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Facial nerve schwannoma (FNS) is a benign, slow-growing nerve sheath tumor arising from Schwann cells of the facial nerve (cranial nerve VII). It can occur anywhere along the nerve course from the pontomedullary junction to the stylomastoid foramen, and often mimics vestibular schwannomas or facial nerve hemangiomas radiologically.

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Epidemiology

Rare: <1% of all intracranial schwannomas
Age: Typically diagnosed in young to middle-aged adults (20–50 years)
Sex: No strong predilection

Anatomy Review – Facial Nerve Segments

Segment	Description
Intracranial	From brainstem to internal auditory canal (IAC)
Intratemporal	→ Meatal segment: Within IAC
	→ Labyrinthine segment: From IAC to geniculate ganglion
	→ Tympanic segment: Horizontal across medial wall of middle ear
	→ Mastoid segment: Vertical, to stylomastoid foramen
Extracranial	Parotid gland and facial branches

Clinical Features

Symptom	Explanation
Progressive facial weakness/palsy	Most common; often gradual
Facial twitching or spasms	Early sign due to nerve irritation
Hearing loss	Conductive (tympanic involvement) or sensorineural (IAC/cisternal segment)
Tinnitus, vertigo	Less common, especially if adjacent to vestibular system
Mass effect	May cause visible swelling in parotid or mastoid region

Facial nerve function may be preserved even with large tumors, unlike in CN VII palsy “Bell’s palsy” (sudden onset)

Radiology

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Key signs:

IAC involvement
Geniculate ganglion enlargement
"Sausage-shaped" mass
Enhancement following facial nerve course </aside>

MR features:

Sequence	Findings
T1-weighted	Iso- to hypointense mass along facial nerve pathway
T2-weighted	Hyperintense; heterogeneous in large lesions
Post-contrast T1	Intense, homogeneous or heterogeneous enhancement
CISS/FIESTA/3D T2	Demonstrates tumor in facial nerve canal and its expansion

HRCT Temporal Bone

Finding	Description
Canal expansion	Smooth bony widening of fallopian canal, often at geniculate ganglion
Erosion	Rare; favors facial nerve hemangioma if present
Calcification	Absent in schwannomas (helps differentiate from hemangiomas)