Diagnostic Performance of Conebeam CT Pixel Values in Active Fenestral Otosclerosis.

Background And Purpose: Quantitative bone densitometry on multidetector CT of the temporal bone is a diagnostic adjunct for otosclerosis in its active (spongiotic) phase, but translating this technique to conebeam CT is limited by the technical variability of conebeam CT pixel values. The purpose of this study was to evaluate the performance of internally calibrated conebeam CT pixel value measurements that can enable the determination of active fenestral otosclerosis (otospongiosis).

Materials And Methods: This study included 37 ears in 22 patients with a clinical diagnosis of otospongiosis in those ears and 35 ears in 22 control patients without the diagnosis. Temporal bone conebeam CT was performed. ROIs were set anterior to the oval window, in the lateral semicircular canal bone island, and in a nearby aerated space. Mean conebeam CT pixel values in these regions determined the relative attenuation ratio of the area anterior to the oval window normalized to normal otic capsule bone and air.

Results: The relative attenuation ratio for cases of otospongiosis was significantly lower than that for controls (< .001). Based on receiver operating characteristic analysis, the optimal cutoff relative attenuation ratio was 0.876, which had an accuracy of 97.2% for the diagnosis of otospongiosis.

Conclusions: Internally calibrated pixel value ratios in temporal bone conebeam CT can feasibly help diagnose active/spongiotic-phase fenestral otosclerosis in an objective manner.