Facial nerve schwannoma: Case report and brief review of the literature

Abstract

Schwannomas are rare nerve sheath tumors that can occur throughout the body, and are symptomatic based on location, size, and impingement on adjacent structures. These tumors are often benign lesions and occur sporadically or from genetic conditions such as neurofibromatosis. Schwannomas may arise from peripheral nerves, gastrointestinal nerves, spinal nerve roots and cranial nerves. Facial nerve schwannomas arise from cranial nerve VII, commonly involving the geniculate ganglion, labyrinthine segment, and internal auditory canal. While small lesions are asymptomatic, larger lesions can cause facial nerve paralysis, and facial spasms. Lesions in the internal auditory canal can cause hearing loss, tinnitus, vertigo, and otalgia. High-resolution CT imaging and MRI imaging are useful for distinguishing between other pathologies that arise from the same region. High-resolution CT scans can show bony degeneration of nearby structures such as the labyrinth or ossicles. MRI imaging shows hypo intensity on T1 imaging, and hyperintensity on T2 imaging. On T1 postcontrast, enhancement can be homogenous or heterogeneous with cystic degeneration if the lesion is large. Nodular enhancement is commonly seen on facial nerve schwannomas within the internal auditory canal. Vestibular schwannomas involving CN VIII are more common, and appear similar to facial nerve schwannomas, but can be distinguished apart due to growth in the geniculate ganglion and/or the labyrinthine segment. Management of asymptomatic or mild lesions is typically conservative with follow up imaging, and surgery for larger lesions. Here, we present a case of a facial nerve schwannoma in a 57-year-old woman.

Keywords: Facial nerve palsy; Facial nerve schwannoma; Geniculate ganglion; Internal auditory canal; MRI.

Fig. 1

CT temporal bone, right-side (A) and normal left-side (B) in a 57-year-old woman with recurrent episodes of dizziness over 6 months. Expansion of the right geniculate ganglion (A, arrow), compared to contralateral normal left side (B, arrow).

Fig. 2

MRI internal auditory canal protocol, coronal T1 postcontrast fat-saturated images (A and B), axial T1 postcontrast fat-saturated images (C and D) and axial T2-weighted non–fat-saturated images (E and F) in a 57-year-old woman with recurrent episodes of dizziness over 6 months. Nodular oval-shaped T2-hypointense enhancing lesion measuring 6 × 7 mm was noted in the right internal auditory canal (white arrow). Furthermore, abnormal enhancement was present in the right geniculate ganglion (yellow arrow). These findings were highly suggestive of a facial nerve schwannoma.

Fig. 3

Axial (A) and coronal (B) T2-weighted images showing internal auditory canal (A, arrow) and geniculate ganglion (B, arrow) in a 57-year-old woman with recurrent episodes of dizziness over 6 months. The lesions demonstrate intrinsic T2 hyperintense signal characteristics.