顔面神経麻痺を伴わない中頭蓋窩巨大顔面神経鞘腫の1例

Huge Facial Nerve Schwannoma Extending into the Middle Cranial Fossa without Facial Palsy: Case Report

Ⅰ．はじめに

　顔面神経鞘腫は，頭蓋内神経鞘腫のうち聴神経鞘腫，三叉神経鞘腫に次ぐ稀な腫瘍（頭蓋内神経鞘腫の1.9％）である．膝神経節より発生し中頭蓋窩に進展した顔面神経鞘腫は，ほぼ全例に顔面神経麻痺を伴うと言われている．今回われわれは，顔面神経麻痺を伴わず，中頭蓋窩に進展した巨大顔面神経鞘腫の1例を経験したので，文献的考察を加えてここに報告する．

　The facial nerve schwannoma is a rare tumor and it seldom extends into the middle cranial fossa. The typical clinical presentations are progressive facial paralysis and hearing disturbance. We report here a case of huge facial nerve schwannoma extending into the middle cranial fossa without facial palsy.

　A 50-year-old man presented with left hearing disturbance. Neurological examination on admission revealed no deficits except for sensorineural hearing loss. MRI demonstrated a cystic tumor extending into the middle cranial fossa from the petrous bone. CT of the temporal bone showed destruction of the surrounding bone around the geniculate ganglion and invasion of the tumor into the tympanic cavity and internal auditory canal. The intracranial tumor was totally removed and the operative specimen demonstrated that the tumor was a schwannoma. The patient was discharged without neurological deficit.

　The facial nerve schwannoma extending into the middle cranial fossa without facial palsy is rare and only 4 cases have been reported in the literature. The tumor origin was in the greater superficial petrosal nerve and geniculate ganglion. The symptom is conductive hearing loss caused by the tumor extending into the tympanic cavity. We should bear in mind that there is a also rare type of facial nerve schwannoma manifesting hearing disturbance alone.