Facial nerve schwannoma

Facial nerve schwannoma (FNS), also known as facial nerve neuroma/neurilemoma, is a schwannoma that arises from the facial nerve. They are generally uncommon, and when involving the temporal bone, make up less than 1% of all temporal bone tumours.

FNS is a rare tumour 2.

They can present with a wide variety of symptoms. More frequently they present with gradual, and often incomplete, facial nerve palsy. A rapid onset which mimics Bells palsy is certainly recognised.

Mass effect on adjacent nerves may well cause sensory neural hearing loss (SNHL) or even conductive hearing loss if growth into the middle ear impairs the normal function of the ossicles. In a minority of cases (~10%) the tumour is extra-cranial, where it presents as an asymptomatic parotid mass.

As schwannomas elsewhere they originate from the surface of the nerve, and displace and splay the nerve fibres over their eccentric growth (this compares favourably to neurofibromas through which the axons are distributed). This allows for potential resection of the tumour while sparing the nerve.

Similar to acoustic schwannomas, they may grow to a quite sizable extent and exert positive mass effect with growth into the cerebellopontine angle

Location

They can occur in any segment of the facial nerve and have a tendency to involve multiple segments. There is a predilection for the region of the geniculate ganglion.

Markers

Typically positive for S100 neuronal staining.

Imaging characteristics of the tumour itself is the same as that of schwannomas elsewhere: homogeneous enhancement on both CT and MRI when small; heterogeneous when large. The best clue that a schwannoma is of the facial nerve rather than the more common vestibulochoclear nerve (CN VIII) is expansion extending along the facial nerve canal - especially along the labyrinthine segment.

CT

In all cases, high resolution thin section bone CT of the temporal bone is required to assess the otic capsule. Bony scalloping and remodelling may be present. Failure to preoperatively diagnose bony erosion can lead to postoperative fistula formation.

MRI 

Signal characteristics include 2:

  • T1: typically iso- to hypointense relative to gray matter 
  • T2: typically hyperintense; large lesion may show heterogeneous signal 
  • T1 C+ (Gd): usually demonstrate homogeneous enhancement with larger lesions with cystic degeneration seen as focal intramural low signal intensity
  • content pending 

Depends on location on lesion along the facial nerve:

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Article Information

rID: 1323
Synonyms or Alternate Spellings:
  • Facial nerve schwannoma (FNS)
  • Facial nerve neuroma
  • Facial nerve neurilemoma

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