Imaging of cochlear and auditory brain stem implantation.

The cochlear implant is an electronic auditory prosthesis with a component that is surgically inserted in the ear and coupled with a detachable component that is worn externally like a hearing aid. It is designed to stimulate the spiral ganglion cells in patients whose hair cells have been lost (1). An auditory brain stem implant is a similar device implanted in or on the brain stem, to stimulate the cochlear nuclei in patients whose cochlear nerves have been lost (2). Both devices give the sensation of sound to otherwise deaf patients. Imaging plays key roles in the preoperative and postoperative evaluation of both devices. Development of the cochlear implant began in the 1960s (3). After slow initial acceptance, cochlear implantation is now firmly established as an effective option in the habilitation and rehabilitation of persons with profound to severe hearing impairment (4). Recent advances in speech processing strategy and continued progress in technology have markedly improved auditory results and patient acceptance. To date, nearly 23,000 implantations have been performed worldwide, approximately 14,000 in adults and 9000 in children, including an estimated 4000 in 1997, of which about half were done in the United States. Initially confined to tertiary referal centers, implantations are now often performed in community practices. Radiologists are thus increasingly likely to be called upon to provide imaging examinations of candidates for cochlear implantation. Auditory brain stem implantation, first attempted in 1979, is now undergoing multicenter clinical trials in the United States under Food and Drug Administration monitoring. Multicenter trials are also being conducted in Europe. Currently, the subjects are limited to patients with bilateral acoustic tumors. To date, somewhat over 100 patients have received implants. This review will highlight the fundamental principles, technology, and anatomy of cochlear implantation as well as the important aspects of imaging in cochlear implantation. The role of imaging in auditory brain stem implantation will be briefly discussed.