Virtual Endoscopy to Plan Transtympanic Approach to Labyrinthine Windows.

Abstract

The aim of this study was to evaluate the position and the accessibility of labyrinthine windows through the external auditory canal (EAC) by virtual endoscopy based on computed tomographic scan images. Prospective cross-sectional study. Tertiary referral center. Sixty-three high-resolution temporal bone computed tomographic scans were obtained from 34 adult patients undergoing various otologic procedures. Images were analyzed by the virtual endoscopy function included in Osirix (www.osirix-viewer.com). The endoscope was constrained in the EAC. The visible surfaces of target anatomic structures were assessed on multiplanar reconstruction views. The optimal angles of the virtual endoscope position showed a relatively high interindividual variability in the axial plane (64 ± 2.4 degrees for the oval window [OW] and 60 ± 2.5 degrees for the round window [RW]) position, but a low interindividual variation was noted in the coronal plane (107 ± 1.5 degrees for the OW and 112 ± 1.7 degrees for the RW). The RW was accessible in 87% of cases. The OW accessibility could be staged as follows: 1, invisible stapedial superstructure (10% of cases); 2, stapedial posterior crus partly visible (33%); 3, entire posterior crus and pyramid visible (44%); 4, posterior and anterior crus visible (13%). Virtual endoscopy through the EAC can evaluate the accessibility of the OW or RW via a transcanal route. This technique seems to be helpful in preplanning minimally invasive procedures by this approach such as cochlear implantation.