Awake craniotomy for auditory brainstem implant in patients with neurofibromatosis type 2:Four case reports

BACKGROUND The auditory brainstem implant(ABI)is a significant treatment to restore hearing sensations for neurofibromatosis type 2(NF2)patients.However,there is no ideal method in assisting the placement of ABIs.In this case series,intraoperative cochlear nucleus mapping was performed in awake craniotomy to help guide the placement of the electrode array.CASE SUMMARY We applied the asleep-awake-asleep technique for awake craniotomy and hearing test via the retrosigmoid approach for acoustic neuroma resections and ABIs,using mechanical ventilation with a laryngeal mask during the asleep phases,utilizing a ropivacaine-based regional anesthesia,and sevoflurane combined with propofol/remifentanil as the sedative/analgesic agents in four NF2 patients.ABI electrode arrays were placed in the awake phase with successful intraoperative hearing tests in three patients.There was one uncooperative patient whose awake hearing test needed to be aborted.In all cases,tumor resection and ABI were performed safely.Satisfactory electrode effectiveness was achieved in awake ABI placement.CONCLUSION This case series suggests that awake craniotomy with an intraoperative hearing test for ABI placement is safe and well tolerated.Awake craniotomy is beneficial for improving the accuracy of ABI electrode placement and meanwhile reduces non-auditory side effects.

Neurofibromatosis type 2 and auditory brainstem implantation

Neurofibromatosis type 2 （NF-2） is one of the most common single gene disorders in the nervous system.For approximately 96% of patients with NF-2 present with bilateral Schwannomas involving the eighth cranial nerves, which may be accompanied by Schwannomas involving other cranial, spinal or peripheral nerves, NF-2 is also referred to as ＂bilateral acoustic neuromas＂. Due to progression of tumors, surgery or radiotherapy, patients with bilateral acoustic neuromas will eventually suffer profound or total hearing loss, resulting in decrease of quality of life （QOL）.

Clinical and scientific innovations in auditory brainstem implants

The auditory brainstem implant(ABI)was originally developed to provide rehabilitation of retrocochlear deafness caused by neurofibromatosis type 2(NF2).Recent studies of the ABI have investigated outcomes in non-NF2 cohorts,such as patients with cochlear nerve aplasia or cochlear ossification and more recently,intractable tinnitus.New technologies that improve the ABI-neural tissue interface are being explored as means to improve performance and decrease side effects.Innovative discoveries in optogenetics and bioengineering present opportunities to continually evolve this technology into the future,enhancing spatial selectivity of neuronal activation in the cochlear nucleus and preventing side effects through reduction in activation of non-target neuronal circuitry.These advances will improve surgical planning and ultimately improve patients1 audiological capabilities.ABI research has rapidly increased in the 21st century and applications of this technology are likely to continually evolve.Herein,we aim to characterize ongoing clinical,basic science,and bioengineering advances in ABIs and discuss future directions of this technology.