Lateral semicircular canal aplasia is a malformation of the inner ear, usually associated with vestibular and cochlear malformations in the context of congenital malformation syndromes. We report a rare case of a young patient with isolated lateral semicircular canal aplasia and no associated vestibular symptoms.

A 20-year-old man with no personal or family history presented with persistent unilateral tinnitus for three years with no associated vestibular symptoms. Moderate unilateral right sensorineural hearing loss was detected. Magnetic resonance imaging demonstrated isolated aplasia of the right lateral semicircular canal. Videonystagmography revealed right hyporeflexia. Vestibular evoked myogenic potentials were absent after stimulation on the right side and normal on the left side.

Although the morphological abnormalities appeared to be isolated on imaging, the patient presented functional signs of global cochlear, semicircular canal and otolithic lesions, probably related to a developmental disorder of the membranous labyrinth. Functional investigations must be performed in the presence of isolated semicircular canal aplasia, even when it is an incidental finding, to exclude more extensive labyrinthine lesions.