Incidence of Complete Insertion in Cochlear Implant Recipients of Long Lateral Wall Arrays

Abstract

Objective High rates of partial insertion have been reported for cochlear implant (CI) recipients of long lateral wall electrode arrays, presumably caused by resistance encountered during insertion due to cochlear morphology. With recent advances in long-electrode array design, we sought to investigate (1) the incidence of complete insertions among patients implanted with 31.5-mm flexible arrays and (2) whether complete insertion is limited by cochlear duct length (CDL). Study Design Retrospective review. Setting Tertiary referral center. Methods Fifty-one adult CI recipients implanted with 31.5-mm flexible lateral wall arrays underwent postoperative computed tomography to determine the rate of complete insertion, defined as all contacts being intracochlear. CDL and angular insertion depth (AID) were compared between complete and partial insertion cohorts. Results Most cases had a complete insertion (96.1%, n = 49). Among the complete insertion cohort, the median CDL was 33.6 mm (range, 30.3-37.9 mm), and median AID was 641° (range, 533-751°). Two cases of partial insertion had relatively short CDL (31.8 mm and 32.3 mm) and shallow AID (542° and 575°). Relatively shallow AID for the 2 cases of partial insertion fails to support the idea that CDL alone prevents a complete insertion. Conclusion Complete insertion of a 31.5-mm flexible array is feasible in most cases and does not appear to be limited by the range of CDL observed in this cohort. Future studies are needed to estimate other variations in cochlear morphology that could predict resistance and failure to achieve complete insertion with long arrays.

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“…Mixed reports are available on this topic, with Nordfalk et al ( 49 ) reporting an 18% failure rate to fully insert the FLEX28 and FLEX SOFT electrodes. Meanwhile, Canfarotta et al ( 50 ) have reported a 0% failure rate to insert the FLEX SOFT electrode fully inside the cochlea. Ishiyama et al ( 47 ) have reported that partial insertion of the electrode is highly associated in patients preoperatively diagnosed with difficult inner ear anatomy or occluded pathology, with an incidence rate of 1–2%.…”

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“…Therefore, the varying levels of modiolar proximity with slim modiolar electrodes can potentially be mitigated in cases with shorter CDL measurements. Future studies have been suggested to estimate other variations in cochlear morphology that could predict resistance and failure to achieve complete insertion with long arrays [56].…”