Triple motor mapping: transcranial, bipolar, and monopolar mapping for supratentorial glioma resection adjacent to motor pathways

Abstract

<jats:sec><jats:title>OBJECTIVE</jats:title><jats:p>Maximal safe resection of gliomas near motor pathways is facilitated by intraoperative mapping. The authors and other groups have described the use of bipolar or monopolar direct stimulation to identify functional tissue, as well as transcranial or transcortical motor evoked potentials (MEPs) to monitor motor pathways. Here, the authors describe their initial experience using all 3 modalities to identify, monitor, and preserve cortical and subcortical motor systems during glioma surgery.</jats:p></jats:sec><jats:sec><jats:title>METHODS</jats:title><jats:p>Intraoperative mapping data were extracted from a prospective registry of glioma resections near motor pathways. Additional demographic, clinical, pathological, and imaging data were extracted from the electronic medical record. All patients with new or worsened postoperative motor deficits were followed for at least 6 months.</jats:p></jats:sec><jats:sec><jats:title>RESULTS</jats:title><jats:p>Between January 2018 and August 2019, 59 operations were performed in 58 patients. Overall, patients in 6 cases (10.2%) had new or worse immediate postoperative deficits. Patients with temporary deficits all had at least Medical Research Council grade 4/5 power. Only 2 patients (3.4%) had permanently worsened deficits after 6 months, both of which were associated with diffusion restriction consistent with ischemia within the corticospinal tract. One patient’s deficit improved to 4/5 and the other to 4/5 proximally and 3/5 distally in the lower limb, allowing ambulation following rehabilitation. Subcortical motor pathways were identified in 51 cases (86.4%) with monopolar high-frequency stimulation, but only in 6 patients using bipolar stimulation. Transcranial or cortical MEPs were diminished in only 6 cases, 3 of which had new or worsened deficits, with 1 permanent deficit. Insula location (p = 0.001) and reduction in MEPs (p = 0.01) were the only univariate predictors of new or worsened postoperative deficits. Insula location was the only predictor of permanent deficits (p = 0.046). The median extent of resection was 98.0%.</jats:p></jats:sec><jats:sec><jats:title>CONCLUSIONS</jats:title><jats:p>Asleep triple motor mapping is safe and resulted in a low rate of deficits without compromising the extent of resection.</jats:p></jats:sec>

Understanding Variable Motor Responses to Direct Electrical Stimulation of the Human Motor Cortex During Brain Surgery

“…When performing subcortical stimulation in descending motor pathways, the use of a train of multiple highfrequency monopolar stimulation pulses at 250-500 Hz may afford the surgeon similar advantages. In one series, the addition of monopolar stimulation to standard bipolar stimulation for the subcortical regions increased identification of descending motor pathways from 30 to 86.4% (66), similar to Szelényi et al's work which improved sensitivity from 54% using bipolar to 92% using monopolar stimulation (65). As mentioned prior, some have chosen to combine bipolar and monopolar stimulation with concurrent motor evoked potential monitoring, termed "triple motor mapping" (66).…”

“…More recent developments include a monopolar technique first described by Taniguchi et al in 1993 that instead uses a train of 5-10 short pulses (10-18 ms) at higher frequencies of 250-500 Hz (63,64). Also known as the "train-of-five, " this technique has been popularized in recent years by Szelényi et al (64) and Bello et al (65), as it has shown higher sensitivity in identifying motor pathways (64,(66)(67)(68) with equal safety and efficacy when compared to bipolar stimulation techniques (69). Some surgeons have chosen to combine both bipolar stimulation, for maximal definitive resolution, with monopolar stimulation, for sensitivity and estimation of distance to motor pathways, to maximize the advantages from both modalities (64,66), and the addition of concurrent motor evoked potential monitoring has been termed "triple motor mapping" (66).…”

“…As discussed above, there is a general movement to combine these modalities into more nuanced mapping/resection strategies, as opposed to using one vs. the other. While bipolar stimulation at 50-60Hz has been the most widely employed method for mapping the motor cortex, advantages to high frequency monopolar stimulation may include fewer intraoperative seizures and increased sensitivity (64,(66)(67)(68). While there is evidence to support this claim, it has not yet been widely adopted as a cortical stimulation technique.…”

The Minimal Subcortical Electronic Threshold Predicts the Motor Deficit and Survivals in Non-Awake Surgery for Gliomas Involving the Motor Pathway

“…Nossek et al (17) concluded that subcortical stimulation with a monopolar probe and high-frequency multi-pulse stimulation is the most efficient to identify the CST. Gogos et al (26) reported that subcortical motor pathways were identified in 51 cases (86.4%) with monopolar highfrequency stimulation, but only in 6 patients using bipolar stimulation. Gomez-Tames et al (27) compared monopolar and bipolar stimulation and found that bipolar stimulation could produce more selective activation if the CST was close to the resection border and monopolar stimulation was more robust and more effective for the CST far from the stimulation point.…”

Intraoperative Neuromonitoring During Resection of Gliomas Involving Eloquent Areas

“…The monopolar stimulation is preferable for identifying corticospinal tract due to the more radiant electric field properties of monopolar probe compared with the bipolar probe and reported to be effective in insular glioma resections (29,30). Recently, a triple brain mapping method including transcranial, monopolar, and bipolar stimulation has been proposed for locating the motor functional area more accurately (31). As a result, the combined application is considered as superior in preserving motor function and enhancing EOR.…”