Cochlear implantation in partial deafness: a case series with preoperatively substantial residual hearing at high frequencies

To expand the current cochlear implant (CI) criteria to include patients with substantial preoperative residual hearing across low, medium, and high frequencies and to evaluate hearing preservation and performance after implantation. Twelve patients aged 37-77 with preoperative hearing loss of 80 dB HL or better at 125-1500 Hz and 70 dB HL or better at 2000-8000 Hz underwent unilateral cochlear implantation. Pure tone audiometry (125-8000 Hz) was performed preoperatively and at 1, 12, and 24 months postoperatively. Total hearing preservation (HP) was assessed using the HEARRING group formula. HP was also separately calculated for low-frequency (0.125-0.5 kHz), medium-frequency (0.75-1.5 kHz), and high-frequency (2-8 kHz) ranges. The monosyllabic word test was used to assess word recognition score (WRS) in free field preoperatively and at 12 and 24 months postoperatively. One month after surgery, 84% of patients had complete or partial HP. High-frequency preservation yielded the best results, with 50% of patients achieving complete HP, while only 25% had complete HP in low and medium frequencies. In the long-term follow-up, gradual hearing deterioration was observed. At 24 months, the mean WRS benefit increased by 65% points in quiet and 51% points in noise, compared to preoperative hearing aid performance. The study confirms that high-frequency hearing preservation is possible after CI surgery, and electrode implantation does not necessarily damage this region of the cochlea. Early implantation should be considered for patients with residual high-frequency hearing, especially when hearing aids are ineffective.