SMS classification of inner ear malformations: our experience with implantation in type II anomalies

To study and analyse the radiological and surgical findings of 24 cochlear implantees with SMS type II cochleovestibular malformation and to compare their outcomes in terms of hearing and speech gains pre- and postoperatively.

Retrospective analysis of cochlear implanted candidates over a period of 8 year 6 months from 3 institutions was undertaken and 24 patients suffering from prelingual profound congenital sensori-neural hearing loss along with the presence of SMS type II cochleovestibular malformation were studied. Preoperative radiology, surgical difficulties and complication, and postoperative hearing and speech outcomes up to a period of 2 years, using IT-MAIS and SIR scores were noted. Statistical comparison pre- and postimplantation was done using Wilcoxon signed rank test and a p value of < 0.05 was considered statistically significant.

In 24 cases, we encountered four cases of SMS type IIa malformation with a smaller modiolus, while the rest 20 were type SMS type IIb with partially defective modiolus. Intraoperatively, CSF leak was observed in 11 patients. Complete electrode insertion and good electrical response (NRT) was detected in all. No facial nerve anomaly was encountered. IT-MAIS and SIR scores increased from a preoperative mean of 5.6 and 1.16-34.56 and 3.88 after 2 years postsurgery, respectively and this difference was found to be statistically significant.

Our experience with SMS Type II malformations show promising and motivating results with less chances of complications. Proper evaluation and surgical planning preoperatively can lead to an uneventful surgery with good outcomes. A simple and uniform classification system of these anomalies is a must for appropriate prognostication and right decision making.