Temporal bone anatomy characteristics in superior semicircular canal dehiscence.

Introduction: Superior semicircular canal dehiscence (SCD) remains difficult to diagnose despite advances in high-resolution computed tomography (HRCT) imaging. We hypothesize possible associations between gross temporal bone anatomy and sub-millimeter pathology of the semicircular canals, which may supplement imaging and clinical suspicion. This pilot study investigates differences in gross temporal bone anatomic parameters between temporal bones with and without SCD.

Methods: Records were reviewed for 18 patients referred to an otology clinic complaining of dizziness with normal caloric stimulation results indicative of non-vestibular findings. Eleven patients had normal temporal bone anatomy while seven had SCD. Three-dimensional reconstruction of every patient's temporal bone anatomy was created from patient-specific computational tomography images. Surface area (SA), volume (V), and SA to V ratios (SA:V) were computed across temporal bone anatomical parameters.

Results: SCD temporal bones have significantly smaller V, and larger temporal bone SA. Mean (±SD) V was 21,484 ± 3,921 mm in temporal bones without SCD and 16,343 ± 34,471 mm for those with SCD. Their respective SA were 13,733 ± 1,603 mm and 18,073 ± 3,002 mm. Temporal bone airspaces and lateral semicircular canals did not demonstrate significant differences where SCD was and was not present. Plots of MV response against computed SCD temporal bone anatomic parameters (SA, V and SA:V) showed moderate to strong correlations: temporal bone SA:V (r = 0.64), temporal bone airspace V (r = 0.60), temporal bone airspace SA (r = 0.55), LSCC SA (r = 0.51), and LSCC-to-TM Distance (r = 0.65).

Conclusions: This analysis demonstrated that SCD is associated with decreased temporal bone volume and density. The defect in SCD does not appear to influence caloric responses.