Grand Rounds  |   June 2003
Dehiscence of Bone Overlying the Superior Semicircular Canal as a Cause of an Air-Bone Gap on Audiometry
Author Notes
Hearing Disorders / Balance & Balance Disorders
Grand Rounds   |   June 2003
Dehiscence of Bone Overlying the Superior Semicircular Canal as a Cause of an Air-Bone Gap on Audiometry
American Journal of Audiology June 2003, Vol.12, 11-16. doi:10.1044/1059-0889(2003/004)
History: Accepted 13 May 2003 , Received 13 Nov 2002
American Journal of Audiology June 2003, Vol.12, 11-16. doi:10.1044/1059-0889(2003/004)
History: Accepted 13 May 2003 , Received 13 Nov 2002

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

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