O3-6-21. Time-dependent changes in intraoperative monitoring findings during microvascular decompression for hemifacial spasm

Publication date: September 2017
Source:Clinical Neurophysiology, Volume 128, Issue 9
Author(s): Masafumi Fukuda, Tetsuro Takao, Tetsuya Hiraishi, Yukihiko Fujii
We analyzed time-dependent changes in the intraoperative monitoring of abnormal muscle responses (AMRs) and facial motor evoked potentials (FMEPs) elicited by transcranial electrical stimulation during microvascular decompression (MVD) in 26 patients with hemifacial spasm. In the orbicularis oculi muscle, the AMRs disappeared in 11 patients before MVD, in six after MVD, and in three during dural closure. The AMRs persisted in six patients. FMEP amplitudes decreased to less than 50% in two patients before MVD, in four after MVD, and in six during dural closure. FMEP amplitudes did not decrease in 14 patients (p<0.005). In the mentalis muscle, the AMRs disappeared in eight patients before MVD, in five after MVD, and in four during dural closure. AMRs persisted in nine patients. FMEPs decreased in two patients before MVD and in two during dural closure, although the remaining 22 patients did not have decreased FMEPs (p<0.001). The differences between the time-dependent changes in AMR and FMEP are likely attributable to the different origins of the two responses. AMRs mainly occur around the compression site of the facial nerve and FMEPs mainly originate in the facial nucleus in the brainstem.



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