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What are brainstem implants and how are they different from cochlear implants?
This option can be considered for individuals who have severe to profound hearing loss due to damage to the inner ear as well as the auditory nerve. While the technology used for ABI is similar to that of cochlear implant, the main difference is that in case of ABI, the electrode array stimulates the hearing pathways in the brainstem, more specifically the cochlear nucleus instead of stimulating the auditory nerve. Also, ABI falls under brain surgery, while cochlear implant is an inner ear surgery.
Candidacy
ABI was initially developed for people with a genetic condition called Neurofibromatosis Type 2 (NF2), in which multiple tumors, also called vestibular schwannomas grow along the auditory nerve. The prolonged removal of the tumors along with radiological management causes irreversible damage to the auditory nerve. The candidacy for ABI has now broadened beyond NF2 and can be used for cases where the auditory nerve is damaged, absent or not fully developed, there is complete absence of inner ear structures (known as aplasia), cochlear otosclerosis or ossification of the inner ear occurs, preventing the insertion of the cochlear implant electrode array.
What to expect from an ABI?
Although ABI does not completely restore hearing, it can significantly improve various auditory aspects including 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.
Pre-surgical evaluation
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.
Contraindications
ABI and management in individuals with multiple disabilities, severe intellectual disabilities, auditory processing deficits, and other cortical lesions can be contraindications for ABI.
