Deficient Cochlear Nerve
The clinical term cochlear nerve deficiency has been established in the otologic literature to indicate a small or absent cochlear nerve on MR imaging. To the best of my knowledge it was first described by the Antwerp cochlear implant group in 1997 (1).
More recently, Buchman, Adunka and colleagues at UNC have shown that cochlear nerve deficiency (CND) is more common than previously recognized in CI candidates. CND may account for up to 20% of those with OAE/SP/ABR indications of auditory neuropathy spectrum disorder (2,3,4).
A new paper from Chang-Gung College of Medicine in Taiwan by Che-Ming Wu and colleagues makes several important observations based on a literature review and experience with 656 children (5).
CND, aplasia is more common than hypoplasia of the cochlear nerve.
Small IACs may make it impossible to differentiate the nerves or diagnose CND.
CND is often but not always associated with HRCT findings of hypoplastic IAC/cochlear nerve canal.
21.2% of pediatric CI candidates had CND.
20% of CND/aplastic on MR could hear some sounds at < 90 dB.
Overall, CND candidates obtain poorer than average CI outcomes.
CND/hypoplasia subjects performed better than CND/aplasia subjects.
CND/hypoplasia outcomes showed no significant difference (p=.02) from non-CND outcomes.
CND is more common than generally recognized
If substantiated by further studies and experience, CND should probably be differentiated into CND/aplasia and CND/hypoplasia due to different prognostic implications.
As an isolated MRI finding, CND/aplastic (unseen cochlear nerve) is not an absolute contraindication to implantation due to the limitations of current imaging.
1. Casselman JW, Offeciers FE, Govaerts PJ, et al. Aplasia and hypoplasia of the vestibulocochlear nerve: diagnosis with MR imaging. Radiology 1997;202:773-81.
2. Buchman CA, Copeland BJ, Yu KK, Brown CJ, Carrasco VN, Pillsbury HC III. Cochlear implantation in children with congenital inner ear malformations. Laryngoscope 2004;114:309-16.
3. Oliver F. Adunka, Patricia A. Roush, Holly F. B. Teagle, Carolyn J. Brown, Carlton J. Zdanski, Valerie Jewells, and Craig A. Buchman. Internal Auditory Canal Morphology in Children with Cochlear Nerve Deficiency. Otology & Neurotology (2006) 27:793 Y 801.
4. Buchman CA, Teagle HF, Roush PA, Park LR, Hatch D, Woodard J, Zdanski C,Adunka OF. Cochlear implantation in children with labyrinthine anomalies and cochlear nerve deficiency: implications for auditory brainstem implantation. Laryngoscope. 2011 Sep;121(9):1979-88. doi: 10.1002/lary.22032. Epub 2011 Aug 16. PubMed PMID: 22024855.
5. Che-Ming W, Li-Ang L, Shin-Kuo C, et al. Impact of Cochlear Nerve Deficiency…on Hearing Outcome in Children with Cochlear Implants. O&N (2015) 36:14-21.)