Auditory Brainstem Implant Array Position Varies Widely Among Adult and Pediatric Patients and Is Associated With Perception

Abstract

Objectives The auditory brainstem implant (ABI) provides sound awareness to patients who are ineligible for cochlear implantation. Auditory performance varies widely among similar ABI cohorts. We hypothesize that differences in electrode array position contribute to this variance. Herein, we classify ABI array position based on postoperative imaging and investigate the relationship between position and perception. Design Retrospective review of pediatric and adult ABI users with postoperative computed tomography (CT). To standardize views across subjects, true-axial reformatted series of scans were created using the McRae line. Using multiplanar reconstructions, basion and electrode array tip coordinates and array angles from vertical were measured. From a lateral view, array angles (V) were classified into Types I-IV, and from posterior view, array angles (T) were classified into Types A-D. Array position was further categorized by measuring distance vertical from basion (D1) and lateral from midline (D2). Differences between array classifications were compared with audiometric thresholds, number of active electrodes, and pitch ranking. Results Pediatric (n=4, 2 with revisions) and adult (n=7) ABI subjects were included in this study. Subjects had a wide variety of ABI array angles, but most were aimed superiorly and posteriorly (Type II, n=7) from lateral view and upright or medially tilted from posterior view (Type A, n=6). Mean pediatric distances were 8 – 42% smaller than adults for D1 and D2. In subjects with perceptual data, electrical thresholds and the number of active electrodes differed among classification types. Conclusions In this first study to classify ABI electrode array orientation, array position varied widely. This variability may explain differences in auditory performance.

Auditory Brainstem Implants: Recent Progress and Future Perspectives

“…One explanation in tumor patients is that the tumor, or surgery to remove it, has damaged CN neurons that are important in coding for speech (Colletti and Shannon, 2005). Also, as mentioned earlier, positions of the ABI array vary from patient to patient (Barber et al, 2017). Finally, there are limitations of electrical stimulation, which is susceptible to channel cross talk, activation of competing pathways, and non-auditory side effects.…”

“…Intraoperative EABRs are used to adjust array position and ensure the array has not shifted during surgical closure of the dura and soft tissue (Puram et al, 2015). However, even with EABR monitoring, the resulting positions of the electrode arrays are highly variable from patient to patient (Barber et al, 2017). This was shown by three-dimensional multiplanar reconstruction of adult and pediatric subjects.…”

“…This was shown by three-dimensional multiplanar reconstruction of adult and pediatric subjects. This novel study that classified the precise position of ABI electrode array in children and adult users demonstrated that this position varied widely among ABI users, with some orientations associated with improved perception and others associated with increased side effects (Barber et al, 2017). These observations lay the foundation for future efforts to use intraoperative navigation to help improve ABI placement.…”

Microstructured thin-film electrode technology enables proof of concept of scalable, soft auditory brainstem implants

“…This situation almost certainly leads to poor electrode contact with neural structures, thus requiring higher currents to stimulate auditory neurons and consequent activation nearby non-auditory areas ( Fig. 1D-E) (11). Side effects observed by ABI users include transitory dizziness, tingling sensations, facial twitching, pain, and the electrodes producing them must be turned off so that the number of auditory channels is reduced (12).…”

Three-Dimensional Surface Reconstruction of the Human Cochlear Nucleus: Implications for Auditory Brain Stem Implant Design

“…[8][9][10][11] The reasons for modest auditory outcomes among ABI users compared with cochlear implant (CI) users are several intractable and tractable factors. Intractable factors include damage to the CN caused by a tumor and/or its removal 12,13 and nonoptimal placement of the ABI electrode array 14 due to blind placement and a small neural target. 13 A potentially tractable cause of poor performance is that current generation ABI arrays are stiff and do not conform to the curved surface of the brain stem.…”