Assessing bone radiodensity and thickness in cochlear implant patients through manual photon-counting CT image segmentation using ITK-SNAP

Bone radiodensity and thickness between the cochlear implant's middle electrodes and the facial nerve were compared across four groups-Facial nerve stimulation (FNS) patients with and without far advanced otosclerosis (FAO), and controls with and without FAO-using manual segmentation of photon counting-computed tomography (PC-CT) to assess FNS risk. This case-control study compared FAO patients with FNS (n = 3) to non-FAO with FNS (n = 2) and two control groups without FNS of post-lingually deafened patients: FAO (n = 2) and non-FAO (n = 2). Clinical data from medical record included surgical details, complications, PC-CT findings (bone thickness between the middle electrodes and the facial nerve), hearing outcomes, and implant fitting at two years. Manual segmentation of PC-CT was performed using ITK-SNAP software to measure the bone radiodensity between the mid-array electrode and the adjacent facial nerve. No significant differences were found between FNS and non-FNS patients in demographics, surgical outcomes, complications, audiometric data, or implant programming at 2 years post-surgery. A significant difference in bone radiodensity was observed in patients with FAO (1483.57 ± 122.37 HU (Hounsfield Units)) compared to those without FAO (2403.51 ± 128.24 HU; p < 0.001). In the non-FAO with FNS group, one patient exhibited an exceptionally short distance (0.13 mm) between the first portion of the facial nerve and the middle electrodes. When comparing FNS and non-FNS patients, no significant differences were observed in bone radiodensity (p = 0.85) or in bone thickness (p = 0.75). ITK-SNAP enables manual PC-CT segmentation to assess bone radiodensity and thickness between cochlear implant electrodes and the facial nerve. In otosclerosis, lower radiodensity alone doesn't explain FNS, but reduced bone thickness may contribute.