Can lateral semicircular canal dysplasia play a role in the genesis of hyperacusis? - La displasia del canale semicircolare laterale può avere un ruolo nella genesi dell’iperacusia?

Hyperacusis can be a prominent and disabling symptom of superior semicircular canal dehiscence associated with autophony and the Tullio phenomenon. We report three clinical cases characterized by disabling hyperacusis in which semicircular canals dehiscence was excluded by temporal bone high-resolution computed tomography. The images disclosed lateral semicircular canal dysplasia, characterized by a small bony island, and dilatation of both the anterior and the posterior arms of the lateral semicircular canal. Cochleo-vestibular examinations (pure tone audiometry, infra-red videonystagmoscopy, vibration-induced nystagmus test, vestibular evoked myogenic potentials) will also be described. To verify the transtympanic ventilation tube effect, bilateral myringotomies tubes were performed in one patient but no long lasting subjective benefit was noted. Concerning the pathophysiology of this condition, we hypothesized that the increased volume of inner ear liquid can modify the micromechanical function of the cochlea and the labyrinthine hydrodynamics. In conclusion, in the case of specific symptoms, such as hyperacusis, it is important to consider the possibility of an inner ear morphological alteration involving the lateral canal and vestibule structures, as well as the existence of bony semicircular canal dehiscence.