Continuous Dynamic Mapping of the Corticospinal Tract in Motor Eloquent Tumor Surgery: Our Experience and Evaluation of the Method

<p><strong>Objective. </strong>The aim of this article is to present our experience with continuous dynamic mapping (CDM) of the corticospinal tract (CST) when removing tumors in motor eloquent regions.</p><p><strong>Methods. </strong>We studied 44 patients with a brain tumor adjacent to the CST where CDM was used. The mapping probe was integrated at the tip of the suction device. Thresholds for eliciting MEPs were recorded. In all patients, along with CDM, MEPs to direct cortical stimulation were also monitored throughout the operation. Motor function was assessed preoperatively, after the procedure and on discharge.</p><p><strong>Results. </strong>In the series, there were 37 patients with gliomas, six with brain metastasis, and one with cavernoma. The threshold to elicit MEPs in CDM was &gt;20 mA in 17 cases, 16–20 mA in six cases, 11–15 mA in six cases, 6–10 mA in nine cases and 2–5 mA in six cases. MEPs to direct cortical stimulation were preserved in all patients. In three cases a new temporary motor deficit was noted. No new permanent motor deficit occurred. Gross total resection was reached in 57% of cases.</p><p><strong>Conclusions. </strong>From our experience, the combined use of CDM and MEPs to direct cortical stimulation improves the safety of surgery in the proximity of the CST, and at the same time offers the possibility of higher rates of gross total resection.</p>

Continuous Dynamic Mapping to Identify the Corticospinal Tract in Motor Eloquent Brain Tumors: An Update

Objective We recently developed a new subcortical mapping technique based on the concept of stimulating the tissue at the site of and synchronously with resection. Our hypothesis was that instead of performing resection and mapping sequentially, a synchronized resection and mapping could potentially improve deficit rates. Methods We report our 5-year series of patients who prospectively underwent tumor surgery adjacent to the corticospinal tract (CST) (defined as < 1 cm using diffusion tension imaging and fiber tracking) with simultaneous subcortical short train cathodal monopolar mapping, equipped with a new acoustic motor evoked potential (MEP) alarm. Continuous (temporal coverage) and dynamic (spatial coverage) mapping was realized technically by integrating the mapping probe at the tip of a new suction device. Motor function was assessed using the Medical Research Council scale (from M1 to M5) 1 day after surgery, at discharge, and at 3 months. Results Technically, the method was successful in all 182 cases. The lowest individual motor thresholds reached during resection were > 10 mA, n = 56; 6–10 mA, n = 31; 4–5 mA, n = 37; and 1–3 mA, n = 58. At 3 months, six patients (3%) had a persisting postoperative motor deficit that was caused by direct mechanical injury in three of these patients (1.7%). Conclusions Continuous dynamic mapping was found to be a feasible and ergonomic technique for localizing the exact site of the CST and distance to the motor fibers. This new technique may improve the safety of motor eloquent tumor surgery.