Long-term Hearing Preservation Outcomes After Cochlear Implantation for Electric-Acoustic Stimulation.

Abstract

This study reviewed outcomes of hearing preservation (HP) surgery in a cochlear implant patient population, with clinical follow-up results up to 11 years after implantation. Retrospective case review. Tertiary referral university hospital. Ninety six patients (103 ears) with partial deafness who underwent HP surgery at the University Hospital Frankfurt since 1999 were included. Electrode carriers were Cochlear Slim Straight, MED-EL Standard, Medium, Flex, and Flex. Cochlear implantation using the HP surgery technique with either the cochleostomy or round window approach. Pure-tone averages for low frequencies (125 Hz, 250 Hz, 500 Hz, PTAlow) and speech perception scores of the Freiburg monosyllable and number tests in quiet. PTAlow shifts were used to evaluate HP as complete for ≤10 dB, partial between 10 and 30 dB, and minimal for ≥30 dB. Time intervals were: preoperative, postoperative, after 12 months, and long-term (>24 months, mean 51.4 months, range 2-11 years). Impacts of electrode design and surgical approach were analyzed. Postoperatively (n = 103), HP was complete in 32 (31.1%), partial in 49 (47.6%), minimal in 14 (13.6%), and loss of hearing occurred in 8 cases (7.8%). After 12 months (n = 81), HP was complete in 22 (27.2%), partial in 33 (40.7%), minimal in 11 (13.6%), and loss of hearing occurred in 7 additional cases. For long-term outcomes (n = 62) HP was complete in 7 (11.3%), partial in 24 (38.7%), minimal in 9 (14.5%), and loss of hearing occurred in 7 additional cases (total 22/103, 21.4%). Cases with residual hearing who could utilize acoustic amplification (i.e., PTAlow < 80 dB HL) were 82/95 (85.3%) postoperatively, 58/66 (87.9%) after 12 months, and 38/40 (95.0%) for long-term outcomes. Long-term HP is feasible in a subset of patients. Patients with sufficient long-term residual hearing had the prerequisite to benefit from additional acoustic stimulation. No correlation of total hearing loss with etiology, electrode design, or surgical approach was evident. Apart from individual effects of structural damage or inflammation, genetic factors are suggested to influence HP. Cases with total hearing loss still demonstrated successful speech perception in long-term monosyllable recognition scores.