Abstract: ObjectiveTo clarify the hearing recovery and residual hearing protection of patients with cochlear malformation and those with normal cochlea but requiring cochlear implantation after minimally invasive cochlear implantation.  
MethodsThe patients were grouped and included by pre-operative temporal bone CT, inner ear hydrography and audiology examination. The data of 38 patients undergoing minimally invasive cochlear implantation were analyzed, including 16 cases of cochlear malformation and 22 cases of normal cochlea. We compared the categories of auditory performance(CAP) and speech intelligibility rating(SIR) scores and residual hearing retention between two groups after cochlear implantation. The criteria for hearing retention were as follows: the mean thresholds of 125, 250 and 500 Hz were ＜10 dBHL higher than those before implantation. 
ResultsThe electrode of artificial cochlea was successfully implanted, and the electrode impedance was detected normally during the operation. After startup, the cochlear implant worked normally and well in both groups. In 16 cochlear implantation patients with cochlear malformation, the low-frequency residual hearing retention rate was 82%, complete hearing retention rate was 33%, and partial hearing retention rate was 49% at 1 year after cochlear implantation. In 22 patients with normal cochlea, low-frequency residual hearing retention rate was 100%, complete hearing retention rate was 82%, and partial hearing retention rate was 18%. There was no change in hearing retention rate between 6-months and 1-year follow-up compared with the data at 1 month. The postoperative CAP and SIR scores were 5.7±1.2 and 3.5±1.0 in patients with cochlear malformation respectively, and 6.4±1.1 and 3.7±0.9 in patients with normal cochlea respectively, and the difference was not statistically significant(P＞0.05). 
ConclusionThere is no significant difference in speech recovery and response ability to voice between patients with cochlear malformation and those with normal cochlea. However, the retention rate of low-frequency residual hearing in cochlear malformation group decreased to a certain extent due to the influence of the cochlear structure. In this study, there is no significant difference in postoperative efficacy and retention of residual hearing between patients with cochlear malformation and those with normal cochlea after minimally invasive cochlear implantation, which provides guidance for clinical diagnosis and treatment of such patients.

Key words: cochlear implantation, minimally invasive surgical procedures, hearing tests