New SMS Classification of Cochleovestibular Anomalies: Our Experience with 25 Cases of Type I Anomaly

To study and analyse the radiological and surgical findings of 25 cochlear implantees with SMS type-I cochleovestibular malformation and to compare their outcomes in terms of hearing and speech gains pre- and post-operatively.

Retrospective analysis of cochlear implanted candidates over a period of 8 year from 3 institutions was undertaken and 25 patients suffering from pre-lingual profound congenital sensori-neural hearing loss along with presence of SMS type I cochleovestibular malformation were studied. Pre-operative radiology, surgical difficulties and complication, and post-operative hearing and speech outcomes upto a period of 2 years, using IT-MAIS scores were noted. Statistical comparison pre- and post-implantation was done using Wilcoxon signed rank test and a p-value of < 0.05 was considered significant.

In 25 cases, we encountered 2 posterior SCC dysplasia, 15 enlarged vestibular aqueducts (LVA), 2 dilated vestibules, 4 superior SCC dysplasia, 2 cases with both posterior and superior SCC dysplasia and of those 1 had a dilated vestibule also. Intra-operatively, CSF leak was observed in 10 patients. Complete electrode insertion and good electrical response (NRT) was detected in all. No facial nerve anomaly was encountered. IT-MAIS scores increased from a pre-operative mean of 4.32 to 34.56 two years post-operatively and this difference was found to be statistically significant.

Our experience with SMS Type I malformations show promising and motivating results with less chances of complications, similar to implant candidates with normal anatomy. The outcomes in this group of patients are definitely not affected by any malformations in semicircular canals, vestibule or vestibular aqueduct.