Surgical Techniques of Cochlear Implantation

Abstract

In 1957, Djourno and Eyries made the observation that activation of theauditory nerve with an electrified device provides auditory stimulation in a patient, this observation was considered what paved the way for modern cochlear implantation. In 1963, Doyle J, and Doyle D’s early experimentsin scala tympani implantation preceded the first House/3M single-channel implantin 1972. Multichannel devices introduced in 1984 have replaced single-channeldevices by virtue of improved speech recognition capabilities. Nowadays three FDA approved companies (MEDEL, Advanced Bionics, Cochlear) and others like Neurelec and Neuroton are competiting in device advancement and electrode improvement. Cochlear implants are the first true bionic sense organs. The human cochleais an electromechanical transducer. Cochlear implants, like other human hair cell,receive mechanical sound energy and convert it into a series of electrical impulses. Cochlear implantation has become a widely accepted and effectivetreatment for profoundly pre- and postlingually deaf patients. Theoutcomes of cochlear implantation have improved significantly over thelast two decades. This is especially due to technical improvements such asthe advancement in electrode designs and speechprocessing strategies.Since the introduction of cochlear implantation in clinical practice, itspreoperative evaluation, implementation, and criteria for use continue toevolve. Patient selection is essential to success in cochlear implantation.The preoperative evaluation is essential to identify appropriate candidatesfor implantation. Radiographic imaging plays a major role in cochlear implantation with regard to preoperative candidacy evaluation, intraoperative monitoring, and postoperative evaluation,as well as research and experimental techniques. At a minimum, successful cochlearimplantation requires that electrical impulses be delivered to a surviving spiralganglion cell population, and that these impulses be transmitted to a functioning auditorycortex by an existent neural connection. Accordingly, imaging the auditorypathway of the implant candidate is necessary to screen for morphologic conditionsthat will preclude or complicate the implantation process. Increasing resolution ofcomputed tomography and magnetic resonance imaging technology hasprovided the clinician with more detailed information about the integrity of the auditorypathway. As technologies evolve, a clear understanding of what information can beobtained as well as the limitations of various imaging modalities is essential to propercandidacy evaluation, and selection of the ear to be implanted in complex cases. The classic surgery involves mastoidectomy, posterior tympanotomy,cochleostomy, and insertion of array of electrodes through the basal coil of thecochlea. The bodyof the implant is inserted into a seat drilled in the skull behind the ear.Altenative techniques include transcanal approach, suprameatal approach, combined approach, middle cranial fossa approach and translabyrinthotomy approach for common cavity anomalies. Endoscopic and robotic are under trials. Skin incisions have been evolved greatly and must be designed to provide coverage of the internal portion of the implant package whilepreserving the blood supply of the postauricular skin. Binaural cochlear implants can assist in the localization of sounds and have thepotential in some individuals to improve speech understanding in quiet and innoise. The problem of predicting outcomes in cochlear implantation haspreoccupied many researchers. Factors affecting the outcome with acochlear implantation are diverse and continually evolving with advancesin implant technology and ever-expanding candidacy criteria.Even within an individual cochlear implant recipient, the significanceof certain variables may change with time, with increasing patient age, newtechnology, or increased experience with the implant.Research into the factors affecting the outcome as well as theircomplex interrelationships, allows both