Spontaneous tegmen defect and semicircular canal dehiscence: same etiopathogenic entity?

To describe the clinical and radiologic features of associated spontaneous tegmen defects (STDs) with semicircular canal dehiscences (SCCDs) and to postulate a novel etiopathogenic hypothesis of these pathologic conditions.

Medical records of all patients with surgically confirmed STD between 2001 and May 2010 were reviewed. We excluded all secondary tegmen defects. Clinical, audiological, and radiologic data were analyzed.

Twenty-three patients matched the inclusion criteria. Semicircular canal dehiscence was associated to STD in 13 patients. Of these patients, 12 (95%) had protruding superior semicircular canals in the middle cranial fossa versus only 3 (30%) of 10 patients for the nondehiscent cases. Twenty-two patients complained of hearing loss. Cerebrospinal fluid leak was found in 13 patients. Four patients had history of meningitis. Vestibular symptoms were present in 8 patients.

This is the largest series of reported coexistence of STD and SCCD in the literature. Protrusion of the superior semicircular canal in the middle cranial fossa is probably an additional factor underlying STD and SCCD etiopathogeny. Semicircular canal dehiscence should always be looked for when STD is present.