O179 Intraoperative blink reflex in microvascular decompression for hemifacial spasm. A case report and proposal of a new method to monitor the efficiency of decompression

Abstract

Objectives To report the utility of blink reflex (BR) monitoring in microvascular decompression (MVD) for hemifacial spasm (HFS). Methods We report a case of a 64-year-old patient with HFS who underwent MVD with continuous intraoperative neurophysiological monitoring (IONM) of motor, sensory and auditory evoked potentials. The abnormal muscle response (AMR) was monitored with stimulation of zygomatic and buccal branch (zAMR, bAMR) and recording from representative muscles innervated by all facial nerve (FN) branches. Additionally the BR was utilized to monitor the FN functionality. Results Before incision, a similar to AMR-spread phenomenon (BR-spread) was observed when the supraorbital branch of trigeminal nerve was stimulated to elicit BR. Both AMRs (zAMR, bAMR) disappeared during MVD, indicating sufficient FN decompression. Concurrently a similar disappearance from BR-spread and FN-MEPs was observed. During closing all responses (AMRs, BR-spread, FN-MEPs) reappeared. The HFS was clinically present right after the surgery but the patient was relieved from the symptoms a few hours later. Discussion The BR-spread and FN-MEPs showed an AMR-like pattern during MVD. The reappearance of AMRs predicted the immediate but not the long term outcome of HFS-MVD. The BR and FN-MEPs are not reliable to monitor the FN integrity in HFS-MVD due to decompression depended responses. We propose further research to investigate the benefits of BR in HFS-MVD. Conclusions The BR-spread is potentially an alternative IONM tool to determine whether the MVD of HFS is sufficient. Significance A new IONM method is proposed to monitor HFS-MVD.