Preoperative multimodal motor mapping: a comparison of magnetoencephalography imaging, navigated transcranial magnetic stimulation, and direct cortical stimulation

Abstract

Object Direct cortical stimulation (DCS) is the gold-standard technique for motor mapping during craniotomy. However, preoperative noninvasive motor mapping is becoming increasingly accurate. Two such noninvasive modalities are navigated transcranial magnetic stimulation (TMS) and magnetoencephalography (MEG) imaging. While MEG imaging has already been extensively validated as an accurate modality of noninvasive motor mapping, TMS is less well studied. In this study, the authors compared the accuracy of TMS to both DCS and MEG imaging. Methods Patients with tumors in proximity to primary motor cortex underwent preoperative TMS and MEG imaging for motor mapping. The patients subsequently underwent motor mapping via intraoperative DCS. The loci of maximal response were recorded from each modality and compared. Motor strength was assessed at 3 months postoperatively. Results Transcranial magnetic stimulation and MEG imaging were performed on 24 patients. Intraoperative DCS yielded 8 positive motor sites in 5 patients. The median distance ± SEM between TMS and DCS motor sites was 2.13 ± 0.29 mm, and between TMS and MEG imaging motor sites was 4.71 ± 1.08 mm. In no patients did DCS motor mapping reveal a motor site that was unrecognized by TMS. Three of 24 patients developed new, early neurological deficit in the form of upper-extremity paresis. At the 3-month follow-up evaluation, 2 of these patients were significantly improved, experiencing difficulty only with fine motor tasks; the remaining patient had improvement to 4/5 strength. There were no deaths over the course of the study. Conclusions Maps of the motor system generated with TMS correlate well with those generated by both MEG imaging and DCS. Negative TMS mapping also correlates with negative DCS mapping. Navigated TMS is an accurate modality for noninvasively generating preoperative motor maps.

Combined noninvasive language mapping by navigated transcranial magnetic stimulation and functional MRI and its comparison with direct cortical stimulation

“…Regarding the mapping of motor function, nTMS has already demonstrated its usefulness for clinical practice. 22,33,35,52,53,77 Furthermore, repetitive navigated TMS (rTMS) and nonnavigated TMS are able to localize cortical language function. 18,19,40,48,69,80 Its clinical applicability and correlation to DCS during awake surgery have repeatedly been shown as well.…”

Functional preoperative and intraoperative mapping and monitoring: increasing safety and efficacy in glioma surgery

“…117 In 12 patients in whom language sites were outlined by MEG for verb generation and object naming, the sites correlated with nTMS sites in 5 of these patients and with DCS sites in 2.…”

“…42,45,65,99,117 Tarapore et al compared nTMS and MEG motor mapping with intraoperative DCS in patients with brain tumor and found a deviation of nTMS, MEG, and DCS motor sites of 4.7-2.1 mm. 117 The use of MEG for motor mapping confirmed functional activity within…”

“…Although there are various methodological flaws inherent to this approach-from the navigational error to the misconception of one hot spot or stable center of gravity for each muscle-all studies on nTMS mapping accuracy reported distances between both methods of 1.1 and 14.8 mm for the hot spot comparison of the adductor pollicis brevis muscle. 27,51,86,117 Due to the low expense of nTMS and the ease of use associated with the sufficient accuracy of this true electrophysiological method, an increasing number of centers use presurgical nTMS mapping when gliomas are located in or near eloquent areas.…”

“…27,28,39,47,50,104,117 For a detailed evaluation of their mapping accuracy, the noninvasive nTMS method and the DCS cortical map of motor function were compared by calculating the distances between the respective hot spots or centers of gravity of target muscles. Although there are various methodological flaws inherent to this approach-from the navigational error to the misconception of one hot spot or stable center of gravity for each muscle-all studies on nTMS mapping accuracy reported distances between both methods of 1.1 and 14.8 mm for the hot spot comparison of the adductor pollicis brevis muscle.…”