Temporal bone anatomy in superior semicircular canal dehiscence: a case control study on bone pneumatization and the level of middle cranial fossa

Objectives:To assess for any association between the presence of superior semicircular canal dehiscence (SSCD) and temporal bone pneumatization and the height of middle fossa in symptomatic patients.Study Design:Retrospective case-control study.Setting:Tertiary, university referral center.Patients:Symptomatic patients with SSCD and a matched group of non-SSCD patients.Intervention:High-resolution computed tomography of the temporal bones.Main Outcome Measures:We graded the temporal bone pneumatization using the Virapongse classification and measured the distance between the middle fossa and the lateral semicircular canal on coronal plane at the most anterior aspect of the lateral and superior semicircular canals. We statistically compared all parameters (level of significance 0.05).Results:We enrolled 30 patients with SSCD, (males=13, females=17) with mean age of 47 years (SD: 26). The matched control group had similar baseline characteristics (p>0.05). Grade 4 pneumatization was noted in 83.3% (n=25) of SSCD patients with the remainder having grade 3. In the control group, 46.6% (n=14) had a grade 4 pneumatization, 36.6% (n=11) grade 3 and 16.6 5 (n=5) grade 2. This difference was statistically significant (p=0.003). The difference in the height of the middle cranial fossa between the two groups was also statistically significant (mean 3.80 [SD: 0.84] in SSCD group and 4.68mm [SD: 0.85] in the control group; p<0.0001).Conclusions:We found better-pneumatized mastoids in patients with SSCD, indicative of a direct association between temporal bone pneumatization and SSCD. Additionally, the middle fossa dura is lying significantly lower in patients with SSCD, factor of surgical importance.