Superior Canal Dehiscence and the Risk of Additional Dehiscences: A Retrospective CT Cohort Study.

ABSTRACT

OBJECTIVE: Determine if superior canal dehiscence (SCD) found on flat-panel CT increases the risk for other defects in the otic capsule. STUDY DESIGN: Retrospective cohort study. SETTING: Tertiary care center. PATIENTS One hundred ears (50 with SCD and 50 matched controls without SCD). INTERVENTIONS: Flat-panel CT imaging. MAIN OUTCOME MEASURES: (1) Prevalence of other dehiscences in SCD ears, (2) dehiscences in controls, and (3) otic capsule thickness in other reported dehiscence locations (cochlea-carotid, lateral semicircular canal [SCC] and mastoid, facial nerve-lateral SCC, vestibular aqueduct, posterior SCC-jugular bulb, posterior SCC-posterior fossa). Between-group comparisons were considered significant at p < 0.007 after applying the Bonferroni correction for multiple comparisons. RESULTS: Not including the SCD, there was a mean of 0.04 additional dehiscences in the SCD group (n = 2/50, 4%) and 0.04 non-SCD dehiscences in the controls (n = 2/50, 4%, p > 0.007). In the SCD group, there was one dehiscence between the cochlea and carotid artery and one between the posterior SCC and posterior fossa. The control group had one enlarged vestibular aqueduct and one dehiscence between the facial nerve and lateral SCC. As a group, SCD ears had wider vestibular aqueducts (0.68 ± 0.20 vs 0.51 ± 0.30 mm, p < 0.007) and thinner bone between the posterior SCC and posterior fossa (3.12 ± 1.43 vs 4.34 ± 1.67 mm, p < 0.007). The bone between the facial nerve and lateral SCC was thicker in SCD ears (0.77 ± 0.23 vs 0.55 ± 0.27 mm, p < 0.007) and no different for cochlea-carotid, and lateral SCC and mastoid (p > 0.007). CONCLUSIONS: SCD does not increase the likelihood of a second dehiscence in the same otic capsule. SCD patients may have congenitally thinner otic capsule bones compared to controls, particularly near the posterior SCC, where the vestibular aqueduct may be enlarged.