The role of high-resolution Computer Tomography in prediction of the round window membrane visibility and the feasibility of the round window electrode insertion

Abstract

Objective: The aim of this work is to assess the role of pre-operative high-resolution computerized tomography (HRCT) in prediction of the round window membrane (RWM) visibility and the feasibility of round window electrode insertion.

Materials and methods: Retrospective study on a series of 97 cases of cochlear implant (CI) who were implanted in tertiary referral centers. We reviewed HRCT of all cases, and we implicated two radiological measurements on HRCT which are membrano-facial angle (MFA) and length of the bony overhang of the round window niche (RWN). We reviewed the intra-operative surgical video recordings of all cases for detection of the type of RWM visibility, according to The St Thomas' Hospital classification.

Results: The MFA was 21.9 ± 14.5. The length of the bony overhang of the RWN was 2.4 ± 0.33 mm. About 37% of the studied patients needed cochleostomy. The best cut-off of MFA in the prediction of the RW (type 2B and 3) was ≥ 15.1o with sensitivity 100%, and specificity 82%.

Conclusion: HRCT offers highly reliable and reproducible measurements for the prediction of RWM visibility and, therefore, prediction of the utility of the RW approach for electrode insertion. Membrano-facial angle (MFA) is a new measurement that can be used for this purpose.

Keywords: Cochlear implant; HRCT; Round window approach; Round window membrane; St thomas’ hospital classification.