Systematic Review of Cochleostomy versus Round window Insertion of Electrodes in Cochlear Implant patients

Abstract

A cochlear implant is an electronic device designed to improve or enable hearing for people with hearing impairment disabilities. Unlike typical hearing aids, which are worn externally, cochlear implants are constituted of an external device and an internal implant. Also, hearing aids simply amplify sounds to enhance sound perception, whereas cochlear implants bypass the outer and middle ear to electrically stimulate acoustic nerves within the auditory system. The expanding indication criteria for cochlear implantation because of the improved postoperative hearing results lead to a worldwide increase in patients with residual hearing who are fitted with a cochlear implant. In the last decade, several research groups have explored various methods of implanting different electrode arrays in the cochlea to preserve the residual hearing and combine acoustic and electric speech processing. The different electrode arrays (hybrid), specifically developed for this purpose, vary in several aspects, shorter length, more flexible, and thinner. Although much attention has been given to minimize trauma by optimizing the electrode design, a minimal traumatic opening of the cochlea and insertion of the electrode is essential for hearing preservation. Over the last years, 2 major atraumatic surgical techniques have been promoted, the round window approach and the ‘‘soft surgery’’ cochleostomy technique. The latter has been proposed by Lenhardt in 1993, who performed a minimal cochleostomy anterior and inferior to the round window and used hyaluronic acid (Healon) to lubricate the electrode and seal the cochleostomy during insertion. Nowadays, this technique has been slightly modified by different surgeons, but the general ‘‘soft surgery’’ principles of drilling a minimal cochleostomy, avoiding suction of the perilymph, and sealing the cochleostomy hole remained identical. Although the round window insertion was the initial technique of cochlear implant electrode placement, the technique became less used because of concerns that the insertion angle in conjunction with the former rigid, straight electrodes, might lead to trauma of the osseous spiral lamina. With the development of more flexible and perimodiolar electrodes new interest for this technique has emerged. Because the round window technique involves only a minimal incision of the round window membrane, advocates of this technique have pointed out the shortcomings that are associated with drilling a cochleostomy, such as acoustic trauma, the presence of bone dust and the higher chance of electrode insertion into the scala vestibuli. The round window approach has the following advantages: It is the surgical approach that most surgeons will be comfortable with because it uses a standard mastoidectomy and posterior tympanotomy. Also, The extent of drilling and therefore the amount of trauma associated with cochleostomy placement is minimal.The approach uses visible and reliable landmarks that improve the probability that the electrode will enter the middle of scala tympani below the basilar membrane and spiral ligament. and It permits an angle of insertion that minimizes trauma. Morever, because the round window membrane is the principal landmark used to locate the cochleostomy, the insertion technique will permit correct electrode placement even in the face of a fairly wide range of anatomic variations of the cochlea. In view of this ongoing debate about the optimal procedure for opening the cochlea during cochlear implantation to preserve residual hearing our main research question was: Is there a difference in postoperative residual hearing comparing round window and cochleostomy insertion techniques in patients with low-frequency residual hearing fitted with a cochlear implant? The results of this review show that there seems to be no clear benefit of a certain surgical approach regarding cochlear implantation, that is, the round window versus cochleostomy approach regarding hearing preservation and insertion depth. To provide solid evidence, a double-blind randomized trial is needed, which compares the clinical outcomes, notably the degree of hearing preservation, of both surgical approaches.