[Effects of cochlear implantation on vestibular function in patients with large vestibular aqueduct syndrome]

Objective:This study aimed to compare the effects of cochlear implantation（CI） on vestibular function in patients with large vestibular aqueduct syndrome（LVAS） and in patients with extremely severe deafness with normal inner ear structure. Methods:A total of 28 LVAS patients and 28 patients with normal inner ear structure who suffered from extremely severe deafness were selected. The parameters of caloric tests, bone conduction evoked cervical vestibular-evoked myogenic potentials（cVEMP）, bone conduction evoked ocular vestibular-evoked myogenic potentials（oVEMP） and video head impulse tests（v-HIT） were compared between the two groups before and after CI. The data were analyzed using SPSS 26.0 software. Results:There was no significant difference in the results of the preoperative caloric test, v-HIT, and oVEMP（P1, N1） between the LVAS group and the control group（P>0.05）. Compared to the control group, the LVAS group exhibited a shorter cVEMP P1[（13.41±0.71）ms vs （16.28±0.89）ms, P<0.000 1], shorter N1[（19.83±0.54）ms vs （28.18±1.56）ms, P<0.000 1], higher amplitude[（123.60±83.80）μV vs （73.92±79.85）μV, P=0.049 4] and higher oVEMP amplitude[（16.60±13.87）μV vs （9.96±10.47）μV, P=0.028 5] before CI. The abnormal rate of caloric test increased in both groups after CI（25.00% vs 57.14%, P=0.028 8, 32.14% vs 82.14%, P=0.000 3, respectively）. There was no significant difference in the v-HIT parameters in both groups before and after the operation. As for the LVAS group, there was no statistically significant difference in cVEMP and oVEMP induction rates before and after operation. In the control group, there was a decrease in cVEMP induction rate（96.42% vs 64.28%, P=0.005 2） and oVEMP induction rate（96.42% vs 57.14%, P=0.000 9） after CI. LVAS group showed a shorter cVEMP P1[（13.41±0.71）ms vs （10.30±0.60）ms, P<0.000 1]; shorter cVEMP N1[（19.86±0.53）ms vs （18.97±1.33）ms, P=0.004 7]; decreased amplitude[（124.50±84.86）μV vs （64.35±61.57）μV, P=0.001 0] and shorter oVEMP amplitude[（15.92±13.03）μV vs （9.16±9.20）μV, P=0.009 9] after CI. The oVEMP N1 in the control group was longer than that before operation[（11.73 ± 0.91）ms vs （13.35 ± 2.60）ms, P=0.019 6], whereas there was no significant difference in other VEMP parameters after CI. Conclusion:Before CI, there was no significant difference in the results of the caloric test and v-HIT between the LVAS group and the control group, but the LVAS group exhibited increased sensitivity to acoustic stimulation-induced myogenic potentials. After CI, the function of the semicircular canal was impaired in both groups in the low-frequency area, and remained largely unaffected in the high-frequency area. Additionally, the function of the otolith in the LVAS group was less affected than that in the control group after CI, which may be related to the fact that the enlarged vestibular aqueduct of the LVAS patients acted as the third window of the inner ear.