Dehiscence of Bone Overlying the Superior Semicircular Canal as a Cause of an Air-Bone Gap on Audiometry

Abstract

Dehiscence of bone overlying the superior semicircular canal can result in a syndrome of vertigo and oscillopsia induced by loud noises or by maneuvers that change middle ear or intracranial pressure. Patients with this disorder can also experience a heightened sensitivity to bone-conducted sounds in the presence of normal middle ear function. High-resolution CT scans of the temporal bones demonstrate the dehiscence. The authors describe a patient with bilateral superior canal dehiscence who had bilateral low-frequency conductive hearing loss, normal middle ear function, intact acoustic reflexes, and intact vestibular-evoked myogenic potentials. These findings would not be expected on the basis of a middle ear cause of the conductive hearing loss. A high-resolution CT scan of the temporal bones in this patient revealed bilateral superior canal dehiscence. Normal acoustic immittance findings in the presence of conductive hearing loss should alert clinicians to the possibility of inner ear cause of an air-bone gap due to superior canal dehiscence.

Bilateral Dehiscence of the Bony Cochlear Basal Turn

“…The same less pronounced increase of immittance could be responsible for the lack of any conductive defects, which contrasts with SCD syndrome usual findings. 7 Despite the nonspecific pattern of the symptoms, which might understandably create some difficulties in reaching a satisfactory diagnosis, an accurate electrophysiologic study played a fundamental role in correct clinical evaluation. This leads us to argue that VEMPs might represent a useful diagnostic tool, even in cases that seem not to have vestibular involvement.…”

La déhiscence du canal semi circulaire supérieur

“…La symptomatologie clinique est variable et dépendrait de la taille de la déhiscence et de sa topographie (9, 10). Les vertiges et les oscillopsies induits par les variations de pression ou par les sons de forte intensité sont les symptômes cliniques les plus typiques (11,12,13). Lʼexamen clinique doit rechercher un nystagmus vertical torsionnel, induit par des variations de pression : manoeuvre de Valsava, effort à glotte fermée, tympanométrie induisant une variation de pression dans le conduit auditif externe.…”

Síndrome de Deiscência de Canal Semicircular Superior

“…Mild to moderate sensorineural hearing loss and conductive hearing loss (reduction in the bone conduction threshold, however with air conduction within normal limits) were less frequently observed. We imagine that the acoustic energy dissipation through the canal dehiscence could be responsible for the apparent conductive hearing deficit 1,3,11,13,16,22,23 .…”

“…Moreover, some of them reported they could hear in the affected side, the movements of their own eyes, their heart beats and cracks when they moved their joints. Very few of them went to see an otorhinolaryngologist having only hearing loss, without vestibular symptoms 1,3,7,11,13,15,16 .…”