A Study of Anomalies of Cochlea and Cochlear Nerve in Children with Congenital Profound Hearing Loss – An Indian Perspective

Background: Congenital Profound hearing loss is one of the leading handicaps that is encountered among children in the Indian subcontinent. There is a great demand for cochlear implantation in the Indian clinical scenario due to the high incidence of congenital hearing loss, due to a multitude of etiological factors. Such factors may also lead to anomalies in the cochlea and cochlear nerve, thus leading to challenges for cochlear implantation. With advancements in high resolution radio-imaging, the selection criteria for cochlear implantation has today become precisely defined. In children born with cochlear nerve aplasia and Michel deformity, auditory brain stem implantation is the only other alternative for auditory rehabilitation. There exits some “grey zones” like cochlear nerve hypoplasia, where the implant of choice cannot be clearly defined. Prevalence of anomalies of cochlea and cochlear nerve in relation to congenital severe to profound hearing loss has evoked much interest and since there is no available data on this subject, considered worthwhile to undertake this study.

Aims: This study focuses on our experience with identifying the prevalence of inner ear malformations, the possible etiologies for these malformations and planning the appropriate management protocols for the same.

Study Design: Retrospective study. Outcome measures compared using student t-test (paired).

Place and Duration of Study: Madras ENT Research Foundation, Chennai, India during the period 2005-2014.

Methodology: The study assessed the prevalence & distribution of Cochlear and Cochlear Nerve malformations in 82 children with profound hearing loss (aged between 9 months – 6 years) presented at Madras ENT Research Foundation, a premier auditory implant institute in South India during the period 2005-2014. The outcomes of CI/ABI in children with inner ear malformations were compared by using standard measures like CAP, SIR, MAIS and MUSS scores at sequential intervals of 6 months and 12 months post implantation.

Results: Eighty-two patients with cochlear and cochlear nerve malformations were identified among a consecutive series of 926 children with congenital severe to profound hearing loss. Of these, bilateral malformations were seen in 74 patients and unilateral malformations in 8 patients. Out of 74 patients, 66 had undergone surgery and among these 66 patients, 56 had CI and 10 had ABI. The study showed that there were significant statistical differences in the results as measured by outcome scores during the study, between 6 months and 12 months post implantation. Complications of surgery, though more common with anomalous anatomy, were not very morbid and could be overcome with appropriate measures.

Conclusion: Improvement in auditory perception and speech development skills among the different group of children with inner ear malformations were good both with CI and ABI. We infer that auditory implants have paved the way forward for children with inner ear malformations to acquire auditory verbal skills, but a judicious selection of cases for appropriate implantation is vital to achieve best outcomes.