A benign, encapsulated nerve sheath tumor arising from Schwann cells, most commonly affecting cranial nerve VIII (vestibular schwannoma) or spinal nerve roots.

Schwannoma

A schwannoma (also known as neurilemmoma or neurinoma) is a benign, encapsulated, slow-growing neoplasm arising from Schwann cells of the nerve sheath ^[1]^[2]^[3].

Breaking down the name:

"Schwann" → derived from Schwann cells, the glial cells that produce the myelin sheath around peripheral nerve axons
"-oma" → tumour/neoplasm

The key biological point is that schwannomas arise eccentrically from the nerve — they push the nerve fibres aside rather than growing through them (unlike neurofibromas, which are entwined within nerve fascicles). This has enormous surgical significance: schwannomas can often be shelled out from the nerve, preserving function; neurofibromas usually cannot.

Schwannomas are the most common benign peripheral nerve sheath tumour (PNST) ^[1]^[2]. They are typically solitary and sporadic, but multiple schwannomas are strongly associated with Neurofibromatosis Type 2 (NF2) or Schwannomatosis ^[2]^[3]^[4].

Key Conceptual Distinction: Schwannoma vs Neurofibroma

Feature	Schwannoma	Neurofibroma
Cell composition	Schwann cells only	Schwann cells + fibroblasts + perineurial cells + mast cells
Relationship to nerve	Eccentric, pushes nerve aside	Diffusely infiltrates nerve fascicles
Encapsulation	Well-encapsulated	Unencapsulated
Surgical separability	Can be separated from nerve	Difficult to separate; may sacrifice nerve
Malignant transformation	Extremely rare	Higher risk, esp. plexiform neurofibroma in NF1
Main syndrome association	NF2, Schwannomatosis	NF1

Epidemiology

Schwannomas account for approximately 8% of all intracranial tumours and are the most common tumour of the cerebellopontine angle (CPA) when arising from CN VIII (vestibular schwannoma / "acoustic neuroma") ^[1]^[2].
In the spine, schwannomas and meningiomas are the most common intradural extramedullary tumours ^[3].
Overall incidence of vestibular schwannoma: ~1–2 per 100,000 per year.
Peak incidence: 4th–6th decade (sporadic); NF2-associated cases present much younger, often in the 2nd–3rd decade ^[1]^[2].
Sex distribution: Sporadic schwannomas — approximately M = F for peripheral and spinal schwannomas ^[3]; intracranial vestibular schwannomas have a slight female predominance. Spinal schwannomas overall M = F ^[3].

Nasopharyngeal carcinoma (NPC) is highly prevalent in Hong Kong and can present as a neck mass or cranial neuropathy — an important differential in any Hong Kong patient presenting with a CPA lesion, hearing loss, or cervical mass ^[1]^[5].
Schwannomas may present as a posterior triangle neck mass — in Hong Kong, always exclude NPC metastatic nodes (Level V) before attributing a posterior neck mass to a benign cause ^[1]^[5].

Risk Factor	Mechanism
NF2 (Neurofibromatosis type 2)	Loss of merlin/schwannomin tumour suppressor on chromosome 22q12 → unregulated Schwann cell proliferation
Schwannomatosis	Mutations in SMARCB1 (INI1) or LZTR1 on chromosome 22 → multiple non-vestibular schwannomas without other NF2 features
Prior radiation exposure	DNA damage → secondary nerve sheath tumours (rare)
Carney complex	AD disorder with cardiac myxomas, schwannomas, endocrine tumours, pigmented skin lesions ^[4]
Sporadic	Somatic biallelic loss of NF2 gene — no inherited predisposition

Carney complex: AD disorder with atrial/extracardiac myxoma, schwannoma, various endocrine tumours, pigmented lentigines and blue nevi on face, neck and trunk ^[4]

NF2 – The Schwannoma Syndrome

NF2 is defined by bilateral vestibular schwannomas — this is virtually pathognomonic. Patients also develop meningiomas, ependymomas, and posterior subcapsular cataracts. Multiple spinal schwannomas or meningiomas should prompt evaluation for NF2. The mnemonic: "22 for NF2" — the NF2 gene sits on chromosome 22.

Anatomy and Function

Understanding schwannoma requires understanding the Schwann cell and the nerve sheath anatomy.

Schwann cells are the myelinating glial cells of the peripheral nervous system (PNS).
Each Schwann cell wraps around a single axon segment to form an internode of myelin.
Schwann cells express S-100 protein (a calcium-binding protein used as an immunohistochemical marker) — this is how schwannomas are confirmed on pathology ^[2].

Endoneurium — surrounds individual nerve fibres
Perineurium — surrounds fascicles (bundles of fibres); this is the blood–nerve barrier
Epineurium — surrounds the entire nerve trunk

Schwannomas arise from Schwann cells and grow eccentrically, displacing the parent nerve to one side. The tumour is enveloped by a true capsule (formed by epineurium/perineurium). This encapsulation is what allows surgical enucleation.

Schwannomas can arise from any myelinated nerve (cranial, spinal, peripheral, autonomic), but certain locations are classic:

Site	Nerve Involved	Clinical Name	Frequency
Cerebellopontine angle	CN VIII (vestibular division)	Vestibular schwannoma ("acoustic neuroma")	~80% of CPA tumours; most common intracranial schwannoma
Spine (intradural extramedullary)	Dorsal nerve roots	Spinal schwannoma	Usually cervical or lumbar ^[3]
Posterior neck	Cervical plexus / sympathetic chain / vagus	Cervical schwannoma	Posterior triangle neck mass ^[1]
Extremities	Major peripheral nerves (ulnar, peroneal, etc.)	Peripheral schwannoma	Common in upper/lower limbs
Mediastinum	Intercostal nerves / sympathetic chain	Mediastinal schwannoma	Posterior mediastinal mass
Retroperitoneum/Pelvis	Sacral plexus, sympathetic chain	Retroperitoneal schwannoma	Rare
Skin/Subcutaneous	Cutaneous sensory nerves	Cutaneous schwannoma	Small, may mimic other skin nodules

Schwannoma appears as a posterior triangle (posterior neck) mass — this is a key localisation point for neck mass differential diagnosis ^[1].

CN VIII has a long intracranial course with a transition zone between central myelin (oligodendrocytes) and peripheral myelin (Schwann cells) — the Obersteiner–Redlich zone near the internal auditory meatus. Schwannomas characteristically arise at or near this transition zone.
Other cranial nerves that can develop schwannomas: CN V (trigeminal), CN VII (facial), less commonly CN IX, X, XI, XII.
CN VII (facial nerve) schwannoma is an important differential for facial nerve palsy and must be distinguished from Bell's palsy, parotid tumours, and cholesteatoma ^[6].

Aetiology and Pathophysiology

The central molecular event in schwannoma development is biallelic inactivation of the NF2 tumour suppressor gene on chromosome 22q12.

Step-by-step mechanism:

The NF2 gene encodes a protein called merlin (also called schwannomin) — a cytoskeletal linker protein in the ERM (ezrin-radixin-moesin) family.
Merlin acts as a tumour suppressor by:
- Mediating contact inhibition of cell growth (when cells are touching each other, merlin signals them to stop dividing)
- Regulating Hippo signalling pathway (YAP/TAZ) — suppressing pro-growth transcription
- Modulating receptor tyrosine kinase signalling (e.g., EGFR, ErbB2)
When both copies of NF2 are lost (Knudson's two-hit hypothesis):
- In sporadic schwannomas: two somatic hits in the same Schwann cell → solitary tumour
- In NF2 syndrome: one germline hit + one somatic hit → multiple tumours (bilateral vestibular schwannomas, multiple meningiomas, ependymomas)
Loss of merlin → unregulated Schwann cell proliferation → encapsulated tumour growth

Pathology

Well-circumscribed, encapsulated, round/ovoid mass
Yellow-tan or grey-white cut surface
May show cystic degeneration, haemorrhage in larger tumours
Attached eccentrically to the parent nerve (nerve fibres are draped over the capsule, not running through it)

Pattern	Description	Significance
Antoni A	Compact, cellular areas with spindle-shaped Schwann cells arranged in palisading rows forming Verocay bodies (alternating nuclear and anuclear zones)	Highly characteristic; diagnostic feature
Antoni B	Loose, myxoid, hypocellular areas with cystic changes and scattered cells	Represents degenerative change; seen in older/larger tumours

Immunohistochemistry: S-100 protein strongly and diffusely positive (this distinguishes schwannoma from other spindle cell tumours) ^[2].
No mitotic figures or very low mitotic activity (benign behaviour).

Histology Pearl

Verocay bodies (palisading nuclei in Antoni A areas) are virtually pathognomonic for schwannoma. If you see them on a histology slide, schwannoma should be your top answer.

Slow-growing — doubling time often measured in years.
Benign — WHO Grade I.
Malignant transformation is exceedingly rare in schwannomas (unlike neurofibromas, which have a significant risk of sarcomatous change especially in NF1) ^[2].
Schwannomas do not invade the nerve — they compress and displace it. Clinical deficits arise from compression rather than destruction.

Classification

Category	Features
Sporadic (~95%)	Solitary, somatic NF2 mutation, peak 4th–6th decade
NF2-associated (~5%)	Bilateral vestibular schwannomas ± multiple other schwannomas, meningiomas, ependymomas; younger onset
Schwannomatosis	Multiple non-vestibular schwannomas, no bilateral vestibular schwannomas, SMARCB1/LZTR1 mutations; prominent pain
Carney complex	Schwannomas + cardiac myxomas + endocrine tumours + skin pigmentation ^[4]

Variant	Features
Conventional	Antoni A + B, S-100+, encapsulated
Cellular schwannoma	Predominantly Antoni A, can mimic sarcoma; still benign
Plexiform schwannoma	Multinodular/plexiform growth pattern; most are sporadic (unlike plexiform neurofibroma which is pathognomonic for NF1)
Melanotic schwannoma	Contains melanin; associated with Carney complex; can behave aggressively
Ancient schwannoma	Longstanding tumour with degenerative atypia (nuclear pleomorphism without mitoses); still benign

Clinical Features

Clinical features depend entirely on the site and size of the schwannoma and which nerve is affected. The tumour is benign and slow-growing, so symptoms typically develop insidiously over months to years. Small schwannomas are frequently incidental findings on imaging performed for other reasons.

The unifying pathophysiological mechanism for all symptoms is:

Compression of the parent nerve → nerve dysfunction (sensory > motor, because schwannomas arise more often from sensory nerves/roots)
Compression of adjacent structures as the tumour enlarges (e.g., brainstem, spinal cord, surrounding soft tissues)

A. Vestibular Schwannoma (Acoustic Neuroma) — Most Common and Most Tested

This is the most common schwannoma and the most common CPA tumour ^[1]^[2].

Symptom	Pathophysiological Basis
Unilateral progressive sensorineural hearing loss (SNHL)	Compression of the cochlear division of CN VIII → disruption of auditory signal transduction; this is the most common presenting symptom (~95%)
Unilateral tinnitus	Irritation/compression of cochlear nerve fibres → abnormal spontaneous neural discharge perceived as ringing/buzzing
Unsteadiness / imbalance	Compression of vestibular division of CN VIII → vestibular hypofunction; true spinning vertigo is less common because the slow growth allows central compensation
Headache	Large tumours cause obstructive hydrocephalus (compression of 4th ventricle / cerebral aqueduct) → raised intracranial pressure
Facial numbness / paraesthesia	Large tumours compress CN V (trigeminal) in the CPA → reduced facial sensation, especially V1/V2
Facial weakness	Large tumours compress CN VII (facial nerve) in the CPA / internal auditory canal → LMN facial palsy (though frank facial palsy is a relatively late feature because CN VII is resistant to compression) ^[6]
Diplopia	Very large tumours may compress CN VI (abducens) → lateral rectus palsy
Dysphagia, hoarseness	Extension to jugular foramen → CN IX, X involvement

Clinical Pearl – Hearing Loss Pattern

The hearing loss in vestibular schwannoma is unilateral sensorineural with characteristically poor speech discrimination scores disproportionate to the pure tone average. This is called "retrocochlear" pattern hearing loss, because the lesion is proximal to the cochlea (in the nerve itself), unlike presbycusis or noise-induced hearing loss which are cochlear.

Common ear diseases and hearing loss: Vestibular schwannoma (acoustic neuroma) presents with unilateral SNHL, tinnitus, and imbalance. It is the most important retrocochlear cause of hearing loss to exclude ^[7].

Sign	Pathophysiological Basis
Rinne positive, Weber lateralises to contralateral (normal) ear	SNHL: bone and air conduction both reduced on affected side (but air > bone preserved = Rinne positive); Weber lateralises away because the affected ear's sensorineural apparatus is damaged
Reduced corneal reflex	Compression of CN V (sensory limb of corneal reflex arc); this is an early and important clinical sign of a CPA mass — test it!
Nystagmus	Vestibular dysfunction → spontaneous nystagmus (typically fast phase away from lesion due to reduced tonic input from affected side)
Ipsilateral cerebellar signs	Large tumours compress the cerebellar peduncle → ipsilateral ataxia, dysdiadochokinesia, intention tremor
Papilloedema	Very large tumours → obstructive hydrocephalus → raised ICP → papilloedema
LMN facial palsy	Direct compression of CN VII; relatively late because CN VII has good tolerance to slow compression ^[6]

Important: facial nerve palsy from schwannoma is a lower motor neuron pattern (entire ipsilateral face affected). Always consider CPA tumour in a patient with gradual-onset unilateral facial weakness, especially if associated with hearing loss ^[6].

B. Spinal Schwannoma

Spinal schwannoma: usually cervical or lumbar intradural extramedullary lesions ^[3].

Symptom	Pathophysiological Basis
Radicular pain	Compression of the dorsal nerve root → dermatomal shooting/burning pain; this is often the earliest symptom
Radicular sensory changes (paraesthesia, numbness)	Compression of sensory fibres in the nerve root → dermatomal sensory loss ^[3]
Progressive weakness in a myotomal distribution	Compression of the ventral nerve root → LMN weakness in the corresponding myotome
Gait difficulty, spasticity	Large tumours compress the spinal cord (myelopathy) → UMN signs below the level of the lesion
Sphincter disturbance (urinary retention, faecal incontinence)	Late feature — compression of sacral cord or cauda equina
Neck pain / back pain	Local compression and stretching of dura/periosteum

Sign	Pathophysiological Basis
Dermatomal sensory loss	Root compression → loss of sensation in corresponding dermatome
LMN signs at the level (wasting, fasciculations, areflexia)	Ventral root compression → denervation of that myotome
UMN signs below the level (hyperreflexia, spasticity, upgoing plantars)	Spinal cord compression → disruption of corticospinal tract
Brown-Séquard syndrome	Lateral cord compression → ipsilateral motor loss + ipsilateral dorsal column loss + contralateral spinothalamic loss (i.e., contralateral pain/temperature loss)

Dumbbell Tumour

A spinal schwannoma can grow through the intervertebral foramen to form a "dumbbell" or "hourglass" shape — with an intradural component and an extradural/paravertebral component connected through the foramen. This is seen in ~15% of spinal schwannomas and is important because it changes the surgical approach.

C. Peripheral Schwannoma (Limbs, Neck, Soft Tissues)

Symptom	Pathophysiological Basis
Slowly growing, painless mass	Benign tumour grows slowly, initially asymptomatic
Pain / tenderness	Direct compression or stretching of the parent nerve → neuropathic pain
Paraesthesia / shooting pain distally	Compression/irritation of sensory fibres → radiculopathy-like symptoms radiating along nerve distribution
Motor weakness (rare unless very large)	Compression of motor fibres — uncommon because motor fibres are pushed aside rather than infiltrated

Sign	Pathophysiological Basis
Well-defined, firm, round/ovoid mass	Encapsulated tumour within nerve sheath
Mobile perpendicular to the nerve, not along it	The tumour is tethered to the nerve (which runs in one axis), so it can be displaced sideways but not along the nerve's course
Positive Tinel's sign	Tapping on the mass elicits tingling/electric shock sensation along the nerve distribution → confirms neural origin ^[2]
Non-tender or mildly tender on palpation	Pressure on the nerve within the mass

The finding that a mass moves perpendicular to, but not along, the axis of a nerve is classic for a nerve sheath tumour (schwannoma or neurofibroma) ^[2].

D. Neck Schwannoma

Schwannoma is listed as a posterior triangle neck mass ^[1]^[5].

Symptom	Pathophysiological Basis
Painless, slow-growing neck mass	Benign tumour of cervical plexus/vagus nerve/sympathetic chain
Hoarseness	Vagus nerve (CN X) schwannoma → recurrent laryngeal nerve compression
Horner's syndrome	Sympathetic chain schwannoma → disruption of sympathetic fibres → ipsilateral miosis, ptosis, anhidrosis
Paraesthesia in neck/shoulder	Cervical plexus nerve involvement

Sign	Pathophysiological Basis
Firm, smooth, well-defined mass in posterior triangle	Encapsulated tumour, often deep to sternocleidomastoid
Non-pulsatile (distinguishes from carotid body tumour)	No vascular component
Non-transilluminant (distinguishes from cystic hygroma)	Solid tumour
Mobile side-to-side, less so vertically	Attached to nerve running longitudinally

In a Hong Kong patient with a posterior triangle neck mass, always consider NPC metastasis (Level V nodes) as a differential. A thorough ENT examination including nasopharyngoscopy is mandatory ^[1]^[5].

Facial nerve schwannoma should be considered in the differential of facial nerve palsy ^[6].

Feature	Detail
Presentation	Slowly progressive facial weakness (unlike Bell's palsy which is acute-onset); may have hearing loss if tumour extends to CPA
LMN facial palsy	All branches affected on one side
Conductive hearing loss	If the tumour involves the tympanic segment of CN VII (middle ear) → ossicular chain disruption
Facial twitching/spasm	Nerve irritation before palsy develops

GC 217: In facial nerve palsy, always consider schwannoma if onset is gradual/progressive, or if there is associated hearing loss, or if facial weakness does not recover after expected time course for Bell's palsy (6–12 weeks) ^[6].

Site	Key Features
Mediastinal (posterior mediastinum)	Often incidental on CXR as a well-defined posterior mediastinal mass; may cause intercostal neuralgia
Retroperitoneal	Large before symptomatic; may cause vague abdominal/back pain
Cutaneous	Small subcutaneous nodule, tender, may mimic lipoma or dermatofibroma; distinguished by Tinel's sign
GI tract	Rare; submucosal mass, usually stomach; can mimic GIST

Site	Most Common Symptom	Key Sign	Key Differential
CPA (CN VIII)	Unilateral SNHL	Reduced corneal reflex	Meningioma, epidermoid, NPC
Spine	Radicular pain	Dermatomal sensory loss ± cord compression	Meningioma, metastasis, ependymoma
Peripheral nerve	Painless mass ± paraesthesia	Mobile ⊥ nerve axis, Tinel's +ve	Neurofibroma, ganglion cyst, lipoma
Posterior neck	Painless neck mass	Firm, non-pulsatile posterior triangle mass	NPC nodes, lymphoma, cystic hygroma
CN VII	Progressive facial weakness	LMN facial palsy	Bell's palsy, parotid tumour, cholesteatoma

High Yield Summary

Schwannoma = benign, encapsulated tumour of Schwann cells; arises eccentrically from the nerve (displaces but does not invade nerve fibres).
Molecular basis: biallelic loss of NF2 gene (chr 22q12) → loss of merlin tumour suppressor → unregulated Schwann cell proliferation.
Histology: Antoni A (compact, Verocay bodies) + Antoni B (loose, myxoid); S-100 positive.
Most common intracranial site: CPA — vestibular schwannoma (CN VIII). Presents with unilateral SNHL, tinnitus, imbalance.
Spinal schwannoma: intradural extramedullary, usually cervical/lumbar. Presents with radicular pain → sensory changes → cord compression.
Peripheral schwannoma: painless mass that is mobile perpendicular to nerve axis, Tinel's sign positive.
Neck schwannoma: posterior triangle mass — always exclude NPC metastasis in Hong Kong.
Key associations: NF2 (bilateral vestibular schwannomas), Schwannomatosis (multiple non-vestibular schwannomas with pain), Carney complex.
Malignant transformation is exceedingly rare (unlike neurofibroma in NF1).
Distinguish from neurofibroma: schwannoma is encapsulated, eccentric, surgically separable; neurofibroma is unencapsulated, diffusely infiltrative, and carries higher malignant potential.

Active Recall - Schwannoma

^[1] Senior notes: MBBS Final MB (Surgery) (Felix PY Lai).pdf, Section III Diagnosis – Mass localization (p.205) ^[2] Senior notes: Ryan Ho Rheumatology.pdf, Section 5.5.2 Neurofibroma (p.170) — used for comparison with schwannoma ^[3] Senior notes: Ryan Ho Neurology.pdf, Section 9.2 Spinal Cord Tumours (p.170) ^[4] Senior notes: Ryan Ho Cardiology.pdf, Section 3.8.3 Cardiac Tumours and Atrial Myxomas — Carney complex (p.198) ^[5] Lecture slides: GC 218. I have a swelling in the neck Neck mass.pdf ^[6] Lecture slides: GC 217. Facial nerve palsy and salivary gland diseases.pdf ^[7] Lecture slides: GC 214. Common ear diseases and hearing loss.pdf

Differential Diagnosis of Schwannoma

The differential diagnosis of schwannoma depends entirely on where the tumour presents — the same tumour in different locations generates completely different differential lists. A CPA schwannoma has a very different differential from a posterior triangle neck mass or a spinal intradural lesion. We will organise this systematically by anatomical site, explaining why each differential mimics schwannoma and how to distinguish them.

The overarching clinical question is always: "Is this mass a schwannoma, another benign lesion, or something malignant?"

Before listing differentials, understand the key clinical features of schwannoma that define the differential space:

Well-circumscribed, slow-growing mass → differentials include other benign tumours and congenital cysts
Neural origin (Tinel's sign, dermatomal symptoms) → differentials include other nerve sheath tumours and neurogenic tumours
Specific anatomical location → determines the main competing diagnoses
Enhancement pattern on imaging (avid, homogeneous in small tumours; heterogeneous with cystic change in large tumours) → imaging differentials vary

This is the most common and most heavily tested location. The differential of a CPA mass is a classic exam question.

CPA tumours: Vestibular schwannoma (acoustic neuroma) is the most common CPA tumour (~80%), followed by meningioma (~10%), then epidermoid cyst (~5%) ^[1]^[8]

Differential	Why It Mimics Schwannoma	How to Distinguish
Meningioma	Second most common CPA mass; also slow-growing, enhancing; causes similar CN compression (hearing loss, facial weakness)	Broad dural base with "dural tail" sign on contrast MRI; typically does not extend into IAC (schwannoma classically does — "ice-cream cone" sign); calcification common; arises from arachnoid cap cells, not Schwann cells; may cause hyperostosis of adjacent bone
Epidermoid cyst	Third most common CPA mass; can cause CN V/VII/VIII dysfunction; well-defined	Does NOT enhance with contrast; restricts on DWI (bright on diffusion); irregular/"cauliflower" margins; CSF-like signal but does not suppress completely on FLAIR (unlike arachnoid cyst)
Arachnoid cyst	Can occur in CPA; may compress CN VII/VIII	Follows CSF signal exactly on all MRI sequences (suppresses on FLAIR, no restriction on DWI); no enhancement; smooth margins; no solid component
Metastasis / leptomeningeal disease	Can involve CPA in patients with known malignancy (especially NPC in Hong Kong, lung, breast)	Known primary malignancy; may be multiple; often irregular enhancement; rapid progression; NPC metastasis should always be considered in Hong Kong patients ^[1]^[5]^[9]
Trigeminal schwannoma	Arises from CN V rather than CN VIII; can extend into CPA	Centred on Meckel's cave rather than IAC; presents with facial numbness/pain rather than hearing loss; may show dumbbell shape crossing middle cranial fossa
Facial nerve schwannoma	Arises from CN VII; can involve CPA/IAC segment	Progressive facial weakness as the dominant symptom rather than hearing loss; may extend along facial nerve course through temporal bone ^[6]^[10]
Glomus jugulare (jugular paraganglioma)	CPA-jugular foramen mass; can cause CN VIII/IX/X/XI dysfunction	Pulsatile tinnitus (vascular tumour); "salt and pepper" appearance on MRI due to flow voids; located at jugular foramen; destructive change of jugular foramen on CT
Cholesteatoma (congenital type)	Can occur in CPA (rare); causes similar cranial neuropathies	Non-enhancing; DWI bright (like epidermoid); clinical history of chronic otitis media for acquired types

GC 015: Imaging of the head and neck — CPA masses include schwannoma, meningioma, epidermoid, and metastatic disease. Always consider malignant adenopathy from head & neck cancer (NPC) in this locality ^[9]

The CPA Mass Triad – Exam Favourite

The three most common CPA masses in order:

Vestibular schwannoma (~80%) — extends into IAC, enhances avidly
Meningioma (~10%) — broad dural base, dural tail, usually does NOT enter IAC
Epidermoid cyst (~5%) — non-enhancing, DWI bright, irregular margins

If you can only remember three differentials for a CPA mass, remember these three.

Schwannoma and meningioma are the most common intradural extramedullary spinal tumours ^[3]^[11]. The differential here is between these two, plus other lesions in this compartment.

Differential	Why It Mimics Schwannoma	How to Distinguish
Spinal meningioma	Also intradural extramedullary; slow-growing; causes radiculopathy and cord compression	Thoracic predominance (schwannoma favours cervical/lumbar); F > > M (9:1); broad dural base, may calcify; homogeneous enhancement; does NOT extend through foramen (no dumbbell shape); a/w NF2 if multiple ^[3]
Neurofibroma	Also a nerve sheath tumour; intradural extramedullary; similar imaging appearance	Unencapsulated, infiltrates nerve (cannot be separated surgically); "target sign" on MRI (peripheral hyperintensity, central low signal on T2); a/w NF1 (not NF2); plexiform pattern suggests NF1 ^[2]^[12]
Spinal ependymoma (myxopapillary type)	Can occur at conus/filum terminale as intradural extramedullary mass	Usually at conus medullaris or filum terminale (not nerve root); intramedullary for conventional type; M > F; may show haemosiderin cap ("cap sign") ^[3]
Metastatic disease (extradural)	Most common cause of spinal cord compression overall; can mimic intradural tumour	90% extradural (vertebral body involvement); known primary (breast, lung, prostate common) ^[11]; rapid progression; bone destruction/collapse on imaging; pain worse lying down
Dermoid / epidermoid cyst	Intradural mass causing cord/root compression	Non-enhancing; DWI bright (epidermoid); fat signal (dermoid); usually congenital
Paraganglioma (filum terminale)	Intradural extramedullary mass at cauda equina; enhancing	Typically at filum terminale; "salt and pepper" appearance; catecholamine secretion possible

Spinal schwannoma: usually cervical or lumbar intradural extramedullary lesions. A/w NF2 if multiple lesions ^[3]

Spinal Tumour Compartment Rule

The compartment (extradural vs intradural extramedullary vs intramedullary) is the single most useful diagnostic discriminator on MRI:

Extradural = think metastasis first
Intradural extramedullary = schwannoma vs meningioma
Intramedullary = ependymoma vs astrocytoma

Intradural schwannoma and meningioma together account for the vast majority of intradural extramedullary tumours ^[3]^[11].

In Hong Kong, this is a critical differential because of the high prevalence of nasopharyngeal carcinoma (NPC), which metastasises to Level V (posterior triangle) lymph nodes ^[1]^[5].

GC 218: Neck mass differential — schwannoma is listed under posterior triangle masses. Malignant adenopathy from NPC is the most important differential to exclude in Hong Kong ^[5]

GC 015: Benign masses in the neck include schwannoma, paraganglioma, lipoma. Neoplastic masses include malignant adenopathy from head and neck cancer (oropharyngeal, nasopharyngeal, parotid) ^[9]

Differential	Why It Mimics Schwannoma	How to Distinguish
NPC metastatic lymph node (Level V)	Posterior triangle mass in a Hong Kong patient; the most important differential to exclude	Hard, fixed, may be matted; associated symptoms: epistaxis, nasal obstruction, conductive hearing loss (serous otitis media), cranial neuropathy; nasopharyngoscopy + biopsy diagnostic; EBV serology ↑ ^[1]^[5]
Lymphoma	Painless, firm posterior triangle mass; may be multiple; can be large	Rubbery, non-tender nodes; B symptoms (fever, night sweats, weight loss); multiple nodal groups involved; confirmed by excisional biopsy ^[1]
Cystic hygroma (lymphatic malformation)	Posterior triangle mass, especially in children/young adults	Brilliantly transilluminant; soft, compressible; multiloculated on US/MRI; typically presents in infancy ^[1]^[5]
Carotid body tumour (paraganglioma/chemodectoma)	Anterior triangle but can extend posteriorly; firm, non-tender mass	Pulsatile; mobile side-to-side but NOT vertically ("Fontaine's sign"); located at carotid bifurcation; "salt and pepper" on MRI; splays ICA and ECA on angiography ("lyre sign") ^[1]
Branchial cleft cyst	Well-defined cystic mass in anterolateral neck, usually anterior to SCM	Fluctuant; typically at anterior border of SCM (not posterior triangle); usually 2nd branchial cleft cyst; may become infected ^[1]^[13]
Cervical rib	Bony/firm mass in posterior triangle/supraclavicular region	Bony hard; may cause thoracic outlet syndrome (vascular/neurogenic symptoms); visible on CXR/CT
Lipoma	Soft tissue mass in neck; painless, slow-growing	Soft, lobulated, non-tender; no neural symptoms; slips away on palpation ("slip sign"); radiolucent (fat signal on MRI)
Neurofibroma	Nerve sheath tumour; similar location and neural signs	Soft, attached to skin (buttonhole sign positive); not encapsulated; a/w NF1 (café-au-lait spots, axillary freckling, Lisch nodules) ^[2]^[12]

Key distinguishing features of neck schwannoma:

Firm, smooth, well-defined, non-pulsatile, non-transilluminant
Mobile perpendicular to nerve axis but not longitudinally
Positive Tinel's sign
No skin attachment (unlike neurofibroma)

Differential	Why It Mimics Schwannoma	How to Distinguish
Neurofibroma	Also a nerve sheath tumour; fusiform mass along nerve; Tinel's positive	Unencapsulated, infiltrates nerve (surgically inseparable); soft, attached to skin, buttonhole sign; plexiform variant pathognomonic for NF1; higher malignant potential ^[2]^[12]^[14]
Malignant peripheral nerve sheath tumour (MPNST)	Neural origin; can arise de novo or (more commonly) from pre-existing neurofibroma; painful mass along nerve	Rapid growth; constant significant pain, change in consistency; usually > 5 cm; a/w NF1 (8-15% lifetime risk); high-grade histology with mitoses; PET-avid ^[8]^[12]
Ganglion cyst	Well-defined, firm mass adjacent to joint/tendon; painless	Transilluminant (cystic); located near joints/tendon sheaths; no neural symptoms; aspiration yields clear viscous fluid
Lipoma	Painless, slow-growing subcutaneous mass	Soft, lobulated, "slip sign"; no Tinel's; MRI shows fat signal
Dermatofibroma	Firm cutaneous nodule; may have buttonhole-like dimple sign	Skin-coloured to brown, < 1 cm; dimple sign on lateral compression (unlike buttonhole sign of neurofibroma); no neural symptoms; located in dermis
Desmoid tumour (fibromatosis)	Firm, deep soft tissue mass; slow-growing; can compress nerves	Locally aggressive (infiltrates surrounding tissues); no capsule; not neural origin; can recur after excision

Schwannoma vs Neurofibroma vs MPNST – The Nerve Sheath Tumour Triad

This is a commonly tested comparison. Don't mix them up:

Feature	Schwannoma	Neurofibroma	MPNST
Capsule	Yes	No	No
Nerve relationship	Eccentric (pushes aside)	Diffusely infiltrates	Destroys/invades
Surgical separability	Usually separable	Not separable	Not separable
Syndrome	NF2	NF1	NF1 (from neurofibroma)
Malignant potential	Extremely rare	Moderate (esp. plexiform in NF1)	Malignant by definition
Buttonhole sign	Negative	Positive	N/A
Pain	Variable	Usually painless	Constant, severe
Growth rate	Slow (years)	Slow	Rapid

MPNST alerting features: constant significant pain, change in consistency, rapid growth ^[8]

GC 217: Causes of facial nerve palsy — acoustic neuroma and facial nerve schwannoma are listed as causes at the CPA/IAM and beyond-stylomastoid-foramen levels respectively ^[6]^[10]

Differential	Why It Mimics Facial Nerve Schwannoma	How to Distinguish
Bell's palsy	Most common cause of unilateral LMN facial palsy; acute onset	Acute onset (schwannoma is gradual/progressive); usually recovers within 6-12 weeks; diagnosis of exclusion ^[10]
Vestibular schwannoma	CPA tumour compressing CN VII; causes facial weakness + hearing loss	Dominant symptom is hearing loss not facial weakness; facial weakness is a late feature; schwannoma is on CN VIII not VII
Ramsay Hunt syndrome	LMN facial palsy with vesicles (herpes zoster oticus); involves geniculate ganglion of CN VII	Triad: ipsilateral facial paralysis + otalgia + vesicles in auditory canal/auricle; acute onset; VZV reactivation ^[10]
Parotid gland tumour (malignant)	Mass beyond stylomastoid foramen causing LMN facial palsy	Palpable parotid mass; facial palsy suggests malignancy (benign parotid tumours almost never cause palsy); rapid onset possible ^[6]^[10]
Cholesteatoma	Middle ear mass eroding facial canal → CN VII palsy	History of chronic otitis media with otorrhoea; conductive hearing loss; CT shows middle ear/mastoid soft tissue with bony erosion
Temporal bone fracture	Acute LMN facial palsy after trauma	Clear history of head trauma; may have haemotympanum, CSF otorrhoea
Brainstem stroke	Nuclear CN VII palsy (LMN pattern); associated with other brainstem signs	Acute onset; other cranial nerve/long tract signs (e.g., CN VI palsy, contralateral hemiplegia = Millard-Gubler syndrome)
Otitis media	Middle ear infection causing CN VII palsy (runs through middle ear)	Acute otitis media symptoms: otalgia, fever, conductive hearing loss; examination shows inflamed TM ± perforation

When schwannoma (particularly vestibular schwannoma) presents with raised ICP or focal neurology, it enters the broader differential of brain tumours.

GC 108: Brain tumours — differential includes primary tumours (gliomas, meningiomas, schwannomas) and secondary tumours (metastases, most common intracranial tumour in adults) ^[8]

Differential	Key Distinguishing Features
Brain metastasis	Most common intracranial tumour in adults ^[8]^[15]; multiple lesions at grey-white junction; known primary; surrounding vasogenic oedema disproportionate to size
Glioma (astrocytoma / GBM)	Intra-axial (within brain parenchyma); irregular enhancement (ring-enhancing for GBM); crosses midline ("butterfly glioma"); not at CPA
Meningioma	Extra-axial; broad dural base + dural tail; calcification; hyperostosis; typically convexity/parasagittal/sphenoid wing
Pituitary adenoma (macroadenoma)	Sellar mass with suprasellar extension; bitemporal hemianopia from chiasmal compression; hormonal dysfunction; enhances uniformly ^[16]
Craniopharyngioma	Suprasellar mass with calcification (50%); bimodal age distribution (children and 40-60y); cystic with enhancing solid component ^[16]
Haemangioblastoma	Posterior fossa; cystic with enhancing mural nodule; a/w von Hippel-Lindau syndrome; polycythaemia (EPO secretion)

Growth rate: Schwannoma grows slowly over years. Rapidly expanding masses suggest malignancy ^[1]^[14].
Associated symptoms: Fever, night sweats, weight loss suggest lymphoma. Hoarseness, dysphagia, otalgia suggest cervical lymph node metastasis from upper aerodigestive tract malignancy ^[1].
Social history: Smoking and alcoholism are classical risk factors for H&N cancer ^[1] — this shifts the differential towards malignancy.
Multiplicity: Multiple schwannomas → think NF2 or Schwannomatosis. Multiple neurofibromas → think NF1. Multiple enhancing intracranial lesions → think metastases.
Hong Kong context: Always consider NPC in any posterior triangle neck mass or CPA lesion. Nasopharyngoscopy is mandatory ^[1]^[5]^[9].

High Yield Summary

CPA mass differential (most tested): Vestibular schwannoma (~80%) > Meningioma (~10%) > Epidermoid (~5%). Schwannoma extends into IAC; meningioma has dural tail and does not enter IAC; epidermoid is non-enhancing and DWI-bright.
Spinal intradural extramedullary: Schwannoma vs Meningioma are the two most common. Schwannoma favours cervical/lumbar, meningioma favours thoracic and is F > > M.
Neck mass: Posterior triangle schwannoma must be distinguished from NPC Level V nodes (Hong Kong!), lymphoma, cystic hygroma, and paraganglioma.
Peripheral nerve mass: Schwannoma vs neurofibroma vs MPNST — differentiated by capsulation, nerve relationship, syndrome association (NF2 vs NF1), growth rate, and malignant potential.
Facial nerve palsy: Schwannoma causes gradual progressive LMN palsy (Bell's palsy is acute; Ramsay Hunt has vesicles; parotid malignancy has palpable mass).
Red flags for malignancy: rapid growth, constitutional symptoms, smoking/alcohol history, hard fixed nodes, known primary cancer.
In Hong Kong, NPC must always be excluded in any patient with posterior triangle neck mass, CPA lesion, or cranial neuropathy — perform nasopharyngoscopy.

Active Recall - Schwannoma Differential Diagnosis

References

^[1] Senior notes: MBBS Final MB (Surgery) (Felix PY Lai).pdf, Section III Diagnosis – Mass localization and history taking (p.205) ^[2] Senior notes: Ryan Ho Rheumatology.pdf, Section 5.5.2 Neurofibroma (p.170) ^[3] Senior notes: Ryan Ho Neurology.pdf, Section 9.2 Spinal Cord Tumours (p.170) ^[5] Lecture slides: GC 218. I have a swelling in the neck Neck mass.pdf ^[6] Lecture slides: GC 217. Facial nerve palsy and salivary gland diseases.pdf ^[8] Lecture slides: GC 108. A mass in the brain brain tumours.pdf ^[9] Lecture slides: GC 015. Imaging of the head and neck.pdf ^[10] Senior notes: MBBS Final MB (Surgery) (Felix PY Lai).pdf, Section IV Causes of facial nerve palsy (p.211) ^[11] Senior notes: Maksim Medicine Notes.pdf, Cord compression – Aetiology (p.47) ^[12] Senior notes: MBBS Final MB (Surgery) (Felix PY Lai).pdf, Neurofibroma (p.149) ^[13] Senior notes: MBBS Final MB (Surgery) (Felix PY Lai).pdf, Differential diagnosis of neck mass – Branchial cleft cyst (p.201) ^[14] Senior notes: Adrian Lui Pediatrics Notes.pdf, NF1 – MPNST (p.148) ^[15] Senior notes: Ryan Ho Neurology.pdf, Section on brain metastasis (p.164) ^[16] Senior notes: Block A - I keep on bumping into people on my side_ pituitary tumours; hypopituitarism.pdf (p.1, p.6)

Overarching Diagnostic Principle

Schwannoma does not have a single set of "diagnostic criteria" like, say, rheumatic fever or SLE. Instead, the diagnosis is built through a convergence of clinical suspicion, imaging characteristics, and histopathological confirmation. The approach differs by anatomical site, but the general framework is:

Clinical suspicion — history and examination suggest a neural tumour (unilateral SNHL, radicular pain, mass on a nerve, etc.)
Imaging — MRI is the gold standard; defines site, size, compartment, and characteristic signal/enhancement pattern
Audiological testing — for vestibular schwannoma specifically
Histopathology — definitive diagnosis; obtained at surgical excision or biopsy
Genetic evaluation — if multiple schwannomas or syndromic features suggest NF2/Schwannomatosis

The key concept: imaging makes the presumptive diagnosis; histology makes the definitive diagnosis. Many small, incidentally found schwannomas are managed with observation alone, so histology is not always obtained up front.

Diagnostic Criteria

There are no formal "diagnostic criteria" analogous to NIH criteria for NF. The diagnosis is made when:

Clinical features are consistent (location-appropriate neurological symptoms; mass with neural characteristics)
MRI shows a well-circumscribed, enhancing mass with classic signal characteristics (see Investigations below)
Histology (when obtained) shows:
- Encapsulated tumour with Antoni A (compact, palisading Verocay bodies) and Antoni B (loose, myxoid) patterns
- Diffuse S-100 positivity on immunohistochemistry
- No infiltration of nerve fascicles (nerve fibres pushed aside, not running through tumour)

When multiple schwannomas are found, or when a vestibular schwannoma presents in a young patient, NF2 must be evaluated. NF2 is defined by bilateral vestibular schwannomas — this is virtually pathognomonic ^[3]^[14]^[17].

Revised Manchester Criteria for NF2 (2024 update):

Criterion	Definition
Definite NF2	Bilateral vestibular schwannomas (any age) OR first-degree relative with NF2 + unilateral VS or any 2 of: meningioma, schwannoma, glioma, neurofibroma, posterior subcapsular cataract
Probable NF2	Unilateral VS at age < 30 + at least 1 of: meningioma, schwannoma, glioma, neurofibroma, posterior subcapsular cataract OR ≥ 2 meningiomas + unilateral VS or any 1 of: schwannoma, glioma, neurofibroma, cataract

NF2: NO Lisch nodules, NO malignant transformation of neurofibromas, NO cognitive impairment. A/w bilateral acoustic schwannomas, meningiomas, ependymomas ^[2]^[14]^[17]

NF1 vs NF2 — Don't Confuse Them

Feature	NF1	NF2
Gene/Chromosome	NF1 / 17q11.2	NF2 / 22q12
Protein	Neurofibromin (Ras inhibitor)	Merlin/Schwannomin
Hallmark tumour	Neurofibromas (esp. plexiform)	Bilateral vestibular schwannomas
Skin findings	Café-au-lait, axillary freckling	Minimal skin findings
Eye findings	Lisch nodules	Posterior subcapsular cataracts
Diagnostic criteria	≥ 2/7 CAFESPOT ^[14]^[17]	Bilateral VS or family history + related tumours
Malignant potential	MPNST (8-15%) from neurofibromas	Low malignant potential

Schwannomatosis is diagnosed when:

≥ 2 non-vestibular schwannomas (at least one histologically confirmed) AND
No bilateral vestibular schwannomas on MRI (excludes NF2) AND
No NF2 germline mutation

The key distinguishing feature from NF2 is the absence of bilateral vestibular schwannomas. Patients typically present with prominent pain as the dominant symptom.

The diagnostic approach varies by presentation. Here is a unified algorithm covering the main clinical scenarios:

Investigation Modalities

1. Audiological Testing (Vestibular Schwannoma)

Why: First-line screening tool for any patient with unilateral SNHL
Principle: Tests hearing threshold at different frequencies (250 Hz to 8 kHz) via air conduction (headphones) and bone conduction (mastoid vibrator)
Key findings in vestibular schwannoma:
- Unilateral or asymmetric sensorineural hearing loss (air and bone conduction both reduced; air > bone preserved = Rinne positive)
- Typically high-frequency loss (though can be any pattern)
- 95% of vestibular schwannomas have abnormal PTA ^[3]^[15]
- Asymmetry ≥ 15 dB at any two adjacent frequencies or ≥ 20 dB at a single frequency is a red flag for retrocochlear pathology

Acoustic neuroma Ix: pure tone audiometry (95% abnormal), MRI contrast (CPA tumour with enhancement) ^[15]

Why: Distinguishes retrocochlear from cochlear pathology
Principle: Patient repeats spoken words at suprathreshold levels; tests the ability of the auditory nerve to transmit complex signals
Key finding: Disproportionately poor speech discrimination relative to the degree of pure tone loss — this is the hallmark of retrocochlear pathology (schwannoma compresses/distorts neural transmission, not just threshold sensitivity)
- e.g., PTA shows mild-moderate loss but speech discrimination is < 50% → strongly suggests retrocochlear lesion

Why: Electrophysiological test that assesses neural conduction along the auditory pathway from cochlea to brainstem
Principle: Surface electrodes record electrical potentials generated by auditory structures (5 waves: I = distal CN VIII, II = proximal CN VIII, III = cochlear nucleus, IV = superior olive, V = lateral lemniscus/inferior colliculus)
Key findings:
- Prolonged I–III and I–V interpeak latencies on affected side → indicates slowed conduction in the auditory nerve (wave I is generated before the tumour; wave III/V after it)
- Absent or attenuated wave V
- Sensitivity ~90-95% for tumours > 1 cm; lower sensitivity for small tumours
Current role: Largely supplementary now that MRI is widely available; still useful for screening when MRI is contraindicated (e.g., non-MRI-compatible implants) or as part of intraoperative monitoring

Why: Assesses function of the vestibular system
Principle: Warm/cold water irrigation of external ear canal → convection current in lateral semicircular canal → nystagmus. Reduced or absent response = canal paresis on that side
Key finding: Unilateral canal paresis (reduced vestibular response) on the affected side — present in ~60% of vestibular schwannoma patients
Mnemonic: COWS = Cold Opposite, Warm Same (direction of fast-phase nystagmus)

Audiological Testing Hierarchy

In clinical practice for suspected vestibular schwannoma:

PTA + SDS = first-line screening (available, cheap, non-invasive)
ABR = second-line if MRI unavailable or for screening programmes
MRI with gadolinium = gold standard confirmatory imaging (see below)

The key point: any patient with unexplained unilateral/asymmetric SNHL needs MRI of the IACs to exclude vestibular schwannoma — this is the most important investigation to order.

2. Imaging — The Cornerstone of Schwannoma Diagnosis

a. MRI with Gadolinium Contrast — Gold Standard

MRI is the single most important investigation for schwannoma at any site. It provides:

Precise anatomical localisation
Relationship to parent nerve and adjacent structures
Characteristic signal and enhancement pattern
Assessment of complications (hydrocephalus, cord compression)

Sequence	Signal	Explanation
T1-weighted	Iso- to hypointense relative to brain/muscle	Solid tumour tissue has similar water content to brain
T2-weighted	Hyperintense (bright)	High water content, especially in Antoni B (myxoid) areas; mixed signal in heterogeneous tumours
T1 + Gadolinium (Gd)	Avid, homogeneous enhancement (small tumours); heterogeneous enhancement with non-enhancing cystic areas (large tumours)	Enhancement occurs because schwannomas lack a blood-brain/blood-nerve barrier → Gd leaks into tumour interstitium. Cystic/necrotic areas in larger tumours do not enhance
DWI	No restriction (cf. epidermoid which restricts)	Schwannoma cells are not densely packed enough to restrict water diffusion

Vestibular schwannoma (CPA/IAC):

MRI contrast: CPA tumour with enhancement, often with extension into and widening of the IAC ("ice-cream cone" sign) ^[15]

Well-circumscribed, enhancing mass centred on the IAC → extends into the CPA as it grows
Widens the internal auditory canal (a key distinguishing feature from meningioma, which typically does not enter the IAC)
"Ice-cream cone" appearance: the intracanalicular component is the "cone" and the CPA component is the "scoop"
Large tumours show heterogeneous enhancement with cystic/necrotic areas
May compress the 4th ventricle → obstructive hydrocephalus
No dural tail (distinguishes from meningioma)
No calcification (meningiomas frequently calcify)

Spinal schwannoma:

Intradural extramedullary mass, usually cervical or lumbar ^[3]
Well-circumscribed, enhancing, displacing the spinal cord to the contralateral side
May show "dumbbell" configuration — extending through the neural foramen with both intradural and extradural components
May widen the neural foramen on imaging (bone remodelling from chronic pressure)
"Target sign" on T2 is more characteristic of neurofibroma (peripheral hyperintense, central hypointense); schwannoma tends to be more homogeneously bright on T2

Peripheral schwannoma:

Well-circumscribed, fusiform mass continuous with and eccentric to a nerve
"Entering and exiting nerve" sign (nerve fibres seen entering one pole and exiting the other)
Homogeneous or heterogeneous enhancement depending on size
"Split fat sign": rim of fat surrounding the mass on T1 (indicates the mass is within the intermuscular fat, typical of nerve sheath tumours)

Feature	Schwannoma	Meningioma	Epidermoid	MPNST
T1	Iso/hypo	Iso/hypo	Hypo (CSF-like)	Variable
T2	Hyperintense	Iso/slightly hyper	Hyperintense	Heterogeneous
Enhancement	Avid, homogeneous/heterogeneous	Homogeneous with dural tail	No enhancement	Irregular, heterogeneous
DWI	No restriction	No restriction	Restriction (bright)	Variable
IAC involvement	Yes (extends into IAC)	Usually no	Possible	N/A
Calcification	Rare	Common	No	Rare
Shape	Round/oval	Broad dural base	Irregular/"cauliflower"	Irregular, infiltrative

CT brain: normal brain tissue does not enhance due to intact BBB. Enhancement indicates either lesion outside BBB (e.g., meningioma) or disruption of BBB (e.g., high-grade tumours, inflammation) ^[15]

CT is not the primary diagnostic modality for schwannoma (MRI is far superior for soft tissue resolution), but it provides useful complementary information:

Temporal bone CT (thin-cut): Shows widening/erosion of the IAC (porus acusticus) on the affected side — compare with the contralateral side. This is a classic finding in vestibular schwannoma
Spinal CT: Can show widened neural foramen (dumbbell schwannoma); bony changes
CT interpretation principles: Location, number, size, shape (round/oval = slow displacing growth), outline (well-defined = benign characteristics), attenuation, contrast enhancement ^[18]
Schwannomas typically appear as isodense to hypodense lesions with avid contrast enhancement

Shape significance on CT: Round/oval = slow, displacing growth pattern (consistent with schwannoma). Irregular/infiltrative = malignancy ^[18]

When: First-line for superficial masses (peripheral limb, neck)
Findings: Well-defined, hypoechoic, oval/fusiform mass continuous with a nerve
Advantages: Readily available, non-invasive, guides FNAC/biopsy
Limitations: Cannot characterise as well as MRI; operator-dependent

When: Primarily to distinguish schwannoma from vascular lesions in the neck (e.g., carotid body tumour/paraganglioma)
Schwannoma: Mild to moderate vascularity; no "lyre sign" (splaying of ICA and ECA, which is characteristic of carotid body tumour)

3. Histopathology — Definitive Diagnosis

Histology provides the gold standard definitive diagnosis. It is obtained either at the time of surgical excision (most common) or via biopsy (for cases where observation/radiosurgery is planned but diagnosis is uncertain).

Well-circumscribed, encapsulated mass
Yellow-tan to grey-white cut surface
Cystic degeneration and haemorrhage in larger tumours
Eccentrically attached to parent nerve (nerve draped over capsule)

Feature	Description	Diagnostic Significance
Antoni A areas	Compact, cellular regions with spindle-shaped Schwann cells; nuclear palisading forming Verocay bodies	Highly characteristic — Verocay bodies are virtually pathognomonic
Antoni B areas	Loose, myxoid, hypocellular regions with cystic changes	Represents degenerative change; common in larger/older tumours
Capsule	True fibrous capsule from epineurium/perineurium	Key distinction from neurofibroma (unencapsulated)
No mitoses	Absent or very rare mitotic figures	Confirms benign nature (WHO Grade I)
No nerve fibre invasion	Nerve fibres pushed aside, not running through tumour	Key distinction from neurofibroma

Marker	Result	Why
S-100 protein	Strongly and diffusely positive	Schwann cell marker (calcium-binding protein); confirms neural crest origin
SOX10	Positive	Transcription factor for Schwann cell differentiation
EMA	Negative in tumour cells (positive in capsule perineurial cells)	Helps distinguish from meningioma (EMA positive)
GFAP	Negative	Distinguishes from astrocytoma (GFAP positive)
Ki-67	Low ( < 5%)	Confirms low proliferative index (benign)
CD34	Negative in tumour cells	Helps distinguish from neurofibroma (CD34 positive in endoneurial fibroblasts)

S-100: The Schwannoma Marker

S-100 protein is the single most important immunohistochemical marker for schwannoma. It is diffusely and strongly positive in virtually all schwannomas. While S-100 is also positive in some other tumours (melanoma, some sarcomas), the combination of S-100 positivity + Antoni A/B pattern + encapsulation = schwannoma.

4. Additional Investigations

No specific blood markers for schwannoma
Baseline bloods (CBC, RFT, LFT, clotting) — pre-operative assessment
If NF2 suspected: genetic testing for NF2 gene mutation (chromosome 22q12)
If Schwannomatosis suspected: SMARCB1 and LZTR1 mutation analysis

Indications: Bilateral vestibular schwannomas, multiple schwannomas, young patient ( < 30 years), family history of NF2
Tests: NF2 gene sequencing (blood sample); if negative and clinical suspicion high, consider mosaic analysis (tumour tissue)
Schwannomatosis: SMARCB1 (INI1) and LZTR1 gene sequencing

Slit-lamp examination: Screen for posterior subcapsular cataracts (NF2)
Fundoscopy: Screen for papilloedema (raised ICP from large intracranial schwannoma causing hydrocephalus)
Visual field testing: If concern about optic pathway compression

Nerve conduction study (NCS): evaluates peripheral neuropathy — axonal injury shows reduced amplitude; demyelination shows reduced conduction velocity. EMG: evaluates myopathy and neuropathy ^[19]

NCS/EMG: May show denervation in the myotome of the affected nerve root (spinal schwannoma) or along the distribution of the affected peripheral nerve
Intraoperative neurophysiological monitoring: CN VII monitoring during vestibular schwannoma surgery (facial nerve EMG); somatosensory evoked potentials (SSEPs) during spinal schwannoma surgery

In Hong Kong, any posterior triangle neck mass or CPA lesion with cranial neuropathy must prompt nasopharyngoscopy to exclude NPC ^[1]^[5]^[9]

Why: NPC metastasising to Level V lymph nodes can mimic a posterior triangle schwannoma; NPC can also directly invade the skull base causing CPA/cranial nerve involvement
Procedure: Flexible fibreoptic nasopharyngoscopy → direct visualisation of nasopharynx → biopsy any suspicious lesion
When: Any posterior triangle neck mass in a Hong Kong patient; any unexplained unilateral SNHL or cranial neuropathy in a young Chinese patient

Vestibular schwannomas are graded by the Koos classification (most widely used):

Koos Grade	Description	Clinical Significance
I	Purely intracanalicular (within IAC)	Small; may be managed with observation
II	Extends into CPA, < 2 cm	Small CPA component; observation or radiosurgery
III	Fills CPA cistern, 2–3 cm, may contact brainstem	Significant mass effect; often requires treatment
IV	> 3 cm, compresses brainstem and/or displaces 4th ventricle	Large; brainstem compression; hydrocephalus risk; requires surgical intervention

The Koos grade guides management decisions — observation is typically offered for Koos I-II in elderly patients with stable/slow growth; active intervention is more likely for Koos III-IV.

Investigation	When to Use	Key Finding in Schwannoma
PTA + SDS	Unilateral SNHL (screening)	Asymmetric SNHL, poor SDS
ABR	If MRI unavailable; intraoperative monitoring	Prolonged I-III and I-V interpeak latencies
MRI with Gd	Gold standard for all schwannomas	Well-circumscribed enhancing mass; extends into IAC (vestibular); intradural extramedullary (spinal); eccentric to nerve (peripheral)
CT temporal bone	Complementary for vestibular schwannoma	Widened IAC
CT spine	Bone assessment in spinal schwannoma	Widened neural foramen
USG	Peripheral/neck mass (first-line)	Hypoechoic, fusiform, nerve-continuous
Histopathology	Definitive diagnosis (at excision)	Antoni A + B, Verocay bodies, S-100+, encapsulated
Genetic testing	Bilateral VS, multiple schwannomas, young age	NF2 gene mutation; SMARCB1/LZTR1 for schwannomatosis
Nasopharyngoscopy	Posterior triangle neck mass / CPA lesion in HK	Exclude NPC
NCS/EMG	Spinal/peripheral nerve deficit assessment	Denervation pattern in affected nerve distribution

High Yield Summary

No formal diagnostic criteria for sporadic schwannoma — diagnosis is clinical + imaging + histology.
NF2 diagnosis: Bilateral vestibular schwannomas is pathognomonic; Manchester criteria for other combinations. Gene: NF2 on chr 22q12, protein: merlin.
Audiological testing for vestibular schwannoma: PTA shows unilateral asymmetric SNHL; SDS is disproportionately poor (retrocochlear pattern); ABR shows prolonged I-V interpeak latency. Any unexplained asymmetric SNHL mandates MRI.
MRI with gadolinium is the gold standard: Schwannoma is T1 iso/hypo, T2 bright, avidly enhancing, well-circumscribed. Vestibular schwannoma extends into IAC (unlike meningioma). No dural tail. No DWI restriction (unlike epidermoid).
CT complementary: Shows widened IAC (vestibular), widened neural foramen (spinal dumbbell). Round/oval shape = slow displacing growth.
Histology is definitive: Antoni A (Verocay bodies) + Antoni B + S-100 diffusely positive + encapsulated + no nerve fibre invasion.
Always screen for NF2 in young patients, bilateral VS, or multiple schwannomas: MRI whole spine + brain, slit-lamp for cataracts, genetic testing.
Hong Kong rule: Nasopharyngoscopy is mandatory for any posterior triangle mass or unexplained CPA lesion to exclude NPC.

Active Recall - Schwannoma Diagnosis and Investigations

^[1] Senior notes: MBBS Final MB (Surgery) (Felix PY Lai).pdf, Section III Diagnosis – Mass localization and history taking (p.205) ^[2] Senior notes: Ryan Ho Rheumatology.pdf, Section 5.5.2 Neurofibroma and NF diagnostic criteria (p.170, p.172) ^[3] Senior notes: Ryan Ho Neurology.pdf, Section 9.2 Spinal Cord Tumours (p.170) ^[4] Senior notes: Ryan Ho Cardiology.pdf, Section 3.8.3 Cardiac Tumours – Carney complex (p.198) ^[5] Lecture slides: GC 218. I have a swelling in the neck Neck mass.pdf ^[9] Lecture slides: GC 015. Imaging of the head and neck.pdf ^[14] Senior notes: Adrian Lui Pediatrics Notes.pdf, NF1 diagnostic criteria CAFESPOT (p.148) ^[15] Senior notes: Ryan Ho Neurology.pdf, Section on acoustic neuroma and brain tumour investigations (p.162, p.167) ^[17] Senior notes: MBBS Final MB (Pediatrics) (Felix PY Lai).pdf, Neurofibromatosis NF1 and NF2 (p.811, p.815) ^[18] Senior notes: Ryan Ho Diagnostic Radiology.pdf, CT interpretation principles (p.39) ^[19] Senior notes: Maksim Medicine Notes.pdf, Neurology investigations – NCS, EMG, neuroimaging (p.235)

Overarching Management Principles

The management of schwannoma is guided by three fundamental considerations:

Schwannomas are benign (WHO Grade I) — there is no urgency to treat every schwannoma. Many can be safely observed.
Treatment-related morbidity can be significant — particularly cranial nerve damage (hearing loss, facial palsy) with vestibular schwannoma surgery. The treatment must not be worse than the disease.
The three pillars of management are:
- Observation ("watch and wait" / "wait and scan")
- Surgery (microsurgical excision)
- Stereotactic radiosurgery (SRS) / stereotactic radiotherapy (SRT)

The choice among these depends on: tumour size, growth rate, symptoms, patient age and fitness, hearing status, and whether the schwannoma is sporadic or NF2-associated.

The fundamental management question for every schwannoma is: "Does the risk of treatment outweigh the risk of observation?" For small, stable, minimally symptomatic tumours in elderly patients, observation is often the best strategy. For large, growing, or symptomatic tumours causing neurological compromise, active intervention is warranted.

Management Algorithm

This is the most commonly tested and most nuanced management decision.

Treatment Modalities

1. Observation ("Watch and Wait" / "Wait and Scan")

Schwannomas are benign and slow-growing. Many vestibular schwannomas grow at only 1-2 mm per year or do not grow at all. Studies show that 40-70% of small vestibular schwannomas remain stable on serial imaging over 5 years. Since treatment carries real risks (hearing loss, facial nerve injury), it makes sense to defer treatment until there is a clear indication.

Serial MRI with gadolinium: Every 6 months for the first year, then annually if stable
Serial audiometry: Every 6-12 months to monitor hearing
Clinical assessment: Symptom review at each visit

Indication	Reasoning
Small tumour (Koos I-II, < 2 cm)	Low risk of neurological compromise; many remain stable
Elderly patient ( > 65-70 years) or significant comorbidities	Surgical risk may outweigh benefit; life expectancy considerations
Minimal or no symptoms	No immediate threat to function
No documented growth on serial imaging	Confirms indolent behaviour
Patient preference	After informed discussion of all options
Only hearing ear	Intervention risks total deafness; extreme caution warranted

Trigger	Action
Documented growth > 2 mm/year	Discuss active treatment
Progressive hearing loss	Consider treatment before hearing is lost completely (better surgical outcomes with serviceable hearing)
New neurological deficit (facial weakness, trigeminal symptoms)	Active treatment
Brainstem compression / hydrocephalus	Urgent surgery
Patient anxiety unmanageable	Consider treatment for quality of life

Observation is NOT Neglect

Observation is an active management strategy, not inaction. It requires structured follow-up with serial imaging and audiometry. The term "wait and scan" is preferred over "watch and wait" because it emphasises the need for regular monitoring. The advantage is avoiding treatment-related morbidity in patients who may never need treatment.

2. Microsurgical Excision

Surgery remains the definitive treatment for schwannoma at all sites. The goal is complete tumour removal while preserving neurological function — particularly the facial nerve (CN VII) and hearing (CN VIII) in vestibular schwannoma surgery.

The choice of approach depends on tumour size, hearing status, and surgeon expertise:

Approach	Route	Hearing Preservation?	Best For	Key Consideration
Translabyrinthine	Through mastoid and labyrinth	No (destroys inner ear)	Any size tumour when hearing is already lost or non-serviceable	Excellent facial nerve exposure; no cerebellar retraction; sacrifices all remaining hearing
Retrosigmoid (suboccipital)	Behind sigmoid sinus, posterior fossa craniotomy	Yes (possible)	Medium-large tumours with serviceable hearing	Good for large CPA component; hearing preservation possible but lower success rate for large tumours; risk of post-operative headache
Middle cranial fossa	Above the ear, extradural middle fossa approach	Yes (best chance)	Small intracanalicular tumours (Koos I) with good hearing	Best hearing preservation rate (~70% for small tumours); limited access for larger tumours; technically demanding

Acoustic neuroma management: surgery or radiosurgery or observation if old + small + limited hearing loss ^[15]

Complete excision is the ideal goal — remove the entire tumour and its capsule
Facial nerve preservation is paramount — the facial nerve is identified using intraoperative monitoring (continuous EMG) and carefully dissected off the tumour capsule
Near-total or subtotal resection may be deliberately chosen if the tumour is adherent to the facial nerve or brainstem, to avoid catastrophic neurological injury. A small residual can be followed or treated with adjuvant SRS.

Maximal safe resection without causing serious neurological sequelae is the key component of treatment ^[20] — this principle, while stated for medulloblastoma in the lecture context, applies equally to all benign intracranial tumours including schwannoma.

Approach: Posterior laminectomy or laminoplasty
Principle: The tumour is encapsulated and eccentric to the nerve root → it can typically be enucleated (shelled out) from the nerve, preserving root function
Dumbbell tumours: May require a combined posterior + anterior or posterolateral approach to access both the intradural and extradural components
Outcomes: Complete excision is achieved in > 90% of cases; recurrence is rare ( < 5%)

Principle: Under magnification (operating microscope or loupes), the capsule is incised and the tumour is enucleated from within the nerve sheath, leaving the nerve fascicles intact
Surgical excision if symptomatic ^[2] — asymptomatic peripheral schwannomas can be observed
Key technical point: Unlike neurofibroma, schwannoma can almost always be separated from the parent nerve because it grows eccentrically and has a true capsule

Nerve Preservation — Why Schwannoma Surgery is Different from Neurofibroma Surgery

Because schwannoma pushes nerve fibres aside (eccentric growth with a capsule), the surgeon can dissect between the tumour capsule and the nerve fascicles, preserving the nerve. In neurofibroma, the tumour infiltrates the nerve fascicles — the nerve runs through the tumour, not around it. Therefore, neurofibroma excision often requires sacrificing the nerve ^[2]^[12].

Indication	Explanation
Large tumour (Koos III-IV)	Mass effect on brainstem; hydrocephalus risk
Progressive neurological deficit	Worsening hearing, facial weakness, ataxia, cord compression
Documented growth	Confirms active tumour behaviour
Diagnostic uncertainty	Need histological confirmation (rule out malignancy)
Spinal cord compression	Myelopathy is an indication for decompressive surgery
Symptomatic peripheral schwannoma	Pain, motor weakness, progressive nerve deficit
Young patient with long life expectancy	Prolonged observation carries cumulative growth risk

Situation	Concern
Elderly with significant comorbidities	Surgical risk may exceed benefit
NF2 with bilateral VS	Risk of bilateral deafness; conservative approach preferred; medical therapy (bevacizumab) emerging
Only hearing ear	Extreme caution — surgery risks total deafness
Patient refusal	Respect autonomy; offer alternative (SRS or observation)

Complication	Mechanism	Frequency
Facial nerve palsy	Surgical manipulation/transection of CN VII draped over tumour	Transient: 20-40%; Permanent: 5-10% (higher for larger tumours)
Hearing loss	Damage to cochlear nerve or labyrinthine artery	Variable; translabyrinthine sacrifices hearing by design; others 30-70% preservation for small tumours
CSF leak	Breach of dura/arachnoid not adequately sealed	5-15%; may require lumbar drain or reoperation
Meningitis	Secondary to CSF leak or surgical contamination	1-3%
Cerebellar injury	Retraction during retrosigmoid approach	Rare with modern microsurgery
Hydrocephalus	Post-operative haemorrhage or adhesions obstructing CSF flow	5-10% for large tumours
Lower cranial nerve palsy	Large tumours extending to jugular foramen — CN IX, X, XI at risk	Uncommon except for very large tumours
Recurrence	Incomplete excision	< 5% for gross total resection; higher for subtotal

3. Stereotactic Radiosurgery (SRS) / Stereotactic Radiotherapy (SRT)

Stereotactic radiosurgery (SRS) delivers a single, highly focused, high-dose fraction of radiation to a precisely defined target, minimising damage to surrounding tissue. Despite the name, no incision is made — it is purely radiotherapy.

Breaking down the name:

"Stereo-" = three-dimensional
"-tactic" = relating to arrangement/positioning
"Radio-" = radiation
"-surgery" = precision akin to surgery

The most commonly used platforms:

Gamma Knife — uses multiple cobalt-60 sources focused to a single point; gold standard for intracranial SRS
CyberKnife — robotic linear accelerator with real-time image guidance
Linear accelerator (LINAC)-based SRS — uses modified LINAC with stereotactic frame

General Principles of Radiation Oncology: Stereotactic radiosurgery/radiotherapy delivers highly focused radiation to a precisely defined target in one or a few fractions ^[21]

Fractionated stereotactic radiotherapy (SRT) delivers the same total dose over multiple smaller fractions (e.g., 25 fractions over 5 weeks), which is preferred for larger tumours or tumours abutting critical structures (e.g., brainstem, cochlea) to reduce late toxicity.

Radiation causes DNA double-strand breaks in tumour cells
Schwann cells in the tumour undergo delayed mitotic cell death or senescence
Tumour blood vessels undergo endothelial damage → progressive obliteration over months to years
Net effect: tumour growth arrest (and sometimes shrinkage). SRS does not typically eliminate the tumour — it stops it from growing

Indication	Rationale
Small to medium vestibular schwannoma (Koos I-III, typically < 3 cm)	Excellent tumour control (~93-97% at 10 years) with lower morbidity than surgery
Elderly or medically unfit patient	Avoids general anaesthesia and craniotomy risks
Patient preference (avoids surgery)	Non-invasive outpatient procedure
Residual/recurrent tumour after subtotal surgery	Adjuvant treatment to control residual disease
NF2 patients	May delay hearing loss compared to surgery; can treat bilateral tumours
Other intracranial schwannomas (CN V, VII)	Same principles as vestibular schwannoma

Contraindication	Reasoning
Large tumour ( > 3 cm / Koos IV)	Radiation dose needed to cover large volume would cause unacceptable brainstem/cranial nerve toxicity
Brainstem compression / hydrocephalus	Needs urgent surgical decompression; SRS effect is too slow (months)
Diagnostic uncertainty	SRS treats without histological confirmation; if diagnosis uncertain, surgery preferred for biopsy
Cystic tumour with mass effect	Cystic component may expand acutely with radiation (paradoxical swelling); surgery preferred

Parameter	Result
Tumour control rate	93-97% at 10 years (growth arrest or shrinkage)
Hearing preservation	50-70% at 5 years (better with lower marginal dose, e.g., ≤ 12 Gy)
Facial nerve preservation	> 95% (significantly better than surgery for small-medium tumours)
Trigeminal nerve preservation	> 95%
Risk of malignant transformation	Exceedingly rare ( < 0.1%) — a theoretical concern but not supported by large studies

Surgery vs SRS — How to Choose?

For small vestibular schwannomas (Koos I-II) in patients who want treatment:

SRS offers lower complication rates (especially facial nerve preservation) and is non-invasive
Surgery offers definitive removal and histological diagnosis

For large vestibular schwannomas (Koos III-IV):

Surgery is generally required (SRS contraindicated for > 3 cm due to toxicity)
Combined approach (subtotal resection + adjuvant SRS) for tumours adherent to brainstem

In practice, the trend worldwide is towards SRS for small-medium tumours and surgery for large tumours.

4. Medical Therapy (NF2-Specific)

There is no standard systemic chemotherapy for sporadic schwannoma. However, for NF2-associated schwannomas, targeted medical therapy has an emerging role:

Mechanism: Schwannomas are highly vascular tumours. VEGF (vascular endothelial growth factor) is overexpressed in NF2-associated schwannomas. Bevacizumab (beva = "beautiful", cizumab = chimeric monoclonal antibody) blocks VEGF → reduces tumour vascularity and permeability → tumour shrinkage and hearing improvement
Indications:
- NF2 patients with growing vestibular schwannomas causing progressive hearing loss
- When surgery/SRS would risk bilateral deafness
- To delay intervention and preserve hearing
Outcomes: ~50% of patients show tumour shrinkage; ~40% show hearing improvement or stabilisation
Side effects: Hypertension, proteinuria, wound healing impairment, thromboembolic events
Limitation: Effect is often not sustained — tumour may regrow on cessation

Agent	Mechanism	Status
Lapatinib	ErbB2/EGFR inhibitor	Limited efficacy in trials
Everolimus	mTOR inhibitor	Phase II trials; some radiographic response
MEK inhibitors (selumetinib)	Downstream of Ras/MAPK pathway	Being explored for NF2-related tumours

Symptom/Complication	Management
Hearing loss	Hearing aids (for mild-moderate SNHL); BAHA (bone-anchored hearing aid) for unilateral deafness; cochlear implant if cochlear nerve intact
Vestibular dysfunction	Vestibular rehabilitation physiotherapy
Facial nerve palsy (post-surgical)	Eye protection (artificial tears, taping at night to prevent exposure keratopathy); gold weight eyelid implant for lagophthalmos; facial reanimation surgery for permanent palsy
Hydrocephalus	VP shunt or ETV (endoscopic third ventriculostomy) if 4th ventricle obstruction
Pain (schwannomatosis, peripheral schwannoma)	Neuropathic pain agents: gabapentin, pregabalin, duloxetine; NSAIDs; escalate to pain clinic if refractory
Spinal cord compression (acute)	Dexamethasone 4 mg IV Q6H if neurological symptoms present ^[11]; urgent surgical decompression

Dexamethasone 4 mg IV Q6H if neurological symptoms present — this principle applies to any cause of cord compression, including spinal schwannoma with acute myelopathy ^[11].

Type	Preferred Treatment	Notes
Vestibular schwannoma, small (Koos I-II), asymptomatic	Observation	Serial MRI + audiometry; treat if grows
Vestibular schwannoma, small-medium, symptomatic or growing	SRS (Gamma Knife) or Microsurgery	SRS preferred for small tumours; surgery for larger/diagnostic uncertainty
Vestibular schwannoma, large (Koos III-IV)	Microsurgery ± adjuvant SRS	Translabyrinthine or retrosigmoid approach
NF2 bilateral vestibular schwannoma	Bevacizumab + conservative surgery/SRS on worse ear	Goal: preserve hearing on better ear as long as possible
Spinal schwannoma	Surgical excision (laminectomy, enucleation)	Complete excision curative in > 90%; recurrence < 5%
Peripheral schwannoma (symptomatic)	Surgical excision with nerve preservation ^[2]	Enucleation from within nerve sheath
Peripheral schwannoma (asymptomatic)	Observation	Treat only if growing, painful, or diagnostic uncertainty
Facial nerve schwannoma	Observation if facial function intact; surgery if progressive palsy	Nerve grafting may be needed if nerve is sacrificed

High Yield Summary

Three pillars of schwannoma management: Observation, Microsurgery, and Stereotactic Radiosurgery (SRS).
Observation is an active strategy for small, stable, asymptomatic schwannomas — serial MRI every 6-12 months + audiometry. 40-70% of small vestibular schwannomas remain stable.
Surgery is the definitive treatment: three approaches for vestibular schwannoma — translabyrinthine (no hearing preservation), retrosigmoid (hearing preservation possible), middle fossa (best hearing preservation for small intracanalicular tumours). Schwannoma can be enucleated from the nerve because of its eccentric encapsulated growth.
SRS (Gamma Knife) is indicated for small-medium vestibular schwannomas ( < 3 cm / Koos I-III): tumour control 93-97% at 10 years, facial nerve preservation > 95%. Contraindicated for large tumours ( > 3 cm) or brainstem compression.
Bevacizumab (anti-VEGF) is used in NF2 patients with growing bilateral vestibular schwannomas to delay hearing loss and tumour growth.
Spinal schwannoma: surgical excision via laminectomy/laminoplasty; enucleation preserves nerve root; dexamethasone 4 mg IV Q6H for acute cord compression.
Peripheral schwannoma: surgical excision if symptomatic; enucleation from within nerve sheath preserves the parent nerve (unlike neurofibroma which cannot be separated).
Post-surgical complications of vestibular schwannoma surgery: facial nerve palsy (most important to counsel about), hearing loss, CSF leak, meningitis, hydrocephalus.
NF2 management is a multidisciplinary decision focused on preserving hearing as long as possible — conservative surgery on worse ear, bevacizumab, SRS, hearing rehabilitation.

Active Recall - Schwannoma Management

^[2] Senior notes: Ryan Ho Rheumatology.pdf, Section 5.5.2 Neurofibroma – Treatment: surgical excision if symptomatic (p.170) ^[11] Senior notes: Maksim Medicine Notes.pdf, Cord compression – Management: Dexamethasone 4mg IV Q6H (p.47) ^[12] Senior notes: MBBS Final MB (Surgery) (Felix PY Lai).pdf, Neurofibroma – surgical separability (p.149) ^[15] Senior notes: Ryan Ho Neurology.pdf, Section on acoustic neuroma – Mx: surgery or radiosurgery or observation (p.167) ^[20] Senior notes: MBBS Final MB (Medicine) (Felix PY Lai).pdf, Treatment principles – maximal safe resection (p.1262) ^[21] Lecture slides: Cancer Block - CMB08a - General Principles of Radiation Oncology.pdf

Complications of schwannoma arise from two fundamentally different sources:

Complications of the tumour itself — from progressive growth causing compression of the parent nerve and adjacent structures
Complications of treatment — from surgery, radiosurgery, or medical therapy

Both must be understood systematically, because in clinical practice (and exams), you need to counsel patients about the natural history risks of leaving the tumour untreated versus the treatment-related risks.

A. Complications of the Tumour Itself (Untreated / Progressive Disease)

The overarching mechanism for all tumour-related complications is compression. Schwannomas are benign and do not invade — they compress, stretch, and displace. The specific complications depend entirely on the anatomical site.

1. Vestibular Schwannoma Complications

This is the most important and most tested set of complications.

Mechanism: The growing tumour compresses the cochlear division of CN VIII within the IAC. Because the IAC is a rigid bony canal, even a small tumour has no room to expand without compressing the nerve.
Progression: Hearing loss is initially unilateral and gradual (months to years), but without treatment, progresses to complete deafness on the affected side.
Why this matters: Hearing loss is often irreversible — once nerve fibres are damaged by chronic compression, they do not regenerate. This is why early detection (MRI for asymmetric SNHL) and timely intervention are emphasised.

Acoustic neuroma: cochlear n. (95%) — SN hearing loss, tinnitus ^[15]

Mechanism: CN VII runs immediately adjacent to CN VIII in the IAC and CPA. As the schwannoma enlarges, it stretches CN VII over its capsule.
Clinical nuance: "NO facial n. involvement: facial n. bundle thick and resilient — usually only stretched over the slowly growing tumour" ^[15]. Facial nerve palsy is therefore a late complication (unlike the early hearing loss). The facial nerve has remarkable tolerance to slow compression, so frank palsy usually indicates a large tumour (Koos III-IV).
Consequence: If palsy occurs, it is LMN pattern (entire ipsilateral face). Permanent palsy causes cosmetic deformity, inability to close the eye (risk of exposure keratopathy and corneal ulceration), and difficulty with eating/drinking.

Mechanism: Large CPA schwannomas compress the trigeminal nerve as it exits the brainstem or enters Meckel's cave.
Trigeminal n. (17%): facial numbness, hyperesthesia, pain ^[15]
Key clinical sign: Reduced corneal reflex — this is an early sign of CPA compression (CN V provides the afferent limb of the corneal reflex). Loss of the corneal reflex puts the eye at risk because the patient cannot feel foreign bodies or dryness.

Mechanism: Large tumours (Koos III-IV) compress the ipsilateral cerebellar hemisphere and middle cerebellar peduncle in the CPA.
Signs: Ipsilateral ataxia, dysdiadochokinesia, intention tremor, wide-based gait.
Significance: Indicates significant mass effect — surgery is usually indicated at this stage.

Acoustic neuroma: cerebellar dysfunction ^[8]

Mechanism: Very large tumours (Koos IV, > 3 cm) compress the brainstem (pons and medulla).
Signs: Long tract signs (contralateral hemiparesis, sensory changes), cranial nerve palsies (CN VI → diplopia; CN IX/X → dysphagia, hoarseness), autonomic dysfunction.
Danger: This is life-threatening. If brainstem compression is severe, it can cause cardiovascular and respiratory compromise.

Acoustic neuroma: brainstem compression & hydrocephalus ^[8]

Mechanism: Very large vestibular schwannomas can obstruct the 4th ventricle or the cerebral aqueduct by compressing them from behind, blocking CSF outflow → dilatation of the lateral and 3rd ventricles → raised intracranial pressure (ICP).
Signs of raised ICP: Headache (worse lying down, morning, with coughing/straining), nausea and vomiting (especially early morning), papilloedema, CN VI palsy (false localising sign from stretching over the clivus), reduced consciousness.

CPA tumors (vestibular schwannoma / meningioma) can cause obstructive hydrocephalus ^[22]

Management: Urgent VP shunt or endoscopic third ventriculostomy (ETV) for the hydrocephalus, followed by definitive tumour surgery ^[22]^[23].

Vestibular Schwannoma — Order of Complications

Understanding the temporal progression is key for exams:

Hearing loss + tinnitus (earliest — CN VIII cochlear division compressed in rigid IAC)
Imbalance (vestibular division — but often compensated centrally)
Facial numbness / absent corneal reflex (CN V compression — medium tumours)
Cerebellar signs (large tumours compressing cerebellum)
Facial palsy (late — CN VII resilient to slow compression)
Brainstem compression + hydrocephalus (very large — Koos IV; life-threatening)

Mechanism: Massive tumours extending inferiorly towards the jugular foramen compress the lower cranial nerves.
Consequences: Dysphagia (CN IX, X), hoarseness (CN X — recurrent laryngeal nerve), shoulder weakness (CN XI), tongue deviation (CN XII).
Risk: Aspiration pneumonia from dysphagia/impaired airway protection.

2. Spinal Schwannoma Complications

Mechanism: Compression of the dorsal and ventral nerve roots at the level of the schwannoma.
Consequence: Dermatomal pain, sensory loss, and segmental weakness (LMN signs at the level) ^[3].

Mechanism: Large schwannomas (especially dumbbell tumours) compress the spinal cord → disruption of ascending/descending long tracts.
Signs: UMN signs below the level (spasticity, hyperreflexia, upgoing plantars), sensory level, sphincter dysfunction.
S/S: radicular sensory changes (pain, sensory loss) → cord compression (at later stages) ^[3]
Urgency: Progressive myelopathy requires urgent surgical decompression — Dexamethasone 4 mg IV Q6H if neurological symptoms present ^[3]^[11].

Mechanism: Schwannomas at L2 and below can compress the cauda equina (nerve roots, not cord).
Signs: Bilateral sciatica, saddle anaesthesia, urinary retention, faecal incontinence, bilateral lower limb weakness (LMN pattern), absent ankle jerks, absent bulbocavernosus reflex ^[11].
Urgency: Surgical emergency — decompression within 48 hours for best functional recovery.

3. Peripheral / Neck Schwannoma Complications

Nerve compression is the primary complication of peripheral schwannoma ^[2]^[22].
Mechanism: As the encapsulated tumour enlarges, it compresses the parent nerve and adjacent nerve fascicles.
Consequence: Progressive sensory loss, weakness, and neuropathic pain in the distribution of the affected nerve.

Mechanism: Cervical sympathetic chain schwannoma compresses sympathetic fibres.
Signs: Ipsilateral miosis, partial ptosis, anhidrosis, enophthalmos.

Mechanism: Schwannoma arising from the vagus nerve (CN X) in the neck compresses the recurrent laryngeal nerve.
Consequence: Hoarseness, weak cough, aspiration risk.

Key Distinction: Schwannoma vs Neurofibroma Malignant Potential

A very common exam misconception is confusing the malignant potential of schwannoma with that of neurofibroma.

Schwannoma: Malignant transformation is exceedingly rare ( < 1% of cases). When it occurs, it is termed malignant schwannoma or is classified as a form of MPNST. There is no well-established risk from NF2 for malignant transformation of schwannomas.
Neurofibroma: Sarcomatous change: especially in plexiform neurofibroma and NF1 (8-15% lifetime risk of MPNST) ^[2]^[14]^[22]. This is a major cause of morbidity and mortality in NF1.

Bottom line: Do not attribute significant malignant risk to schwannoma. If asked about malignant transformation of nerve sheath tumours in an exam, the answer is neurofibroma (especially plexiform in NF1), NOT schwannoma.

Rate: < 5% after gross total resection; higher (10-30%) after subtotal resection.
Mechanism: Residual tumour cells continue to proliferate slowly. This is why post-operative surveillance MRI is important.
Management of recurrence: Re-excision or SRS for residual/recurrent disease.

B. Complications of Treatment

These are the most commonly tested treatment complications because vestibular schwannoma surgery involves manipulating multiple cranial nerves in a tight space.

Complication	Mechanism	Frequency	Prevention/Management
Facial nerve palsy	Surgical manipulation, stretching, thermal injury, or transection of CN VII (which is draped over the tumour capsule)	Transient: 20-40%; Permanent: 5-10% (higher for larger tumours)	Intraoperative CN VII monitoring (continuous EMG); meticulous microsurgical dissection; near-total resection if nerve adherent
Hearing loss	Damage to cochlear nerve, internal auditory artery, or cochlea during surgery	Translabyrinthine: 100% (by design); Retrosigmoid: 30-50% preservation; Middle fossa: 50-70% preservation	Choice of approach based on hearing status; intraoperative ABR monitoring
CSF leak	Inadequate closure of dura/mastoid after surgery; CSF tracks through middle ear or wound	5-15%	Meticulous dural closure; fat/muscle graft packing of IAC; lumbar drain if persistent
Meningitis	Bacterial contamination (secondary to CSF leak or direct surgical contamination)	1-3%	Prophylactic antibiotics; prompt treatment of CSF leak; aseptic technique
Haemorrhage (posterior fossa)	Post-operative haematoma in surgical cavity compressing brainstem/cerebellum	1-2%	Close monitoring in ICU; urgent re-exploration if neurological deterioration
Cerebellar oedema/injury	Retraction injury (especially retrosigmoid approach)	Rare	Minimal retraction; appropriate approach selection
Hydrocephalus (post-operative)	Blood products or adhesions blocking CSF pathways	5-10% for large tumours	VP shunt or ETV if persistent ^[22]^[23]
Lower cranial nerve palsy	Injury to CN IX, X, XI during excision of large tumours extending towards jugular foramen	Rare (more common for Koos IV)	Awareness of anatomy; intraoperative monitoring
Wound infection	Surgical site contamination	1-3%	Standard surgical prophylaxis
Cerebrovascular injury	Damage to AICA (anterior inferior cerebellar artery), which supplies the lateral pons and cerebellum and gives off the labyrinthine artery	Rare but devastating	Knowledge of vascular anatomy; microsurgical technique

Post-op complications of brain tumour surgery include: haematoma, infection, CSF leak, focal neurological deficit, seizure ^[15]

Facial Nerve Palsy — The Most Important Complication to Counsel About

Patients should be informed that facial nerve weakness is the most significant risk of vestibular schwannoma surgery. Even with intraoperative monitoring, transient palsy occurs in 20-40% of cases. Risk increases with tumour size — for Koos IV tumours, the rate of significant facial palsy may exceed 30%. This is why small tumours are often offered SRS instead of surgery — facial nerve preservation is > 95% with radiosurgery vs 90-95% for small tumour surgery.

Management of Post-Surgical Facial Nerve Palsy

Grade	Management
Transient (House-Brackmann II-III)	Eye care (artificial tears, taping at night); most recover within weeks to months
Prolonged (months)	Consider physiotherapy, facial nerve rehabilitation exercises
Permanent (House-Brackmann V-VI)	Gold weight eyelid implant (for lagophthalmos → prevent exposure keratopathy); tarsal strip/canthoplasty; facial reanimation surgery (nerve grafting, hypoglossal-facial nerve anastomosis, free gracilis muscle transfer)

Complication	Mechanism	Frequency	Notes
Transient tumour swelling	Radiation-induced oedema within the tumour; peaks at 6-12 months post-SRS	10-30% (imaging finding); rarely symptomatic	Usually self-limiting; dexamethasone if symptomatic
Hearing loss (delayed)	Radiation damage to cochlear nerve or cochlea → progressive neural degeneration	30-50% lose serviceable hearing by 10 years	Lower with marginal dose ≤ 12 Gy to tumour; distance from cochlea matters
Facial nerve dysfunction	Radiation injury to CN VII	< 5% with modern dosing (≤ 12-13 Gy)	Much lower than surgical rates
Trigeminal neuropathy	Radiation injury to CN V	2-5%	Facial numbness, paraesthesia
Hydrocephalus	Tumour swelling obstructing 4th ventricle, or radiation-induced arachnoiditis	Rare	VP shunt or ETV
Malignant transformation	Radiation-induced secondary malignancy from DNA damage to surviving cells	Exceedingly rare ( < 0.1%)	Theoretical concern; not a practical deterrent; 20+ year latency
Radiation necrosis	Focal brain tissue necrosis from high-dose radiation	Very rare with current dosing	Distinguished from tumour progression on MRI (may need PET or spectroscopy)

Complication	Mechanism
Hypertension	VEGF normally promotes NO-mediated vasodilation; blocking VEGF → vasoconstriction → ↑BP
Proteinuria / Nephrotoxicity	VEGF is essential for glomerular endothelial health; blockade → podocyte injury → proteinuria
Impaired wound healing	VEGF is critical for angiogenesis in wound repair
Thromboembolic events	Endothelial dysfunction from VEGF blockade → pro-thrombotic state
GI perforation (rare)	VEGF blockade impairs mucosal integrity
Tumour regrowth on cessation	Effect is cytostatic, not cytotoxic — tumour may regrow when drug is stopped

If a VP shunt is placed for schwannoma-related hydrocephalus, it carries its own complications:

Complications of CSF shunt: shunt blockage (MC — 80% proximal), shunt infection (S. epidermidis, S. aureus — most serious), overshunting (postural headache → subdural haematoma) ^[23]

Complication	Detail
Shunt blockage	Most common complication; 80% proximal (choroid plexus), 10% valve, 10% distal
Shunt infection	Most serious; pathogens: S. epidermidis, S. aureus; presents with fever, meningism, raised ICP
Overshunting	Postural headache (worse standing, better lying); stretching of bridging veins → subdural haematoma
Distal catheter complications	Inguinal hernia, perforated viscus, peritonitis, intraperitoneal CSF pseudocyst, tumour seeding

Patients with NF2 develop not just schwannomas but multiple tumour types, leading to a broader complication profile:

Complication	Mechanism
Bilateral deafness	Progressive growth of bilateral vestibular schwannomas → bilateral CN VIII compression. This is the most devastating functional complication of NF2.
Multiple cranial neuropathies	Multiple schwannomas on different cranial nerves (CN V, VII, others)
Spinal cord compression	Multiple spinal schwannomas and meningiomas
Cataracts	Posterior subcapsular cataracts (non-tumour manifestation of NF2); may require lens replacement
Meningiomas	Can cause seizures, focal deficits, raised ICP depending on location
Ependymomas	Can cause syringomyelia, myelopathy

Category	Complication	Site	Mechanism	Urgency
Tumour	Deafness	CPA	CN VIII compression	Chronic
Tumour	Facial palsy	CPA	CN VII stretch (late)	Chronic
Tumour	Hydrocephalus	CPA	4th ventricle obstruction	Urgent
Tumour	Brainstem compression	CPA	Direct compression	Emergency
Tumour	Cord compression	Spine	Myelopathy	Urgent
Tumour	Cauda equina syndrome	Lumbar spine	Nerve root compression	Emergency
Tumour	Nerve compression	Peripheral	Direct compression	Chronic
Surgery	Facial nerve palsy	CPA surgery	CN VII surgical injury	Post-op
Surgery	CSF leak	CPA surgery	Dural breach	Post-op
Surgery	Meningitis	CPA surgery	Infection	Post-op
SRS	Hearing decline	CPA	Radiation damage to CN VIII/cochlea	Delayed (years)
SRS	Tumour swelling	CPA	Radiation oedema	6-12 months
Medical	Hypertension	Systemic	VEGF blockade → vasoconstriction	During treatment

High Yield Summary

Tumour complications follow a predictable temporal order for vestibular schwannoma: hearing loss → imbalance → facial numbness/absent corneal reflex → cerebellar signs → facial palsy → brainstem compression → hydrocephalus. Early complications are from CN VIII in the rigid IAC; late complications from mass effect in the CPA.
Facial nerve palsy is late because CN VII is "thick and resilient" — it tolerates slow compression. Hearing loss is early because the cochlear nerve is more vulnerable in the IAC.
Hydrocephalus from 4th ventricle obstruction by large CPA schwannomas is life-threatening and requires urgent VP shunt or ETV.
Spinal schwannoma can cause radiculopathy progressing to cord compression (UMN below, LMN at level) or cauda equina syndrome — both are surgical emergencies.
Malignant transformation of schwannoma is exceedingly rare ( < 1%). Do NOT confuse with neurofibroma in NF1, which has 8-15% lifetime risk of MPNST.
Most important surgical complication: facial nerve palsy (transient 20-40%, permanent 5-10%) — risk increases with tumour size. SRS has much lower facial nerve risk ( < 5%).
CSF leak (5-15%) is the most common technical surgical complication; can lead to meningitis if untreated.
VP shunt complications: blockage (commonest), infection (most serious — S. epidermidis), overshunting → subdural haematoma.
NF2-specific: bilateral deafness from bilateral VS is the most devastating outcome; management aims to preserve hearing as long as possible.

Active Recall - Schwannoma Complications

^[2] Senior notes: Ryan Ho Rheumatology.pdf, Section 5.5.2 Neurofibroma — complications: nerve compression, sarcomatous change (p.170) ^[3] Senior notes: Ryan Ho Neurology.pdf, Section 9.2 Spinal Cord Tumours — spinal schwannoma S/S and cord compression (p.170) ^[8] Lecture slides: GC 108. A mass in the brain brain tumours.pdf — Acoustic Neuroma slide (p.24): cerebellar dysfunction, brainstem compression and hydrocephalus, CN V/VII symptoms, surgery/radiosurgery ^[11] Senior notes: Maksim Medicine Notes.pdf, Cord compression — Dexamethasone 4mg IV Q6H (p.47) ^[14] Senior notes: Adrian Lui Pediatrics Notes.pdf, NF1 — MPNST 8-15% risk (p.148) ^[15] Senior notes: Ryan Ho Neurology.pdf, Section on acoustic neuroma — S/S, no facial nerve involvement (thick and resilient), investigations, management (p.167) ^[22] Senior notes: Ryan Ho Fundamentals.pdf, Neurofibroma complications: nerve compression, sarcomatous change (p.166); Senior notes: Maksim Surgery Notes.pdf, Skull base tumours and hydrocephalus complications (p.360) ^[23] Senior notes: Maksim Surgery Notes.pdf, Complications of CSF shunt — blockage, infection, overshunting (p.360)

High Yield Summary

Schwannoma = benign, encapsulated tumour of Schwann cells; arises eccentrically from the nerve (displaces but does not invade nerve fibres).
Molecular basis: biallelic loss of NF2 gene (chr 22q12) → loss of merlin tumour suppressor → unregulated Schwann cell proliferation.
Histology: Antoni A (compact, Verocay bodies) + Antoni B (loose, myxoid); S-100 positive.
Most common intracranial site: CPA — vestibular schwannoma (CN VIII). Presents with unilateral SNHL, tinnitus, imbalance.
Spinal schwannoma: intradural extramedullary, usually cervical/lumbar. Presents with radicular pain → sensory changes → cord compression.
Peripheral schwannoma: painless mass that is mobile perpendicular to nerve axis, Tinel's sign positive.
Neck schwannoma: posterior triangle mass — always exclude NPC metastasis in Hong Kong.
Key associations: NF2 (bilateral vestibular schwannomas), Schwannomatosis (multiple non-vestibular schwannomas with pain), Carney complex.
Malignant transformation is exceedingly rare (unlike neurofibroma in NF1).
Distinguish from neurofibroma: schwannoma is encapsulated, eccentric, surgically separable; neurofibroma is unencapsulated, diffusely infiltrative, and carries higher malignant potential.

High Yield Summary

CPA mass differential (most tested): Vestibular schwannoma (~80%) > Meningioma (~10%) > Epidermoid (~5%). Schwannoma extends into IAC; meningioma has dural tail and does not enter IAC; epidermoid is non-enhancing and DWI-bright.
Spinal intradural extramedullary: Schwannoma vs Meningioma are the two most common. Schwannoma favours cervical/lumbar, meningioma favours thoracic and is F > > M.
Neck mass: Posterior triangle schwannoma must be distinguished from NPC Level V nodes (Hong Kong!), lymphoma, cystic hygroma, and paraganglioma.
Peripheral nerve mass: Schwannoma vs neurofibroma vs MPNST — differentiated by capsulation, nerve relationship, syndrome association (NF2 vs NF1), growth rate, and malignant potential.
Facial nerve palsy: Schwannoma causes gradual progressive LMN palsy (Bell's palsy is acute; Ramsay Hunt has vesicles; parotid malignancy has palpable mass).
Red flags for malignancy: rapid growth, constitutional symptoms, smoking/alcohol history, hard fixed nodes, known primary cancer.
In Hong Kong, NPC must always be excluded in any patient with posterior triangle neck mass, CPA lesion, or cranial neuropathy — perform nasopharyngoscopy.

High Yield Summary

No formal diagnostic criteria for sporadic schwannoma — diagnosis is clinical + imaging + histology.
NF2 diagnosis: Bilateral vestibular schwannomas is pathognomonic; Manchester criteria for other combinations. Gene: NF2 on chr 22q12, protein: merlin.
Audiological testing for vestibular schwannoma: PTA shows unilateral asymmetric SNHL; SDS is disproportionately poor (retrocochlear pattern); ABR shows prolonged I-V interpeak latency. Any unexplained asymmetric SNHL mandates MRI.
MRI with gadolinium is the gold standard: Schwannoma is T1 iso/hypo, T2 bright, avidly enhancing, well-circumscribed. Vestibular schwannoma extends into IAC (unlike meningioma). No dural tail. No DWI restriction (unlike epidermoid).
CT complementary: Shows widened IAC (vestibular), widened neural foramen (spinal dumbbell). Round/oval shape = slow displacing growth.
Histology is definitive: Antoni A (Verocay bodies) + Antoni B + S-100 diffusely positive + encapsulated + no nerve fibre invasion.
Always screen for NF2 in young patients, bilateral VS, or multiple schwannomas: MRI whole spine + brain, slit-lamp for cataracts, genetic testing.
Hong Kong rule: Nasopharyngoscopy is mandatory for any posterior triangle mass or unexplained CPA lesion to exclude NPC.

High Yield Summary

Three pillars of schwannoma management: Observation, Microsurgery, and Stereotactic Radiosurgery (SRS).
Observation is an active strategy for small, stable, asymptomatic schwannomas — serial MRI every 6-12 months + audiometry. 40-70% of small vestibular schwannomas remain stable.
Surgery is the definitive treatment: three approaches for vestibular schwannoma — translabyrinthine (no hearing preservation), retrosigmoid (hearing preservation possible), middle fossa (best hearing preservation for small intracanalicular tumours). Schwannoma can be enucleated from the nerve because of its eccentric encapsulated growth.
SRS (Gamma Knife) is indicated for small-medium vestibular schwannomas ( < 3 cm / Koos I-III): tumour control 93-97% at 10 years, facial nerve preservation > 95%. Contraindicated for large tumours ( > 3 cm) or brainstem compression.
Bevacizumab (anti-VEGF) is used in NF2 patients with growing bilateral vestibular schwannomas to delay hearing loss and tumour growth.
Spinal schwannoma: surgical excision via laminectomy/laminoplasty; enucleation preserves nerve root; dexamethasone 4 mg IV Q6H for acute cord compression.
Peripheral schwannoma: surgical excision if symptomatic; enucleation from within nerve sheath preserves the parent nerve (unlike neurofibroma which cannot be separated).
Post-surgical complications of vestibular schwannoma surgery: facial nerve palsy (most important to counsel about), hearing loss, CSF leak, meningitis, hydrocephalus.
NF2 management is a multidisciplinary decision focused on preserving hearing as long as possible — conservative surgery on worse ear, bevacizumab, SRS, hearing rehabilitation.

High Yield Summary

Tumour complications follow a predictable temporal order for vestibular schwannoma: hearing loss → imbalance → facial numbness/absent corneal reflex → cerebellar signs → facial palsy → brainstem compression → hydrocephalus. Early complications are from CN VIII in the rigid IAC; late complications from mass effect in the CPA.
Facial nerve palsy is late because CN VII is "thick and resilient" — it tolerates slow compression. Hearing loss is early because the cochlear nerve is more vulnerable in the IAC.
Hydrocephalus from 4th ventricle obstruction by large CPA schwannomas is life-threatening and requires urgent VP shunt or ETV.
Spinal schwannoma can cause radiculopathy progressing to cord compression (UMN below, LMN at level) or cauda equina syndrome — both are surgical emergencies.
Malignant transformation of schwannoma is exceedingly rare ( < 1%). Do NOT confuse with neurofibroma in NF1, which has 8-15% lifetime risk of MPNST.
Most important surgical complication: facial nerve palsy (transient 20-40%, permanent 5-10%) — risk increases with tumour size. SRS has much lower facial nerve risk ( < 5%).
CSF leak (5-15%) is the most common technical surgical complication; can lead to meningitis if untreated.
VP shunt complications: blockage (commonest), infection (most serious — S. epidermidis), overshunting → subdural haematoma.
NF2-specific: bilateral deafness from bilateral VS is the most devastating outcome; management aims to preserve hearing as long as possible.

Schwannoma

Schwannoma

Definition

Epidemiology

General

Hong Kong Context

Risk Factors

Anatomy and Function

Schwann Cells

Nerve Sheath Layers (from inside out)

Anatomical Sites of Schwannoma

Cranial Nerve Schwannomas — Why CN VIII?

Aetiology and Pathophysiology

Molecular Pathogenesis

Pathology

Gross Appearance

Histology — Two Classic Patterns (Antoni A and Antoni B)

Growth Behaviour

Classification

By Location

By Aetiology

By Histological Variant

Clinical Features

General Principles

A. Vestibular Schwannoma (Acoustic Neuroma) — Most Common and Most Tested

Symptoms

Signs

B. Spinal Schwannoma

Symptoms

Signs

C. Peripheral Schwannoma (Limbs, Neck, Soft Tissues)

Symptoms

Signs

D. Neck Schwannoma

Symptoms

Signs

E. Facial Nerve Schwannoma

F. Other Sites

Summary of Key Clinical Features by Site

Active Recall - Schwannoma

References

Differential Diagnosis of Schwannoma

Conceptual Framework for the Differential

A. Cerebellopontine Angle (CPA) / Internal Auditory Canal

B. Spinal (Intradural Extramedullary)

C. Neck Mass (Posterior Triangle)

D. Peripheral Nerve Mass (Limbs / Soft Tissues)

E. Facial Nerve Palsy (When Schwannoma Presents as CN VII Dysfunction)

F. Intracranial Mass (General Brain Tumour Differential)

Systematic Differential Diagnosis Summary Diagram

Key Principles for Narrowing the Differential

Active Recall - Schwannoma Differential Diagnosis

References

Diagnostic Criteria, Diagnostic Algorithm & Investigations for Schwannoma

Overarching Diagnostic Principle

Diagnostic Criteria

A. Sporadic Schwannoma (Solitary)

B. NF2-Associated Schwannomas — Manchester/Revised Criteria

C. Schwannomatosis Criteria

Diagnostic Algorithm

Investigation Modalities

1. Audiological Testing (Vestibular Schwannoma)

a. Pure Tone Audiometry (PTA)

b. Speech Discrimination Score (SDS) / Word Recognition Score

c. Auditory Brainstem Response (ABR)

d. Caloric Testing / Vestibular Function Tests

2. Imaging — The Cornerstone of Schwannoma Diagnosis

a. MRI with Gadolinium Contrast — Gold Standard

MRI Signal Characteristics of Schwannoma

Site-Specific MRI Findings

How MRI Distinguishes Schwannoma from Key Differentials

b. CT Scan — Complementary Role

c. Ultrasound (USG) — Peripheral and Neck Schwannomas

d. Angiography / MR Angiography

3. Histopathology — Definitive Diagnosis

Macroscopic Findings

Microscopic Findings

Immunohistochemistry

4. Additional Investigations

a. Blood Tests