Skull Base Deficiency in Superior Semicircular Canal Dehiscence (SSCD): Evidence for Incomplete Development

OBJECTIVE: Determine whether Superior semicircular canal dehiscence (SSCD) patients have thinner skull bases compared with controls and spontaneous cerebrospinal fluid leak (sCSFL) patients. STUDY DESIGN: Case control. SETTING: Tertiary referral center. PATIENTS: Radiographically confirmed SSCD, temporal bone sCSFL, matched (BMI and age), and unmatched control cohorts. INTERVENTION: Measurement of calvarium, zygomatic arch, and lateral skull base thickness. MAIN OUTCOME MEASURES: Compare BMI, average skull base, calvarial, and zygomatic arch thicknesses of controls and sCSFL patients. RESULTS: SSCD patients have an average [SD] BMI similar to unmatched controls (29.2 [7.7] vs. 31.4 [7.9] kg/m2, P=0.18), but significantly lower BMI than sCSFL patients (29.2 [7.7] vs. 38.5 [10.6] kg/m2, P<0.001). The average skull base thickness of SSCD patients was 50% thinner than matched control patients (2.12 [0.92] vs. 4.23 [1.13] mm, P<0.001, Cohen d=2.05) and 33% thinner than sCSFL patients (2.12 [0.92] vs. 3.13 [1.46] mm, P<0.001, Cohen d=0.83). No significant difference in skull base thickness was observed between symptomatic and asymptomatic SSCD patients (P=0.45). SSCD patients had a small yet significantly reduced calvarium to zygomatic arch thickness ratio compared with controls (0.44 [0.09] vs. 0.51 [0.11], P<0.001, Cohen d=0.70), but not sCSFL patients (0.44 [0.09] vs. 0.47 [0.12], P=0.09). CONCLUSIONS: SSCD patients possess dramatically thinner skull bases than control and sCSFL patients, despite a lack of predisposing factors like obesity. These data implicate a developmental deficiency in the pathophysiology of SSCD.