A New Method for Identifying Cochlear Ossification in Cochlear Implant Candidates with Deafness following Meningitis

Objectives: To develop a new method to determine the presence of intracochlear ossification and/or fibrosis in candidates for cochlear implantation (CI) with deafness following meningitis. Methods: This study involved 13 patients (15 ears: normal structures, soft tissue alone, partial bony occlusion, and complete bony occlusion in 4, 3, 2, and 6 ears, respectively) with profound deafness due to meningitis who underwent CI. We measured the radiodensity in Hounsfield Units (HU) using 0.5-mm-thick, axial, high-resolution computed tomography (CT) image slices at 3 different points in the basal turn, including the fenestration site and inferior and ascending segment sites, which were located along the electrode-insertion path. Pixel-level analysis on the DICOM viewer yielded actual CT values of intracochlear soft tissues by eliminating the partial volume effect. The values were compared with the intraoperative findings. Results: Values for ossification (n = 12) ranged from +547 HU to +1137 HU (n = 12); for fibrosis (n = 11), from +154 HU to +574 HU (n = 11); and for presence of fluid (n = 22), from −49 HU to +255 HU. From these values, we developed 2 presets of window width (WW) and window level (WL): 1) WW: 1800, WL: 1100 (200 HU to 2000 HU) and 2) WW: 1500, WL: 1250 (500 HU to 2000 HU). The results using these 2 presets corresponded well with the intraoperative findings. Conclusions: Our new method is easy and feasible to preoperatively determine the presence of cochlear ossification and/or fibrosis that develop following meningitis.