Cochlear implantation: relationship between speech development and insertion depth in children

Abstract

The goal in pediatric cochlear implantation is improved hearing leading to better speech development, which may allow their integration into mainstream schools. Whether the intracochlear position of the electrode array has an influence on speech development or not is controversially discussed. Between 1996 and 1998 29 children ranging from 1.5 to 11.8 years (median 4 years) were provided with a Nucleus 22M or 24M cochlear implant system. Speech and language skills were assessed by a closed-set test (Mainzer test) and by the Schmid-Giovannini score for hearing development pre-implantation and at 6, 12, 18 and 24 months post-implantation. The position of the electrode array was determined by the surgical record and by a postoperative transorbital x-ray. Since the promontory has a thickness of one to two electrode bands, we defined deep insertion as more than 24 bands intracochlear. The patients were divided into 2 groups according to the insertion depth: Group 1 (n = 8) 24 bands (22 electrodes and 2 stiffening rings correspond to < or = 18 mm) or less and group 2 (n = 21) more than 24 bands intracochlear correspond to > 18 mm). The mean closed-set test scores 12 months post-implantation were 51.4% and 68.5% for group 1 and group 2, respectively. Schmid-Giovannini test scores were 8.7 for group 1 and 10.1 for group 2. There was no significant statistical difference in the closed-set and Schmid-Giovannini test scores. We observed incomplete insertion (i.e. less than 22 active bands are intracochlear) because of electrode extrusion in only one child. Speech development in children does not improve with deeper insertion of the cochlear implant electrode array.