Cochlear Implantation in Cases of Inner Ear Malformation: A Novel and Simple Grading, Intracochlear EABR, and Outcomes of Hearing

OBJECTIVE: To propose a simple grading of inner ear malformation (IEM) and investigate intracochlear electrical auditory brainstem response (EABR) and outcomes for hearing in terms of the novel grading system. STUDY DESIGN: Retrospective case review. SETTING: Tertiary referral center. PATIENTS: Sixty patients with IEMs who received cochlear implants. INTERVENTION: Grading according to observation of modiolus deficiency and/or internal auditory canal (IAC) cochlear nerve deficiency (CND). MAIN OUTCOME MEASURE: Intracochlear EABR and categories of auditory performance (CAP) scores were assessed; children in school were categorized according to the type of school attended. RESULTS: Among 60 patients, 38% were classified as Grade I (modiolus present + normal cochlear nerve), 22% as grade II (modiolus deficiency + normal cochlear nerve), 33% as grade III (modiolus present + IAC CND), and 7% as grade IV (modiolus deficiency + IAC CND). During the operation, 93% of Grade I, 36% of Grade II, 23% of Grade III, and 50% of Grade IV patients showed typical EABR waves. CAP scores of 4 or more were obtained from 91% of Grade I, 62% of Grade II, 35% of Grade III, and 25% of Grade IV. Whereas none of children in Grades III and IV entered main stream school, 55% of Grade I and 25% of Grade II entered mainstream schools. CONCLUSIONS: Outcomes of hearing with cochlear implantations in IEM children depend on the severity of IEM and IAC CND. Our novel grading of IEM is simple and can be useful for understanding the severity of IEM.