Electrodiagnostics

Clinical neurophysiology provides valuable information in neurosurgery, serving as: a diagnostic tool that can quantify type and severity of damage to the central and peripheral nervous system, a means of monitoring the safety of structures within and around the surgical site, and a method to map structures. As such it aides in identifying structures (e.g. finding sacral nerve roots within a spinal lipoma or nuclei within the thalamus), assessing functional integrity (e.g. motor pathways from cortex to any relevant accessible muscle), and monitoring their function while surgery occurs near to structures (e.g. VII while retraction during trigeminal microvascular decompression, and in scoliosis surgery) and provide guidance to technical operative steps (e.g. for selective dorsal rhizotomy). Intraoperative monitoring is not new, though the advances in equipment and technique of recent years have seen an explosion in the useful ways that neurophysiology can aid the neurosurgeon and protect the patient. The development of techniques to localize epileptic foci and map eloquent cerebral cortex in the 1950s produced major scientific advances as well as revolutionizing epilepsy surgery. Since the 1960s Tasker in Toronto, and Gillingham in Edinburgh, were recording from microelectrodes in the human thalamus to guide movement disorder surgery. Pioneers such as Møller have extended the applications of neurophysiological monitoring in skull base surgery. This chapter describes neurophysiological mapping and monitoring, and the different tools that are useful in different situations.