TRIO Best Practice articles are brief, structured reviews designed to provide the busy clinician with a handy outline and reference for day-to-day clinical decision making. The ENTtoday summaries below include the Background and Best Practice sections of the original article. To view the complete Laryngoscope articles free of charge, visit Laryngoscope.
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September 2019Background
Cochlear implants (CI) restore hearing by stimulating spiral ganglion neurons via multichannel electrodes inserted into the cochlea. Many types of electrode arrays have been developed and fall into three categories based on intracochlear position: perimodiolar (PM), lateral wall (LW), and midscala (MS) electrodes. PM electrodes are designed to hug the medial wall to reduce the distance between the electrodes and the spiral ganglion neurons and typically do not coil around the apex. LW electrodes are designed to remain laterally in the scala tympani, with longer array options capable of reaching the apex. MS electrodes are a new type of electrode designed to remain in the middle of the scala tympani, thereby avoiding contact with either the medial or lateral walls to decrease trauma and fibrosis. It has been hypothesized that PM electrodes may have improved hearing performance and longer battery life given their closer proximity to the spiral ganglion. With less electrical current needed to stimulate the spiral ganglion neurons at each electrode position, PM electrodes theoretically should offer improved speech discrimination. When considering electrode type, however, the surgeon must also consider other factors that vary based on electrode type, such as insertional trauma, development of intracochlear fibrosis, transcalar positioning, battery life, and extrusion rates. This article summarizes the major advantages and disadvantages of these electrodes to help guide this decision.
Best Practice
Clinical presentation must drive electrode choice. LW electrodes have improved hearing preservation compared to PM, likely due to decreased entry into scala vestibuli; therefore, LW electrodes should be favored in hearing preservation cases. For adults with profound SNHL, data are still lacking to support one electrode type over another. For those looking for the lowest threshold levels, PM electrodes may be the best option, although more studies are needed to determine whether this translates into improved speech discrimination. In the pediatric population, the decision can be more complicated. Although PM electrodes can result in lower thresholds and improved word recognition, revision surgery is more likely over the lifetime of these patients, making LW electrodes an attractive choice because more force is required to remove PM than LW electrodes. For advanced otosclerosis causing SNHL, PM electrodes should be chosen to minimize risk of facial nerve stimulation postoperatively. Inner ear malformations require special attention to the type of deformity. More data are needed to see how MS electrodes compare in these outcomes. No single type of electrode array is suitable for all scenarios; however, as the criteria for cochlear implantation continues to expand and include more adults with residual hearing, the current trend to minimize insertion trauma and preserve hearing has led to increased popularity of the LW electrode. Other factors such as electrode length, stiffness, and insertion speed should be investigated further and may also prove to be important determinants to overall outcomes in addition to the designed intracochlear position of the electrode array (Laryngoscope. 2019;129:1962–1963).