Clinical impact of integrated functional neuronavigation and subcortical electrical stimulation to preserve motor function during resection of brain tumors

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The authors evaluated the clinical impact of combining functional neuronavigation with subcortical electrical stimulation to preserve motor function following the removal of brain tumors.


Forty patients underwent surgery for treatment of brain tumors located near pyramidal tracts that had been identified by fiber tracking. The distances between the electrically stimulated white matter and the pyramidal tracts were measured intraoperatively with tractography-integrated functional neuronavigation, and correlated with subcortical motor evoked potentials (MEPs) and clinical symptoms during and after resection of the tumors.

Motor function was preserved after appropriate tumor resection in all cases. In 18 of 20 patients, MEPs were elicited from the subcortex within 1 cm of the pyramidal tracts as measured using intraoperative neuronavigation. During resection, improvement of motor weakness was observed in two patients, whereas transient mild motor weakness occurred in two other patients. In 20 patients, the distances between the stimulated subcortex and the estimated pyramidal tracts were more than 1 cm, and MEPs were detected in only three of these patients following stimulation.


Intraoperative functional neuronavigation and subcortical electrical stimulation are complementary techniques that may facilitate the preservation of pyramidal tracts around 1 cm of resected tumors.

Abbreviations used in this paper:CT = computed tomography; DICOM = digital imaging and communications in medicine; DT = diffusion-tensor; MEP = motor evoked potential; MPRAGE = magnetization prepared rapid gradient echo; MR = magnetic resonance; ROI = region of interest.

Article Information

Address reprint requests to: Nobuhiro Mikuni, M.D., Ph.D., Department of Neurosurgery, Kyoto University Graduate School of Medicine, 54 kawahara-cho, Shogoin, Sakyo-ku, Kyoto 6068507, Japan. email:

© AANS, except where prohibited by US copyright law.



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    Subcortical MEPs elicited intraoperatively in a 36-year-old woman with a right frontal diffuse astrocytoma. Her neurological examination was normal preoperatively. A: Intraoperative T2-weighted MR images showing a hyperintense area (yellow area in upper left panel) close to the pyramidal tract identified by fiber tracking (green). During the removal of the tumor, subcortical stimulation elicited MEPs at the bottom of the tumor (intersection of yellow lines) 8 mm from the edge of the estimated pyramidal tract. No further removal was performed to avoid causing neurological deficits. B: Postoperative MR images demonstrating that the pyramidal tracts identified by fiber tracking (red) are preserved. C: A typical waveform of MEP response elicited from the left biceps muscle by subcortical stimulation during tumor removal.



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