Sensorineural hearing loss and word deafness caused by a mesencephalic lesion: clinicoelectrophysiologic correlations.

Objective: To assess the role of inferior colliculi as a generator of Wave V of brainstem auditory evoked potentials and in modulating the olivocochlear efferent auditory system.

Study Design: Case review.

Setting: University and tertiary referral centers.

Patients: Case report of a patient with word deafness caused by mesencephalic hemorrhage according to audiologic and electrophysiologic findings.

Results: The patient is a 48-year-old woman who suffered word deafness caused by hemorrhage localized at the quadrigeminal plate (including the inferior colliculi). At a follow-up visit, her pure-tone audiogram revealed symmetric severe sensorineural hearing loss that had partially resolved, whereas speech audiometry showed persistent word deafness. Acoustic reflexes were elicited, with normal thresholds bilaterally. Transient evoked otoacoustic emissions were recorded from both ears, with normal response and signal-to-noise ratio, but there was a failure for their amplitude to be suppressed with contralateral sound stimulation. Brainstem auditory evoked potentials were of normal amplitude and latencies bilaterally.

Conclusion: The finding of normal brainstem auditory evoked potentials supports the view that the neural generator of Wave V lies caudally to the inferior colliculi. Moreover, the abnormal suppression of transient evoked otoacoustic emissions indicates that descending collicular input is capable of modulating levels of excitability within the olivary nucleus and the cochlea.