Awake craniotomy with transcortical motor evoked potential monitoring for resection of gliomas in the precentral gyrus: utility for predicting motor function

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OBJECTIVE

Resection of gliomas in the precentral gyrus carries a risk of severe motor dysfunction. To prevent permanent, severe postoperative motor dysfunction, reliable intraoperative predictors of postoperative function are required. Since 2005, the authors have removed gliomas in the precentral gyrus with combined functional mapping and estimation of intraoperative voluntary movement (IVM) during awake craniotomy and transcortical motor evoked potentials (MEPs). The purpose of the current study was to evaluate whether intraoperative findings of combined monitoring of IVM during awake craniotomy and transcortical MEP monitoring were useful for predicting postoperative motor function of patients with gliomas in the precentral gyrus.

METHODS

The current study included 30 patients who underwent resection of precentral gyrus gliomas during awake craniotomy from April 2000 to January 2018. All tumors were removed with monitoring of IVM during awake craniotomy and transcortical MEPs. Postoperative motor function was classified as stable or declined, with the extent of decline categorized as mild, moderate, or severe. We defined moderate and severe deficits were those that hindered daily life.

RESULTS

In 28 of 30 cases, available waveforms were obtained with transcortical MEPs. The mean extent of resection (EOR) was 93%. Relative to preoperative status, motor function 6 months after surgery was considered stable in 20 patients and was considered to show mild decline in 7, moderate decline in 2, and severe decline in 1. Motor function 6 months after surgery was significantly correlated with IVM (p = 0.0096), changes in transcortical MEPs (decline ≤ or > 50%) (p = 0.0163), EOR, and ischemic lesions on postoperative MRI. Six patients with no change in IVM showed stable motor function 6 months after surgery. Only 2 patients with a decline in IVM and a decline in MEPs ≤ 50% had a decline in motor function 6 months after surgery (18%; 2/11 patients), whereas 11 patients with a decline in IVM and a decline in MEPs > 50% had such a decline in motor function (73%; 8/11 patients) including 2 patients with moderate and 1 with severe deficits. Three patients with moderate or severe motor deficits showed the lowest MEP values (< 100 µV).

CONCLUSIONS

Combined judgment from monitoring of IVM during awake craniotomy and transcortical MEPs is useful for predicting postoperative motor function during removal of gliomas in the precentral gyrus. Maximum resection was achieved with an acceptable morbidity rate. Thus, these tumors should not be considered unresectable.

ABBREVIATIONS CMAP = compound muscle action potential; DWI = diffusion-weighted imaging; EOR = extent of resection; IVM = intraoperative voluntary movement; MEP = motor evoked potential; WHO = World Health Organization.

Article Information

Correspondence Yoshihiro Muragaki: Tokyo Women’s Medical University, Tokyo, Japan. ymuragaki@twmu.ac.jp.

INCLUDE WHEN CITING Published online March 15, 2019; DOI: 10.3171/2018.11.JNS182609.

Disclosures The authors report no conflict of interest concerning the materials or methods used in this study or the findings specified in this paper.

© AANS, except where prohibited by US copyright law.

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Figures

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    Key preoperative MR images obtained in 30 patients with gliomas in the precentral gyrus. The key images for cases 1–30 are shown in panels A–DD, respectively.

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    Flowchart showing cases in which the combination of IVM monitoring during awake craniotomy and transcortical MEP monitoring was used and the correlation between findings on intraoperative monitoring and the percentage of cases in which patients showed a decline in motor function 6 months after surgery. MEP monitoring was performed by direct cortical stimulation via the strip electrode (train of stimulation, 5; frequency, 500 Hz; pulse duration, 0.5 msec).

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    Three representative cases of a glioma in the primary motor area. A–C: Case 24; example of a case with a stable IVM and a decline in MEPs ≤ 50%. Preoperative T2-weighted MRI (axial image in A) revealed a tumor with isointense and hyperintense signal in the superior and middle portion of the left precentral gyrus. Changes in transcortical MEPs were observed during surgery (B; upper: control, lower: during tumor removal). Postoperative MRI (axial T2-weighted image in C) revealed total resection of the tumor. D–F: Case 12; example of a case with a decline in IVM and a decline in MEPs ≤ 50%. Preoperative T2-weighted MRI (axial image in D) revealed a high–signal intensity mass centered in the inferior part of the left precentral gyrus. Changes in transcortical MEPs were observed during surgery (E; upper: control, lower: during tumor removal). Postoperative MRI (axial T2-weighted image in F) revealed 95% resection of the tumor. G–I: Case 10; example of a case with a decline in IVM and a decline in MEPs > 50%. Preoperative T2-weighted MRI (axial image in G) revealed a high–signal intensity mass in the superior portion of the right precentral gyrus. Changes were observed in transcortical MEPs during surgery (H; upper: control; lower: the lowest MEP during tumor removal). Postoperative MRI (axial T2-weighted image in I) revealed 85% resection of the tumor. APB = abductor pollicis brevis; d-MEP = direct MEP; Quad = quadriceps.

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