Radiological Prevalence of Superior Semicircular Canal Dehiscence with Ultra-High-Resolution Photon-Counting Detector CT.

Abstract

Purpose: To determine the radiological prevalence of superior semicircular canal (SSC) dehiscence in a Japanese cohort using ultra-high-resolution (0.2 mm slice thickness) photon-counting detector CT (PCD-CT) and compare it with historical data from cadaveric and conventional CT studies.

Methods: This study involved a retrospective analysis of 402 temporal bones from consecutive 201 patients (age range 0-87 years; mean 41.0 ± 26.5 years) who underwent temporal bone PCD-CT for various otologic indications, none of whom had a pre-existing diagnosis of superior semicircular canal dehiscence syndrome (SSCDS). SSC bone thickness was measured, and the presence of dehiscence or thinning was assessed using multiplanar reconstructions, primarily in the Pöschl plane. For cases with identified dehiscence or thinning, a retrospective review of clinical and audiological data was performed.

Results: The mean thickness of the bone overlying the SSC was 0.87 ± 0.50 mm (range 0-3.52 mm). A definite dehiscence was identified in only 1 of the 402 temporal bones, yielding a radiological prevalence of 0.25% (95% CI: 0.00%-1.54%). Significant thinning of the SSC roof, where the bone was present but too thin to be resolved by the measurement caliper, was noted in an additional 12 temporal bones (2.99%, 95% CI: 1.66%-5.20%). Clinical review revealed that the single case of dehiscence was asymptomatic, and in the thinning cases, otologic symptoms were attributable to co-existing pathologies.

Conclusions: The radiological prevalence of SSC dehiscence identified with 0.2 mm PCD-CT is substantially lower than that reported by most conventional CT studies and closely approximates the true anatomical prevalence of 0.4-0.6% established in cadaveric studies. This finding suggests that the ultra-high spatial resolution of PCD-CT significantly reduces or eliminates false-positive findings attributable to partial volume effects, representing a new benchmark for the accurate radiological assessment of SSCDS.