Flat Panel Computed Tomography in the Diagnosis of Superior Semicircular Canal Dehiscence Syndrome

Flat panel computed tomography (FPCT) provides more accurate measurements of dimensions for superior semicircular canal dehiscence (SCD) than multislice CT (MSCT).

SCD syndrome occurs when a bony defect of the superior semicircular canal causes vestibular and auditory symptoms. MSCT can overestimate the size of the canal defect, with possible over-diagnosis of SCD and suboptimal selection of surgical approach. The higher resolution of FPCT should afford more accurate measurements of these defects.

Radiographic and surgical measurements were compared in 22 patients (mean age 49.4) with clinical SCD syndrome and canal defects confirmed at surgery. Twenty second FPCT scans were acquired before surgery with parameters: 109Kv, small focus, 200 degrees rotation angle, and 0.4 degree per frame angulation step. Dehiscence dimensions were measured from orthogonal multiplanar reconstructions on a high-resolution liquid crystal display monitor and compared with actual measurements recorded during microsurgery.

SCD dimensions by FPCT (x) were 2.8 ± 1.6 mm for length and 0.72 ± 0.28 mm for width. The surgical measurements (y) were 2.8 ± 1.7 mm for length and 0.72 ± 0.34 mm for width. Linear fits between x and y yielded R values of 0.93 (length) and 0.66 (width). Our previous study using MSCT had R values of 0.28 (length) and 0.48 (width). The average difference between each FPCT and corresponding surgical measurement was not significantly different from zero, whereas the results for MSCT were significantly different.

FPCT can provide more accurate measurements of SCD than MSCT. Clinicians should consider using FPCT for imaging suspected SCD.