Clinical Pearls and Methods for Intraoperative Motor Mapping

Abstract

Resection of brain tumors involving motor areas and pathways requires the identification and preservation of various cortical and subcortical structures involved in motor control at the time of the procedure, in order to maintain the patient's full motor capacities. The use of brain mapping techniques has now been integrated into clinical practice for many years, as they help the surgeon to identify the neural structures involved in motor functions. A common definition of motor function, as well as knowledge of its neural organization, has been continuously evolving, underlining the need for implementing intraoperative strategies at the time of the procedure. Similarly, mapping strategies have been subjected to continuous changes, enhancing the likelihood of preservation of full motor capacities. As a general rule, the motor mapping strategy should be as flexible as possible and adapted strictly to the individual patient and clinical context of the tumor. In this work, we present an overview of current knowledge of motor organization, indications for motor mapping, available motor mapping, and monitoring strategies, as well as their advantages and limitations. The use of motor mapping improves resection and outcomes in patients harboring tumors involving motor areas and pathways, and should be considered the gold standard in the resection of this type of tumor.

Targeting Primary Motor Cortex (M1) Functional Components in M1 Gliomas Enhances Safe Resection and Reveals M1 Plasticity Potentials

“…The intraoperative identification of two M1 functional components requires us to add to the qualitative approach currently practiced [11][12][13][15][16][17] the on-line measurement of many quantitative neurophysiological parameters: the number of pulses needed for effective stimulation, Motor-Threshold, MEP amplitude and latency. The evaluation of such parameters needs the combination of the "standard" HF-To5 paradigm and the reduced train (HF-To2) paradigm, in asleep anesthesia.…”

“…We here demonstrate that the intraoperative identification of the two M1 components requires the on-line measurement of quantitative neurophysiological parameters in addition to the qualitative approach (type of muscle activated) characterizing the standard technique [10][11][12][15][16][17], and, specifically: the minimum number of pulses needed for effective stimulation, Motor-Threshold, MEPs amplitude and latency. Our approach constitutes a novel "advanced motor mapping technique" allowing the identification of the two M1 functional components during surgical procedures [5].…”

“…In this respect, gliomas originating within M1 represent a challenge for neurosurgeons. To resect M1 tumors, surgeons must identify and preserve, using a brain mapping technique, the M1 neural structures essential for movement [10][11][12]. Standard mapping uses Low-Frequency (LF) or High-Frequency (HF) to identify essential sites within M1 [11,[13][14][15][16][17][18], affording different degrees of tumor resection and permanent motor morbidity according to the clinical context [10][11][12][13][14][15][16][17][18][19][20][21].…”

“…To resect M1 tumors, surgeons must identify and preserve, using a brain mapping technique, the M1 neural structures essential for movement [10][11][12]. Standard mapping uses Low-Frequency (LF) or High-Frequency (HF) to identify essential sites within M1 [11,[13][14][15][16][17][18], affording different degrees of tumor resection and permanent motor morbidity according to the clinical context [10][11][12][13][14][15][16][17][18][19][20][21]. LF affords a 50% rate of complete resection and 10% incidence of moderate to severe motor deficits; HF a 72.5% of complete resection and a 3.9% incidence of moderate motor deficits.…”

“…LF affords a 50% rate of complete resection and 10% incidence of moderate to severe motor deficits; HF a 72.5% of complete resection and a 3.9% incidence of moderate motor deficits. HF-To5 is particularly efficient in tumors reaching the M1 surface and with well-defined borders, while in those with irregular borders and/or deep-seated it induces motor responses all over the precentral gyrus, preventing the identification of a safe entry zone and/or evoked motor responses since the earlier stages of the resection, affording only the achievement of a partial resection or a biopsy [10,11]. The achievement of a larger Extent of Resection (EOR), correlated to a better oncological outcome, stands on the ability to use the intraoperative neurophysiological tools to identify the essential sites within M1 at the cortical and subcortical levels [11,[13][14][15][16][17][18].…”