SY5.2. Intraoperative monitoring and mapping during brain tumor surgery

Abstract

The aggressive removal of a glioma is expected to improve long-term patient survival and quality of life. However, removal of a supratentorial glioma, particularly in proximity to the eloquent cortex, poses a great risk of creating new functional deficits. Thus, it is critical to consider functional and oncological outcomes simultaneously when treating patients with supratentorial glioma. Neurophysiological intraoperative monitoring (NIOM) has long been regarded as the “gold standard” for glioma resection, allowing for maximal resection of lesions while preserving sensorimotor function. NIOM during surgery involves the use of both mapping and monitoring strategies with multiple modalities. Brain mapping is necessary due to individual variability in cortical organization and the unexpected displacement of normal anatomic landmarks by tumor growth. Typically, the median somatosensory evoked potential phase reversal technique is used to localize the central sulcus, followed by direct cortical stimulation with a monopolar electrode and multipulse train stimulation, to confirm the location of the eloquent motor cortex. During resection, motor and somatosensory evoked potentials (MEP and SSEP) from the contralateral hemibody and direct waves (d waves), if indicated, are monitored to safeguard the integrity of functional structures. If resection extends beyond the cortical boundary, subcortical mapping can be used to confirm the approximate distance from the resection cavity to the corticospinal tract. Concomitant use of subcortical mapping and MEP monitoring is believed to be associated with more extensive resection and fewer severe late functional deficits. In addition, a meta-analysis indicated that use of intraoperative brain mapping during glioma surgery resulted in a 2-fold reduction of long term neurological deficits. Further, this was not at the expense of extent of resection. In conclusion, while functional deficits are still possible even with NIOM during the surgical procedure, in most cases, the use of this technique significantly improves patient outcomes.