Intraoperative neurophysiologic monitoring in microvascular decompression for hemifacial spasm

Abstract

The majority of primary hemifacial spasm (HFS) patients are related to a vascular compression of the facial nerve root at its entry zone. Non-surgical treatment methods of HFS are anti-epileptic drugs and local botulinum toxin injection, but their outcomes are often not satisfactory in relieving symptoms. Microvascular decompression (MVD) is a surgical treatment method of HFS. Nowadays, intraoperative neurophysiologic monitoring is being used during MVD for two main objectives. The first and main objective is to prevent and reduce the risk of hearing impairment. Brainstem auditory evoked potentials (BAEPs) is monitored during surgery, to monitor the cranial nerve VIII and determine hearing sense preservation. Researches on BAEPs has enabled near real-time and safe monitoring, as warning indicators and advanced techniques to get results faster has been discovered. The second objective is to optimize the effectiveness of surgery. Despite the surgery, some patients had persisted symptoms or recurrence of spasm for some reasons, in few cases. The lateral spread response (LSR) monitoring is performed to guide the operator during surgery. LSR shows modest sensitivity. Nevertheless, it shows high specificity in predicting the symptom-free status after MVD. Low sensitivity precluded the use of the LSR monitoring as an exclusive solitary diagnostic modality. The disappearance of LSR during MVD appears to be not effectively in predicting long-term outcomes, but it demonstrated limited prognostic values in predicting favorable short-term outcomes. These results implements that, intraoperative monitoring of LSR during MVD can provide considerable value for investigating the adequacy of MVD before cranial bone closure.