Auditory brainstem implants for neurofibromatosis type 2

Neurofibromatosis type 2 (NF2) produces benign Schwann cell tumors on many cranial nerves, in particular on the vestibular portions of the VIIIn bilaterally. Removal of these vestibular schwannomas usually severs the auditory portion of the VIIIn, thus deafening the patients. The auditory brainstem implant (ABI) was designed to provide prosthetic electric stimulation of the cochlear nucleus in the brainstem to restore some hearing sensations to patients deafened by bilateral removal of vestibular schwannomas. This study will review the new developments and improving outcomes of the ABI.

From its initial application in 1979 until about 2005, the ABI provided modest but useful auditory sensations to NF2 patients. However, application of the ABI in non-NF2 populations and in children with congenital malformations demonstrated better results, showing that the ABI could provide high levels of speech recognition. Recent results show excellent speech recognition in NF2 patients as well. This study will discuss the potential causes of the variability in ABI outcomes.

ABIs activate neurons in the cochlear nucleus to recreate hearing sensations in people who have become deaf as a result of the loss of the auditory nerve. Most NF2 patients show functional hearing benefit from the ABI, with awareness and recognition of environmental sounds and enhancement of lipreading. It is now clear that ABIs can produce excellent speech recognition in some patients with NF2, allowing even conversational telephone use. Although the factors leading to this improved performance are not completely clear, these new results show that excellent hearing is possible for NF2 patients with the ABI.