Technical Aspects of Motor and Language Mapping in Glioma Patients

Abstract

Gliomas are infiltrative primary brain tumors that often invade functional cortical and subcortical regions, and they mandate individualized brain mapping strategies to avoid postoperative neurological deficits. It is well known that maximal safe resection significantly improves survival, while postoperative deficits minimize the benefits associated with aggressive resections and diminish patients’ quality of life. Although non-invasive imaging tools serve as useful adjuncts, intraoperative stimulation mapping (ISM) is the gold standard for identifying functional cortical and subcortical regions and minimizing morbidity during these challenging resections. Current mapping methods rely on the use of low-frequency and high-frequency stimulation, delivered with monopolar or bipolar probes either directly to the cortical surface or to the subcortical white matter structures. Stimulation effects can be monitored through patient responses during awake mapping procedures and/or with motor-evoked and somatosensory-evoked potentials in patients who are asleep. Depending on the patient’s preoperative status and tumor location and size, neurosurgeons may choose to employ these mapping methods during awake or asleep craniotomies, both of which have their own benefits and challenges. Regardless of which method is used, the goal of intraoperative stimulation is to identify areas of non-functional tissue that can be safely removed to facilitate an approach trajectory to the equator, or center, of the tumor. Recent technological advances have improved ISM’s utility in identifying subcortical structures and minimized the seizure risk associated with cortical stimulation. In this review, we summarize the salient technical aspects of which neurosurgeons should be aware in order to implement intraoperative stimulation mapping effectively and safely during glioma surgery.

The “state of the art” of intraoperative neurophysiological monitoring: An Italian neurosurgical survey

“…The main IOM techniques reported are MEPs (94%), SSEPs (89%), DCS (85%) and subcortical stimulation (80%). Intraoperative MEPs are the gold standard for supratentorial glioma surgery in eloquent areas ( Al-Adli et al, 2023 ). The two techniques by which the MEPs can be evoked are transcranial stimulation (TES), that utilize a high-voltage electrical stimulus through the scalp/skull to activate the motor cortex and descending pathways, and DCS, by stimulating through a strip electrode that is placed over the primary motor cortex ( Abboud et al, 2021 ).…”

Glioblastoma Therapy: Past, Present and Future

“…These include functional monitoring, fluorescence-based visualization of the tumor using 5-aminolevulinic acid (5-ALA), ultrasonography, and intraoperative MRI (ioMRI) [ 268 , 269 , 271 ]. Additionally, techniques like evoked potentials, electromyography, and brain mapping in awake patients, under local anesthesia, are used to monitor and preserve language and cognition during resections in critical brain areas [ 272 ]. The use of the amino acid 5-Ala helps to identify tumor volume and areas of neoplastic infiltration through fluorescent visualization, improves PFS, OS, and reduces postoperative neurological damages [ 269 , 273 , 274 , 275 , 276 ].…”

Advances in Intraoperative Glioma Tissue Sampling and Infiltration Assessment

“…Surgical expertise in resecting these tumors, which are sometimes nearly indistinguishable from the adjacent normal tissue, is necessary for minimizing post-operative morbidity [5]. Moreover, it is well known that intraoperative adjuncts such as stimulation mapping reduce the risk of injury to critical cortical and subcortical structures [6]. However, at the periphery of resection, identifying the tumor boundaries remains a challenge, and stopping prematurely may result in suboptimal resections, while overly aggressive resections may cause unnecessary postoperative deficits.…”