Description

‘What has been will be again, what has been done will be done again; there is nothing new under the sun’ Ecclesiastes 1: 914.

Current literature is full of examples of small variations or additions to an established body of medical knowledge. The description of the previously unrecognised clinical condition of superior semicircular canal (SSCD) dehiscence by Minor et al. represents a true discovery.

The diagnosis of this condition provides a potential explanation for the cohort of patients with the perplexing group of symptoms of sound and/or pressure induced dizziness, conductive hyperacusis and persistent conductive deafness with optimal middle ear function.

SSCD probably arises from failure of postnatal bone development. The bilateral nature of thinning and the mature lamellar bone on the margins of the thin areas point toward a developmental cause. Studies on cadaveric temporal bones have found a dehiscence of the bone overlying the superior canal occurred in approximately 0.4 to 0.5% of temporal bone specimens.2,3 A study by Carey et al3 showed that in an additional 1.4% of specimens (1.3% of individuals), the bone was markedly thin (<0.1 mm), such that it might appear dehiscent even on ultra-high resolution computed tomography.

This article reviews the symptoms, signs and investigations with a clinico-physiological correlation to help in the better recognition of the condition.