Microvascular Decompression for Cranial Nerve Disorders

Microvascular decompression (MVD) is a neurosurgical technique for the treatment of vasculature related compression of various cranial nerves, mainly CN V, VII, and IX/X, that cause trigeminal neuralgia, hemifacial spasm, and glossopharyngeal neuralgia (GPN), respectively. Trigeminal neuralgia causes unilateral recurrent episodes of sharp pain. Failing medical treatments require vascular decompression. Complications of the surgery include local ischemia and damage or irritation of the cranial nerve. Neurophysiological intraoperative monitoring (IOM) can be used to identify functional changes that can result in minimizing such complications. Changes of IOM signals can alert the surgeon to reverse course in order to preserve function. IOM changes can be of technical, physiological, pharmacological, positional, or surgical origin. Proper and timely management of such changes may prevent postoperative neurological deficits. Hemifacial spasm (HFS) is characterized by unilateral spasms of the facial musculature beginning with the orbicularis oculi muscle and later spreading to other muscles of facial expression. While the disease is not life-threatening, it can profoundly reduce quality of life (Heuser et al., Eur J Neurol 14:335-340, 2007; Samii et al., Neurosurgery 50:712-718, 2002; Sekula et al., Muscle Nerve 48:770-776, 2013). One proposed etiology of HFS is vascular compression of the centrally myelinated portion of the facial nerve. In this respect, MVD is the only treatment of HFS that directly addresses etiology of the disease and achieves success in nearly 90% of initial operations (Miller and Miller, Br J Neurosurg 26:438-444, 2012). The role of electrophysiology and magnetic resonance imaging (MRI) in these patients has become an indispensable tool in identifying surgical candidates. Glossopharyngeal neuralgia (GPN) is an uncommon cause of facial pain and it is characterized by intermittent, lancinating pain involving the posterior tongue and pharynx, often with radiation to deep ear structures (Resnick et al., Neurosurg 36:64-68, 1995). MVD is indicated in drug intolerant and medically refractory cases of GPN and has improved success rates in the last few decades. IOM using brainstem auditory-evoked potentials and cranial nerve VII, IX, X electromyography (EMG) during MVD reduces postoperative incidence of hearing loss, facial paresis, and dysphonia/dysphagia (Habeych et al., J Clin Neurophysiol 31:337-343, 2014).