A 39-year-old female patient presented to us with a history of unilateral hearing loss ever since she was a child. Pure tone audiometry confirmed deafness of the affected ear. Both auditory brainstem response (ABR) and distortion-product otoacoustic emission (DPOAE) response were absent. Caloric test revealed severe canal paresis. Cervical vestibular evoked myogenic potentials (cVEMP) were also absent in the affected ear, even though the patient had never experienced balance problems. Her facial nerve function was normal. Computed tomography (CT) of the temporal bone revealed internal auditory canal stenosis on the affected side. Magnetic resonance imaging (MRI) failed to reveal the vestibulocochlear nerve on the affected side.
A diagnosis of congenital internal auditory canal (IAC) stenosis related to hypoplasia of the vestibulocochlear nerve was considered, given that the patient had no history of acquired disease that could be the cause of the hearing loss. A nerve defect is indicative of retrocochlear dysfunction, whereas absence of a DPAOE response suggests impairment of the membranous labyrinth despite normal radiological findings of the bony labyrinth.
