Figure Legends
Fig. 1 Procedure for intraoperative facial nerve monitoring
In the measurement before tumor resection, we stimulated the trunk at the time of its discovery and measured the electrical potential evoked in response to the stimulation. In the measurement after tumor resection, we stimulated the exposed trunk (△) and each of the four branches (▽) in the operative field and measured the electrical potential evoked in response to stimulation (Fig. 1).
Fig. 2A Comparison of evoked responses to facial nerve trunk stimulation before and after tumor resection
In group A, the median electrical potential in response to trunk stimulation before resection was 460 µV for TB, 219 µV for ZB, 471 µV for BB, and 989 µV for MB. The median electrical potential in response to trunk stimulation after resection was 691 µV for TB, 350 µV for ZB, 671 µV for BB, and 1271 µV for MB. Compared to the electrical potential in response to trunk stimulation before resection, those after resection were significantly higher for all branches (p = 0.02, 0.005, 0.014, and 0.001 for TB, ZB, BB and mandibular, respectively). In group B, the median electrical potential in response to trunk stimulation before resection was 475 µV for TB, 373 µV for ZB, 597 µV for BB, and 674 µV for MB. The median electrical potential in response to trunk stimulation after resection was 442 µV for TB, 352 µV for ZB, 479 µV for BB, and 979 µV for MB. No significant differences were observed in electrical potential before and after resection for all branches. In group C, the median electrical potential before resection was 596 µV for TB, 308 µV for ZB, 1081 µV for BB, and 744 µV for MB. The median electrical potential after resection was 23 µV for TB, 53 µV for ZB, 578 µV for BB, and 97 µV for MB. Compared to the values before resection, electrical potentials after resection were significantly lower for MB (p = 0.01), but no significant differences were observed for TB, ZB, or BB.
Fig. 2B Ratio of evoked responses to facial nerve trunk stimulation after/before resection (ARR1)
In group A, the median ARR1 was 1.16 for TB, 1.43 for ZB, 1.24 for BB, and 1.28 for MB. In group B, the median ARR1 was 1.01 for TB, 1.29 for ZB, 1.11 for BB, and 1.53 for MB. In group C, the median ARR1 was 0.04 for TB, 0.23 for ZB, 0.39 for BB, and 0.24 for MB.
Fig. 3A Comparison of evoked responses to trunk and peripheral stimulation after resection
In group A, the median electrical potential in response to trunk stimulation after tumor resection was 691 µV for TB, 350 µV for ZB, 671 µV for BB, and 1271 µV for MB. The median electrical potential in response to peripheral stimulation was 705 µV for TB, 363 µV for ZB, 661 µV for BB, and 1428 µV for MB. In group A, no significant differences were observed in electrical potential between trunk stimulation and peripheral stimulation for all branches.
In group B, the median electrical potential in response to trunk stimulation after tumor resection was 442 µV for TB, 352 µV for ZB, 479 µV for BB, and 979 µV for MB. The median electrical potential in response to peripheral stimulation was 599 µV for TB, 410 µV for ZB, 559 µV for BB, and 958 µV for MB. In group B, no significant differences were observed in electrical potential between trunk stimulation and peripheral stimulation for all branches.
In group C, the median electrical potential in response to trunk stimulation after tumor resection was 23 µV for TB, 53 µV for ZB, 578 µV for BB, and 97 µV for MB. The median electrical potential in response to peripheral stimulation was 389 µV for TB, 361 µV for ZB, 783 µV for BB, and 949 µv for MB.
Fig. 3B Ratio of evoked responses to trunk/peripheral stimulation after resection (ARR2)
In group A, the median ARR2 was 0.97 for TB, 0.95 for ZB, 1.02 for BB, and 0.98 for MB. In group B, the median ARR2 was 0.94 for TB, 0.95 for ZB, 0.87 for BB, and 0.86 for MB. In group C, the median ARR2 was 0.08 for TB, 0.24 for ZB, 0.49 for BB, and 0.10 for MB.
Fig. 4A Recovery time of postoperative facial nerve palsy and ARR1
Fig. 4B Recovery time of postoperative facial nerve palsy and ARR2
Comparisons of recovery time of paralysis and ARR1 and ARR2 revealed that y = −0.1368x + 0.7014, R ² = 0.1544, andy = −0.0566x + 0.394, R ² = 0.1461, respectively, showing no significant correlations for either ratio.
Table 1 Patient clinical characteristics
Table 2 Presence or absence of paralysis, and site of paralysis