What are brainstem implants and how are they different from cochlear implants?
Auditory Brainstem Implant (ABI) is another surgically implantable option for individuals who have severe to profound hearing loss due to damage to the inner ear as well as the auditory nerve. The ABI uses technology that is similar to that of a cochlear implant, but instead of stimulating the auditory nerve, the electrode array stimulates the hearing pathways in the brainstem, more specifically the cochlear nucleus. While cochlear implant is an inner ear surgery, ABI falls under brain surgery.
ABI was initially developed for people with a condition called Neurofibromatosis Type 2 (NF2). NF2 is a genetic condition in which multiple tumors grow along the auditory nerve. They are also called vestibular schwannomas as they derive from the Schwann cells and usually appear first in the vestibular division of the vestibulo-cochlear nerve. In such cases, prolonged removal of the tumors along with radiological management causes irreversible damage to the auditory nerve. Although initially a treatment option for NF2, the candidacy for ABI has broadened. ABI can be beneficial in – cases where the auditory nerve is damaged, absent or not fully developed, complete absence of inner ear structures (known as aplasia), cochlear otosclerosis or ossification of the inner ear which prevents the insertion of the cochlear implant electrode array.
What to expect from an ABI?
An ABI does not completely restore hearing, but it can provide significant improvements in various auditory aspects, such as improvement in sound awareness and ability to identify and differentiate between various environmental and speech sounds. Children with or without NF2 develop language and continue to improve over the years.
Similar to the pre-surgical assessment in cochlear implants, thorough audiological and medical examinations need to be completed. Audiological and electrophysiological tests will provide information about the extent of hearing loss, while medical and imaging studies are done to examine the condition of the cochlea, auditory nerve and surrounding structures.
ABI and management in individuals with multiple disabilities, severe intellectual disabilities, auditory processing deficits, and other cortical lesions can be contraindications for ABI.