Virtual endoscopic evaluation of labyrinthine fistulae resulting from cholesteatoma

Fistulae of the otic capsule occur in approximately 10% of cholesteatoma cases. Preoperative imaging of this complication is valuable in limiting intraoperative morbidity. Three-dimensional virtual endoscopic imaging provides a new method for analysis of conventional computed tomography (CT) imaging data. The purpose of the study was to examine the feasibility and efficacy of this technique in detecting labyrinthine fistulae caused by cholesteatoma.

Retrospective case study.

Fifteen patients with surgically confirmed lateral semicircular canal fistula and preoperative CT scan were included. Scans meeting inclusion criteria were imported into a software program for production of virtual endoscopic images. Dehiscent and normal lateral semicircular canals were navigated while varying threshold values for surrounding bone. Changes in threshold values produce the effect of thickening or thinning the bone enveloping the semicircular canal. Threshold parameters that produced easy circumnavigation ("open") and intact inner surface of the lateral canal ("closed") were recorded.

The fistula group demonstrated a significantly lower "closed" threshold level and, consequently, a greater range of navigation between "open" and "closed" thresholds. Intrasubject absolute differences in threshold values between normal and abnormal ears appeared to be the most accurate method for detecting a fistula. The suggested imaging parameters displayed an overall sensitivity for fistula detection of 67% with a specificity of 93%.

The three-dimensional virtual endoscopic algorithm shows promise as a method for confirmation of otic capsule dehiscences. Sensitivity for detection is suboptimal but can be improved by alterations in image acquisition parameters.