Ganglioneuroma of the Internal Auditory Canal

Introduction: Ganglioneuromas are benign slow growing neurogenic tumors that are thought to originate from neural crest cells. While these tumors typically arise from sympathetic or peripheral nerves, particularly in the posterior mediastinum or retroperitoneum, there have been a few reported cases of ganglioneuroma arising at the skull base. We report another such one of these cases with a ganglioneuroma arising from the cochlear nerve in the distal internal auditory canal (IAC). This is the second case of ganglioneuroma arising within the IAC reported in the literature.

Case Description: Our patient is a 43-year-old woman who presented with gradually worsening right-sided sensorineural hearing loss for the past five years. MRI of the IAC (Fig. 1) demonstrated a 6 × 4 mm intracanalicular enhancing lesion within the right distal IAC thought to be consistent with a vestibular schwannoma. She was deemed to have nonserviceable hearing with a pure tone average of 35dB HL and 24% word discrimination. She elected to undergo a translabyrinthine resection of the IAC lesion. Intraoperatively, the tumor appeared to be a yellowish lesion (less vascular than a schwannoma) arising from the cochlear nerve in the distal IAC. Final pathology demonstrated nerve tissue, spindle cells, fibrous stroma and adipocytes, and mature ganglion cells without atypia consistent with ganglioneuroma (Figs. 2 and 3). Immunohistochemistry revealed that the ganglion cells were positive for chromogranin and scantly positive for calretinin supporting both the neoplastic nature of the cells and the diagnosis of ganglioneuroma.

Discussion: Ganglioneuroma is a rare benign lesion in the IAC, but it should be considered on the differential diagnosis. It is important to distinguish ganglioneuroma from other more aggressive neuroblastic tumors such as ganglioneuroblastoma.

Fig. 1 Axial MRI T1 postcontrast sequence at the level of the IAC demonstrating a 6 x 4 mm enhancing intracanalicular lesion in the right internal auditory canal.

Fig. 2 Low-power magnification of hematoxylin and eosin (H&E) stain of right internal auditory canal lesion.

Fig. 3 High-power magnification of hematoxylin and eosin (H&E) stain of right internal auditory canal lesion. Visualized are nerve tissue, spindle cells, fibrous stroma and adipocytes. Likewise, mature ganglion cells without atypia are visualized with compact eosinophilic cytoplasm with a single eccentric nucleus.