituitary | 1y, 2y, 5y, 10y post-surgery [2]; then every 3–5y if stable | Detect recurrence |
| Hormonal panel | 6-monthly for first 2 years; then annually | Detect new deficiencies; monitor replacement adequacy |
| Visual fields | Pre-op, post-op (3 months), then annually if macroadenoma | Monitor chiasmal function |
| Complication screening | Acromegaly: colonoscopy, cardiac assessment, glucose; Cushing's: metabolic panel, bone density | Systemic complications of hormone excess |
High Yield Summary — Management of Pituitary Adenoma
- Prolactinoma = dopamine agonist FIRST (cabergoline preferred over bromocriptine) — normalises PRL and shrinks tumour in > 90%; surgery only if DA-refractory or intolerant [4][5]
- GH, ACTH, TSH-secreting adenomas = surgery FIRST (transsphenoidal) [4]
- Non-functioning microadenoma = observe (FU every 3–6 months) [5]
- Non-functioning macroadenoma with mass effect = surgery [2]
- Radiotherapy / radiosurgery = adjunct for residual or recurrent disease [4]; NOT used if tumour < 5 mm from optic chiasm [2]
- Acromegaly surgery: 80–90% cure for micro, < 50% for macro → SSA, pegvisomant, or DA if incomplete [3]
- Cushing's disease surgery: 60–70% curative → repeat surgery, RT, medical Rx, or bilateral adrenalectomy if persistent (risk of Nelson syndrome) [2]
- Complications of transsphenoidal surgery: DI, hypopituitarism, CSF leak + meningitis, vision loss, vascular injury, intracranial haemorrhage, ENT symptoms [4][10]
- Replace cortisol BEFORE thyroxine in hypopituitarism
- Pituitary apoplexy = IV hydrocortisone FIRST → urgent surgery if compressive signs [2][10]
Active Recall - Management of Pituitary Adenoma
References
[2] Senior notes: Ryan Ho Endocrine.pdf (Section 5: Pituitary Gland, pp. 104–111; Cushing's management pp. 63–64; Prolactinoma management p. 110) [3] Senior notes: Ryan Ho Fundamentals.pdf (Section 3.8.4: Pituitary Tumour, pp. 441–444) [4] Lecture slides: GC 108. A mass in the brain brain tumours.pdf (pp. 41–42, 48) [5] Senior notes: felixlai.md (Pituitary adenoma — Treatment section) [9] Senior notes: Ryan Ho Chemical Path.pdf (Section 4: Diagnostic Function Tests, pp. 33–34) [10] Senior notes: Ryan Ho Neurology.pdf (Pituitary Adenoma management, p. 166; Brain tumour surgery, p. 163) [11] Senior notes: maxim.md (Cushing syndrome management, pp. 434–435)
Complications of Pituitary Adenoma
Complications of pituitary adenoma arise from three distinct sources: (A) the tumour itself (mass effect and hormonal derangement), (B) treatment (surgery, radiotherapy, medical therapy), and (C) specific hormonal syndromes (the systemic damage wrought by chronic hormone excess). Let's work through each systematically, always explaining the "why."
1. Complications of the Tumour Itself
Pituitary apoplexy is a neurosurgical emergency [2][4][10].
- Definition: Acute haemorrhagic infarction of a pituitary adenoma — a catastrophic event where the adenoma suddenly outgrows its blood supply, undergoes ischaemic necrosis, and haemorrhages. The confined bony sella cannot accommodate the sudden volume expansion → acute compression of surrounding structures.
- Why it happens: Pituitary adenomas are more vascular than normal pituitary tissue yet have fragile, disorganised neovasculature. Precipitants include anticoagulation, post-surgical hypotension, dynamic endocrine testing, pregnancy, and sometimes no identifiable trigger.
Clinical presentation [2][4][10]:
- Acute haemorrhagic infarction ± SAH [4]
- Headache, visual loss, coma [4]
- Acute cortisol insufficiency requiring replacement [4]
- Diplopia (CN III compression in cavernous sinus)
- Meningism if blood leaks into subarachnoid space
Key management principles from the lecture slides [4]:
- Give cortisol before T4 — this is emphasised on the lecture slide because levothyroxine increases cortisol metabolism; giving T4 without cortisol cover in an acutely hypopituitary patient precipitates adrenal crisis [4]
- "Which can predispose DI" [4] — acute cortisol insufficiency in apoplexy can unmask or predispose to diabetes insipidus because cortisol normally suppresses ADH release; when you give cortisol replacement, the ADH suppression is restored and polyuria may become apparent
- Urgent surgery for decompression — if visual deterioration, altered consciousness, or signs of raised ICP [4][10]
Bitemporal hemianopia is the classic visual complication [4]:
- Pathophysiology: Suprasellar extension of a macroadenoma compresses the optic chiasm from below. The crossing nasal retinal fibres (subserving temporal visual fields) are most vulnerable because they sit in the inferior-central part of the chiasm, directly above the pituitary.
- Progression: Upper temporal quadrantanopia (early, inferior chiasmal fibres affected first) → complete bitemporal hemianopia → decreased visual acuity → optic atrophy (chronic compression → irreversible axonal degeneration)
- Why it matters: Visual field defects may be reversible if decompressed early (within weeks to months), but chronic compression leads to optic atrophy and permanent visual loss. This is why close visual monitoring post-op is essential [4].
Visual Loss is a Surgical Indication
Progressive visual field loss in a patient with a pituitary macroadenoma is an urgent indication for surgery. Delay risks permanent blindness. Even in prolactinoma (where medical therapy is first-line), if there is rapid visual deterioration, surgery may take priority over waiting for the dopamine agonist to shrink the tumour.
As the adenoma grows, it compresses and destroys the surrounding normal pituitary tissue. The consequences depend on which hormonal axes are lost:
| Axis Lost | Complication | Pathophysiology | Clinical Consequence |
|---|---|---|---|
| GH (first lost) | GH deficiency | Loss of GH anabolic effects on body composition, bone, and metabolism | Increased visceral fat, decreased muscle mass, reduced bone mineral density, fatigue, impaired quality of life; growth failure in children |
| FSH/LH (second) | Hypogonadotropic hypogonadism | Loss of gonadal stimulation → ↓oestrogen/testosterone | Amenorrhoea, infertility, erectile dysfunction, decreased libido, osteoporosis (chronic oestrogen/testosterone deficiency → ↑bone resorption) |
| ACTH (third) | Secondary adrenal insufficiency | Loss of cortisol → inability to mount stress response | Fatigue, weight loss, hypotension; life-threatening adrenal crisis during intercurrent illness, surgery, or trauma if not recognised. Unlike Addison's, no hyperkalaemia (aldosterone preserved via RAAS) and no hyperpigmentation (ACTH is low) |
| TSH (fourth) | Central hypothyroidism | Loss of thyroid stimulation → ↓T4 | Fatigue, cold intolerance, weight gain, constipation, bradycardia, cognitive slowing |
| PRL (rarely) | Inability to lactate | Only with total gland destruction (e.g., Sheehan's syndrome) | Failure of postpartum lactation |
Classical order of hormone loss: GH → FSH/LH → ACTH → TSH [2][3]
Hypopituitarism can cause shock (cortisol) [4] — this is explicitly highlighted on the lecture slide. Acute cortisol deficiency (from tumour compression, apoplexy, or post-surgery) is the most dangerous endocrine complication because cortisol is essential for vascular tone, gluconeogenesis, and the stress response. Without cortisol replacement, patients can develop refractory hypotension and die.
Hydrocephalus (at III ventricle) [4]:
- Pathophysiology: Very large or giant adenomas ( > 4 cm) can extend superiorly to obstruct the foramen of Monro or compress the third ventricle → obstructive hydrocephalus → raised ICP
- Symptoms: Headache (worse in the morning, with coughing/straining), nausea/vomiting, drowsiness, papilloedema, eventual coning if untreated
- Management: Urgent neurosurgical decompression; CSF diversion (external ventricular drain or shunt) if rapid deterioration [11]
Cranial nerve palsy [4]:
- Mechanism: Lateral extension of the adenoma into the cavernous sinus compresses CN III (most commonly), CN IV, CN VI, CN V1, or CN V2
- CN III palsy is most common because it runs most medially along the cavernous sinus wall, closest to the expanding pituitary adenoma [8]
- Clinical features: Diplopia, ptosis, "down and out" eye (CN III); lateral gaze palsy (CN VI); facial numbness (CN V1/V2)
- Cavernous sinus invasion is a marker of an aggressive/invasive adenoma and often precludes complete surgical resection
2. Complications of Treatment
This is explicitly listed as essential knowledge in the lecture slides: "Treatment principles for pituitary adenoma & complications of transsphenoidal surgery" [4]
The lecture slide lists these complications directly [4]:
| Complication | Pathophysiology | Frequency | Key Details |
|---|---|---|---|
| Mortality | All surgical causes combined | Very rare [4][10] | < 0.5% in experienced centres |
| Hypopituitarism | Surgical removal of or damage to normal pituitary tissue; stalk injury interrupts hypothalamic releasing hormones to anterior pituitary | Variable (5–20% new deficits for macroadenomas) | Can cause shock (cortisol) [4] — the most immediately dangerous deficit. Patients require post-operative cortisol assessment and replacement. May need lifelong multihormone replacement [5] |
| Diabetes insipidus | Injury to the posterior pituitary or infundibular stalk → loss of ADH → kidneys cannot concentrate urine | 10–20% transient; 1–5% permanent | Polyuria, haemoconcentration [4]. Monitor urine output hourly, serum Na Q6–12h post-op. Treat with desmopressin (DDAVP). Can follow the triphasic pattern: DI → SIADH → permanent DI |
| CSF leakage and meningitis | Defect in the dural repair of the sellar floor or diaphragma sellae → CSF drains through the nose (rhinorrhoea) | 0.5–4% [5] | Detected by beta-2-transferrin positivity [4] (beta-2-transferrin is a protein uniquely present in CSF and perilymph — finding it in nasal discharge confirms CSF leak). Pneumocephaly [4] (air entering the intracranial cavity through the defect) on post-op imaging is another sign. Failure to stop CSF leakage increases risk of meningitis [5]. Managed with lumbar CSF drainage; re-operation to repack the adenoma bed if unsuccessful |
| Visual loss | Intra-operative injury to optic nerves or chiasm; post-operative haematoma compressing optic pathways | Rare ( < 1%) | Close monitoring post-op [4] — serial visual acuity and field testing. Any new visual deterioration post-op warrants urgent imaging to rule out haematoma |
| ENT symptoms | Epistaxis, anosmia, sinusitis [4]; also nasal crusting, septal perforation | Common but usually minor | Transnasal approach traverses the nasal cavity and sphenoid sinus; mucosal trauma is expected. Post-op nasal care (saline irrigation) minimises complications |
| Vascular injury | Injury to the internal carotid artery running in the cavernous sinus just lateral to the sella | Very rare but catastrophic | Uncontrolled arterial haemorrhage; stroke; carotid-cavernous fistula. Pre-operative CTA/MRA maps vascular anatomy to reduce risk |
| Intracranial haemorrhage | Bleeding from the tumour bed, venous sinuses, or carotid injury → expanding haematoma | Rare | Immediate surgical evacuation if significant; deteriorating consciousness = emergency |
Beta-2-Transferrin — The CSF Leak Marker
Beta-2-transferrin is positive in CSF (and perilymph) but absent in normal nasal secretions, tears, and blood [4]. If you suspect a post-operative CSF leak (clear, watery nasal discharge), send the fluid for beta-2-transferrin assay. A positive result confirms CSF rhinorrhoea and mandates treatment (lumbar drain → re-operation if persistent) to prevent ascending meningitis.
Radiotherapy (conventional EBRT or stereotactic radiosurgery) carries its own set of long-term complications:
| Complication | Pathophysiology | Timeframe | Details |
|---|---|---|---|
| Progressive hypopituitarism | Radiation damages normal pituitary cells; GH-producing somatotrophs are most sensitive | Months to years (50% at 5 years; 80–100% at 10–20 years) | GH deficiency first, then gonadotropins, then ACTH, then TSH — same order as compression. All irradiated patients require lifelong annual hormonal monitoring |
| Optic neuropathy | Radiation-induced damage to optic nerve/chiasm; risk increases when tumour is < 5 mm from chiasm and with single high-dose fractions | 6 months to 3 years | This is why stereotactic radiosurgery is NOT used if the tumour is < 5 mm from the optic chiasm [2]. Fractionated RT is safer for tumours close to the optic apparatus |
| Secondary malignancy | Radiation induces DNA mutations in surrounding brain tissue → meningioma, glioma, sarcoma in the irradiated field | 10–30+ years | Very rare (~2–3% lifetime risk) but important for young patients who have decades of life ahead |
| Cerebrovascular disease | Radiation-induced accelerated atherosclerosis in intracranial vessels (especially the ICA and circle of Willis) | 5–20+ years | Increased stroke risk; may require cardiovascular risk factor management |
| Neurocognitive decline | Radiation damage to temporal lobes, hippocampi, white matter tracts | Years | Memory impairment, executive dysfunction; more common with conventional EBRT than SRS |
| Hypothalamic damage | Direct radiation to hypothalamus | Variable | Hyperphagia, obesity, sleep disturbance, temperature dysregulation — more common in children receiving RT for craniopharyngioma |
2.3 Complications of Medical Therapy
| Side Effect | Mechanism | Notes |
|---|---|---|
| Nausea | D2 receptor stimulation in the chemoreceptor trigger zone (area postrema) | More common with bromocriptine than cabergoline [5]; mitigated by taking with food, starting at low dose |
| Orthostatic hypotension | D2 receptor activation → peripheral vasodilation + decreased sympathetic tone | Start low, titrate slowly; warn patients to rise slowly from sitting/lying |
| Nasal congestion | Vasodilation in nasal mucosa | Minor but bothersome [5] |
| Impulse control disorders | D2/D3 receptor stimulation in mesolimbic reward pathways | Hypersexuality, compulsive gambling, compulsive shopping — must specifically ask about these at every visit; may require dose reduction or switch |
| Cardiac valvulopathy | Serotonin 5-HT2B receptor agonism on cardiac valves → fibrotic valve thickening | Primarily a concern with high-dose cabergoline (as used in Parkinson's disease); at standard prolactinoma doses ( < 2 mg/week), risk is very low; still recommended to perform periodic echocardiography if using > 2 mg/week for > 2 years |
| CSF rhinorrhoea (during treatment of macroprolactinoma) | Rapid tumour shrinkage by DA → the tumour was acting as a "plug" for eroded sellar floor; when it shrinks, CSF leaks through the defect | Rare but important; can lead to meningitis. Monitor for clear nasal discharge when starting DA for macroprolactinoma |
| Side Effect | Mechanism |
|---|---|
| Gallstones (10–30%) | SSA inhibits gallbladder contraction (cholecystokinin-mediated) + ↑bile lithogenicity → biliary sludge and gallstones |
| GI side effects | ↓pancreatic exocrine secretion + ↓gut motility → diarrhoea, steatorrhoea, flatulence, abdominal cramps |
| Hyperglycaemia | SSA suppresses insulin secretion from pancreatic β-cells (via SST5 and SST2 receptors) → impaired glucose tolerance. Paradoxically, in acromegaly, GH also causes insulin resistance, so the net effect on glucose depends on the balance between GH reduction and insulin suppression |
| Injection site reactions | Local inflammation, lipodystrophy at injection site |
| Side Effect | Mechanism |
|---|---|
| Hepatotoxicity | Idiosyncratic; monitor LFTs every 4–6 weeks for 6 months then periodically |
| Tumour growth | Does NOT reduce tumour size (blocks GH action peripherally but removes IGF-1 negative feedback on pituitary → theoretical risk of somatotroph adenoma growth). Monitor with MRI |
| Injection site lipohypertrophy | Local reaction |
3. Complications of Specific Hormonal Excess Syndromes
These are the systemic complications caused by chronic, uncontrolled hormonal hypersecretion. They are the reason we treat pituitary adenomas aggressively.
Overall mortality 1.72× compared to the general population, mainly due to cardiovascular risk [2][3]
| System | Complication | Pathophysiology |
|---|---|---|
| Cardiovascular | HTN (~40%) | GH/IGF-1 → sodium retention + increased vascular resistance + direct vascular remodelling |
| LVH | GH/IGF-1 → direct myocardial hypertrophy (cardiomyocyte growth) independent of BP | |
| Cardiomyopathy with diastolic HF | Myocardial fibrosis + hypertrophy → stiff ventricle → impaired relaxation → diastolic dysfunction | |
| CV mortality (2×) [2] | HTN + LVH + cardiomyopathy + metabolic syndrome combine to accelerate atherosclerosis | |
| Valvular heart disease | GH/IGF-1 → fibrosis and thickening of cardiac valves (especially mitral and aortic) | |
| Metabolic | IGT (~40%), T2DM (~20%) | GH is a counter-regulatory hormone → insulin resistance (impaired glucose uptake in muscle, increased hepatic gluconeogenesis) |
| Dyslipidaemia | GH-driven lipolysis → ↑free fatty acids → mixed dyslipidaemia | |
| Hypercalcaemia + hyperphosphataemia | GH stimulates 1α-hydroxylase in kidney → ↑1,25-dihydroxyvitamin D → ↑intestinal Ca absorption; GH also ↑renal phosphate reabsorption via IGF-1 | |
| Respiratory | OSA (~50%) | Macroglossia + pharyngeal soft tissue hypertrophy → upper airway obstruction during sleep [2][3] |
| Musculoskeletal | Hypertrophic arthropathy | Synovial tissue and cartilage overgrowth → joint space widening → secondary osteoarthritis; pseudogout (calcium pyrophosphate deposition) |
| Carpal tunnel syndrome (~50%) | Soft tissue swelling in the carpal tunnel compresses the median nerve | |
| Gastrointestinal | ↑Risk of colon CA, polyps, diverticulosis | GH/IGF-1 promotes colonic epithelial cell proliferation; IGF-1 is a mitogenic growth factor → screening colonoscopy recommended at diagnosis and periodically thereafter [2][3] |
| Other malignancy | ↑Risk of other cancers | IGF-1 is mitogenic and anti-apoptotic; epidemiological data suggest modestly increased risk of thyroid, breast, and possibly prostate cancer |
| Renal | Renal stones (hypercalciuria) | ↑1,25-dihydroxyvitamin D → ↑intestinal Ca absorption → ↑urinary Ca excretion → nephrolithiasis [2] |
Why Screen for Colon Cancer in Acromegaly?
IGF-1 is a powerful mitogen — it stimulates cell proliferation and inhibits apoptosis. The colonic epithelium is particularly sensitive to IGF-1. Studies show acromegalic patients have a 2–3× increased risk of colonic polyps and adenocarcinoma. This is why colonoscopy at diagnosis and every 3–10 years depending on findings is recommended [2][3].
Untreated Cushing's syndrome is often fatal due to cardiovascular and thromboembolic complications [2]
| System | Complication | Pathophysiology |
|---|---|---|
| Cardiovascular | HTN, accelerated atherosclerosis, stroke, MI | Cortisol has mineralocorticoid activity at high concentrations (overwhelms 11β-HSD2 enzyme which normally inactivates cortisol in mineralocorticoid-responsive tissues) → sodium retention + volume expansion + vasoconstriction. Also ↑renin substrate (angiotensinogen) and ↑vascular reactivity to catecholamines |
| Thromboembolic | VTE (DVT/PE) | Cortisol ↑clotting factors (fibrinogen, factor VIII, von Willebrand factor) + ↓fibrinolysis → hypercoagulable state. This is a major cause of mortality in uncontrolled Cushing's. Perioperative DVT prophylaxis is essential [2][3] |
| Metabolic | T2DM/IGT, dyslipidaemia | Cortisol → hepatic gluconeogenesis + peripheral insulin resistance → hyperglycaemia. Also ↑lipolysis → dyslipidaemia |
| Musculoskeletal | Proximal myopathy, osteoporosis, fractures | Cortisol → protein catabolism (muscle wasting, especially proximal); cortisol → ↓osteoblast activity + ↑osteoclast activity → bone loss; ↓intestinal Ca absorption |
| Immunological | Increased susceptibility to infections (opportunistic infections including PCP, fungal) | Cortisol → immunosuppression (↓lymphocytes, ↓neutrophil migration, ↓cytokine production) |
| Psychiatric | Depression (50–80%), psychosis, cognitive impairment, insomnia | Cortisol has direct neurotoxic effects on hippocampal neurons; disrupts serotonin and dopamine signalling |
| Skin | Easy bruising, poor wound healing, purple striae, skin thinning | Cortisol → collagen breakdown + dermal atrophy → fragile skin + visible dermal vessels |
| Reproductive | Amenorrhoea, infertility, decreased libido | Cortisol inhibits GnRH pulsatility + adrenal androgen excess disrupts gonadal axis |
Cushingoid features generally resolve 2–12 months after definitive treatment [2], but some complications (osteoporosis, cardiovascular remodelling, neurocognitive effects) may be irreversible.
| Complication | Pathophysiology |
|---|---|
| Osteoporosis | PRL-induced hypogonadotropic hypogonadism → chronic oestrogen/testosterone deficiency → ↑bone resorption |
| Infertility | PRL inhibits GnRH → ↓FSH/LH → anovulation (F), azoospermia (M) |
| Sexual dysfunction | Decreased libido, erectile dysfunction (M), vaginal dryness (F) — from hypogonadism |
| Psychological | Anxiety, depression — both from hypogonadism and the direct effects of PRL on mood/behaviour |
Nelson syndrome occurs in 8–25% of adults (> 50% in children) following bilateral adrenalectomy for Cushing's disease [2]:
- Pathophysiology: Bilateral adrenalectomy removes all cortisol production, completely eliminating negative feedback on the pituitary corticotroph adenoma. Without the cortisol "brake," the residual ACTH-secreting tumour grows aggressively and hypersecretes ACTH.
- Clinical features:
- Plasma ACTH > 200 pg/mL [2]
- Intense skin hyperpigmentation — very high ACTH (and its co-secreted precursor POMC-derived α-MSH) stimulates melanocytes
- Enlarging pituitary tumour — can cause visual loss, headache, cavernous sinus invasion
- Diagnosis: Rising ACTH + hyperpigmentation + growing sellar mass on MRI [2]
- Treatment: Transsphenoidal surgery before the tumour becomes a macroadenoma [2]
- Prevention: Pituitary irradiation should be performed before bilateral adrenalectomy in Cushing's disease to minimise the risk of Nelson syndrome [2]
Nelson Syndrome — Prevention is Key
This complication is entirely iatrogenic. Bilateral adrenalectomy should be a last resort in Cushing's disease. If it must be performed, prophylactic pituitary irradiation prior to adrenalectomy reduces the risk of corticotroph tumour progression. Lifelong MRI surveillance of the pituitary and ACTH monitoring are mandatory after bilateral adrenalectomy [2].
- All pituitary adenoma subtypes carry a risk of recurrence after treatment
- Rates vary by subtype and completeness of resection:
- Non-functioning macroadenoma: ~15–25% recurrence at 10 years after gross total resection; higher if subtotal
- GH-secreting macroadenoma: ~30–40% if not biochemically cured
- ACTH-secreting: ~15–20% recurrence after initially successful surgery
- Prolactinoma: ~30–40% relapse after DA withdrawal; recurrence after surgery ~15–20%
- Long-term MRI surveillance is essential (at 1y, 2y, 5y, 10y post-surgery) [2]
- Exceedingly rare (< 0.2% of pituitary tumours)
- Defined by: craniospinal or systemic metastasis (not by histological features of the primary tumour)
- Cannot be predicted reliably by histology alone, though high Ki-67 index ( > 3%), p53 positivity, and certain aggressive subtypes (Crooke's cell, sparsely granulated somatotroph) carry higher risk
- Management: surgery + RT + temozolomide (alkylating chemotherapy agent with some evidence in aggressive pituitary tumours)
| Category | Key Complications |
|---|---|
| Tumour mass effect | Visual loss (bitemporal hemianopia → optic atrophy), headache, CN palsies (III, IV, V, VI), hydrocephalus (III ventricle obstruction), hypopituitarism |
| Pituitary apoplexy | Excruciating headache, acute visual loss, CN III palsy, adrenal crisis, SAH [4] |
| Transsphenoidal surgery | Hypopituitarism (can cause shock), DI (polyuria, haemoconcentration), CSF leak (beta-2-transferrin +ve, pneumocephaly) and meningitis, visual loss, ENT symptoms (epistaxis, anosmia, sinusitis), vascular injury, intracranial haemorrhage [4] |
| Radiotherapy | Progressive hypopituitarism, optic neuropathy, secondary malignancy, cerebrovascular disease, neurocognitive decline |
| Dopamine agonists | Nausea, postural hypotension, impulse control disorders, cardiac valvulopathy (high-dose), CSF rhinorrhoea (rapid macroprolactinoma shrinkage) |
| SSA | Gallstones, GI symptoms, hyperglycaemia |
| Acromegaly systemic | CVD (HTN, LVH, cardiomyopathy), T2DM, OSA, colon cancer/polyps, arthropathy, CTS |
| Cushing's systemic | CVD, VTE, T2DM, infections, osteoporosis, myopathy, psychiatric |
| Nelson syndrome | Post-bilateral adrenalectomy: ACTH > 200, hyperpigmentation, enlarging pituitary tumour [2] |
| Recurrence | All subtypes; requires lifelong surveillance |
High Yield Summary — Complications of Pituitary Adenoma
- Pituitary apoplexy = emergency: haemorrhagic infarction → headache, visual loss, coma, acute cortisol insufficiency. Give cortisol before T4. Urgent surgical decompression [4]
- Complications of transsphenoidal surgery (lecture slide essential knowledge): mortality (very rare), hypopituitarism (can cause shock from cortisol deficiency), DI (polyuria, haemoconcentration), CSF leak + meningitis (beta-2-transferrin +ve, pneumocephaly), visual loss, ENT symptoms (epistaxis, anosmia, sinusitis), vascular injury, intracranial haemorrhage [4]
- CSF leak detected by beta-2-transferrin positivity — unique to CSF. Failure to seal → meningitis [4][5]
- Acromegaly complications: CVD (HTN 40%, LVH, cardiomyopathy), T2DM (20%), OSA (50%), colon CA/polyps (need screening colonoscopy), arthropathy, CTS. Overall mortality 1.72× [2]
- Cushing's disease: untreated is often fatal (CVD, VTE, infections). Perioperative steroid cover and DVT prophylaxis essential [2]
- Nelson syndrome (8–25%): occurs after bilateral adrenalectomy; enlarging corticotroph adenoma + ACTH > 200 pg/mL + hyperpigmentation. Prevent with pituitary irradiation before adrenalectomy [2]
- Radiotherapy late effects: progressive hypopituitarism (50–100% at 10–20 years), optic neuropathy, secondary malignancy, cerebrovascular disease
- Order of hormone loss: GH → FSH/LH → ACTH → TSH — same whether from tumour compression or radiation damage
Active Recall - Complications of Pituitary Adenoma
References
[2] Senior notes: Ryan Ho Endocrine.pdf (Section 5: Pituitary Gland, pp. 107–111; Cushing's management pp. 64; Nelson syndrome p. 64) [3] Senior notes: Ryan Ho Fundamentals.pdf (Section 3.8.4: Pituitary Tumour, pp. 441–444; Acromegaly complications p. 444) [4] Lecture slides: GC 108. A mass in the brain brain tumours.pdf (pp. 41–42, 45–46, 48) [5] Senior notes: felixlai.md (Pituitary adenoma — Surgical complications) [8] Senior notes: Ryan Ho Opthalmology.pdf (CN III palsy, pp. 82–83) [10] Senior notes: Ryan Ho Neurology.pdf (Pituitary Adenoma, p. 166; Brain tumour surgery, p. 163) [11] Senior notes: maxim.md (Skull base tumours and CSF shunt complications, pp. 769–770)
High Yield Summary
Pituitary Adenoma — Key Points for Exams:
- Most common sellar mass in adults; 10–15% of intracranial neoplasms; found in 20–25% at autopsy [4]
- Classification: Microadenoma ( < 1 cm) vs Macroadenoma ( > 1 cm) vs Giant ( > 4 cm); Functioning vs Non-functioning
- Prolactinoma is the most common functioning adenoma; non-functioning adenomas are the most common macroadenoma (usually gonadotroph origin)
- Bitemporal hemianopia is the classic visual field defect (optic chiasm compression from below)
- Stalk effect: any mass compressing the pituitary stalk → mild hyperprolactinaemia ( < 100–200 ng/mL) by blocking dopamine delivery; PRL > 200 ng/mL almost always = true prolactinoma
- Order of hormone loss in hypopituitarism: GH → FSH/LH → ACTH → TSH
- Pituitary apoplexy = neurosurgical emergency: sudden headache + diplopia (CN III) + hypopituitarism (adrenal crisis); manage with IV hydrocortisone + urgent surgery if compressive signs
- Treatment paradigm: Prolactinoma → dopamine agonist first; GH/ACTH/TSH-secreting → surgery first; Non-functioning microadenoma → observe [4]
- MEN1 = Parathyroid + Pancreatic NETs + Pituitary adenoma (prolactinoma most common)
- Always exclude aneurysm before operating on a "sellar mass" [4]
- MRI pituitary (with gadolinium contrast) is the imaging modality of choice; CT is better for calcification (craniopharyngioma, meningioma) [2]
High Yield Summary — DDx of Pituitary Adenoma
- Structural DDx of sellar mass: Pituitary adenoma (most common in adults) > craniopharyngioma (most common in children, calcified, cystic) > meningioma (dural tail) > metastasis (posterior pituitary, DI) > Rathke's cleft cyst > germ cell tumour > ICA aneurysm > lymphocytic hypophysitis > pituitary abscess
- Always exclude ICA aneurysm before surgery (CTA/MRA) [4]
- CT is better than MRI for detecting calcification (craniopharyngioma, meningioma) [2]
- Stalk effect (PRL < 100–200) vs prolactinoma (PRL > 200, proportional to size) — this distinction dictates whether you give a dopamine agonist or operate
- Cushing's DDx: Iatrogenic (commonest overall) > Cushing's disease (65–70% of endogenous) > ectopic ACTH > adrenal tumour
- DI at presentation of a sellar mass → think non-adenoma pathology (craniopharyngioma, metastasis, germinoma, hypophysitis)
- Non-functioning adenomas: 70–90% are gonadotroph in origin [5]
High Yield Summary — Diagnosis of Pituitary Adenoma
- Three diagnostic pillars: Biochemistry (hormonal excess + deficiency) → Imaging (MRI with gadolinium) → Visual assessment (perimetry)
- Mode of secretion determines the test: Pulsatile hormones (GH, ACTH) need dynamic tests; constant hormones (PRL, TSH, LH/FSH) need direct measurement [2]
- Prolactinoma dx: Serum PRL > 200 ng/mL (> 10× ULN); always correlate PRL level with tumour size; request serial dilutions if large mass with low PRL (hook effect) [2][3]
- Acromegaly dx: Elevated age-adjusted IGF-1 ± failure of GH suppression on OGTT (GH nadir > 1 ng/mL) [2][3]
- Cushing's disease dx: ≥ 2 screening tests abnormal (UFC, overnight DST, late-night salivary cortisol) → ACTH-dependent → HDDST suppresses / CRH test exaggerated rise → pituitary MRI ± IPSS [2][3][9]
- MRI pituitary with gadolinium = imaging modality of choice; CT better for calcification [2][3][5]
- If lesion is separate from normal pituitary on MRI → NOT a pituitary adenoma [5]
- Always exclude ICA aneurysm (CTA/MRA) before transsphenoidal surgery [4]
- ITT = gold standard for GH + cortisol reserve; normal peak cortisol > 550 nmol/L, GH > 20 mU/L [9]
- Hypopituitarism sequence: GH → FSH/LH → ACTH → TSH [2][3]
High Yield Summary — Management of Pituitary Adenoma
- Prolactinoma = dopamine agonist FIRST (cabergoline preferred over bromocriptine) — normalises PRL and shrinks tumour in > 90%; surgery only if DA-refractory or intolerant [4][5]
- GH, ACTH, TSH-secreting adenomas = surgery FIRST (transsphenoidal) [4]
- Non-functioning microadenoma = observe (FU every 3–6 months) [5]
- Non-functioning macroadenoma with mass effect = surgery [2]
- Radiotherapy / radiosurgery = adjunct for residual or recurrent disease [4]; NOT used if tumour < 5 mm from optic chiasm [2]
- Acromegaly surgery: 80–90% cure for micro, < 50% for macro → SSA, pegvisomant, or DA if incomplete [3]
- Cushing's disease surgery: 60–70% curative → repeat surgery, RT, medical Rx, or bilateral adrenalectomy if persistent (risk of Nelson syndrome) [2]
- Complications of transsphenoidal surgery: DI, hypopituitarism, CSF leak + meningitis, vision loss, vascular injury, intracranial haemorrhage, ENT symptoms [4][10]
- Replace cortisol BEFORE thyroxine in hypopituitarism
- Pituitary apoplexy = IV hydrocortisone FIRST → urgent surgery if compressive signs [2][10]
High Yield Summary — Complications of Pituitary Adenoma
- Pituitary apoplexy = emergency: haemorrhagic infarction → headache, visual loss, coma, acute cortisol insufficiency. Give cortisol before T4. Urgent surgical decompression [4]
- Complications of transsphenoidal surgery (lecture slide essential knowledge): mortality (very rare), hypopituitarism (can cause shock from cortisol deficiency), DI (polyuria, haemoconcentration), CSF leak + meningitis (beta-2-transferrin +ve, pneumocephaly), visual loss, ENT symptoms (epistaxis, anosmia, sinusitis), vascular injury, intracranial haemorrhage [4]
- CSF leak detected by beta-2-transferrin positivity — unique to CSF. Failure to seal → meningitis [4][5]
- Acromegaly complications: CVD (HTN 40%, LVH, cardiomyopathy), T2DM (20%), OSA (50%), colon CA/polyps (need screening colonoscopy), arthropathy, CTS. Overall mortality 1.72× [2]
- Cushing's disease: untreated is often fatal (CVD, VTE, infections). Perioperative steroid cover and DVT prophylaxis essential [2]
- Nelson syndrome (8–25%): occurs after bilateral adrenalectomy; enlarging corticotroph adenoma + ACTH > 200 pg/mL + hyperpigmentation. Prevent with pituitary irradiation before adrenalectomy [2]
- Radiotherapy late effects: progressive hypopituitarism (50–100% at 10–20 years), optic neuropathy, secondary malignancy, cerebrovascular disease
- Order of hormone loss: GH → FSH/LH → ACTH → TSH — same whether from tumour compression or radiation damage
Non-toxic/simple Goitre (inc. Retrosternal)
Non-toxic simple goitre is a diffuse or nodular enlargement of the thyroid gland without hyperthyroidism or hypothyroidism, which may extend retrosternally and cause compressive symptoms in the thoracic inlet.
Primary Hyperparathyroidism (adenoma, Hyperplasia, Carcinoma)
Primary hyperparathyroidism is excessive parathyroid hormone secretion caused by a parathyroid adenoma (most common), multigland hyperplasia, or rarely carcinoma, leading to hypercalcemia and its systemic complications.