Auditory brainstem implants: current neurosurgical experiences and perspective

Abstract

The objective of this study was to present aspects of the current treatment protocol, such as patient evaluation and selection for therapy, multimodality monitoring for optimal auditory brainstem implant (ABI) positioning and radiological evaluation, that might have an impact on the functional results of ABI.Out of a series of 145 patients with bilateral vestibular schwannomas 10 patients received an ABI, eight of which are reported here. Patient selection was based on disease course, clinical and radiological criteria (according to the Hannover evaluation and prognosis scaling of neuro bromatosis type 2 (NF2)), extensive otological test battery and psycho-social factors. ABI placement was controlled by multimodality electrophysiological monitoring in order to activate the auditory pathway and to prevent false stimulation of the cranial nerve nuclei or long sensory or motor tracts. Results of hearing function were correlated with patients' ages, duration of deafness, tumour extension, tumour-induced compression or deformation of the brainstem, and numbers of activated electrodes without any side-effects.Out of 59 patients with pre-operative deafness eight patients received an ABI of the Nucleus 22 type. All these patients became continuous users without any side effects and experienced improved quality of life. Speech reception in combination with lip-reading was markedly improved, with further improvement over a long period. A short duration of deafness may be favourable for achieving good results, while age was not a relevant factor. Lateral recess obstruction may necessitate a more meticulous dissection, but did not prevent good placement of the ABI in the lateral recess. Pre-existing brainstem compression did not prevent good results, but brainstem deformation and ipsi-and contralateral distortion were followed by a less favourable outcome.Among the factors that can be in uenced by the therapy management are the selection of patients with a slow progressing NF2 disease, a short duration of deafness, a careful analysis of brainstem deformation and consideration of either side for implantation. Long-standing brainstem deformation might not lead to recovery, but instead lead to a low number of active electrodes and possibly only moderate results.ABI treatment is a safe procedure that can increase a patient's quality of life considerably. ABI placement along with neurophysiological control helps to prevent side effects and to improve acoustic activation. Further studies on structural and functional changes of the brainstem after previous tumour compression and distortion should increase our understanding and facilitate a decision on the best side for ABI implantation.

Auditory Brainstem Implantation Improves Speech Recognition in Neurofibromatosis Type II Patients

“…All patients were implanted using the surgical procedure as described by Matthies et al [16] (2000), Behr et al [18] (2007) and Jackson et al [22] (2002); 6 participants received the MED-EL COMBI 40+ and 26 the ABI. The ABI is a development of the COMBI 40+ offering an electronic platform, which allows a maximum stimulation rate of 50.760 compared to 18.180 pulses/second, which was possible with the COMBI 40+.…”

“…Several studies indicate that ABIs are effective and safe in providing useful auditory sensations in most patients with NF2 who would otherwise be totally deaf [9,14,15,16,17,18,19,20,21]. However, only a minority of the patients in the aforementioned studies achieved open-set speech discrimination and the speech recognition of individuals with an ABI varied considerably; most patients use their ABI to facilitate lip-reading and can only recognize environmental sounds [9,15,16,17,18,19,22].…”

“…However, only a minority of the patients in the aforementioned studies achieved open-set speech discrimination and the speech recognition of individuals with an ABI varied considerably; most patients use their ABI to facilitate lip-reading and can only recognize environmental sounds [9,15,16,17,18,19,22]. Importantly, even those with strongly limited speech recognition reported being very satisfied with their implant, showing that NF2 patients can gain remarkable objective and subjective benefits from ABI use [18].…”

Auditory brainstem implants in neurofibromatosis Type 2: is open speech perception feasible?

“…anatomy, previous radiation or radiosurgery, long-standing deafness, hemorrhage, and meningitis that have been encountered so far. 17,38 Nonetheless, none of these factors means an absolute exclusion from ABI surgery because there are single positive results despite those negative predictors. Grayeli and colleagues 17 reported on 5 (22%) of 23 patients with neurofibromatosis who had no auditory sensations; 3 of them had large tumors.…”

“…Therefore, brainstem compression and deformation from large tumors are hypothesized to be the main negative predictors in hearing rehabilitation. 17,38 As a consequence, some colleagues advocate tumor surgery and prosthesis implantation when tumors are at very small stages to achieve good auditory results. 17 Still, ABIs after resection of small tumors give only modest results far inferior to cochlear implants.…”