Virtual endoscopic evaluation of labyrinthine fistulae resulting from cholesteatoma

Objectives/Hypothesis: Fistulae of the otic capsule occur in approximately 10% of cholesteatoma cases. Preoperative imaging of this complication is va luable in limiting intraoperative morbidity. Three-dimensional virtual endo scopic imaging provides a new method for analysis of conventional computed tomography (CT) imaging data. The purpose of the study was to examine the f easibility and efficacy of this technique in detecting labyrinthine fistula e caused by cholesteatoma. Study Design: Retrospective case study. Methods: Fifteen patients with surgically confirmed lateral semicircular canal fist ula and preoperative CT scan were included. Scans meeting inclusion criteri a were imported into a software program for production of virtual endoscopi c images. Dehiscent and normal lateral semicircular canals were navigated w hile varying threshold values for surrounding bone. Changes in threshold va lues produce the effect of thickening or thinning the bone enveloping the s emicircular canal. Threshold parameters that produced easy circumnavigation ("open") and intact inner surface of the lateral canal ("closed") were rec orded. Results: The fistula group demonstrated a significantly lower "close d" threshold level and, consequently, a greater range of navigation between "open" and "closed" thresholds. Intrasubject absolute differences in thres hold values between normal and abnormal ears appeared to be the most accura te method for detecting a fistula. The suggested imaging parameters display ed an overall sensitivity for fistula detection of 67% with a specificity o f 93%. Conclusions: The three-dimensional virtual endoscopic algorithm show s promise as a method for confirmation of otic capsule dehiscences. Sensiti vity for detection is suboptimal but can be improved by alterations in imag e acquisition parameters.