Auditory Brainstem Implants in Neurofibromatosis Type 2: Early and Long-term Results

Objective: To analyze the evolution of auditory function after auditory brainstem implant (ABI) surgery along the difficult course of Neurofibromatosis Type 2 (NF2).

Methods: After resection of CPA tumors in 29 NF2 patients, ABI implantations were performed, by the interdisciplinary oto-neuro-surgical team, under multimodality monitoring including mapping of the dorsal cochlear nucleus for electrical auditory brainstem responses (E-ABR). Auditory results were evaluated by standardized syllable and word tests and HSM (Hochmair-Schulz-Moser) sentence test at auditory-only and audio-visual conditions at regular intervals of 3 to 6 months.

Results: Out of 29 implanted patients there were 26 successful hearing restorations. Causes of failures were radiotherapy, anatomical variation or fast disease progress. In 14 patients open set speech perception could be documented at a range of 10% to 99% correct understanding of unknown text in auditory-only mode, mean 36%. Patients’ average number of active electrodes were 7 out of 12. In 11 patients 13 recurrence operations were performed ipsi- or contra-laterally to the ABI side; in two patients, tumor infiltration caused ABI failure, and new ABI placing after recurrence removal became necessary. Best functional outcome is achieved in short deafness durations below 2 years (p < 0.1).

Conclusions: Precise ABI placing under functional measures will, in the majority of cases, be followed by useful auditory function improving and stabilizing even after over 3 years. If secondary ABI malfunction is caused by schwannoma or meningioma recurrence, the previously useful ABI function will recover at the previous level by resection of the recurrence and functional intra-operative ABI testing. Only in few cases an exchange by a new ABI will become necessary yielding mostly hearing results at the previous level, but possibly at different dynamics.