Vestibulo-ocular reflex (VOR) preserved in bilateral severe vestibular malformations with internal auditory canal stenosis

Abstract

A 60-year-old woman, who has suffered from bilateral deafness throughout her life, visited our outpatient clinic. Computed tomography (CT) revealed inner ear malformations, which comprise cochlear aplasia with hypoplastic vestibule in the right ear and a common cavity in the left ear, and narrow internal auditory canals. We performed electronystagmography with caloric stimulation and stimulation of earth-vertical axis rotation (EVAR) or off-vertical axis rotation (OVAR), and studied vestibular evoked myogenic potentials (VEMPs) and vestibular ocular reflex (VOR). Slight horizontal nystagmus was induced by the stimulation of EVAR but not by caloric stimulation. Slight vertical nystagmus was observed during OVAR, whereas the VEMP test elicited no response. The result of horizontal or vertical VOR performed in the dark was almost normal. These findings suggest that VOR can be acquired even with severe malformation of the inner ear whose labyrinthine functions markedly reduce bilaterally until nystagmus is slightly induced by rotation stimulation.

• Inner ear
• cochlear aplasia
• hypoplastic vestibule
• common cavity
• EVAR
• OVAR
• VOR
• caloric response
• VEMP