Assessing the Significance of Abnormal Inserted Perimodiolar Slim Electrodes: Perception and Management Strategies

Slim perimodiolar electrodes (PSEs) are designed for close modiolar proximity, but deviations from ideal placement may affect speech perception. This study investigates the prevalence, radiologic characteristics, and audiologic outcomes of abnormally positioned PSE arrays and proposes intraoperative management strategies.

We retrospectively reviewed 239 adults implanted with Cochlear® PSE arrays (2015-2023). Postoperative CT scan identified arrays positioned laterally to mid-scala without tip fold-over. Objective metrics such as angular insertion depth (AID), intracochlear position index (ICPI), wrapping factor (WF), and maximum insertion angle were compared to a control group with normal positioning (n = 52). Speech perception outcomes at 3 and 12 months were assessed using monosyllabic word tests and compared to a reference cohort (n = 1,414).

Abnormal positioning occurred in 3% (n = 7). All arrays remained within scala tympani but had shallower insertions (AID 296° vs. 392°), greater lateralization (ICPI 0.52 vs. 0.33), and higher WF (0.62 vs. 0.36). Compared to controls, speech scores were lower at 3 months (33% vs. 65%) and 12 months (45% vs. 74%). Intraoperative X-rays did not detect these deviations.

Abnormal PSE placement is uncommon but associated with poorer speech outcomes. Surgeons should assess electrode shape intraoperatively and consider reinsertion if the classic curl is absent. Postoperative CT remains critical for quality assurance. Tailored intraoperative strategies are needed to prevent lateralization and optimize outcomes.