Early and Long-Term Outcome in Auditory Brainstem Implants in Neurofibromatosis Type 2

Objective: To analyze auditory function by auditory brainstem implants (ABI) in the complex tumor history of Neurofibromatosis Type 2 (NF2) including recurrence after implantation.

Methods: Out of a consecutive series of 37 ABI implantations, 27 were performed in patients with NF2 by our interdisciplinary neuro-otological neurosurgical team. Tumor and ABI surgery were performed under multimodality monitoring including mapping of the dorsal cochlear nucleus for electrical auditory brainstem responses (E-ABR). Clinical outcome was evaluated by standardized MTP tests (syllable and word) and HSM (Hochmair-Schulz-Moser) sentence test at auditory-only and audio-visual conditions.

Results: Out of 27 implanted patients there were 24 successful hearing restorations with an average of 84% MTP understanding in auditory-only mode from 3 months onwards. In 19 patients some open set speech perception could be documented at a range of 10% to 99% HSM, (Ø 51%), at a mean of 38 months follow-up. Causes of failures were radiotherapy, anatomical variation or fast disease progression. In 9 patients 11 recurrence operations were performed, 4 ipsi- and 7 contra-laterally to the ABI; in 2 patients, tumor infiltration caused ABI failure, and necessitated recurrence resection and new ABI placing.

Conclusion: After exact ABI placing with subsequent good auditory function, hearing quality will improve and stabilize further over years. Even if recurrent tumor development causes temporary malfunction, the useful ABI function will be recuperated by recurrence resection and functional intra-operative ABI testing; hereby, those rare cases in need of ABI exchange will be identified; by either way the functional outcome after revision will be comparable to the previous level.