gms | German Medical Science

Introduction: Dehiscence of the bone covering the superior semicircular canal is an aberration where the membranous labyrinth fits directly to the dura. The resulting symptoms can be understood based upon abnormal pressure transmission in the system of the inner ear. Some of the patients not only show vestibular symptoms but also auditory symptoms such as conductive hearing loss in spite of an intact middle ear.

Method: In this experimental study the influence of superior semicircular canal dehiscence on conductive hearing was measured in temporal bone with intact ossicles. A sound of fixed volume and various frequencies was applied to the external ear canal and measured with a microphone at the round window either with intact or defective bone over the superior semicircular canal.

Results: Disruption of the bone covering the superior semicircular canal showed a frequency dependant conductive hearing loss up to 2500 Hz. Especially in lower frequencies, values to the point of 20 dB were reached.

Conclusion: Dehiscence of the bone covering the superior semicircular canal leads to conductive hearing loss in temporal bone despite intact air conduction mechanisms in the middle ear. This apparent conductive hearing loss could be due to a third window formed by the dehiscence which causes a dissipation of acoustic energy transmitted through altered inner ear fluid-movements. Removal of the dehiscence leads to reconstituted inner ear mechanics.