Auditory Brainstem Implantation: An Overview

Abstract

An auditory brainstem implant (ABI) is a surgically implanted central neural auditory prosthesis for the treatment of profound sensorineural hearing loss in children and adults who are not cochlear implant candidates due to a lack of anatomically intact cochlear nerves or implantable cochleae. The device consists of a multielectrode surface array which is placed within the lateral recess of the fourth ventricle along the brainstem and directly stimulates the cochlear nucleus, thereby bypassing the peripheral auditory system. In the United States, candidacy criteria for ABI include deaf patients with neurofibromatosis type 2 (NF2) who are 12 years or older undergoing first- or second-side vestibular schwannoma resection. In recent years, several non-NF2 indications for ABI have been explored, including bilateral cochlear nerve avulsion from trauma, complete ossification of the cochlea due to meningitis, or a severe cochlear malformation not amenable to cochlear implantation. In addition, growing experience with ABI in infants and children has been documented with encouraging outcomes. While cochlear implantation generally remains the first-line option for hearing rehabilitation in NF2 patients with stable tumors or post hearing preservation surgery where hearing is lost but a cochlear nerve remains accessible for stimulation, an ABI is the next alternative in cases where the cochlear nerve is absent and/or if the cochlea cannot be implanted. Herein, we review ABI device design, clinical evaluation, indications, operative technique, and outcomes as it relates to lateral skull base pathology.

Keywords: auditory brainstem implant; auditory nerve; auditory prosthesis; electric stimulation; hearing loss; neurofibromatosis type 2.

Fig. 1

Cochlear corporation auditory brainstem implant device. ( A ) External component including microphone, sound processor, and magnet. ( B ) Internal component including the receiver–stimulator and electrode array. ( C ) Close-up view of the electrode contact paddle which interfaces with the brainstem. Image courtesy of Cochlear Americas, © 2019.

Fig. 2

( A ) Postauricular incision for placing an auditory brainstem implant through a translabyrinthine approach. The postauricular incision is curved posteriorly at the superior aspect. An anteriorly based periosteal (Palva) flap provides exposure to the mastoid cortex. ( B ) A bony well contoured to the shape of the device is drilled posteriorly and superiorly to the lateral sinus. This may be taken down to the dura if necessary. A trough is also drilled for placement of the electrode array. Inferior and superior tie down holes are drilled. ( C ) After exposure and identification of the lateral recess of the fourth ventricle, the device is then placed into the bony well and sutured tightly into place. The lead wires are placed in the trough, and free ground wire is placed medial to the temporalis muscle.

Fig. 3

Exposure of the brainstem via the translabyrinthine approach. Note the foramen of Luschka—where auditory brainstem implant is inserted—is identified at the lateral border of the pontomedullary sulcus. The junction of the glossopharyngeal and vagus nerves with the brainstem is just ventral to the foramen and the junction of the facial and vestibulocochlear nerves with the brainstem is anteroinferior to it. The junction of the accessory and hypoglossal nerves with the brainstem is anteroinferior to the foramen as well. The cerebellar flocculus is directly superior to the foramen. Also note the severely hypoplastic eighth cranial nerve in this patient.