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.

Exam domain	One-glance essentials
Definition / diagnosis	Simple goitre is benign thyroid enlargement without neoplasia, inflammation, thyrotoxicosis or hypothyroidism (euthyroid) ^[1] May be diffuse or nodular/multinodular ^[1]
Epidemiology / risks	Risk increases with age, female sex, iodine imbalance and prior ionising radiation exposure ^[1] Long-standing multinodular goitre may progress to subclinical or overt thyrotoxicosis ^[1]
Core mechanism	Recurrent mild impairment of hormone synthesis raises TSH, driving follicular-cell hyperplasia and hypertrophy while maintaining euthyroidism ^[1] Repeated hyperplasia and involution produces nodules; autonomous nodules may later cause toxic MNG ^[1]
Clinical picture	Typically a slowly enlarging, soft, non-tender diffuse or multinodular swelling that moves on swallowing ^[1] Retrosternal extension may cause dyspnoea, dysphagia, tracheal deviation or positive Pemberton sign ^[1] Painful rapid enlargement suggests haemorrhage into a nodule/cyst, not uncomplicated simple goitre ^[1]
Investigations	First-line: TSH and free T4, plus thyroid ultrasound to define morphology and suspicious nodules ^[1] If TSH is suppressed, perform scintigraphy; hot nodules are rarely malignant, while cold nodules require risk-based assessment ^[1] Suspected retrosternal extension requires CXR and CT/MRI; flow-volume loops assess upper-airway obstruction ^[1]
Management	Small, asymptomatic, stable euthyroid goitres can be observed with clinical review and periodic TFTs ^[1] Thyroidectomy is indicated for compression, retrosternal extension, progressive enlargement, malignancy suspicion or significant cosmesis ^[1] Correct thyrotoxicosis before surgery; antithyroid drugs do not treat non-toxic goitre definitively ^[1]
Complications	Airway obstruction, dysphagia and venous obstruction are key complications of large retrosternal goitre ^[1] Haemorrhage into a cystic nodule can cause sudden painful enlargement and acute airway compromise ^[1] Long-standing MNG may develop toxic MNG, atrial fibrillation or harbour malignancy within a dominant nodule ^[1]
Prevention / follow-up	Monitor stable MNG with periodic TFTs to detect evolution to toxic MNG ^[1] Reassess clinically and with ultrasound if a nodule enlarges, becomes dominant, or new compressive symptoms develop ^[1] Before thyroidectomy, document vocal-cord function and optimise thyroid status when abnormal ^[1]
Exam traps	Normal TFTs do not exclude malignancy: a dominant or suspicious nodule in MNG needs separate evaluation ^[1] Do not order scintigraphy routinely when TSH is normal; reserve it for a nodule with suppressed TSH ^[1] Do not label a goitre simple without excluding thyroiditis, autoimmune disease, toxic states and neoplasia ^[1]

References

^[1] Lecture slides: GC 177. A thyroid nodule benign thyroid nodules; thyroid cancer.pdf (p4 — Goitre Classification)

Non-Toxic / Simple Goitre (Including Retrosternal Goitre)

Simple goitre (also called non-toxic goitre) is defined as any thyroid enlargement that is not a result of neoplasia or inflammation, and that is not associated with thyrotoxicosis or hypothyroidism (i.e., the patient is euthyroid) ^[1]^[2].

The word "goitre" comes from the Latin guttur = throat. It simply means an enlarged thyroid gland.
"Non-toxic" = no excess thyroid hormone secretion (i.e., no thyrotoxicosis).
"Simple" = the enlargement is due to a benign, non-inflammatory, non-neoplastic process.
It is essentially a diagnosis of exclusion — you must rule out Hashimoto's thyroiditis, destructive thyroiditis, Graves' disease, and neoplasia before labelling a goitre as "simple" ^[2].

It may present as either:

Diffuse — uniform enlargement of the entire gland
Nodular — one or more nodules (multinodular goitre, MNG) ^[1]^[3]

The key concept: the thyroid is enlarged, but thyroid function is normal. The gland is simply bigger than it should be.

Retrosternal (substernal) goitre refers to extension of an enlarged thyroid gland below the thoracic inlet into the superior mediastinum. By convention, a goitre is called retrosternal when > 50% of the gland lies below the thoracic inlet, although some define it as any thyroid tissue extending below the plane of the sternal notch. This is important because it can cause significant compressive symptoms on the trachea, oesophagus, and great vessels.

2. Epidemiology

Prevalence of thyroid nodules is extraordinarily common ^[2]:
- 3–7% by palpation
- > 30% by autopsy or ultrasound
- Prevalence depends on iodine status, ionising radiation exposure, gender, and age
Simple diffuse goitre usually presents in the 15–25 year age group ^[2]
Multinodular goitre (MNG) usually presents in patients > 35 years ^[2]
Female predominance: F:M ≈ 4–5:1 (oestrogen may play a role in thyroid growth)

Feature	Endemic Goitre	Sporadic Goitre
Definition	Goitre affecting > 5% of the population in a geographic region	Occurs in non-endemic areas
Main cause	Dietary iodine deficiency (mountainous/inland regions)	Unknown aetiology (?goitrogens, ?mild synthesis defects)
Geography	Himalayas, Andes, central Africa, parts of inland China	Worldwide, including Hong Kong
Mechanism	↓ Iodine → ↓ T4 synthesis → ↑ TSH → thyroid hyperplasia	Exacerbated by ↑ thyroid hormone requirement (puberty, pregnancy)

Hong Kong is not an iodine-deficient region (coastal, seafood-rich diet), so endemic goitre due to iodine deficiency is rare.
Most simple goitres in HK are sporadic.
However, multinodular goitre is extremely common in the elderly Hong Kong population and is a frequent cause of subclinical thyrotoxicosis and atrial fibrillation in this group ^[2].
The prevalence of thyroid nodules detected incidentally on imaging (USG, CT, PET) is rising due to widespread use of cross-sectional imaging.

3. Anatomy and Function

The thyroid gland is a butterfly-shaped endocrine organ located in the anterior neck, at the level of C5–T1 vertebrae.
It consists of two lateral lobes connected by an isthmus across the 2nd–4th tracheal rings.
A pyramidal lobe (remnant of the thyroglossal duct) is present in ~50% of people, extending superiorly from the isthmus.
Weight: normally 15–25 g in adults.

Key anatomical relations (critical for understanding compressive symptoms and surgical risks):

Structure	Relation	Clinical Relevance
Trachea	Directly posterior to isthmus	Tracheal compression/deviation → stridor, dyspnoea
Oesophagus	Posterolateral (left side)	Dysphagia from posterior goitre extension
Recurrent laryngeal nerve (RLN)	Runs in the tracheo-oesophageal groove	Hoarseness of voice if invaded by malignancy or injured in surgery
Superior laryngeal nerve (external branch)	Runs with superior thyroid artery near upper pole	Injury → loss of high-pitched phonation (cricothyroid palsy)
Parathyroid glands	Posterior surface of thyroid (2 superior, 2 inferior)	Hypocalcaemia if removed during thyroidectomy
Carotid sheath	Lateral	Carotid body tumour in differential of neck mass
Strap muscles	Anterior	Invasion suggests aggressive malignancy
Thoracic inlet	Inferior	Retrosternal extension

Superior thyroid artery (first branch of external carotid artery)
Inferior thyroid artery (from thyrocervical trunk of subclavian artery)
Thyroidea ima artery (variable, from brachiocephalic trunk or aortic arch — present in ~3%; important in retrosternal goitre surgery)
Venous drainage: superior, middle, and inferior thyroid veins → internal jugular vein and brachiocephalic veins

Central compartment (Level VI) nodes → lateral neck (Levels II–V) → mediastinal nodes
Level VI is the first echelon of thyroid lymphatic drainage — critical in thyroid cancer staging

Understanding thyroid hormone synthesis is essential to understanding why goitres form:

Iodine trapping: The sodium-iodide symporter (NIS) on the basolateral membrane of thyroid follicular cells actively transports iodide (I⁻) into the cell against its concentration gradient (this is what radioactive iodine and pertechnetate exploit for scintigraphy).
Organification: Iodide is oxidised by thyroid peroxidase (TPO) and bound to tyrosine residues on thyroglobulin (Tg) at the apical membrane → monoiodotyrosine (MIT) and diiodotyrosine (DIT).
Coupling: MIT + DIT → T3 (triiodothyronine); DIT + DIT → T4 (thyroxine).
Storage: T3 and T4 are stored as part of the thyroglobulin colloid in the follicular lumen.
Secretion: TSH stimulates endocytosis of colloid → proteolysis → release of T4 (90%) and T3 (10%) into the bloodstream.
Peripheral conversion: T4 → T3 (the active form) by deiodinases in peripheral tissues (liver, kidney, muscle).
Feedback: T3/T4 → negative feedback on the hypothalamus (↓ TRH) and anterior pituitary (↓ TSH).

Why does the gland enlarge in simple goitre?

If there is any impairment in T4 synthesis (e.g., iodine deficiency, goitrogens, mild enzyme defects), T4 levels dip slightly → TSH rises even marginally → TSH stimulates hyperplasia and hypertrophy of follicular cells → the gland enlarges to maintain adequate T4 output → the patient remains euthyroid at the cost of a bigger gland.
Over time, if this cycle repeats, you get recurrent episodes of hyperplasia and involution → this is the pathogenesis of multinodular goitre ^[2].

4. Etiology (Focus on Hong Kong)

Category	Examples	Mechanism
Iodine deficiency (endemic)	Mountainous/inland regions (rare in HK)	↓ I₂ → ↓ T4 synthesis → ↑ TSH → thyroid hyperplasia
Iodine excess	Kelp, seaweed, iodinated contrast, amiodarone	Wolff-Chaikoff effect: acute excess iodine paradoxically blocks organification → transient ↓ T4 → ↑ TSH → goitre (if escape mechanism fails)
Goitrogens	Cassava (thiocyanate), cruciferous vegetables (cabbage, broccoli), soy, lithium, amiodarone	Interfere with iodine uptake or organification → ↓ T4 → ↑ TSH
Increased physiological demand	Puberty, pregnancy	↑ TBG (oestrogen-driven), ↑ renal iodine clearance in pregnancy, ↑ metabolic demands → relative T4 insufficiency → ↑ TSH
Mild thyroid hormone synthesis defects (sporadic)	Subtle/subclinical enzymatic defects (e.g., mild TPO deficiency)	Subclinically impaired T4 production → compensatory TSH rise
Dyshormonogenesis	Genetic defects in NIS, TPO, thyroglobulin, Pendrin (Pendred syndrome)	Defective hormone synthesis → ↑ TSH → goitre (often presents in childhood)

Hong Kong Specific

In Hong Kong, sporadic non-toxic goitre is by far the most common form. Iodine deficiency is rare because of the coastal diet rich in seafood. Think of puberty, pregnancy, and goitrogens (including medications like lithium) as the main precipitants. Multinodular goitre in elderly patients is the most clinically significant presentation — often presenting with atrial fibrillation or compressive symptoms.

"Goitrogen" = goitre + Greek -gen (to produce) = substances that produce goitre.

Goitrogen	Source	Mechanism
Thiocyanate	Cassava, smoking	Competitively inhibits NIS → ↓ iodine uptake
Perchlorate	Environmental contaminant	Competitively inhibits NIS
Lithium	Psychiatric medication (bipolar disorder)	Inhibits thyroid hormone release; also inhibits organification
Amiodarone	Anti-arrhythmic (37% iodine by weight)	Can cause goitre via Wolff-Chaikoff effect OR thyrotoxicosis (Jod-Basedow effect)
Cruciferous vegetables	Cabbage, broccoli, kale, cauliflower	Contain thioglucosides → thiocyanate → ↓ iodine uptake (clinically significant only with extreme consumption + borderline iodine intake)
Soy isoflavones	Soy products	Inhibit TPO → ↓ organification (mainly relevant in iodine-deficient states)

5. Pathophysiology

This is a continuum. The pathophysiology of non-toxic goitre proceeds through predictable stages:

The key pathological principle: recurrent episodes of hyperplasia and involution (due to unknown/multiple stimuli) → hyperplastic nodules growing at varying rates ^[2].

Why do nodules form rather than uniform enlargement?

Not all thyroid follicular cells respond equally to TSH stimulation. There is intrinsic heterogeneity in growth potential among follicular cells.
Cells with higher intrinsic growth rates form nodules; cells that involute more readily form colloid-filled areas.
Over time, some nodules develop somatic mutations (e.g., activating mutations in TSH receptor or Gsα) that allow autonomous function independent of TSH — this is how a non-toxic MNG can evolve into a toxic MNG (Plummer's disease) ^[2].

Feature	Simple Diffuse Goitre	Multinodular Goitre
Gross	Diffusely enlarged, smooth, soft	Asymmetrically enlarged, nodular, may be very large (> 100 g)
Cut surface	Glistening, homogeneous colloid	Heterogeneous: areas of haemorrhage, fibrosis, calcification, cystic change
Microscopy	Hyperplastic follicles with ↑ cellularity, small colloid	Variable: hyperplastic follicles, involuted follicles distended with colloid, areas of haemorrhage, fibrosis, calcification
Capsule	No true capsule	Nodules may have partial pseudocapsules from compressed tissue

The thyroid gland is enclosed by the pretracheal fascia but the fascial planes of the neck are continuous with the superior mediastinum.
As the gland enlarges, the path of least resistance is inferiorly through the thoracic inlet, because:
- Superiorly: restricted by the hyoid bone and strap muscles
- Laterally: restricted by the carotid sheaths and sternocleidomastoid
- Posteriorly: trachea and oesophagus
- Inferiorly: the thoracic inlet is relatively open — gravity and negative intrathoracic pressure during inspiration pull the enlarged gland downward
Most retrosternal goitres extend into the anterior mediastinum (in front of the trachea and great vessels)
Less commonly, extension is posterior to the trachea/oesophagus (posterior mediastinum) — this is more likely to cause dysphagia and airway compromise

Retrosternal Goitre — Why It Matters

A retrosternal goitre can be entirely asymptomatic or can present as a surgical emergency with acute airway obstruction. Always assess the lower border of a goitre — if you cannot get below it, think retrosternal extension. This is a classic physical examination finding.

6. Classification

Goitre Classification:

Category	Subtypes
Simple goitre (endemic or sporadic)	Diffuse / Nodular
Toxic goitre	Diffuse toxic (Graves') / Toxic nodular (Plummer's) / Toxic/functioning adenoma
Neoplastic goitre	Benign / Malignant
Thyroiditis	Bacterial (acute suppurative) / Viral (subacute) / Lymphocytic/Hashimoto/autoimmune (chronic)

Grade	Description
0	No goitre (thyroid not palpable or visible)
1	Palpable goitre but not visible with neck in normal position
1a	Palpable but not visible even with neck extended
1b	Palpable and visible only with neck extended
2	Visible goitre with neck in normal position
3	Very large goitre visible from a distance

Type	Description
Diffuse goitre	Uniform enlargement without palpable nodules
Uninodular goitre	Single palpable nodule (must exclude neoplasm)
Multinodular goitre (MNG)	Multiple palpable nodules of varying size

Type	TSH	fT4/fT3	Clinical State
Non-toxic (simple) goitre	Normal	Normal	Euthyroid
Subclinical toxic MNG	↓ (suppressed)	Normal (upper range)	Clinically euthyroid but biochemically suppressed TSH
Toxic MNG (Plummer's)	↓↓	↑	Thyrotoxic

25% of MNG patients have complete suppression of TSH, with T4/T3 within reference range (subclinical thyrotoxicosis) or elevated (toxic MNG) ^[2].

Type	Location
Cervical goitre	Entirely within the neck
Retrosternal/substernal goitre	Extends below the thoracic inlet into the mediastinum
Intrathoracic goitre	Entirely within the thorax (rare; may have separate blood supply from intrathoracic vessels)

7. Clinical Features

7.1 Symptoms

The symptoms of simple/non-toxic goitre can be divided into those from the mass itself, compressive symptoms, and systemic symptoms (which should be absent in true non-toxic goitre).

Symptom	Pathophysiological Basis
Neck swelling (the presenting complaint)	Direct enlargement of the thyroid gland due to hyperplasia/nodule formation; moves with swallowing because the gland is enclosed in pretracheal fascia which is attached to the larynx
Cosmetic concern	Visible anterior neck mass, especially in thin patients; may be the only reason for presentation
Awareness of a lump / tightness	Stretching of the thyroid capsule and surrounding tissues
Pain (uncommon in simple goitre)	Not typical for simple goitre; if present, think of haemorrhage into a nodule/cyst (sudden painful swelling), subacute thyroiditis, or anaplastic carcinoma

Key point from the lecture: Acute painful enlargement can arise from haemorrhage into a nodule/cyst ^[2]^[3]. If a patient with known MNG presents with sudden neck pain and rapid enlargement, haemorrhage into a degenerating nodule is the most likely cause.

Symptom	Structure Compressed	Pathophysiological Basis
Dyspnoea / stridor	Trachea	Large goitre (especially retrosternal) compresses or deviates the trachea → narrowing of airway lumen → inspiratory stridor (extrathoracic) or biphasic stridor (intrathoracic/fixed)
Dysphagia	Oesophagus	Posterior extension of goitre compresses the oesophagus against the vertebral column → difficulty swallowing solids initially, then liquids
Hoarseness of voice (HOV) / dysphonia	Recurrent laryngeal nerve (RLN)	In simple goitre, RLN compression is very rare (the nerve is displaced, not invaded). HOV in the setting of a goitre should raise suspicion for malignancy (invasion of the nerve)
Facial plethora / SVC obstruction symptoms	Superior vena cava (SVC) or brachiocephalic veins	Large retrosternal goitre can compress the great veins in the thoracic inlet → venous congestion of the face, neck, and upper extremities (SVC syndrome); Pemberton's sign positive
Horner syndrome (rare)	Sympathetic chain	Very large retrosternal goitre compressing the cervical sympathetic chain → ipsilateral miosis, ptosis, anhidrosis
Phrenic nerve palsy (rare)	Phrenic nerve	Retrosternal extension compressing the phrenic nerve → diaphragmatic paralysis → dyspnoea

Pemberton's Sign

Pemberton's sign is a clinical test for thoracic inlet obstruction by a retrosternal goitre: ask the patient to raise both arms above the head for 1–2 minutes. A positive sign = facial plethora, cyanosis, distension of neck veins, and respiratory distress. This occurs because raising the arms further narrows the thoracic inlet, compressing the already-compromised venous return.

Symptom	What It Suggests
Thyrotoxic symptoms (weight loss, heat intolerance, tremor, palpitations, diarrhoea, anxiety, sweating)	Toxic MNG, Graves' disease, toxic adenoma
Hypothyroid symptoms (fatigue, weight gain, cold intolerance, constipation, bradycardia)	Hashimoto's thyroiditis, late-stage MNG with gland destruction
Rapid, painless enlargement	Lymphoma, anaplastic carcinoma
Fixation / cervical lymphadenopathy	Malignancy

The classic presentation of toxic MNG in the elderly: AF + multinodular goitre ^[2]. Always check TFTs in any patient with MNG to exclude subclinical or overt thyrotoxicosis.

7.2 Signs

Physical examination of a goitre should follow a structured approach: inspection → palpation → percussion → auscultation → thyroid status assessment → complications ^[3]^[4].

Sign	Pathophysiological Basis / Significance
Visible anterior neck swelling	Enlarged thyroid gland; may be symmetrical (diffuse goitre) or asymmetrical (dominant nodule in MNG)
Swallowing test positive: mass rises with swallowing	The thyroid is invested by the pretracheal fascia, which is attached to the laryngeal cartilages; swallowing elevates the larynx → thyroid gland and any thyroid mass moves up
Tongue tug test negative	Positive tongue tug test = mass moves with tongue protrusion → this suggests thyroglossal cyst (attached to foramen caecum via thyroglossal duct), NOT thyroid goitre
Surgical scars	Previous thyroid surgery (hemithyroidectomy, total thyroidectomy)
Skin changes	Radiotherapy marks (previous H&N radiation); dilated veins over the chest/neck (SVC obstruction from retrosternal goitre)

Stand behind the patient. Ask about tenderness before palpating.

Sign	Description	Pathophysiological Basis / Significance
Diffuse goitre vs nodular goitre vs solitary nodule vs dominant nodule in MNG	Careful palpation distinguishes these	Diffuse → simple goitre, Graves', Hashimoto's; Nodular → MNG; Solitary → adenoma, cyst, carcinoma; Dominant nodule in MNG → must exclude malignancy
Size	Estimated by palpation (measure with tape measure)	Document for follow-up comparison
Consistency	Soft: simple diffuse goitre. Firm: MNG, Hashimoto's. Hard: calcification, malignancy. Rubbery: lymphoma	Simple goitre is characteristically soft and diffuse without tenderness, lymphadenopathy, or overlying bruit ^[2]
Tenderness	Present → thyroiditis (de Quervain's), haemorrhage into cyst, anaplastic CA	Not a feature of simple goitre
Surface	Smooth → diffuse goitre; Lobulated/irregular → MNG
Lower border	Can you get below it? If you cannot feel the lower border, suspect retrosternal extension	This is a critical clinical finding — the thoracic inlet prevents your fingers from reaching below the gland
Tracheal position	Midline or deviated?	Large goitre can push the trachea to the contralateral side
Cervical lymph nodes	Palpate all levels (I–VI)	Lymphadenopathy suggests malignancy or lymphoma; absent in simple goitre

Sign	Technique	Significance
Retrosternal dullness	Percuss over the manubrium/upper sternum	Dullness to percussion suggests retrosternal extension of the goitre (normally resonant over the lung/trachea)

Percussion is only relevant in assessing retrosternal extension of goitre ^[4].

Sign	Significance
No bruit (in simple goitre)	A thyroid bruit suggests increased vascularity — think Graves' disease (diffuse, vascular, hyperfunctioning gland). A simple goitre should NOT have a bruit

In simple/non-toxic goitre, the thyroid status examination should be entirely normal. However, always perform a full thyroid status assessment to confirm euthyroid status and to exclude the differential diagnoses:

Domain	What to Check	Finding in Simple Goitre
Eyes	Proptosis, lid retraction, lid lag, chemosis, ophthalmoplegia	All normal (these are features of Graves' ophthalmopathy)
Hands	Tremor, sweating, tachycardia, thyroid acropachy, palmar erythema	All normal
Pulse	Rate and rhythm	Regular, normal rate (tachycardia/AF suggests thyrotoxicosis)
Lower limbs	Proximal myopathy, pretibial myxoedema, reflexes	Normal (pretibial myxoedema = Graves'; delayed relaxation of reflexes = hypothyroidism)

Simple goitre: soft, diffuse goiter without tenderness, lymphadenopathy and overlying bruit ^[2]

TFT normal, no anti-thyroid Ab ^[2]

8. Special Consideration: Retrosternal Goitre

Retrosternal goitre accounts for ~5–15% of mediastinal masses and is the most common cause of a superior mediastinal mass in the anterior compartment.
Most retrosternal goitres (> 95%) are extensions of a cervical goitre — truly ectopic intrathoracic thyroid tissue (with an intrathoracic blood supply) is very rare (~1%).
More common in long-standing MNG (years to decades of progressive growth).

Feature	Explanation
Cannot palpate the lower border	The lower pole extends below the thoracic inlet
Pemberton's sign positive	Raising arms → further thoracic inlet narrowing → venous congestion → facial plethora, cyanosis, JVD, stridor
Retrosternal dullness	Percussion over manubrium is dull rather than resonant
Tracheal deviation on CXR	Goitre displaces the trachea laterally
Superior mediastinal widening on CXR	The mass is visible on chest X-ray as a mediastinal shadow, often with calcification
Stridor (may be positional)	Tracheal compression; may worsen when lying flat or with neck flexion
SVC obstruction syndrome	Compression of SVC → facial plethora, neck vein distension, upper limb oedema

Exam Tip: 'Getting Below the Swelling'

A common exam mistake is forgetting to assess the lower border of a thyroid swelling. If you cannot get your fingers beneath the lower pole of the goitre, you MUST mention retrosternal extension as a possibility and describe the relevant further investigations (CXR, CT thorax, flow-volume loop).

Investigation	Purpose
CXR	Superior mediastinal widening, tracheal deviation, calcification
CT/MRI thorax	Assessment of extent of retrosternal extension, degree of tracheal displacement or compression ^[2]^[3]
Flow-volume loop (spirometry)	Screen for significant tracheal compression — upper airway obstruction (UAO) results in a blunted flow-volume loop ^[2]^[3]
Thyroid scintigraphy	Can show functioning thyroid tissue in the mediastinum; may help distinguish from other mediastinal masses

Further Ix for obstructive/retrosternal goitre: CXR/CT/MRI thorax for assessment of extent + Flow-volume loop study for airway obstruction ^[2]^[3]

Key points:

Simple goitre usually presents 15–25 years ^[2]
MNG usually presents > 35 years ^[2]
The natural history is one of progressive enlargement over years to decades
Some nodules may secrete thyroid hormone autonomously (toxic MNG, Plummer disease) ^[2]
Haemorrhage into a nodule/cyst → sudden painful swelling ^[2]
Long-standing MNG may rarely harbour malignancy (especially papillary carcinoma); however, the risk of malignancy in any individual nodule within an MNG is the same as for a solitary nodule (~5–10%)
The progression from non-toxic → toxic MNG is driven by somatic activating mutations in TSH receptor or Gsα in autonomously functioning nodules

High Yield Summary

Definition: Simple/non-toxic goitre = thyroid enlargement not due to neoplasia or inflammation, with normal thyroid function (euthyroid). It is a diagnosis of exclusion.
Types: Endemic (iodine deficiency) vs Sporadic (unknown, ?goitrogens, ?↑ demand); Diffuse vs Nodular (MNG).
Epidemiology: Diffuse simple goitre peaks at 15–25y; MNG peaks at > 35y; extraordinarily common (> 30% on USG).
Hong Kong: Sporadic goitre is the common form (not iodine deficient). MNG in elderly is very common — watch for AF.
Pathophysiology: Recurrent cycles of TSH-driven hyperplasia and involution → heterogeneous nodule formation → MNG. Some nodules may develop autonomous function (→ toxic MNG).
Classification (from lecture): Simple (diffuse/nodular) | Toxic (Graves'/Plummer's/toxic adenoma) | Neoplastic (benign/malignant) | Thyroiditis (bacterial/viral/autoimmune).
Clinical features: Soft, diffuse/nodular goitre; no tenderness, no lymphadenopathy, no bruit; moves with swallowing; euthyroid status.
Compressive symptoms: Dyspnoea/stridor (trachea), dysphagia (oesophagus), dysphonia (RLN — think malignancy), SVC syndrome (great veins).
Retrosternal goitre: Cannot get below the swelling; Pemberton's sign positive; retrosternal dullness; investigate with CXR, CT/MRI thorax, flow-volume loop.
Key investigations: TFT (must be normal), USG (for all goitres), ± FNAC of suspicious nodules, scintigraphy if ↓ TSH, CT/flow-volume loop if retrosternal.
25% of MNG patients have suppressed TSH — subclinical thyrotoxicosis is common and clinically important (risk of AF, osteoporosis).

Active Recall - Non-Toxic / Simple Goitre

^[1] Lecture slides: GC 177. A thyroid nodule benign thyroid nodules; thyroid cancer.pdf (p4 — Goitre Classification) ^[2] Senior notes: Ryan Ho Endocrine.pdf (p17, p31–32 — Goitre, Thyroid Nodules, Simple and Multinodular Goitre) ^[3] Senior notes: Ryan Ho Fundamentals.pdf (p425–429 — Goitre and Thyroid Nodules) ^[4] Senior notes: Ryan Ho Rheumatology.pdf (p160 — Examination of Lumps and Bumps: percussion for retrosternal goitre) ^[5] Senior notes: maxim.md (Approach to thyroid nodules, Physical examination) ^[6] Senior notes: felixlai.md (Definitions, Causes of thyrotoxicosis) ^[7] Senior notes: Ryan Ho Diagnostic Radiology.pdf (p59–60 — Thyroid Scintigraphy)

Differential Diagnosis of Non-Toxic / Simple Goitre

When a patient walks into clinic with an anterior neck mass that moves with swallowing, your brain must instantly start running through the differential diagnosis. The question is not just "is this a simple goitre?" — the question is "what else could this thyroid swelling be, and which of those alternatives am I legally obligated not to miss?"

Simple goitre is, remember, a diagnosis of exclusion ^[2]. You must systematically rule out neoplasia, inflammation (thyroiditis), autoimmune disease, and toxic states before you can comfortably label a goitre as "simple." The differential diagnosis is therefore framed around the clinical presentation of the thyroid swelling itself.

1. Organising Framework: DDx by Morphology and Thyroid Function

The most clinically useful way to approach the differential of a thyroid swelling is to cross-reference the morphology (what it looks/feels like) with the thyroid functional status (TFT result). This is the framework used in both the lecture slides and senior notes ^[1]^[2]^[3].

A diffuse, smooth enlargement of the entire gland without distinct nodules.

Thyroid Status	Differential Diagnosis	Key Distinguishing Features
Euthyroid	Simple diffuse goitre (e.g., pregnancy, iodine deficiency, goitrogen, pubertal)	Soft, non-tender, no bruit, no Ab, TFT normal — diagnosis of exclusion
Euthyroid	Early MNG	May feel diffuse on palpation but USG reveals early nodularity
Euthyroid	Infiltrative disease (e.g., lymphoma)	Rapid enlargement, firm/rubbery, may have B-symptoms (fever, night sweats, weight loss); long-standing Hashimoto's is a risk factor
Euthyroid	Treated Graves' disease	History of prior RAI or ATD treatment; may still have a palpable goitre
Hypothyroid	Hashimoto's thyroiditis	Firm, "rubbery" goitre; anti-TPO and anti-Tg antibodies strongly positive (90–100% and 80–90% respectively ^[8]); ↑ TSH, ↓ fT4
Hyperthyroid	Graves' disease	Diffuse toxic goitre: diffuse, non-tender, vascular with audible bruit; eye signs (proptosis, lid retraction, ophthalmoplegia); TRAb positive; scintigraphy shows diffuse ↑ uptake
Mixed (fluctuating)	Destructive thyroiditis (de Quervain's / subacute)	Tender goitre, preceding viral illness, pain radiating to jaw/ears, ↑ ESR; fluctuating thyroid status (thyrotoxic → hypothyroid → resolution); ↓ iodine uptake on scintigraphy

Why does this framework matter? Because the TFT result immediately narrows your differential. If you get a normal TSH back, you've already excluded Graves', toxic MNG, and overt Hashimoto's in one test. That's why TFT (ultrasensitive TSH ± fT4) is the first-line investigation ^[2]^[3].

Multiple palpable nodules of varying size — the gland feels irregular, lumpy, asymmetric.

Thyroid Status	Differential Diagnosis	Key Distinguishing Features
Euthyroid	Non-toxic multinodular goitre	The direct "evolved" form of simple goitre; TFT normal; may be large with compressive symptoms or retrosternal extension
Hyperthyroid (overt or subclinical)	Toxic multinodular goitre (Plummer's disease)	Classically AF + multinodular goitre in elderly ^[2]; ↓ TSH ± ↑ fT4/fT3; scintigraphy shows patchy uptake with hot and cold areas
Either	Malignancy within MNG	Any dominant nodule in an MNG must be evaluated separately — the risk of malignancy in a dominant nodule is the same as for a solitary nodule (~5–10%)

Around 10–15% of nodules are malignant ^[5]. A multinodular goitre does NOT protect you from cancer — always look for and investigate dominant or suspicious nodules within an MNG.

A single palpable nodule within the thyroid, or a dominant nodule against a background of MNG.

Category	Differential Diagnosis	Key Features
Non-neoplastic (70%)	Colloid nodule, haemorrhagic nodule, complex/cystic nodule, hyperplastic/adenomatous nodule, dominant nodule in MNG	These are by far the most common cause of a solitary thyroid nodule; usually benign on FNAC
Benign neoplasm (15%)	Follicular adenoma — non-toxic (more common) or toxic adenoma	Toxic adenoma: functioning/hot on scintigraphy, autonomously secreting T4, ↓ TSH; non-toxic adenoma: euthyroid, cold/indeterminate on scintigraphy
Malignant neoplasm (~10–15%)	Papillary carcinoma (most common ~80%), Follicular carcinoma, Medullary carcinoma, Anaplastic carcinoma, Thyroid lymphoma, Metastatic disease	See section below for features suggesting malignancy

Simple Cyst vs Colloid Nodule vs Neoplasm

A true simple cyst (purely fluid-filled, thin-walled, no solid component) is almost always benign. A colloid nodule is a follicle distended with colloid from cycles of hyperplasia and involution — also benign. The danger lies in complex cystic nodules (mixed solid-cystic with irregular septa or eccentric solid component) which may harbour malignancy within the solid component. This is why USG characterisation is critical.

Not every anterior neck mass is a goitre. If the mass does not move with swallowing, or has atypical features, consider:

Condition	Location / Features	How to Distinguish from Goitre
Thyroglossal duct cyst	Midline, upper neck (60% at thyrohyoid membrane level); tongue tug test positive (moves with tongue protrusion because it is attached to the foramen caecum via the thyroglossal duct) ^[5]	Goitre: swallowing test +ve, tongue tug -ve. Thyroglossal cyst: BOTH swallowing test +ve (attached to hyoid) AND tongue tug +ve
Branchial cleft cyst	Anterior to SCM, usually at angle of mandible (2nd cleft = most common); smooth, fluctuant	Does not move with swallowing; lateral position; presents in late childhood/early adulthood ^[8]
Cervical lymphadenopathy	Multiple rubbery or hard nodes; may be in any cervical level	Does not move with swallowing; consider reactive, infective (TB in HK!), lymphoma, metastatic (NPC in HK!)
Dermoid cyst	Midline, subcutaneous, doughy, does not transilluminate well	Fixed to skin (unlike goitre which is deep to strap muscles); does not move with swallowing
Lymphoma	Rapidly enlarging, rubbery, non-tender mass; may involve thyroid itself (primary thyroid lymphoma) or cervical nodes	B-symptoms; association with long-standing Hashimoto's thyroiditis
Carotid body tumour (paraganglioma)	At carotid bifurcation (level II); pulsatile; mobile laterally but NOT vertically (Fontaine's sign)	Pulsatile; does not move with swallowing; Doppler USG shows hypervascular mass
Laryngocele / Pharyngeal pouch	Lateral neck; may increase in size with Valsalva	Does not move with swallowing in the same way as thyroid
Lipoma	Soft, mobile, subcutaneous, "slip sign" positive	Superficial; does not move with swallowing

Summary from lecture ^[9]: Diagnosis of a neck mass depends on age, location, and clinical features. Investigation includes imaging, FNA, and excision. Treatment depends on nature of pathology.

When you are evaluating a goitre or thyroid nodule, you must actively look for "red flags" that shift the probability from simple goitre towards malignancy. This is where the differential diagnosis directly influences your investigation pathway.

Domain	Feature	Why It's Concerning
Demographics	Male sex	Thyroid nodules are less common in males but more likely to be malignant when they occur ^[3]
Demographics	Age < 14 or > 70	Nodules in the 3rd–6th decade are usually benign; extremes of age carry higher risk ^[3]
Symptom	Solitary or dominant nodule	More likely to be malignant than multiple nodules ^[3]
Symptom	Slow but progressive growth (weeks to months)	Suggests neoplastic growth; simple goitre grows very slowly over years
Symptom	Pressure symptoms / RLN palsy (hoarseness)	Indicates rapid growth rate with invasion — highly suspicious for malignancy (can be absent in well-differentiated CA) ^[3]
Symptom	Rapid painless enlargement	Think anaplastic carcinoma, primary thyroid lymphoma, or haemorrhage into necrotic nodule ^[3]
Sign	Firm/hard consistency, fixation to surrounding tissues	Soft = reassuring; hard and fixed = invasion of surrounding structures → malignancy
Sign	Cervical lymphadenopathy (esp Level VI)	Level VI is the first site of metastasis for thyroid CA ^[3]
PMHx	Previous neck irradiation	↑ Risk of papillary carcinoma; ask about previous H&N cancer, NPC, thymoma ^[3]
FHx	Family history of thyroid CA	~20% of medullary CA (MEN II), ~5% of papillary CA are familial ^[3]

The following flowchart shows how you systematically work through the differential diagnosis when a patient presents with a thyroid swelling, starting from the clinical examination and TFT, to arrive at a working diagnosis:

Key reasoning at each branch:

Swallowing test — Quickly separates thyroid from non-thyroid masses (the pretracheal fascia attaches the thyroid to the larynx → swallowing elevates the larynx → thyroid mass rises).
Tongue tug test — Thyroglossal duct remnant is connected to the foramen caecum of the tongue → protrusion of the tongue pulls the cyst upward. A goitre does NOT move with tongue protrusion.
TFT (TSH) — The single most important discriminator. Normal TSH immediately excludes Graves', toxic adenoma, and overt Hashimoto's. TSH level is the MOST sensitive indicator of thyroid function ^[8].
USG — Defines morphology (diffuse vs nodular vs solitary), identifies suspicious features, guides FNAC.
Anti-thyroid antibodies — If TSH is normal but you're still not sure it's "simple," check anti-TPO and anti-Tg. If positive, consider early/subclinical autoimmune thyroiditis. In simple goitre: TFT normal, no anti-thyroid Ab ^[2].
Thyroid scintigraphy: only indicated if nodule + ↓ TSH ^[2]^[3] — to determine if the nodule is "hot" (functioning/autonomous → rarely malignant) or "cold" (non-functioning → 10–20% malignancy risk → needs FNAC).

Feature	Simple Goitre	Graves' Disease	Hashimoto's	De Quervain's Thyroiditis	Thyroid Malignancy	Toxic MNG
Morphology	Diffuse or multinodular	Diffuse	Diffuse (firm, rubbery)	Diffuse, may be asymmetric	Solitary hard nodule or dominant nodule	Multinodular
Consistency	Soft	Soft–firm	Firm, rubbery	Firm, tender	Hard, fixed	Variable, firm
Tenderness	No	No	No (unless flare)	Yes (pain radiates to jaw)	Usually no (unless anaplastic)	No
Bruit	No	Yes (vascular)	No	No	No	No
Lymphadenopathy	No	No	Possible	No	Yes (Level VI first)	No
TFT	Normal	↓ TSH, ↑ fT4	↑ TSH, ↓ fT4 (or normal early)	Fluctuating	Usually normal	↓ TSH ± ↑ fT4
Antibodies	Negative	TRAb +ve (80–90%)	Anti-TPO +ve (90–100%)	Low-titre Ab (transient)	N/A (check Tg, calcitonin)	Usually negative
ESR	Normal	Normal	May be mildly ↑	Markedly ↑	Normal (unless anaplastic)	Normal
Scintigraphy	Normal or patchy	Diffuse ↑ uptake	Normal or ↓ uptake	↓ uptake (globally)	Cold nodule	Patchy hot + cold
Eye signs	No	Yes (GO in 20–25%)	No	No	No	No

The Big Three to Exclude

Before calling any goitre "simple," you must confidently exclude:

Hashimoto's thyroiditis — check anti-TPO antibodies (the most sensitive marker; positive in 90–100% of Hashimoto's ^[8])
Graves' disease — check TFT (↓ TSH, ↑ fT4) and look for bruit, eye signs
Malignancy — USG for suspicious features, FNAC of any suspicious nodule

If TFT is normal, antibodies are negative, and USG shows no suspicious features, THEN you can call it simple goitre.

When a goitre extends retrosternally, it enters the differential for superior mediastinal masses. The differential for an anterior superior mediastinal mass follows the classic "4 T's" mnemonic:

"T"	Examples
Thyroid (retrosternal goitre)	The most common cause of a superior mediastinal mass; usually extension of a cervical MNG
Thymoma	Associated with myasthenia gravis, pure red cell aplasia, hypogammaglobulinaemia
Terrible lymphoma	Hodgkin's or non-Hodgkin's lymphoma
Teratoma / germ cell tumour	May contain fat, calcification, teeth on CT

How to distinguish retrosternal goitre from other mediastinal masses:

Continuity with cervical thyroid on CT/MRI — retrosternal goitre shows direct extension from the neck
Calcification pattern — coarse/eggshell calcification typical of long-standing MNG
Thyroid scintigraphy — functioning thyroid tissue lights up in the mediastinum (thymoma/lymphoma will not)
Clinical: cannot get below the swelling on palpation; positive Pemberton's sign; moves (at least partially) with swallowing

Retrosternal goitre requires CT because: (1) cannot be visualised by USG, (2) surgical planning, (3) retrosternal goitre may be malignant ^[5]

This integrates the framework from the lecture and senior notes ^[1]^[2]^[3]:

Morphology	Thyroid Status	Differential Diagnoses
Diffuse goitre	Euthyroid	Simple diffuse goitre (pregnancy, iodine deficiency, goitrogen, pubertal), early MNG, infiltrative disease (lymphoma), treated Graves
Diffuse goitre	Hypothyroid	Hashimoto's thyroiditis
Diffuse goitre	Hyperthyroid	Graves' disease
Diffuse goitre	Mixed / fluctuating	Destructive thyroiditis (de Quervain's, postpartum, subacute lymphocytic)
Multinodular goitre	Euthyroid	Non-toxic multinodular goitre
Multinodular goitre	Hyperthyroid	Toxic multinodular goitre (Plummer's disease)
Nodular goitre	Any	Non-neoplastic nodules (70%): colloid, haemorrhagic, complex, cystic, hyperplastic, adenomatous nodules, dominant nodule in MNG
Nodular goitre	Any	Benign follicular adenoma (15%): non-toxic (more common), toxic
Nodular goitre	Any	Thyroid malignancies: follicular, papillary, medullary, anaplastic, lymphoma, metastatic

High Yield Summary

Simple goitre is a diagnosis of exclusion — must rule out Hashimoto's (anti-TPO), Graves' (TFT + bruit + eye signs), destructive thyroiditis (ESR, pain), and malignancy (USG ± FNAC).
Framework: Cross-reference morphology (diffuse / multinodular / solitary nodule) with thyroid function (euthyroid / hypo / hyper / mixed) to narrow the differential.
Swallowing test separates thyroid from non-thyroid masses. Tongue tug test distinguishes thyroglossal cyst from goitre.
TFT is the single most important first-line discriminator: normal TSH essentially excludes Graves' and toxic states.
Around 10–15% of thyroid nodules are malignant — always evaluate dominant/suspicious nodules even within an MNG.
Red flags for malignancy: male sex, age extremes ( < 14 or > 70), solitary/hard/fixed nodule, RLN palsy (hoarseness), cervical lymphadenopathy (esp. Level VI), prior neck irradiation, family history of thyroid CA/MEN II.
Scintigraphy only if ↓ TSH + nodule: hot nodules are rarely malignant ( < 1%); cold nodules have 10–20% malignancy risk.
Retrosternal goitre DDx: anterior superior mediastinal mass — "4 T's" (Thyroid, Thymoma, Terrible lymphoma, Teratoma). CT is essential because USG cannot visualise below the thoracic inlet.

Active Recall - Differential Diagnosis of Non-Toxic / Simple Goitre

References

^[1] Lecture slides: GC 177. A thyroid nodule benign thyroid nodules; thyroid cancer.pdf (p4 — Goitre Classification; p13 — Other investigations) ^[2] Senior notes: Ryan Ho Endocrine.pdf (p17, p19, p31–32 — Goitre DDx, Investigations, Simple and Multinodular Goitre) ^[3] Senior notes: Ryan Ho Fundamentals.pdf (p172, p425–427, p429 — Thyroid mass DDx, Examination, Investigations) ^[5] Senior notes: maxim.md (Approach to thyroid nodules DDx table, Retrosternal goitre CT indications, Thyroglossal cysts) ^[7] Senior notes: Ryan Ho Diagnostic Radiology.pdf (p59–60 — Thyroid scintigraphy, principles and indications) ^[8] Senior notes: felixlai.md (Thyroid antibodies table, Bethesda classification, Evaluation flowcharts, Branchial cleft cysts, Biochemical tests) ^[9] Lecture slides: GC 218. I have a swelling in the neck Neck mass.pdf (p13 — Summary: diagnosis by age, location, clinical features)

Diagnostic Criteria, Algorithm and Investigations for Non-Toxic / Simple Goitre

There is no single diagnostic criterion or scoring system for simple (non-toxic) goitre. Unlike Graves' disease (where TRAb is nearly pathognomonic) or Hashimoto's thyroiditis (where anti-TPO titres clinch it), simple goitre is established by systematically excluding every other cause of thyroid enlargement.

Think of it this way: the thyroid is big, but everything else is normal. The diagnosis rests on three pillars:

Pillar	What It Confirms	What It Excludes
1. Normal TFT (normal TSH ± fT4)	Euthyroid state	Graves' disease, toxic MNG, toxic adenoma (all have ↓ TSH); Hashimoto's with overt hypothyroidism (↑ TSH)
2. Negative anti-thyroid antibodies (anti-TPO, anti-Tg)	No autoimmune process	Hashimoto's thyroiditis (anti-TPO +ve 90–100%), Graves' disease (TRAb +ve 80–90%) ^[8]
3. No suspicious features on USG ± FNAC	No neoplasia	Thyroid malignancy, follicular neoplasm

Additionally:

No tenderness or ↑ ESR → excludes subacute (de Quervain's) thyroiditis
No bruit → excludes Graves' disease
No cervical lymphadenopathy → excludes malignancy

Simple goitre: Ix → TFT normal, no anti-thyroid Ab ^[2]. Tx: not required ^[2].

The Diagnosis in One Sentence

Simple goitre = enlarged thyroid + normal TSH + negative thyroid antibodies + no suspicious USG features + no evidence of inflammation. If all of these are met, you've excluded Graves', Hashimoto's, thyroiditis, and malignancy — what's left is simple goitre.

The following algorithm shows the systematic approach from the moment a patient presents with a thyroid swelling to the point of reaching a working diagnosis. The logic at each branch point is explained below the diagram.

Logic at each branch point:

TSH is the single most important first test because it immediately triages the patient into euthyroid, hyperthyroid, or hypothyroid — each of which has a completely different differential ^[2]^[3].
USG is routine for ALL goitres/nodules ^[1]^[2]^[3] — it extends the physical examination, defines anatomy, identifies suspicious features, and guides FNAC.
Thyroid scintigraphy is only indicated when there is a nodule + ↓ TSH ^[2]^[3]^[8] — because you need to determine if the nodule is "hot" (autonomous, rarely malignant) or "cold" (non-functioning, 10–20% malignancy risk). If TSH is normal, scintigraphy should NOT be done because even cold nodules are mostly benign and it would lead to unnecessary biopsies ^[3].
FNAC is selective — only for nodules with suspicious USG features, cold nodules on scintigraphy, dominant/atypical nodules in MNG, nodules associated with abnormal LN, or complex/recurrent cystic nodules ^[8].
Anti-thyroid antibodies (anti-TPO, anti-Tg) are checked when you want to exclude autoimmune thyroiditis in a euthyroid diffuse goitre, or to establish Hashimoto's in a hypothyroid patient ^[2]^[8].

3. Investigation Modalities — Comprehensive Detail

3.1 Routine Investigations (For ALL Patients with Goitre/Nodule)

Routine for all patients: History + Physical exam, TFT, thyroid USG +/− FNAC ^[5]

Blood tests: TSH + free T4 ^[1]

Test	What It Measures	Why It Matters
Ultrasensitive TSH	Pituitary TSH level (most sensitive indicator of thyroid function)	TSH is the MOST sensitive indicator of thyroid function due to its short half-life ^[8] — even subtle thyroid dysfunction is reflected in TSH before fT4 changes. A normal TSH essentially confirms euthyroid status.
Free T4 (fT4)	Unbound, biologically active thyroxine	Confirms the degree of hyper- or hypothyroidism if TSH is abnormal. fT4 is preferred over total T4 because it is not affected by changes in binding proteins (e.g., ↑ TBG in pregnancy, OCP) ^[8].
Free T3 (fT3)	Unbound triiodothyronine	Only needed if TSH is low but fT4 is normal → to detect T3 thyrotoxicosis (occurs in 2–5% of thyrotoxic patients) ^[8]. Not routine.

Interpretation in simple goitre:

TSH: normal (within reference range)
fT4: normal
If TSH is suppressed (even mildly): think subclinical thyrotoxicosis — 25% of MNG patients have complete suppression of TSH ^[2]

Why measure fT4 rather than total T4? Because T3 and T4 are highly protein-bound (~99.97% for T4). Many factors alter thyroxine-binding globulin (TBG) levels — pregnancy and OCP increase TBG, androgens and hypoalbuminaemia decrease TBG. Total T4 changes with TBG levels even when the patient is euthyroid. Free T4 reflects only the biologically active fraction and is therefore more reliable ^[8].

USG is the cornerstone investigation for all patients with goitre or palpable nodules ^[1]^[2]^[3].

Investigation: Ultrasonography (USG) ^[1]:

B-mode real-time
Non-invasive, no radiation, convenient and cheap
Highly sensitive but relatively low specificity
Role:
- Extend physical examination
- Select nodules for FNAC
- Guide needle aspiration
- For all patients with goitre/palpable nodule
- Not recommended as a screening test

Technical details: 7.5 or 10 MHz probes, B mode ^[2]^[3]. High-frequency probes give excellent resolution for superficial structures like the thyroid (typically < 4 cm from skin surface).

What USG assesses:

Domain	What to Look For	Significance
Thyroid gland	Overall size, volume, echogenicity	Diffuse enlargement with normal echogenicity = simple goitre; heterogeneous echogenicity = Hashimoto's, MNG
Nodule characteristics	See TI-RADS features below	Risk-stratify for malignancy → decide FNAC
Cervical lymph nodes	Especially deep nodes, e.g., Level VI ^[5]	Suspicious LN features suggest metastatic thyroid CA
Trachea	Position, compression	Deviated = large goitre compressing; midline = reassuring
Retrosternal extension	Can partially assess but limited by sternum	If suspected → CT/MRI needed (USG cannot visualise below thoracic inlet)

USG Features of the Nodule Itself (Suspicious vs Reassuring):

Feature	Suspicious (High Risk of CA)	Reassuring (Low Risk of CA)
Echogenicity	Hypoechoic, heterogeneous	Hyperechoic, isoechoic
Calcification	Microcalcifications ( < 0.2 mm) — represents Psammoma bodies of papillary CA	Large coarse calcifications (dystrophic, from degeneration)
Shape	Taller than wide (AP dimension > transverse — suggests growth against tissue planes)	Wider than tall
Margins	Irregular (infiltrative/microlobulated)	Regular, smooth
Internal structure	Solid, or cystic with irregular septa	Spongiform appearance (multiple microcystic spaces > 50% of volume — very reassuring, < 1% malignancy)
Perilesional halo	Absent or incomplete (halo = compressed tissue without invasion)	Complete halo
Vascularity	Intranodular (central) vascularity	Peripheral vascularity
Extrathyroidal extension	Local invasion, esp. into strap muscles	Contained within thyroid

Mnemonic from senior notes for suspicious sonographic features: "SHIT CME" — Solid, Hypoechoic (most important), Irregular margins, Taller than wide, Calcification (micro), Margin irregular, Extrathyroidal extension ^[5]

USG Features of Surrounding Tissues:

Feature	Suspicious Finding
Other nodules	Presence of multiple nodules (likely MNG) is somewhat reassuring but does NOT exclude malignancy in any individual nodule
Parenchymal abnormalities	Heterogeneous background → Hashimoto's
Cervical lymph nodes	Suspicious LN: absent hilum, microcalcification, round shape (loss of normal kidney-bean shape), peripheral vascularity, hyperechoic, > 2 cm, intranodal cystic/coagulative necrosis ^[2]^[3]^[8]

The American Thyroid Association (ATA) 2015 guidelines (still current as of 2025/2026) stratify nodules into patterns that determine whether FNAC is indicated and at what size threshold:

Sonographic Pattern	USG Findings	Risk of Malignancy	Size Cutoff for FNAC
High suspicion	Solid hypoechoic nodule OR solid hypoechoic component of partially cystic nodule + ≥ 1 of: microcalcifications, rim calcification with extrusive soft tissue, taller than wide, irregular margins, extrathyroidal extension	> 70–90%	* > 1 cm*
Intermediate suspicion	Hypoechoic solid nodule WITHOUT microcalcifications, taller-than-wide, or extrathyroidal extension	10–20%	* > 1 cm*
Low suspicion	Hyperechoic or isoechoic solid nodule, OR partially cystic with eccentric solid areas, WITHOUT suspicious features	5–10%	* > 1.5 cm*
Very low suspicion	Spongiform or partially cystic WITHOUT any suspicious features	* < 3%*	* > 2 cm (or observe)*
Benign	Purely cystic (no solid component)	* < 1%*	No FNAC

Key Principle

The worse the USG looks, the smaller the nodule needs to be before you stick a needle in it. A highly suspicious nodule gets FNAC at > 1 cm; a very-low-suspicion spongiform nodule may not need FNAC until > 2 cm (or may just be observed). A purely cystic nodule needs no FNAC at all.

3.2 Selective Investigations (Based on Clinical Scenario)

FNAC (+molecular testing) ^[1]

Technique: 23–27 gauge needle, usually USG-guided, aspirating cells from the nodule for cytological examination.
Core needle biopsy is NOT performed for thyroid nodules because the thyroid is a very vascularised structure → risk of massive bleeding; also, FNAC is very accurate in identifying the type of thyroid cancer ^[8].

Indications for FNAC ^[8]:

Sonographic criteria for FNAC (as per ATA risk stratification above)
Hypofunctioning (cold) nodules on thyroid scintigraphy
Dominant or atypical nodule in multinodular goitre
Nodules associated with abnormal cervical lymph nodes
Complex or recurrent cystic nodules

Bethesda System for Reporting Thyroid Cytopathology (the universal classification for FNA results):

Class	Diagnostic Category	Cancer Risk	Recommended Management
I	Non-diagnostic / Unsatisfactory	1–4%	Repeat FNAC
II	Benign	0–3%	Clinical follow-up
III	Atypia of undetermined significance (AUS) OR Follicular lesion of undetermined significance (FLUS)	5–15% (updated to ~6–18% in Bethesda III 2023)	Repeat FNAC ± molecular testing
IV	Follicular neoplasm / Suspicious for follicular neoplasm	15–30%	Diagnostic surgical lobectomy
V	Suspicious for malignancy	60–75%	Lobectomy ± frozen section → total thyroidectomy
VI	Malignant	97–99%	Total thyroidectomy

Why can't FNAC distinguish follicular adenoma from follicular carcinoma? This is a classic exam question. Follicular carcinoma is defined by capsular and/or vascular invasion — features that can only be assessed on histological examination of the entire nodule, not on cytology (which only shows individual cells). That's why Bethesda IV ("follicular neoplasm") always goes to diagnostic lobectomy — you need the whole specimen under the microscope ^[8].

Thyroidectomy: diagnostic ± therapeutic ^[1]^[2] — In cases where FNAC is indeterminate (Bethesda III–IV), surgical excision serves both a diagnostic and therapeutic purpose.

Molecular testing (e.g., Afirma Gene Expression Classifier, ThyroSeq): Increasingly used for Bethesda III/IV nodules to further risk-stratify and potentially avoid unnecessary surgery. Detects mutations like BRAF V600E (highly specific for papillary CA), RAS, RET/PTC rearrangements, etc.

Radio-isotope scintigraphy (I-123 or Tc-99m) ^[1]

When to order (indications):

Thyroid scintigraphy: only indicated if nodule + ↓ TSH ^[2]^[3]

The reason is logical: if TSH is suppressed, something is autonomously making thyroid hormone. You need to know if it's the nodule (toxic adenoma → hot), the whole gland (Graves' → diffuse uptake), or multiple nodules (toxic MNG → heterogeneous uptake). If TSH is normal, the nodule by definition is NOT hyperfunctioning, so scintigraphy adds nothing — cold nodules at normal TSH are mostly benign and you'd just do USG-guided FNAC directly ^[3].

From the lecture slides ^[1]:

Diagnosis of malignancy: low sensitivity and specificity
Functional assessment in thyrotoxic patients

Radiopharmaceuticals ^[7]:

99mTc pertechnetate (trapped by NIS only — does not undergo organification; similar ionic size as iodide ^[7])
123I or 131I (trapped AND organified — more physiological but more expensive, less available)

Principle: Radioactive iodine is handled in the same manner as normal iodine. Level of uptake (and hence metabolic activity) is reflected by localisation of radioactive iodine ^[7].

Interpretation:

Scintigraphy Pattern	Interpretation	Clinical Significance
Diffuse ↑ uptake	Graves' disease vs secondary hyperthyroidism	Diffuse autonomous stimulation of entire gland
Heterogeneous ↑ uptake	Toxic MNG	Patchy areas of autonomous function amidst suppressed normal tissue
Focal ↑ uptake with ↓ uptake elsewhere	Toxic adenoma	Single autonomously functioning nodule suppressing the rest of the gland via negative feedback (↓ TSH → rest of gland suppressed)
Diffuse ↓ uptake	Destructive thyroiditis vs factitious thyrotoxicosis	Follicles are damaged and cannot trap iodine; or no endogenous thyroid activity (exogenous T4 intake)
"Hot" nodule	Hyperfunctioning — uptake > surrounding tissue	Rarely malignant ( < 1%) → does NOT require FNAC ^[2]^[3]^[8]
"Cold" nodule	Hypofunctioning — uptake < surrounding tissue	10–20% risk of malignancy → requires FNAC (provided sonographic criteria met) ^[2]^[3]^[8]

Why Hot Nodules Are Rarely Malignant

A "hot" nodule is one that is actively trapping iodine and making thyroid hormone — it is a well-differentiated, functioning follicular cell. Malignant thyroid cells (especially papillary and follicular carcinomas) are generally less differentiated and less efficient at iodine trapping compared to normal thyroid tissue, so they tend to appear as "cold" (reduced uptake) on scintigraphy. The rare exception is some follicular carcinomas that retain enough differentiation to appear warm/hot.

Further Ix for obstructive/retrosternal goitre ^[2]^[3]:

Investigation	Indication	Key Findings / Interpretation
CXR (thoracic inlet) ^[1]	Screen for mediastinal extension, tracheal deviation	Superior mediastinal widening; tracheal deviation to contralateral side; calcification within the mass; retrosternal soft tissue shadow
CT scan / MRI ^[1]^[2]^[3]	Retrosternal goitre (cannot be visualised by USG) ^[5]; surgical planning; retrosternal goitre may be malignant ^[5]; locally advanced thyroid cancer	Defines extent of retrosternal extension, degree of tracheal compression/displacement, relationship to great vessels and oesophagus; CT/MRI for retrosternal extension and staging — NOT routine ^[2]^[3]
Flow-volume loop (spirometry)	Screen for significant tracheal compression ^[2]^[3]	Upper airway obstruction (UAO) results in a blunted flow-volume loop ^[2]^[3]: fixed UAO → flattened inspiratory AND expiratory limbs; variable extrathoracic UAO → flattened inspiratory limb; variable intrathoracic UAO → flattened expiratory limb

CT Contrast and Radioactive Iodine

The use of iodinated contrast (for CT) may affect post-operative radioactive iodine body scan ^[2]. Iodinated contrast delivers a massive iodine load → saturates the NIS → ↓ uptake of subsequent RAI for 6–12 weeks. If you anticipate the patient may need RAI therapy (e.g., for thyroid cancer), avoid iodinated contrast or plan RAI accordingly. Use MRI instead if possible.

Test	Indication	Interpretation
ESR, anti-thyroid antibodies (ATA)	For thyroiditis ^[2]^[3]	↑ ESR + painful goitre = de Quervain's; anti-TPO/anti-Tg positive = autoimmune (Hashimoto's, subclinical autoimmune thyroiditis)
Calcitonin	If Hx or clinical suspicion of familial medullary carcinoma or MEN2 ^[2]^[3]	Elevated calcitonin = medullary thyroid carcinoma (95% of MTC produce calcitonin); also used as tumour marker for monitoring
Serum thyroglobulin (Tg)	Baseline tumour marker if suspected/confirmed differentiated thyroid CA	NOT useful for diagnosis (elevated in many benign conditions); useful post-thyroidectomy as recurrence marker
Anti-Tg antibodies	Measured to assess whether thyroglobulin can be used as a tumour marker ^[8]	If anti-Tg Ab are present, they interfere with Tg assays → Tg levels are unreliable for monitoring
CEA	Baseline marker in medullary thyroid CA	80% of MTC produce CEA ^[8]
Genetic testing (RET proto-oncogene)	All patients with MTC	All patients with MTC should be tested for RET mutation ^[8] → genetic counselling and family screening
Serum calcium, phosphate	Pre-operative baseline; exclude hypercalcaemia of malignancy	Hypercalcaemia may indicate parathyroid involvement or metastatic disease; also critical as post-op baseline for hypoparathyroidism

Procedure	Indication	What It Shows
Direct laryngoscopy	For RLN palsy ^[2]^[3] — should be done pre-operatively in ALL patients undergoing thyroidectomy to document baseline vocal cord function	Vocal cord mobility; unilateral cord paralysis = RLN palsy (suggests malignancy if pre-operative; iatrogenic if post-operative)
OGD	For oesophageal involvement ^[2]^[3]	Extrinsic compression or direct invasion of oesophagus by aggressive thyroid malignancy

PET scan ^[1]: No diagnostic role in the routine workup of a thyroid nodule or goitre ^[5].
However, incidental thyroid uptake on FDG-PET (performed for other reasons) is found in ~1–2% of PET scans and has a ~30–35% risk of malignancy — these warrant USG + FNAC.
PET is used in post-treatment surveillance of thyroid cancer (especially RAI-refractory differentiated thyroid CA and anaplastic/medullary CA).

Investigation	Routine or Selective	Key Purpose
History + Physical exam	Routine ✓	Clinical assessment, morphology, thyroid status, red flags for malignancy
TFT	Routine ✓	Determine thyroid functional status; triage into euthyroid/hypo/hyper
USG thyroid ± FNAC	Routine ✓	Define anatomy, identify nodules, risk-stratify for malignancy, guide FNAC
Thyroid scintigraphy	Selective — only in ↓ TSH + nodules	Determine hot vs cold nodule; functional assessment in thyrotoxicosis
CT scan / MRI	Selective — only for retrosternal goitre or locally advanced CA	Cannot be visualised by USG; surgical planning; delineation of cervical fascia structures
PET scan	Selective — no diagnostic role	Post-treatment surveillance; incidental thyroid FDG uptake warrants USG + FNAC
Anti-thyroid Ab (TPO, Tg)	Selective — if autoimmune thyroiditis suspected	Exclude Hashimoto's; assess if Tg reliable as tumour marker
ESR	Selective — if thyroiditis suspected	↑ in de Quervain's
Calcitonin, CEA	Selective — if MTC suspected	Tumour markers for medullary CA
RET mutation testing	Selective — all confirmed MTC	Identify hereditary MTC / MEN2
Flow-volume loop	Selective — retrosternal / obstructive goitre	Screen for UAO
Direct laryngoscopy	Selective — pre-op or if hoarseness present	Document vocal cord function
Thyroidectomy	Selective — diagnostic ± therapeutic	Definitive histological diagnosis when FNAC indeterminate (Bethesda III–V)

From the lecture ^[1]: Thyroid nodule investigations → Blood tests: TSH + free T4; Ultrasound; FNAC (+molecular testing); ESR, thyroid antibodies, calcitonin, genetic testing; Imaging: radioisotope scan, CT scan/MRI, PET scan; Endoscopy; Thyroidectomy: diagnostic + therapeutic

To bring this full circle — what do you actually find in simple goitre on each investigation?

Investigation	Expected Finding in Simple Goitre
TFT	Normal TSH, normal fT4
Anti-TPO, anti-Tg	Negative
ESR	Normal
USG	Diffuse enlargement OR multinodular pattern; no suspicious features (no microcalcifications, no solid hypoechoic nodules, no taller-than-wide, no irregular margins); possibly colloid nodules, cystic change
FNAC (if performed for dominant nodule)	Bethesda II — benign (colloid, macrophages, benign follicular cells)
Scintigraphy (if performed — usually not needed)	Normal or slightly heterogeneous uptake; no focal hot or cold areas
CXR	Normal if no retrosternal extension; mediastinal widening + tracheal deviation if retrosternal
CT thorax (if retrosternal)	Goitre extending below thoracic inlet; may show tracheal compression/deviation; no invasion
Flow-volume loop (if retrosternal)	May show blunted loop if significant UAO; normal if no obstruction

High Yield Summary

Simple goitre has no specific diagnostic test — it is a diagnosis of exclusion requiring: normal TFT + negative anti-thyroid Ab + no suspicious USG features + no inflammation.
Three routine investigations for ALL goitres: (1) TFT (ultrasensitive TSH ± fT4), (2) USG thyroid, (3) FNAC of suspicious nodules only.
Thyroid scintigraphy: ONLY if ↓ TSH + nodule. Hot nodules are rarely malignant ( < 1%), do not need FNAC. Cold nodules have 10–20% malignancy risk → FNAC.
USG risk stratification (ATA): High suspicion (solid hypoechoic + microcalcifications/taller-than-wide/irregular margins) → FNAC at > 1 cm. Purely cystic → no FNAC.
Bethesda classification: I = repeat; II = follow-up; III = repeat/molecular; IV = lobectomy; V = lobectomy ± total; VI = total thyroidectomy.
Retrosternal goitre needs: CXR + CT/MRI (USG cannot visualise below thoracic inlet) + flow-volume loop (UAO → blunted loop). Avoid iodinated contrast if RAI planned.
FNAC cannot distinguish follicular adenoma from carcinoma (needs capsular/vascular invasion on histology) → Bethesda IV always goes to diagnostic lobectomy.
Pre-op laryngoscopy for ALL thyroidectomy patients to document baseline vocal cord function.

Active Recall - Diagnostic Criteria, Algorithm and Investigations

References

^[1] Lecture slides: GC 177. A thyroid nodule benign thyroid nodules; thyroid cancer.pdf (p4 — Classification; p5 — Pathology; p7 — Investigations; p8 — USG; p13 — Other investigations/scintigraphy; p14 — Benign nodule indications for treatment) ^[2] Senior notes: Ryan Ho Endocrine.pdf (p13 — Scintigraphy indications/findings; p17 — Goitre DDx, subclinical thyrotoxicosis; p19 — Investigations, USG features; p32 — Simple goitre and MNG) ^[3] Senior notes: Ryan Ho Fundamentals.pdf (p425–429 — Goitre investigations, USG, scintigraphy, management of benign goitre) ^[5] Senior notes: maxim.md (Routine vs selective investigations table, retrosternal goitre CT indications, SHIT CME mnemonic) ^[7] Senior notes: Ryan Ho Diagnostic Radiology.pdf (p59–60 — Thyroid scintigraphy principles, radiopharmaceuticals, congenital hypothyroidism) ^[8] Senior notes: felixlai.md (TFT interpretation, thyroid antibodies table, USG suspicious features, ATA sonographic criteria for FNAC, Bethesda classification, scintigraphy interpretation, FNAC indications)

Management of Non-Toxic / Simple Goitre (Including Retrosternal Goitre)

Before diving into the algorithm, let's establish the fundamental logic of managing simple/non-toxic goitre:

Simple goitre is benign and euthyroid — there is no hormonal emergency, no malignancy, no inflammation. Many patients require no treatment at all.
The decision to treat is driven entirely by symptoms, size, growth trajectory, complications (compression/retrosternal extension), suspicion of malignancy, or cosmesis — NOT by the mere existence of a goitre.
Treatment (Tx) is not required for small, asymptomatic, stable simple goitres ^[2].
For MNG: the natural history is progressive enlargement → early definitive treatment for large or toxic MNG, as relapse is invariable after cessation of ATD ^[2]. This is fundamentally different from Graves' disease, where antithyroid drugs (ATD) are first-line because the autoimmune process may spontaneously remit after 12–18 months. In MNG, there is no autoimmune process to remit — the nodules keep growing.
The "4C" mnemonic for indications for thyroidectomy in benign thyroid disease is invaluable:

3Cs (from senior notes) — Cancer (confirmed or suspicious FNAC Bethesda IV–VI), Compressive symptoms (dysphagia, dysphonia, dyspnoea, retrosternal goitre), Cannot be treated medically (frequent relapses requiring definitive Tx, when RAI unsuitable or large goitre > 80 g) + Cosmesis ^[2]

Benign thyroid nodules — Indications of treatment ^[1]:

Indication	Explanation
Symptomatic (size of goitre/nodule)	Pressure sensation, neck tightness, discomfort with swallowing
Increase in goitre size	Progressive enlargement despite observation → suggests ongoing stimulus or autonomous growth
Trachea compression or deviation	Airway compromise → dyspnoea, stridor; this is potentially life-threatening
Retrosternal extension	Even if asymptomatic, retrosternal goitres tend to grow and can cause acute airway obstruction; surgical access becomes more difficult with time
Suspected malignancy	Suspicious FNAC (Bethesda IV–VI), suspicious USG features, or clinical red flags
Cosmetic considerations / patient wish	Visible goitre causing psychological distress; patient preference after counselling

4. Treatment Modalities — Detailed Breakdown

This is the management for the majority of patients with small, asymptomatic, non-toxic goitres.

No treatment + annual TFT to screen for toxic MNG in small, non-toxic MNG ^[2]

Aspect	Detail
Who	Small goitre ( < 80 mL), asymptomatic, euthyroid, no suspicious nodules, no retrosternal extension
What to monitor	TFT + neck exam every 1 year ^[2]^[3] — to detect progression to subclinical/overt thyrotoxicosis (toxic MNG) or significant growth
USG follow-up	Repeat USG if clinical change (new symptoms, palpable growth, new nodule); some guidelines suggest USG at 12–24 months then less frequently if stable
When to escalate	Growth causing symptoms, development of compressive symptoms, TSH suppression, new suspicious features

Why is observation reasonable? Because simple goitre is benign, most are slow-growing, and the risk of malignancy in a goitre with no suspicious features is very low. Intervention carries its own risks (surgical complications, lifelong T4 replacement). The cost-benefit ratio favours watchful waiting unless there is a clear indication to act.

Consider T4 suppression therapy in selected patients → aim low-normal TSH ^[2]

Aspect	Detail
Mechanism	Administration of exogenous levothyroxine (T4) → negative feedback on pituitary → ↓ TSH → ↓ size of goitre ^[3]. TSH is the main growth factor for thyroid follicular cells; removing the TSH drive theoretically shrinks the goitre.
Target	Aim for TSH at the low-normal end of the reference range (~0.4–1.0 mU/L). Do NOT fully suppress TSH (that would cause iatrogenic subclinical hyperthyroidism).
Who benefits	Patients with goitre associated with ↑ TSH (e.g., Hashimoto's thyroiditis, subclinical hypothyroidism, iodine deficiency) — in these patients, removing the elevated TSH stimulus genuinely helps.
Controversy	Efficacy in euthyroid patients is controversial ^[3] — if TSH is already normal, further suppressing it yields marginal benefit on goitre size (typically < 20% reduction) and exposes the patient to long-term side effects of subclinical hyperthyroidism.
Side effects	Long-term S/E of subclinical hyperthyroidism: bone (↑ bone resorption → osteoporosis, especially postmenopausal women) and heart (↑ risk of AF, cardiac hypertrophy) ^[3]
Current consensus	NOT recommended routinely for euthyroid simple goitre. May be considered in young patients with small diffuse goitres in iodine-deficient areas. ETA guidelines discourage this in iodine-sufficient regions.

Why ATD Don't Work for Simple/Non-Toxic Goitre

A common misconception is trying antithyroid drugs (ATD) for non-toxic MNG. ATD is 1st line in Graves' disease because the underlying autoimmune process may subside after 18 months. This is not the case in MNG or simple goitre ^[2]. In toxic MNG, ATD can control thyrotoxicosis temporarily but relapse is invariable after cessation ^[2] — so ATD is NOT definitive. For non-toxic MNG, there is no excess hormone to suppress in the first place. ATD have no role.

4.3 Thyroidectomy (Surgical Management) — The Mainstay of Active Treatment

Thyroidectomy is the preferred active treatment for most patients with large, symptomatic, or growing goitres ^[2]^[3].

Indications: 3Cs ^[2]:

Indication	Detail
Cancer (or suspicion)	Confirmed CA or suspicious FNAC (Bethesda IV–VI)
Compressive symptoms	Dysphagia, dysphonia, dyspnoea, trachea compression or deviation, retrosternal extension ^[1]
Cannot be treated medically	Frequent relapses of thyrotoxicosis (toxic MNG), require definitive Tx when RAI unsuitable (e.g., large goitre > 80 g)
+ Cosmesis	Cosmetic considerations / patient wish ^[1]

Additional specific indications from the lecture slides ^[1]:

Symptomatic (size of goitre/nodule)
Increase in goitre size
Suspected malignancy

Procedure	What Is Removed	Indications	Advantages	Disadvantages
Hemithyroidectomy (lobectomy)	One lobe + isthmus ± pyramidal lobe	Usually for suspicious thyroid nodules ^[2]; unilateral benign goitre; Bethesda IV–V	Preserves contralateral lobe → often avoids lifelong T4 replacement; lower risk of bilateral RLN injury and hypoparathyroidism	Risk of re-operation (recurrence rate 8.4%) ^[2]^[3] if disease is bilateral; may need completion thyroidectomy if histology shows cancer
Total / near-total thyroidectomy	Entire gland ± preservation of small remnant near RLN	Large bilateral MNG, compressive symptoms, retrosternal goitre, cosmetic concerns ^[2]; confirmed malignancy; Bethesda VI	Recurrence rate 0.2% ^[3]; no need for re-operation; allows RAI remnant ablation if cancer found	Lifelong T4 replacement required; ↑ risk of hypoparathyroidism (1–2%) ^[2]^[3]; risk of bilateral RLN injury

Decision framework (from senior notes) ^[5]:

	Solitary nodule	Multinodular
Euthyroid	Observe; Hemithyroidectomy if 3Cs/4Cs	Observe; Total thyroidectomy if 3Cs/4Cs
Hyperthyroid	Hemithyroidectomy	Total thyroidectomy

Total thyroidectomy for large goitres with compression or cosmetic concerns ^[2]

For euthyroid simple goitre, pre-operative preparation is straightforward (no thyrotoxicosis to control). However, if the patient has subclinical or overt thyrotoxicosis (toxic MNG), special pre-operative measures are critical to prevent thyroid storm:

Patients should be brought to euthyroid before surgery to avoid possible thyroid storm ^[8]

Step	Drug/Measure	Rationale
1	Antithyroid medications until euthyroid	Block new hormone synthesis (carbimazole/methimazole inhibit TPO → ↓ organification and coupling → ↓ T3/T4 production)
2	β-blockers for 2 weeks	Control adrenergic symptoms (tachycardia, tremor, sweating) until euthyroid state achieved
3	Lugol's iodine solution 10 days prior	↓ thyroid secretion and ↓ vascularity and size of thyroid gland ^[2] — the Wolff-Chaikoff effect: acute excess iodine transiently blocks organification + inhibits thyroglobulin proteolysis → ↓ hormone release; also ↓ blood flow to the gland → makes surgery technically easier (less bleeding)
4	Direct laryngoscopy	Document baseline vocal cord function pre-operatively ^[3]
5	Serum calcium	Baseline for post-op monitoring of hypoparathyroidism
6	Cross-match blood	Thyroid is highly vascular; risk of intra-operative haemorrhage

Lugol's Iodine — Timing Matters

Lugol's iodine must be given 10 days before surgery and only AFTER antithyroid drugs have been started (at least 1 hour after the first thionamide dose). If you give iodine to a thyrotoxic patient without prior ATD blockade, the iodine becomes substrate for new hormone synthesis (Jod-Basedow effect) and can precipitate thyroid storm. The Wolff-Chaikoff effect is transient — "escape" occurs after ~10–14 days, so surgery must happen within this window ^[2]^[8].

Concern	Detail
T4 replacement	Lifelong T4 replacement after total thyroidectomy — typically levothyroxine 1.6 μg/kg/day, adjusted to TSH. Not always needed after hemithyroidectomy (remaining lobe compensates in ~80%).
Calcium monitoring	Check serum calcium and PTH at 6–12 h post-op → early detection of hypoparathyroidism. If symptomatic (perioral tingling, Chvostek's/Trousseau's sign, tetany): IV calcium gluconate.
Vocal cord assessment	If voice changes → direct laryngoscopy to assess RLN function.
Histology	Await final histology for incidental malignancy (found in ~5–10% of thyroidectomy specimens for "benign" disease).

RAI is an alternative to surgery, particularly useful in patients who are not surgical candidates or who have small toxic goitres.

Aspect	Detail
Mechanism	Taken up and processed by thyroid gland in the same way as normal iodide → specificity to thyroid is due to preferential uptake via Na-I cotransporter (NIS) → becomes incorporated into thyroglobulin → emits β-radiation → destruction of thyroid gland (necrosis of follicular cells) ^[8]
Indications for non-toxic/toxic MNG	RAI for small toxic goitres ^[2]; RAI if high surgical risk ^[3]; patients who refuse or are unfit for surgery
Not suitable for	Large goitre > 50 mL (or > 80 g) — RAI may worsen goitre transiently (due to radiation thyroiditis and swelling) + cause obstruction in the short term, especially in retrosternal goitre ^[2]; suspected malignancy (need histology)

Advantages ^[3]:

↓ Cost, ↓ subjective side effects, can be repeated if needed

Disadvantages ^[3]:

Restricted proximity to other persons (especially if there are kids at home) — radiation safety precautions
Slow response — goitre shrinkage occurs over months
Risk of thyroiditis (3%) — radiation-induced inflammation
Transition to Graves' disease (5%) — ?destruction of radiosensitive intrathyroid T-suppressor cells or ?release of thyroid antigens
Hypothyroidism (15–20%) — expected outcome in many cases; requires lifelong T4 replacement

Contraindications ^[8]:

Pregnancy and lactation — ¹³¹I crosses the placenta and is concentrated by fetal thyroid (after 12 weeks gestation); secreted in breast milk → absolute contraindication
Children and adolescents — avoid potential teratogenicity
Large goitre with compressive symptoms (risk of acute airway compromise from transient swelling)
Active moderate-to-severe Graves' orbitopathy (can worsen)

Preparation for RAI ^[8]:

Discussion of treatment options + patient consent
Avoid iodine-containing food, medicine, or radiological contrast for ≥ 4 weeks before ¹³¹I therapy (to maximise RAI uptake by depleting stable iodine pools)
Avoid antithyroid medications for ≥ 4 weeks before ¹³¹I therapy (thionamides ↓ organification → ↓ RAI retention in gland)
Pregnancy test for women of childbearing potential
Symptomatic control with β-blockers (propranolol)

Post-RAI ^[8]:

Symptomatic control with β-blockers
Radiation safety: limit close contact, especially with children and pregnant women
Monitor TFT at 6–8 weeks, then Q3 months for the first year → lifelong annual monitoring for hypothyroidism

These modalities are increasingly available and offer options for patients who decline or are unfit for surgery and are not ideal candidates for RAI:

Modality	Mechanism	Indications	Notes
HIFU (High-Intensity Focused Ultrasound)	Focused ultrasound energy → thermal ablation of nodule tissue	Benign nodule < 5 cm ^[3]; cosmetic/symptomatic; patient declines surgery	Non-invasive (no skin incision); emerging modality; not 100% curative
RFA (Radiofrequency Ablation)	Needle electrode inserted into nodule → radiofrequency energy → thermal coagulative necrosis	Benign symptomatic/growing nodules; recurrent benign cysts	Increasingly established; can achieve 50–80% volume reduction; may need repeat sessions
Ethanol Ablation (PEI)	USG-guided injection of ethanol into nodule → chemical necrosis, thrombosis of vessels	Primarily for benign thyroid cysts (especially recurrent after aspiration)	Cheap and effective for cysts; less effective for solid nodules; risk of pain, transient voice change

Non-operative measures, e.g., RFA, HIFU, ethanol ablation (not 100% curative) ^[3]

Key Principle for Non-Operative Treatments

All non-operative treatments (RFA, HIFU, ethanol ablation) are palliative / volume-reducing — they shrink the nodule/goitre but do NOT provide histological diagnosis and are NOT considered curative. If there is any suspicion of malignancy, these are not appropriate — the patient needs surgery for histology.

Retrosternal goitre deserves separate emphasis because the management considerations are unique:

Aspect	Detail
General principle	Retrosternal extension is itself an indication for treatment ^[1] — even if asymptomatic, because: (a) it will continue to grow, (b) acute airway obstruction can occur, (c) surgical access becomes harder with time, (d) malignancy cannot be excluded
Preferred treatment	Total thyroidectomy — via cervical approach in the vast majority (~95%) of cases. The blood supply of retrosternal goitres is almost always from the cervical thyroid vessels (inferior thyroid artery), so the gland can be delivered upward through the thoracic inlet. A sternotomy is rarely needed ( < 5% of cases) and is reserved for: (a) truly intrathoracic goitre with an ectopic mediastinal blood supply, (b) very large posterior mediastinal extension, (c) invasion into mediastinal structures.
Pre-operative workup	CT/MRI thorax (extent, tracheal compression, vessel relationships); flow-volume loop (assess UAO); direct laryngoscopy (baseline vocal cords)
Anaesthetic considerations	May have difficult airway due to tracheal deviation/compression → awake fibre-optic intubation may be needed; anticipate the possibility of tracheomalacia after excision (weakened tracheal rings from chronic compression → airway collapse post-removal)
RAI for retrosternal goitre	Generally not preferred — risk of transient swelling causing acute airway obstruction; also, retrosternal tissue may not take up RAI as well as cervical tissue. May be considered only in patients truly unfit for surgery.

This is a common clinical scenario in Hong Kong: an elderly patient with a known MNG is found to have a suppressed TSH on routine screening but normal fT4/fT3.

Subclinical thyrotoxicosis: often found in older patients with multinodular goiter ^[3]

TSH Level	Risk Profile	Management
TSH < 0.1 mIU/L	↑ Risk of AF (1.68×), osteoporosis, IHD ^[2]	Workup + treat ^[2]^[3] — definitive treatment (RAI for small goitre, thyroidectomy for large/compressive)
TSH 0.1–0.4 mIU/L	Lower but not negligible risk	Consider treatment if > 65 years, at risk of osteoporosis, underlying IHD ^[3]; otherwise observe + monitor

Clinical Scenario	Management
Small, asymptomatic, stable, euthyroid simple goitre	No treatment + annual TFT monitoring ^[2]
Goitre with ↑ TSH (e.g., Hashimoto's)	T4 suppression therapy to normalise TSH → ↓ goitre size ^[3]
Euthyroid goitre — selected young patients	Consider T4 suppression (controversial) → aim low-normal TSH ^[2]
Large/growing goitre with compressive symptoms	Total thyroidectomy ^[2]
Retrosternal goitre	Thyroidectomy (even if asymptomatic) ^[1]
Cosmetic concern / patient wish	Thyroidectomy or non-operative (RFA/HIFU) ^[1]^[3]
Suspected malignancy (Bethesda IV–VI)	Thyroidectomy (hemi or total) per Bethesda management ^[8]
Small toxic MNG (subclinical or overt thyrotoxicosis)	RAI preferred ^[2]
Large toxic MNG	Total thyroidectomy (after pre-op preparation to render euthyroid) ^[2]
High surgical risk, not suitable for surgery	RAI ^[3]; or RFA / HIFU / ethanol ablation ^[3]
Benign nodule < 5 cm, symptomatic/cosmetic	HIFU or RFA ^[3]
Recurrent benign cyst	Ethanol ablation (PEI) ^[3]

Treatment	Contraindications
T4 suppression therapy	Elderly patients, osteoporosis, cardiac disease (risk of iatrogenic subclinical hyperthyroidism → AF, bone loss); already euthyroid with normal TSH (controversial benefit)
Thyroidectomy	Uncontrolled thyrotoxicosis (must render euthyroid first → risk of thyroid storm); unfit for general anaesthesia (severe comorbidities); uncorrectable coagulopathy
RAI	Pregnancy and lactation (absolute) ^[8]; children/adolescents; large goitre with compressive symptoms (risk of acute obstruction from transient swelling); suspected malignancy (need histology); active moderate-severe Graves' orbitopathy
RFA / HIFU / Ethanol ablation	Suspected malignancy (no histology obtainable); very large goitres (limited efficacy); significant retrosternal extension (inaccessible)

High Yield Summary

Most small, stable, euthyroid simple goitres need NO treatment — just annual TFT + clinical monitoring.
Indications for treatment (lecture slides): symptomatic size, increasing goitre, tracheal compression/deviation, retrosternal extension, suspected malignancy, cosmetic/patient wish.
Surgery (thyroidectomy) is the mainstay of active treatment: hemithyroidectomy for unilateral/solitary nodule; total thyroidectomy for large bilateral MNG, compression, retrosternal extension, cosmesis (3Cs + Cosmesis).
RAI is preferred for small toxic goitres and high surgical risk patients. Not for large/retrosternal goitres (risk of transient swelling → airway obstruction).
T4 suppression only useful if TSH is elevated (Hashimoto's, iodine deficiency). Controversial in euthyroid patients. Risks: subclinical hyperthyroidism → AF + osteoporosis.
Non-operative alternatives (RFA, HIFU, ethanol ablation): for selected benign nodules; not 100% curative; no histology.
ATD have NO role in non-toxic goitre and are NOT definitive in toxic MNG (relapse invariable after cessation).
Pre-op for thyrotoxic patients: ATD until euthyroid → β-blocker for 2 weeks → Lugol's iodine 10 days prior → surgery.
Retrosternal goitre = indication for surgery even if asymptomatic (risk of progressive growth and acute airway obstruction).
Post-total thyroidectomy: lifelong T4 replacement; monitor calcium for hypoparathyroidism; check vocal cords.

Active Recall - Management of Non-Toxic / Simple Goitre

References

^[1] Lecture slides: GC 177. A thyroid nodule benign thyroid nodules; thyroid cancer.pdf (p14 — Benign thyroid nodules: indications of treatment) ^[2] Senior notes: Ryan Ho Endocrine.pdf (p21 — Mx for benign goitre; p25 — Thyroid surgery, RAI, pre-op preparation; p32 — Simple goitre Tx not required, MNG management, ATD vs definitive Tx) ^[3] Senior notes: Ryan Ho Fundamentals.pdf (p425 — Subclinical thyrotoxicosis management; p429 — Mx for benign goitre: monitoring, thyroidectomy, HIFU, RAI, RFA, T4 suppression) ^[5] Senior notes: maxim.md (Solitary/multinodular decision table, pre-op preparation, thyrotoxicosis treatment indications) ^[8] Senior notes: felixlai.md (Treatment of hyperthyroidism: thionamides/RAI/surgery details, RAI contraindications and preparation, Bethesda classification management, tracheostomy for retrosternal goitre) ^[10] Senior notes: Ryan Ho Psychiatry.pdf (p53 — Lithium-induced goitre and thyroid effects)

Complications of Non-Toxic / Simple Goitre

Complications of simple/non-toxic goitre fall into two broad categories: (A) complications of the disease itself (i.e., what happens if you leave the goitre alone) and (B) complications of treatment (mainly thyroidectomy, but also RAI and non-operative modalities). Both are high-yield for exams, and understanding why each complication occurs from first principles makes them far easier to recall.

A. Complications of the Disease Itself

These are the complications that arise from the natural history of a growing, untreated goitre. They are the very reasons we treat large goitres.

As the goitre progressively enlarges — especially in multinodular goitre and retrosternal goitre — surrounding structures are compressed. The thyroid is tightly enclosed within the pretracheal fascia, surrounded by the trachea, oesophagus, great vessels, and nerves. There is limited room for expansion, particularly at the thoracic inlet.

Complication	Structure Compressed	Pathophysiology	Clinical Manifestation
Airway obstruction (stridor / dyspnoea)	Trachea	Large goitre (especially retrosternal) compresses or deviates the trachea → narrowing of airway lumen. Trachea compression or deviation is an indication for treatment ^[1]. Fixed obstruction causes biphasic stridor; variable extrathoracic causes inspiratory stridor.	Progressive dyspnoea, inspiratory stridor, positional (worse supine), may present acutely if haemorrhage into nodule rapidly enlarges gland
Dysphagia	Oesophagus	Posterior extension of goitre compresses the oesophagus against the vertebral column → progressive difficulty swallowing solids, then liquids	Difficulty swallowing, sensation of food "sticking"
SVC syndrome / venous obstruction	Superior vena cava, brachiocephalic veins	Large retrosternal goitre compresses the great veins at the thoracic inlet → impaired venous return from head, neck, and upper limbs → venous congestion	Facial plethora, cyanosis, neck vein distension, upper limb oedema; positive Pemberton's sign
Dysphonia (hoarseness)	Recurrent laryngeal nerve	In benign goitre, RLN compression is actually rare — the nerve is typically displaced rather than invaded. New hoarseness in the setting of a goitre should raise strong suspicion for malignancy (nerve invasion). However, very large or calcified goitres can occasionally cause traction injury to the RLN.	Hoarseness, weak voice, ineffective cough
Horner syndrome (rare)	Cervical sympathetic chain	Very large retrosternal goitre compresses the sympathetic chain → ipsilateral sympathetic denervation	Miosis, ptosis, anhidrosis (ipsilateral)
Phrenic nerve palsy (rare)	Phrenic nerve	Retrosternal extension compressing the phrenic nerve → hemidiaphragm paralysis	Unexplained dyspnoea, elevated hemidiaphragm on CXR

Acute Airway Emergency in Goitre

The most feared complication of a large retrosternal goitre is acute airway obstruction. This can occur from: (1) rapid haemorrhage into a degenerating nodule/cyst → sudden enlargement of the gland, (2) post-RAI radiation thyroiditis → transient swelling, (3) post-operative tracheomalacia. This is why retrosternal extension is an indication for treatment even if asymptomatic ^[1] — you don't want to wait for an emergency.

Haemorrhage into nodule/cyst → sudden painful swelling ^[2]

Pathophysiology: Within MNG, some nodules undergo cystic degeneration (central necrosis from outgrowing blood supply) or have thin-walled blood vessels. Spontaneous haemorrhage into these degenerated nodules causes rapid increase in nodule size.
Clinical presentation: Sudden, painful neck swelling over hours. This is one of the few causes of acute pain in a previously non-tender goitre. If the haemorrhage is large enough, it can cause acute airway compromise (especially in a retrosternal goitre).
Management: Usually self-limiting; analgesia, observation. USG-guided aspiration if large/symptomatic. Rarely requires emergency surgery.

Some nodules may secrete thyroid hormone autonomously (toxic MNG, Plummer disease) ^[2]

Pathophysiology: Over years to decades, some follicular cells within nodules acquire somatic activating mutations in the TSH receptor or the Gsα subunit → these nodules produce thyroid hormone independently of TSH stimulation → ↓ TSH via negative feedback, but the autonomous nodules keep secreting.
Progression: Non-toxic MNG → subclinical thyrotoxicosis (25% of MNG patients have complete suppression of TSH ^[2]) → overt toxic MNG.
Clinical significance: Classically AF + multinodular goitre in elderly ^[2]. Subclinical thyrotoxicosis is associated with ↑ risk of AF (1.68×), osteoporosis (↑ bone resorption, ↓ bone density), IHD (1.20–1.39×), HF ^[2]^[3].
This is why annual TFT monitoring is recommended even for stable non-toxic MNG — to detect this transition early.

The risk of a nodule within an MNG being malignant is the same as for any solitary thyroid nodule (~5–10% per nodule). The question of whether long-standing simple goitre itself transforms into cancer is debated, but the practical point is: always evaluate dominant or new nodules within an existing MNG for malignancy (USG ± FNAC).
Long-standing Hashimoto's thyroiditis (which may coexist or be misdiagnosed as simple goitre) carries a 60× risk of thyroid lymphoma ^[2].

A visible goitre can cause significant psychological distress, self-consciousness, and social embarrassment — this is a legitimate reason for intervention (cosmetic considerations / patient wish ^[1]).

B. Complications of Treatment (Thyroidectomy)

Thyroidectomy is the main active treatment for large or symptomatic non-toxic goitre. Understanding its complications is extremely high-yield for exams.

The complications are classically organised by timing: Immediate (intraoperative / < 24 h) → Intermediate (1 day – 1 month) → Late ^[2]^[8].

B1. Immediate Complications ( < 24 hours)

Haematoma (1.25%): uncommon but fatal ^[2]

Aspect	Detail
Incidence	~1.25% ^[2]
Pathophysiology	Bleeding from thyroid bed vessels (superior/inferior thyroid arteries or their branches) → haematoma usually in paratracheal region below strap muscles → causes venous obstruction → acute laryngeal oedema → risk of airway compromise ^[2]
Why is it so dangerous?	The thyroid bed is a relatively closed space bounded by the strap muscles anteriorly, trachea medially, and carotid sheath laterally. Expanding haematoma compresses the jugular veins → venous congestion of the larynx → laryngeal oedema → airway obstruction. The haematoma itself doesn't directly obstruct the airway — it's the venous congestion and secondary laryngeal oedema that kills.
Signs	Large, tense, firm, immobile neck swelling + SOB ^[2]; increasing stridor, tachypnoea, desaturation
Emergency management	Cut subcuticular stitches and stitches holding strap muscles (evacuate all blood) → call seniors for intubation ^[2]. This should be done at the bedside WITHOUT waiting for the operating theatre — delay is fatal. Keep a stitch-cutter at the bedside of every post-thyroidectomy patient.

Bedside Haematoma Evacuation

This is a true surgical emergency. Every medical student must know: if a post-thyroidectomy patient develops a tense neck swelling and respiratory distress, you open the wound at the bedside — remove skin sutures and divide the strap muscle stitches to decompress the haematoma. Do NOT wait for the patient to go back to theatre. This buys time for definitive airway management.

RLN injury → vocal cord paralysis ( < 1%) ^[2]

Aspect	Detail
Anatomy	The RLN runs in the tracheo-oesophageal groove and enters the larynx at the cricothyroid joint. It supplies all intrinsic muscles of the larynx except the cricothyroid ^[8]. The nerve adducts the vocal cords (via thyroarytenoid, lateral cricoarytenoid) and abducts them (via posterior cricoarytenoid — the only abductor).
Mechanism of injury	Can be transient (tractional neuropraxia from retraction) or permanent (transection or thermal injury from diathermy) ^[2]
Unilateral RLN injury	Unilateral vocal cord palsy → presents with hoarseness and ineffective cough ^[8]. The affected cord lies in a paramedian position (partially adducted). The contralateral cord compensates over time. Management: medialization (inject fat or silicone into paralysed vocal cord to improve apposition) ^[2] → allows the healthy cord to meet the medialised cord, improving voice and swallow.
Bilateral RLN injury	Bilateral vocal cord palsy → presents with stridor and dyspnoea (airway obstruction) ^[8]. Both cords lie in the paramedian/median position → nearly complete airway obstruction → requires immediate re-intubation ± tracheostomy ^[2]. This is a catastrophic complication.
Risk factors	Total thyroidectomy > hemithyroidectomy; re-operative surgery (scarring distorts anatomy); cancer surgery (nerve may be adherent to tumour); failure to identify the nerve intra-operatively
Prevention	Careful surgical technique with visual identification of the nerve; intra-operative nerve monitoring (not universally available but increasingly used)
↑ Risk of aspiration pneumonia	↑ Risk of aspiration pneumonia ^[8] — because the impaired vocal cord cannot fully adduct during the cough reflex → ineffective glottic closure → aspiration of secretions/food

SLN injury → weak voice, cannot sing high pitch ^[2]

Aspect	Detail
Anatomy	The external branch of the SLN runs with the superior thyroid artery near the upper pole of the thyroid. SLN supplies the cricothyroid muscle which lengthens (tenses) the vocal cord to produce high-pitched sound ^[8].
Clinical presentation	Vocal fatigue and changes in voice quality ^[8] — particularly loss of ability to project the voice and produce high-pitched sounds. Often subtle and under-recognised.
Clinical pearl	Important to ask if the patient is a professional singer pre-op ^[2] — SLN injury may be career-ending for vocalists, even though it is often dismissed as "minor"

Complication	Detail
Oesophageal injury	Rare; from dissection of posterior thyroid capsule. Can lead to mediastinitis if unrecognised ^[8].
Tracheal injury	Rare; direct damage during dissection. Risk increased in invasive cancer surgery.
Thyroid storm	Thyroid storm develops in patients with longstanding untreated hyperthyroidism which is precipitated by acute event such as surgery ^[8]. Caused by rapid ↑ in serum thyroid hormone levels → increased response to sympathetic inputs from catecholamines (adrenaline/noradrenaline) by permissive effect ^[8]. Leads to hyperpyrexia, tachycardia, hypertension → followed by heart failure with hypotension and arrhythmia ^[8]. Prevention: ensure the patient is euthyroid before surgery (ATD + β-blocker + Lugol's iodine).

B2. Intermediate Complications (1 day – 1 month)

Hypoparathyroidism leading to hypocalcaemia — MOST common complication ^[8]

This is the most commonly tested thyroidectomy complication. Here's why it happens from first principles:

Aspect	Detail
Anatomy	The four parathyroid glands (2 superior, 2 inferior) sit on the posterior surface of the thyroid, supplied by the inferior thyroid artery. They are tiny (~5 mm), easily damaged, devascularised, or inadvertently removed during thyroidectomy.
Pathophysiology	Damage to the parathyroid glands → ↓ PTH secretion → ↓ renal calcium reabsorption + ↓ 1,25-dihydroxyvitamin D production + ↓ bone resorption → hypocalcaemia
Incidence	Transient: 10–20% (especially from ischaemia, e.g., in benign disease) ^[2]; Permanent: 1–4% (especially in cancer surgery where extensive dissection is required) ^[2]
Reason	Often due to compromise of the inferior thyroid artery ^[2] — this is the main blood supply to the parathyroids. Even if the glands are not physically removed, ligation of the inferior thyroid artery trunk (rather than branches close to the gland) devascularises them.
Symptoms	Symptoms of hypocalcaemia: perioral and acral paraesthesia, carpopedal spasm, muscle spasms and cramps ^[8]
Signs	Trousseau's sign (carpal spasm when BP cuff inflated above systolic for 3 minutes — reduces blood supply to median nerve → neuromuscular hyperexcitability) and Chvostek's sign (facial muscle twitch when tapping over the facial nerve anterior to the ear) ^[8]
Severe	Convulsions, arrhythmias, tetany, laryngospasm ^[2] — remembered by the mnemonic "CATS GO NUMB" (Convulsion, Arrhythmia, Tetany, laryngoSpasm, NUMBNESS — perioral, distal) ^[2]
Investigations	Check serum corrected Ca²⁺ level or PTH level postoperatively ^[8]; ECG: prolonged QT interval ± arrhythmia ^[2]
Management — acute	Fast replacement: IV 10–20 mL of 10% calcium gluconate over 10 minutes (slow bolus) ^[8]; cardiac monitoring
Management — chronic	Replacement: calcium carbonate + calcitriol (active vitamin D) ^[8] — calcitriol is needed because without PTH, the kidney cannot convert 25-hydroxyvitamin D to the active 1,25-dihydroxyvitamin D form

CATS GO NUMB — Hypocalcaemia Signs

C = Convulsion, A = Arrhythmia, T = Tetany, S = LaryngoSpasm; GO NUMB = perioral and distal NUMBness. This is the classic mnemonic for symptoms and signs of hypocalcaemia post-thyroidectomy ^[2].

Hungry bone syndrome may occur in those with pre-operative hyperthyroidism ^[2]

Aspect	Detail
Pathophysiology	In pre-operative thyrotoxicosis (e.g., toxic MNG), there is chronically elevated bone turnover (thyroid hormone directly stimulates osteoclasts → ↑ bone resorption → ↑ serum calcium). After thyroidectomy, the thyrotoxicosis resolves and PTH is simultaneously reduced (post-surgical hypoparathyroidism) → sudden ↓ PTH + resolution of high bone turnover → massive ↑↑↑ bone ossification (unopposed bone formation) → rapid influx of calcium into bone → profound hypocalcaemia ^[2]
Clinical picture	Severe, refractory hypocalcaemia post-thyroidectomy out of proportion to degree of hypoparathyroidism; also hypophosphataemia and hypomagnesaemia (all absorbed by bone)
Management	Aggressive IV and oral calcium replacement; may require large doses; monitor closely

Tracheomalacia: can arise post-operatively due to degeneration of cartilage following removal of compression by large goitre ^[2]

Aspect	Detail
Pathophysiology	Chronic compression of the trachea by a large goitre → weakening and softening of the tracheal cartilage rings over time. While the goitre is present, it paradoxically "splints" the weakened trachea. When the goitre is surgically removed, the external support is gone → the weakened tracheal wall collapses inward on inspiration → airway obstruction.
Clinical presentation	Stridor and respiratory distress upon extubation
Management	May require prolonged intubation, tracheostomy, or tracheal stenting in severe cases

Complication	Detail
Seroma	Superficial, mobile (self-limiting) ^[2] — collection of serous fluid in the thyroid bed; usually resolves spontaneously
Wound infection	Uncommon (thyroidectomy is a clean surgical procedure); treat with antibiotics
Dysphagia	?Reason, usually resolves ^[2] — thought to be from oedema, scarring, or disruption of the strap muscles; typically transient
Hyperthyroidism ± thyroid storm	↑ Release of stored thyroid hormone into bloodstream ^[2] — manipulation of the gland during surgery can squeeze stored T4/T3 from follicular colloid into the circulation. This is why pre-operative euthyroid preparation is critical.

Complication	Detail
Recurrence ^[8]	Goitre regrowth after hemithyroidectomy — recurrence rate 8.4% for hemithyroidectomy vs 0.2% for total thyroidectomy ^[3]. The remaining thyroid lobe can undergo the same process of hyperplasia and involution → new MNG.
Hypertrophic scar and keloid formation ^[8]	The thyroidectomy incision (Kocher's incision in a natural skin crease) is in the anterior neck — a cosmetically sensitive area. Keloid formation is more common in certain ethnicities (including Chinese).
Permanent hypoparathyroidism	Lifelong calcium + calcitriol replacement; 1–4% risk with total thyroidectomy ^[2]
Permanent RLN palsy	If nerve transected; requires speech therapy ± medialization thyroplasty
Hypothyroidism	Inevitable after total thyroidectomy → lifelong levothyroxine (T4) replacement. After hemithyroidectomy, ~20% develop hypothyroidism (remaining lobe may not fully compensate).

Complication	Pathophysiology	Incidence / Notes
Hypothyroidism	Destruction of functioning thyroid follicular cells by β-radiation → ↓ T4 production	Transient 3.5–28%; Permanent 10–15% in first 2 years, then 3%/year ^[8]. Requires lifelong T4 replacement.
Radiation thyroiditis	Acute inflammation from radiation damage → transient painful swelling + transient ↑ T4 release (thyroid hormones released from damaged follicles)	~3% ^[3]; can cause acute airway compromise if retrosternal goitre (this is why RAI is avoided in large retrosternal goitres)
Transition to Graves' disease	?Destruction of radiosensitive intrathyroid T-suppressor cells or ?release of thyroid antigens → new autoimmune stimulation	~5% ^[3]
Worsening of Graves' orbitopathy	Release of thyroid antigens → ↑ TRAb → worsening orbital inflammation	Risk mitigated by concurrent short course of corticosteroids
Fetal thyroid damage	RAI crosses the placenta and is concentrated by fetal thyroid (> 12 weeks gestation) → fetal hypothyroidism/thyroid destruction	Absolute contraindication in pregnancy ^[8]
Salivary gland damage (sialadenitis)	Salivary glands also express NIS → take up RAI → radiation damage → dry mouth	More with higher doses (used in cancer ablation); less common with goitre doses

From the lecture slides — Table 2: Minimally Invasive Techniques ^[1]:

Modality	Common Complications	Mechanism
Percutaneous ethanol injection (PEI)	Pain, burning sensation, haematoma, dyspnoea, voice change	Ethanol leaking beyond the nodule capsule → chemical damage to surrounding tissues including RLN
Radiofrequency ablation (RFA)	Overall complication rate 2.17% (major 1.27%): voice change, nodule rupture, hypothyroidism, brachial plexus injury; minor: pain, thermal propagation, fever, skin burns, haematoma, transient hyperthyroidism/thyroiditis	Thermal energy beyond targeted nodule → damage to adjacent nerves/tissues
HIFU	Hypothyroidism (1.4–2.3%), hoarseness, neck swelling	Focused ultrasound causing thermal damage to non-targeted tissue
Microwave ablation (MWA)	Pain (25%), transient voice change (1%), haematoma, burns, Horner syndrome	Similar thermal injury mechanism to RFA

Category	Key Complications
Disease (untreated goitre)	Compressive symptoms (airway obstruction, dysphagia, SVC syndrome), haemorrhage into nodule, progression to toxic MNG (AF, osteoporosis), rare malignant transformation, cosmetic
Thyroidectomy — Immediate	Haematoma (fatal if airway compromise), RLN injury (unilateral = hoarseness; bilateral = airway obstruction), SLN injury (weak voice), thyroid storm, oesophageal/tracheal injury
Thyroidectomy — Intermediate	Hypoparathyroidism / hypocalcaemia (MOST common) ^[8], hungry bone syndrome, tracheomalacia, seroma, wound infection, dysphagia
Thyroidectomy — Late	Recurrence (8.4% hemi vs 0.2% total), hypothyroidism, permanent hypoparathyroidism, permanent RLN palsy, keloid
RAI	Hypothyroidism (most common), radiation thyroiditis, transition to Graves', worsening orbitopathy, sialadenitis
Non-operative (RFA/HIFU/PEI)	Pain, voice change, haematoma, thermal injury, hypothyroidism

High Yield Summary

Disease complications: Progressive compressive symptoms (airway, oesophagus, great veins), haemorrhage into nodule (sudden painful swelling), progression to toxic MNG (25% develop ↓ TSH; risk of AF and osteoporosis), rare malignancy.
Post-thyroidectomy haematoma: Uncommon (1.25%) but potentially fatal — paratracheal haematoma → venous obstruction → laryngeal oedema → airway compromise. Emergency: open wound at bedside, evacuate blood, call for intubation.
RLN injury ( < 1%): Unilateral = hoarseness + ineffective cough (manage by vocal cord medialization). Bilateral = stridor + airway obstruction → immediate re-intubation ± tracheostomy.
Hypoparathyroidism → hypocalcaemia: MOST common complication of thyroidectomy. Transient 10–20%, permanent 1–4%. Signs: CATS GO NUMB (Convulsion, Arrhythmia, Tetany, Laryngospasm, Numbness). Ix: serum Ca²⁺, PTH, ECG (↑ QT). Mx acute: IV calcium gluconate; chronic: oral calcium + calcitriol.
Hungry bone syndrome: Occurs in pre-op hyperthyroid patients — sudden ↓ PTH + resolution of high bone turnover → massive calcium influx into bone → severe refractory hypocalcaemia.
Tracheomalacia: Weakened tracheal cartilage from chronic compression collapses when goitre removed — stridor on extubation.
Thyroid storm: Prevented by ensuring euthyroid state pre-operatively. Triggered by surgery releasing stored thyroid hormones.
RAI complications: Hypothyroidism (most common, 15–20%), radiation thyroiditis (3%), transition to Graves' (5%). Contraindicated in pregnancy and large retrosternal goitre.

Active Recall - Complications of Non-Toxic Goitre and Its Treatment

References

^[1] Lecture slides: GC 177. A thyroid nodule benign thyroid nodules; thyroid cancer.pdf (p14 — Benign thyroid nodules: indications of treatment; p17 — Table 2: Minimally invasive techniques and adverse effects) ^[2] Senior notes: Ryan Ho Endocrine.pdf (p22 — Thyroidectomy complications: haematoma, RLN injury, SLN injury, tracheomalacia, hypocalcaemia, hungry bone syndrome, thyroid storm; p32 — MNG complications: haemorrhage into nodule, toxic MNG, compressive symptoms) ^[3] Senior notes: Ryan Ho Fundamentals.pdf (p425 — Subclinical thyrotoxicosis complications: AF, osteoporosis; p429 — Mx for benign goitre: recurrence rates hemi vs total, RAI complications) ^[8] Senior notes: felixlai.md (p1501 — Complications of thyroidectomy: classification table, RLN injury details, SLN injury, hypoparathyroidism management, hungry bone syndrome; p1465 — RAI contraindications and side effects)

Non-toxic/simple Goitre (inc. Retrosternal)

References

Non-Toxic / Simple Goitre (Including Retrosternal Goitre)

2. Epidemiology

3. Anatomy and Function

4. Etiology (Focus on Hong Kong)

5. Pathophysiology

6. Classification

7. Clinical Features

7.1 Symptoms

7.2 Signs

8. Special Consideration: Retrosternal Goitre

Active Recall - Non-Toxic / Simple Goitre

Differential Diagnosis of Non-Toxic / Simple Goitre

1. Organising Framework: DDx by Morphology and Thyroid Function

Active Recall - Differential Diagnosis of Non-Toxic / Simple Goitre

References

Diagnostic Criteria, Algorithm and Investigations for Non-Toxic / Simple Goitre

3. Investigation Modalities — Comprehensive Detail

3.1 Routine Investigations (For ALL Patients with Goitre/Nodule)

3.2 Selective Investigations (Based on Clinical Scenario)

Active Recall - Diagnostic Criteria, Algorithm and Investigations

References

Management of Non-Toxic / Simple Goitre (Including Retrosternal Goitre)

4. Treatment Modalities — Detailed Breakdown

4.3 Thyroidectomy (Surgical Management) — The Mainstay of Active Treatment

Active Recall - Management of Non-Toxic / Simple Goitre

References

Complications of Non-Toxic / Simple Goitre

A. Complications of the Disease Itself

B. Complications of Treatment (Thyroidectomy)

B1. Immediate Complications ( < 24 hours)

B2. Intermediate Complications (1 day – 1 month)

Active Recall - Complications of Non-Toxic Goitre and Its Treatment

References

On this page

Non-toxic/simple Goitre (inc. Retrosternal)

1. Definition

2. Epidemiology

2.1 Prevalence

2.2 Endemic vs Sporadic

2.3 Hong Kong Context

3. Anatomy and Function

3.1 Gross Anatomy of the Thyroid

3.2 Blood Supply

3.3 Lymphatic Drainage

3.4 Thyroid Physiology (First Principles)

4. Etiology (Focus on Hong Kong)

4.1 Causes of Simple / Non-Toxic Goitre

4.2 Goitrogens — A Closer Look

5. Pathophysiology

5.1 Simple Diffuse Goitre → Multinodular Goitre: The Natural History

5.2 Pathology

5.3 Why Does Retrosternal Extension Occur?

6. Classification

6.1 Classification of Goitre (from Lecture Slides) [1]

6.2 WHO Classification of Goitre by Size

6.3 Classification by Morphology

6.4 Classification by Function

6.5 Classification by Location

7. Clinical Features

7.1 Symptoms

7.1.1 Mass-Related Symptoms

7.1.2 Compressive Symptoms (Especially in Large/Retrosternal Goitre)

7.1.3 Symptoms That Should Be ABSENT in Simple Non-Toxic Goitre

7.2 Signs

7.2.1 Inspection

7.2.2 Palpation

7.2.3 Percussion

7.2.4 Auscultation

7.2.5 Thyroid Status Assessment

7.2.6 Summary of Signs in Simple Goitre

8. Special Consideration: Retrosternal Goitre

8.1 Definition and Epidemiology

8.2 Clinical Features Specific to Retrosternal Goitre

8.3 Investigations Specific to Retrosternal Goitre

9. Natural History and Progression

Active Recall - Non-Toxic / Simple Goitre

References

The Core Problem: A Patient Presents with a Thyroid Swelling — What Is It?

1. Organising Framework: DDx by Morphology and Thyroid Function

1.1 Diffuse Goitre

1.2 Multinodular Goitre

1.3 Solitary / Nodular Goitre

2. Non-Thyroid Differential Diagnoses (The "It Might Not Be Thyroid" List)

3. Features Suggesting Malignancy Within a Goitre

4. Algorithmic Approach to Differential Diagnosis

5. Differentiating Simple Goitre from Its Key Mimics — Side-by-Side

6. Special Differential: Retrosternal Goitre vs Other Mediastinal Masses

7. Summary Differential Diagnosis Table — Thyroid Masses

Active Recall - Differential Diagnosis of Non-Toxic / Simple Goitre

1. Diagnostic Criteria — Why Simple Goitre Is a Diagnosis of Exclusion

2. Master Diagnostic Algorithm

3. Investigation Modalities — Comprehensive Detail

3.1 Routine Investigations (For ALL Patients with Goitre/Nodule)

3.1.1 Thyroid Function Tests (TFT)

3.1.2 Ultrasound of Thyroid (USG)

3.1.3 ATA Sonographic Risk Stratification (TI-RADS Principles)

3.2 Selective Investigations (Based on Clinical Scenario)

3.2.1 Fine Needle Aspiration Cytology (FNAC)

3.2.2 Thyroid Scintigraphy (Radio-isotope Scan)

3.2.3 Further Investigations for Retrosternal/Obstructive Goitre

3.2.4 Other Selective Blood Tests

3.2.5 Endoscopy

3.2.6 PET Scan

4. Putting It All Together — Summary Investigation Table

5. Specific Findings in Simple / Non-Toxic Goitre

Active Recall - Diagnostic Criteria, Algorithm and Investigations

1. Overarching Principles

2. Indications for Treatment of Benign Thyroid Nodules / Non-Toxic Goitre

3. Management Algorithm

4. Treatment Modalities — Detailed Breakdown

4.1 Observation (Conservative Management / Watch-and-Wait)

4.2 T4 Suppression Therapy (TSH-Suppressive Levothyroxine)

4.3 Thyroidectomy (Surgical Management) — The Mainstay of Active Treatment

4.3.1 Indications for Thyroidectomy in Benign Thyroid Disease