Prevalence of Spontaneous Asymptomatic Facial Nerve Canal Meningoceles: A Retrospective Review

Abstract

Background and purpose: The prevalence of patent facial nerve canals and meningoceles along the facial nerve course is unknown. This study aimed to assess the frequency of such findings in asymptomatic patients.

Materials and methods: A retrospective review was completed of patients with high-resolution MR imaging of the temporal bone whose clinical presentations were unrelated to facial nerve pathology. Facial nerve canals were assessed for the presence of fluid along each segment and meningoceles within either the labyrinthine segment (fluid-filled distention, ≥1.0-mm diameter) or geniculate ganglion fossa (fluid-filled distention, ≥2.0-mm diameter). If a meningocele was noted, images were assessed for signs of CSF leak.

Results: Of 204 patients, 36 (17.6%) had fluid in the labyrinthine segment of the facial nerve canal and 40 (19.6%) had fluid in the geniculate ganglion fossa. Five (2.5%) had meningoceles of the geniculate ganglion fossa; no meningoceles of the labyrinthine segment of the canal were observed. No significant difference was observed in the ages of patients with fluid in the labyrinthine segment of the canal or geniculate ganglion compared with those without fluid (P = .177 and P = .896, respectively). Of the patients with a meningocele, one had a partially empty sella and none had imaging evidence of CSF leak or intracranial hypotension.

Conclusions: Fluid within the labyrinthine and geniculate segments of the facial nerve canal is relatively common. Geniculate ganglion meningoceles are also observed, though less frequently. Such findings should be considered of little clinical importance without radiologic evidence of CSF otorrhea, meningitis, or facial nerve palsy.

Fig 1.

A 55-year-old woman who presented with persistent dizziness. From inferior to superior, axial T2 SPACE images demonstrate fluid-filled remodeling/expansion of the right geniculate ganglion fossa (straight arrows), compatible with a meningocele (A–C). The labyrinthine segment of the facial nerve canal (curved arrow) is 0.9 mm in diameter, which is at the upper limit of normal but does not meet the defined size criteria for a meningocele. The normal left side is shown for comparison (D).

Fig 2.

A 45-year-old woman who underwent imaging to follow up a known right vestibular schwannoma. Axial T2 SPACE images demonstrate fluid within the geniculate ganglion of the left facial nerve canal, with dilation measuring up to 2.7 mm, compatible with a meningocele (long arrows, A and B). Fluid is also seen tracking along the expected course of the proximal left greater superficial petrosal nerve (short arrow, B). The known vestibular schwannoma is seen in the contralateral right internal auditory canal, extending through the porus acusticus (curved arrow, C).

Fig 3.

A 64-year-old woman who presented with bilateral sensorineural hearing loss. Axial T2 SPACE imaging demonstrates fluid-filled dilation of the right geniculate ganglion fossa, compatible with a meningocele (solid straight arrow, A and B). Fluid is seen in the left labyrinthine (curved arrow, C) and geniculate (dashed straight arrow, C and D) segments of the left facial nerve canal without remodeling/dilation of the osseous canal.