Chapter 10 - Intraoperative neurophysiological monitoring during surgical and endovascular treatment of cerebral arteriovenous malformations

Intraoperative neurophysiological monitoring (IONM) has emerged over the past two decades as a valuable technique to promptly identify an impending injury to the nervous system, in time for corrective measures to be taken and, therefore, avoid or minimize post-operative neurological deficits. In cerebrovascular surgery, IONM provides a continuous assessment of the functional integrity of various neural pathways, including motor, sensory, auditory and visual, by monitoring evoked potentials.The treatment of cerebral AVMs can be either surgical or endovascular. Both these treatments expose to the risk of neurological injury and IONM has been increasingly used to prevent, rather than merely predict, brain ischemia during the dissection of the AVM and temporary arterial occlusion. Depending on the location of the AVM and the degree of involvement of cortical and subcortical vascular territories, IONM techniques may include motor evoked potentials, somatosensory evoked potentials, visual evoked potentials, and brainstem auditory evoked potentials. Furthermore, mapping techniques in asleep patients may assist the surgeon to localize the motor cortex and subcortical motor pathways whenever these cannot be identified anatomically, while awake surgery allows to extend neurophysiological mapping to speech and other cognitive areas.The use of IONM has been applied also during endovascular embolization of AVMs in general anesthesia, when associated with provocative tests. A superselective injection of short-acting barbiturates and/or local anesthetics is done before the embolization of the feeder in order to mimic the effects of the embolization. Based on the results of the provocative test, embolization can either proceed or be abandoned.This chapter will provide a review of different neurophysiologic monitoring and cortical/subcortical mapping techniques as well as a critical review of the state-of-the art in the use of these techniques in intracranial vascular neurosurgery.