Semicircular Canal Dehiscence
From bonepath
This is the presentation of thin or open bone of the endocranial petrous temporal bone, in the surface overlying the semicircular canals of the inner ear. Potentially any of the bone overlying the vestibular area could become dehiscent, although the superior canal is the most likely to be exposed, and therefore syndromic (as Superior Semicircular Canal Dehiscence, SSCD: Carey et al. 2000, Minor 2000, Manzari 2010).
The vestibulo-cochlear system of the inner-ear is involved in hearing and balance, and communicates with the brain by way of detecting pressure changes within the ear labyrinth. Dehiscence overlying this system exposes a ‘third window’ (to the round and oval windows between the middle and inner ear) that can affect labyrinthine pressure. Thus dehiscence of bone overlying the semicircular canals can manifest clinically as vertigo, occilopsia, dizziness, disequilibrium, and hearing loss (Minor 2000, Strupp and Arbusow 2001, Chien et al. 2011).
The etiology of this pathology is unclear. Carey and colleagues (2000) analyzed a large series of adult and subadult temporal bones to study the manifestation of dehiscence. Their results suggested the pathology arises because of a congenital developmental defect, in which the petrous bone overlying the semicircular canals fails to thicken during ontogeny (Chien et al. 2011). Alternatively, Strupp and Arbusow (2001) described SSCD as a type of perilymph fistula, which could arise from “barotraumas.” That is, contra Carey and colleagues, dehiscence could be due to erosion of bone rather than a failure to develop. Vestibular schwannoma (neoplastic growth around nerves) may also cause erosion or thinning of bone in region around the semicircular canals (Carey et al. 2000). Finally, later-stage effects of syphilis can affect the bony labyrinth, possibly leading to thinned bone around the semicircular canals.
[edit] Examples from Ford Collection
[edit] References
Carey JP, Minor LB, Nager GT. 2000. Dehiscence or thinning of bone overlying the superior semicircular canal in a temporal bone survey. Archives of otolaryngology--head & neck surgery 126:137
Chien WW, Carey JP, Minor LB. 2011. Canal dehiscence. Curr Opin Neurol 24:25-31
Manzari L. 2010. Multiple dehiscences of bony labyrinthine capsule: A rare case report and review of the literature. Acta Otorhinolaryngologica Italica 30:317-20
Minor LB. 2000. Superior canal dehiscence syndrome. Otology & Neurotology 21:9
Strupp M, Arbusow V. 2001. Acute vestibulopathy. Current opinion in neurology 14:11
