[The imaging characteristics and prognosis of patients with cochlear implants whose cochlear nerves are not shown on MRI]

Abstract

Objective: To analyze the temporal bone CT and inner ear magnetic resonance imaging characteristics of cochlear implant patients with no cochlear nerve display in the inner auditory canal under MRI. To retrospectively analyze the long-term hearing and speech rehabilitation effects of such patients after cochlear implant. And to analyze the correlation between the results of imaging examinations and the postoperative effects of cochlear implant patients with this type of cochlear nerve deficiency. Methods: A total of 88 children with cochlear nerve deficiency, who underwent cochlear implantation in Shandong Provincial ENT Hospital from May 2014 to October 2018, were enrolled. Patients with cochlear malformations were excluded,only the patients with cochlear nerve deficiency whose cochlear structure was normal and no cochlear nerve displayed in inner auditory canal under MRI were enrolled. There were 64 patients, including 4 bilaterally implanted, 68 ears in total, with an average age of (2.8±1.7) years (range 1-6 years) at the time of implantation. The implanted product was Cochlear, including 24RECA and 512 models. All patients underwent inner ear magnetic resonance imaging and temporal bone CT scan before operation. Auditory speech function assessments were performed at 12 months, 24 months, and 36 months after surgery, including categories of auditory performance (CAP), speech intelligibility rating (SIR) and hearing aid threshold test. The imaging evaluation content included the width of the cochlear nerve canal of temporal bone CT, the width of the internal auditory canal, the width of the auditory nerve at the cerebellopontine angle of the inner ear MRI, and the ratio of the facial nerve to the width of the auditory nerve at the cerebellopontine angle. The correlations between the results of postoperative hearing aid hearing threshold, CAP, SIR and imaging results were analyzed. Results: Among the 64 cases of cochlear nerve not shown under MRI, 56 ears with CT data showed that the width of the cochlear nerve canal in temporal bone CT was (0.72±0.30) mm (mean±standard deviation, the same below), and the width of the internal auditory canal was (4.07±1.10) mm; 66 ears with MRI data showed that the diameter of the auditory nerve at the cerebellopontine angle of the inner ear MRI was (1.58±0.27) mm, the diameter of the facial nerve was (1.57±0.27) mm, and the ratio of the diameter of the facial nerve to the auditory nerve was (1.02±0.23). The average hearing thresholds at 12, 24, and 36 months after surgery were (46.8±2.5) dB HL, (40.7±0.8) dB HL, and (36.8±1.5) dB HL, respectively. The preoperative and postoperative CAP scores at 12, 24 and 36 months were (1.0±1.0), (3.8±1.4), (4.5±1.4) and (5.1±0.7) points, respectively. The preoperative and postoperative SIR scores at 12, 24, and 36 months were (1.1±0.3), (1.9±0.9), (2.5±0.9), and (2.9±0.6) points, respectively. The hearing threshold at 24 months after surgery was negatively correlated with the width of the internal auditory canal of temporal bone CT (r=-0.349, P=0.037), and the hearing threshold at 36 months after surgery was positively correlated with the ratio of the diameter of the facial nerve to the auditory nerve at the cerebellopontine angle of the inner ear MRI (r=0.740, P=0.001). Conclusions: Children with cochlear implants whose cochlear nerves are not shown on MRI can benefit from cochlear implantation, and their speech and auditory functions can improve significantly after surgery. The width of the internal auditory canal in the temporal bone CT and the ratio of the diameter of the facial nerve to the auditory nerve at the cerebellopontine angle of the inner ear MRI may be related to the long-term hearing threshold after surgery.