The association between semicircular canal dehiscence and Chiari type I malformation.

OBJECTIVE To investigate the association between semicircular canal dehiscence (SCD) and Chiari type I malformation (CM-I). DESIGN Retrospective case series. SETTING Military tertiary referral center. PATIENTS Adult patients with SCD. INTERVENTION Review of records of patients diagnosed as having SCD for the radiologic diagnosis of CM-I and presenting symptoms. MAIN OUTCOME MEASURES The prevalence of CM-I among patients with SCD and the presenting symptoms of patients with SCD with and without a coexistent CM-I. RESULTS Of 32 patients diagnosed as having SCD, 30 underwent magnetic resonance imaging of the brain. Seven patients (23%; 95% confidence interval [CI], 12%-41%) were found to have a CM-I. Chiari type I malformation was associated with superior SCD in 3 of 26 patients (12%; 95% CI, 3%-30%). Of 10 patients with bilateral superior SCD, 2 (20%; 95% CI, 5%-52%) had a CM-I. Five of 6 patients (83%; 95% CI, 42%-99%) had a CM-I with unilateral or bilateral posterior SCD. Twenty-nine records were reviewed for presenting symptoms, and no significant difference was observed between patients with SCD alone and those with an associated CM-I (P = .09-.64). CONCLUSIONS Among patients with SCD, the prevalence of CM-I is elevated. This association is especially marked in patients with posterior SCD. This finding suggests a relationship between CM-I and SCD, particularly with posterior SCD.