Subcortical Motor Mapping Research Articles

Impact of function-guided glioma treatment on oncological outcome in the elderly

IntroductionMany patients with high-grade gliomas (HGG) are of older age. Research questionWe hypothesize that pre- and intraoperative mapping and monitoring preserve functional status in elderly patients while gross total resection (GTR) is the aim, resulting in overall survival (OS) rates comparable to the general population with HGG. Material and methodsWe subdivided a prospective cohort of 168 patients above 65 years with eloquent high-grade gliomas into four groups ([years/cases] 1: 65–69/58; 2: 70–74/47; 3: 75–79/43; 4: >79/20). All patients underwent preoperative noninvasive mapping, which was also used for decision-making, intraoperative neuromonitoring in 138 cases, direct cortical and/or subcortical motor mapping in 66 and 50 cases, and awake language mapping in 11 cases. ResultsGTR and subtotal resection (STR) could be achieved in 65% and 28%, respectively. Stereotactic biopsy was performed in 8% of cases. Postoperatively, we found transient and permanent functional deficits in 13% and 11% of cases. Postoperative Karnofsky Performance Scale (KPS) did not differ between subgroups. Patients with long-term follow-up (51%) had a progression-free survival of 5.5 (1–47) months and an overall survival of 10.5 (0–86) months. Discussion and conclusionThe interdisciplinary glioma treatment in the elderly is less age-dependent but must be adjusted to the functional status. Function-guided surgical resections could be performed as usual, with maximal tumor resection being the primary goal. However, less network capacity in the elderly to compensate for deficits might cause higher rates of permanent deficits in this group of patients with more fast-growing malignant gliomas.

Intraoperative Stimulation Mapping in Neurosurgery for Anesthesiologists—Part 1: The Technical Nuances

AbstractBrain mapping has evolved tremendously in the past decade, fueled by advances in functional neuroimaging technology in neuro-oncology and epilepsy surgery. Despite this, wide anatomic-functional interindividual variability and intraoperative brain shift continue to challenge neurosurgeons performing surgery within or near eloquent brain regions. As such, intraoperative direct cortical and subcortical stimulation mapping remains the gold standard for localizing eloquent brain regions with precision for a safe and tailored resection. Intraoperative stimulation mapping (ISM) allows for maximizing the extent of resection while minimizing postoperative neurological deficits, resulting in better patient outcomes. Understanding the technical nuances of ISM is imperative for the anesthesiologist to provide better anesthetic management tailored to the surgery and stimulation mapping planned. A comprehensive search was performed on electronic databases to identify articles describing intraoperative cortical and subcortical mapping, language, and motor mapping. In the first part of this narrative review, we summarize the salient technical aspects of ISM and the common neurophysiological tasks assessed intraoperatively relevant to the anesthesiologist.

The current state of the art of primary motor mapping for tumor resection: A focused survey

IntroductionCortical and subcortical motor mapping has advanced the notion of maximal safe resection of intra-axial brain tumours, thereby preserving neurological functions as well as improving survival. Despite being an age-old and established neurosurgical procedure across the world, the strategy and techniques involved in motor mapping have a gamut of variation due to a lack of defined standard protocols. MethodsWe disseminated a structured survey among focused group of neurosurgeons with established practices involving brain mapping. It consisted of 40 questions, split into five sections assessing the practice description, general approach for motor mapping, preference for asleep versus awake mapping, operative techniques and approach to representative tumor cases. Practice-patterns during primary motor mapping for brain tumours were analysed from responses of 51 neurosurgeons. Results60.8 % felt that any lesion even near (without infiltration) was suffice to define “involvement” of the cortical/subcortical motor pathways. 82.4 % felt that motor mapping was necessary for brain tumours involving motor pathways, irrespective of the tumor histology or patient age. 90.2 % opined that tumor location was the predominant factor affecting their choice between awake or asleep mapping. 31.4 % believed that all cases should be performed awake unless patient-related medical, psychological, or anaesthetic contraindications exist, whereas 45.1 % felt that all cases should be performed asleep unless language mapping is required. MRI, DTI-based tractography and intra-operative fluorescence were the most commonly employed surgical adjuncts. ConclusionsThe data from this survey may serve as a preliminary foundation for a more standardized approach to patient selection and the approach to motor mapping for brain tumors.

Commentary: Awake Microsurgical Resection of a Motor Cortex Glioma With Cortical and Subcortical Motor Mapping, Image Guidance, and Augmented Reality.

Commentary: Awake Microsurgical Resection of a Motor Cortex Glioma With Cortical and Subcortical Motor Mapping, Image Guidance, and Augmented Reality.

Intraoperative cortical and subcortical stimulation for lesions related to eloquent motor cortex and corticospinal tract in a developing country

ObjectiveSurgery for lesions related to the eloquent motor cortex and the corticospinal tract is challenging. Intraoperative cortical and subcortical stimulation are reliable techniques for motor cortex and corticospinal tract (CST) mapping. Pre-operative functional magnetic resonance imaging (fMRI) and diffusion tensor imaging (DTI) are able to provide helpful data for safe surgical planning with both cortical and subcortical lesion resection. The authors combine these imaging techniques with intraoperative stimulation to identify and preserve cortical and subcortical motor tissue. MethodsThis is a prospective analysis of 56 patients between May 2020 and June 2021, who underwent lesion resection. Thirty-one patients underwent preoperative DTI, thirteen patients underwent preoperative fMRI and their data were used for a tractography-based neuronavigation system. All patients were operated under general anesthesia. Intraoperative mapping data were collected from operative protocol and neurophysiologist’s notes. The assessment of paresis was done by an independent neurosurgeon and was carried out using the motor strength scale of 0–5 according to the Medical Research Council scale. All patients with new or worsened postoperative motor deficits were followed for 6 months. ResultsNone of the patients exhibited a seizure during the operation. There were eight cases that experienced immediate motor deficits after surgery. At six months after surgery, only two patients (3.6%) had permanent motor deficits (motor strength scale rating 3 in one case and 4 in the other). The average distance between the lesions and CSTs in the positive subcortical stimulation response group was 3.39 ± 2.19 mm and 8.59 ± 3.27 mm in the negative group. Using a 5 mA stimulation threshold value resulted in a sensitivity of 12.5% and a specificity of 92.7%, corresponding to a negative predictive value of 84.4% and a positive predictive value of 25% for motor function. ConclusionsIntraoperative cortical and subcortical motor mapping in lesion resection resulted in a low ratio of permanent postoperative deficits. Subcortical alert threshold ≤ 5 mA is supposed to be a safe threshold in lesion resection with a high specificity of 92.7% and a negative predictive value of 84.4%.

Continuous Microdebrider-Based Dynamic Subcortical Motor Mapping: A Technical Advance in Tubular Retractor-Assisted Surgery.

Transsulcal minimally invasive parafasicular (TsMIP) approaches to brain tumor resection use tubular retractors to minimize iatrogenic brain injury. Dynamic cortical and subcortical continuous neurophysiological mapping facilitates safer resection of motor-eloquent tumors. To describe a new technique to address the challenge of combining TsMIP with tubular retractors and dynamic subcortical mapping using a single electrified stimulating microdebrider instrument. We adapted the NICO Myriad microdebrider with continuous monopolar stimulation electrification using high-frequency stimulation with the train-of-5 technique. We performed continuous subcortical mapping using this device and compared it with standard dynamic monopolar subcortical mapping using a suction stimulation device. We found no significant difference in recorded stimulation response. Using a single operating instrument that provides synchronous tumor resection and monopolar subcortical mapping with the NICO Brainpath tubular retractor, we observed increased degrees of movement, faster surgical resection times with an enlarged working channel down the retractor, and improved safety because the stimulating probe sits 2 mm deep to the resection window. We show that the adapted device is reliable and provides similar stimulation response as conventional subcortical mapping. We advocate the use of our adapted microdebrider in TsMIP tubular retractor approaches.

Motor Mapping of the Brain: Taniguchi Versus Penfield Method.

Intraoperative neurophysiological monitoring (IONM) techniques continue to prove useful as an adjunct in select surgeries for reducing the incidence of various postoperative deficits in motor function through the monitoring of motor evoked potentials (MEPs). The Penfield and Taniguchi methods of direct electrical cortical stimulation (DECS) stand in contrast to each other. Penfield’s method uses lower-frequency stimulation over a longer duration, while Taniguchi’s method uses a relatively higher frequency over a short duration. DECS motor mapping is considered suitable for tumor resections, aneurysm surgeries, arteriovenous malformation, and epilepsy surgeries. While subcortical motor mapping works efficiently with both methods, it aligns with Taniguchi’s method more effectively. Taniguchi’s method has a lower risk of seizures relative to Penfield’s method. While only cortical neurons are excited in Penfield’s stimulation technique, Taniguchi’s technique excites the whole corticospinal tract (CST), so it can be used for mapping in a stand-alone fashion. The Penfield technique remains the method of choice for language mapping. In all motor mapping, Train-of-Four (TOF) stimulation during the surgical procedure ensures that the patient’s muscles are not unduly relaxed.

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

PurposeDirect subcortical motor mapping is the golden criterion to detect and monitor the motor pathway during glioma surgery. Minimal subcortical monopolar threshold (MSCMT) means the minimal distance away from the motor pathway and is critical to decide to continue or interrupt glioma resection. However, the optimal cutoff value of MSCMT for glioma resection in non-awake patients has not been reported discreetly. In this study, we try to establish the safe cutoff value of MSCMT for glioma resection and analyzed its relationship with postoperative motor deficit and long-term survivals.MethodsWe designed this prospective study with high-frequency electronic stimulus method. The cutoff MSCMT of postoperative motor deficits was statistically calculated by receiver operating characteristic (ROC) curve, and its relationship with motor deficit and survivals was analyzed by logistic and Cox regression, respectively.ResultsThe cutoff MSCMT to predict motor deficit after surgery was 3.9 mA on day 1, 3.7 mA on day 7, 5.2 mA at 3 months, and 5.2 mA at 6 months. MSCMT ≤3.9 mA and MSCMT ≤5.2 mA independently predicted postoperative motor deficits at four times after surgery (P < 0.05) but had no effect on the removal degree of tumor (P > 0.05). In high-grade gliomas, MSCMT ≤3.9 mA independently predicted shorter progression-free survival [odds ratio (OR) = 3.381 (1.416–8.076), P = 0.006] and overall survival [OR = 3.651 (1.336–9.977), P = 0.012]. Power model has the best fitness for paired monopolar and bipolar high-frequency thresholds.ConclusionsThis study showed strong cause–effect relation between MSCMT and postoperative motor deficit and prognoses. The cutoff MSCMT was dug out to avoid postoperative motor deficit. Further studies are needed to establish the results above.

Investigation of Asleep versus Awake Motor Mapping in Resective Brain Surgery

To develop an asleep motor mapping paradigm for accurate detection of the corticospinal tract during glioma surgery and compare outcomes with awake patients undergoing glioma resection. A consecutive cohort of adult patients undergoing craniotomy for suspected diffuse glioma with tumor in a perirolandic location who had awake or asleep cortical and subcortical motor mapping with positive areas of motor stimulation were assessed for postoperative extent of resection (EOR), permanent neurological deficit, and proximity of stimulation to diffusion tensor imaging-based corticospinal tract depiction on preoperative magnetic resonance imaging. Outcome data were compared between asleep and awake groups. In the asleep group, all 16 patients had improved or no change in motor function at last follow-up (minimum 3 months of follow-up). In the awake group, all 23 patients had improved function or no change at last follow-up. EOR was greater in the asleep group (mean [SD] EOR 88.71% [17.56%]) versus the awake group (mean [SD] EOR 80.62% [24.44%]), although this difference was not statistically significant (P= 0.3802). Linear regression comparing distance from stimulation to corticospinal tract in asleep (n= 14) and awake (n= 4) patients was r=-0.3759, R2= 0.1413, P= 0.1853, and 95% confidence interval=-0.4453 to 0.09611 and r= 0.7326, R2= 0.5367, P= 0.2674, and 95% confidence interval=-7.042 to 14.75, respectively. In this small patient series, asleep motor mapping using commonly available motor evoked potential hardware appears to be safe and efficacious in regard to EOR and functional outcomes.

Penfield motor homunculus revisited: New data from cortical and subcortical intraoperative motor mapping

Penfield motor homunculus revisited: New data from cortical and subcortical intraoperative motor mapping

Intraoperative mapping of pre-central motor cortex and subcortex: a proposal for supplemental cortical and novel subcortical maps to Penfield\u2019s motor homunculus

Penfield’s motor homunculus describes a caricaturised yet useful representation of the map of various body parts on the pre-central cortex. We propose a supplemental map of the clinically represented areas of human body in pre-central cortex and a novel subcortical corticospinal tract map. We believe this knowledge is essential for safe surgery in patients with eloquent brain lesions. A single-institution retrospective cohort study of patients who underwent craniotomy for motor eloquent lesions with intraoperative motor neuromonitoring (cortical and subcortical) between 2015 and 2020 was performed. All positive cortical and subcortical stimulation points were taken into account and cartographic maps were produced to demonstrate cortical and subcortical areas of motor representation and their configuration. A literature review in PubMed was performed. One hundred and eighty consecutive patients (58.4% male, 41.6% female) were included in the study with 81.6% asleep and 18.4% awake craniotomies for motor eloquent lesions (gliomas 80.7%, metastases 13.8%) with intraoperative cortical and subcortical motor mapping. Based on the data, we propose a supplemental clinical cortical and a novel subcortical motor map to the original Penfield’s motor homunculus, including demonstration of localisation of intercostal muscles both in the cortex and subcortex which has not been previously described. The supplementary clinical cortical and novel subcortical motor maps of the homunculus presented here have been derived from a large cohort of patients undergoing direct cortical and subcortical brain mapping. The information will have direct relevance for improving the safety and outcome of patients undergoing resection of motor eloquent brain lesions.

Introduction of a novel connection clip for the ultrasonic aspirator for subcortical continuous motor mapping

IntroductionA connection clip to the ultrasonic aspirator handpiece was introduced for simultaneous resection and mapping of corticospinal motor tract (CST) (Kombos et al., 2001).Research questionTo report retrospectively the use of this clip in cerebral surgery with CST mapping.Material and methodsEight women and four men were included (mean: 55.8 years, SD 17.3 years). The ultrasonic aspirator handpiece was stimulated every second (5 biphasic pulses, 0.4 ​ms per phase, max 14 ​mA). Motor evoked potentials (MEPs) (Taniguchi et al., 1993), with transcranial and direct cortical stimulation, were alternated with CST mapping. The distances between the stimulus locations to the CST (diffusion tensor imaging based fibre tractography) were determined postoperatively. Muscle strength was evaluated pre-operatively, at discharge and 3 months.ResultsMotor mapping thresholds ranged between 2 and 13 ​mA, in 12 consecutive patients (7 post-central, 5 insular). The distance of the stimulation site to the CST was fitted (y ​= ​0.63x+2.33, R2 ​= ​0.33; x, mA; y, mm), approximating the rule of thumb of 1 ​mA indicating 1 ​mm (R2 ​= ​0.22). One patient presented with a deterioration of motor function (wrist, M4+). No intraoperative seizures were observed.DiscussionThe concept that 1 ​mA corresponds to 1 ​mm from the CST, was roughly observed within this low current range. This rule must be applied, integrating the confidence limits, when getting close to the CST, in conjunction with MEPs.ConclusionThe standardization of this clip, for continuous stimulation of the ultrasonic aspirator with simultaneous tissue resection, made the guided surgical flow smoother, more refined and very natural.

Novel Use of Stimulating Fence-Post Technique for Functional Mapping of Subcortical White Matter During Tumor Resection: A Technical Case Series.

Maximal safe resection remains a key principle in infiltrating glioma management. Stimulation mapping is a key adjunct for minimizing functional morbidity while "fence-post" procedures use catheters or dye to mark the tumor border at the start of the procedure prior to brain shift. To report a novel technique using stereotactically placed electrodes to guide tumor resection near critical descending subcortical fibers. Navigated electrodes were placed prior to tumor resection along the deep margin bordering presumed eloquent tracts. Stimulation was administered through these depth electrodes for subcortical motor and language mapping. Twelve patients were included in this preliminary technical report. Seven patients (7/12, 58%) were in asleep cases, while the other 5 cases (5/12, 42%) were performed awake. Mapping of motor fibers was performed in 8 cases, and language mapping was done in 1 case. In 3 cases, both motor and language mapping were performed using the same depth electrode spanning corticospinal tract and the arcuate fasciculus. Stereotactic depth electrode placement coupled with stimulation mapping of white matter tracts can be used concomitantly to demarcate the border between deep tumor margins and eloquent brain, thus helping to maximize extent of resection while minimizing functional morbidity.

The transcortical equatorial approach for gliomas of the mesial temporal lobe: techniques and functional outcomes.

OBJECTIVEMany surgical approaches have been described for lesions within the mesial temporal lobe (MTL), but there are limited reports on the transcortical approach for the resection of tumors within this region. Here, the authors describe the technical considerations and functional outcomes in patients undergoing transcortical resection of gliomas of the MTL.METHODSPatients with a glioma (WHO grades I-IV) located within the MTL who had undergone the transcortical approach in the period between 1998 and 2016 were identified through the University of California, San Francisco (UCSF) tumor registry and were classified according to tumor location: preuncus, uncus, hippocampus/parahippocampus, and various combinations of the former groups. Patient and tumor characteristics and outcomes were determined from operative, radiology, pathology, and other clinical reports that were available through the UCSF electronic medical record.RESULTSFifty patients with low- or high-grade glioma were identified. The mean patient age was 46.8 years, and the mean follow-up was 3 years. Seizures were the presenting symptom in 82% of cases. Schramm types A, C, and D represented 34%, 28%, and 38% of the tumors, and the majority of lesions were located at least in part within the hippocampus/parahippocampus. For preuncus and preuncus/uncus tumors, a transcortical approach through the temporal pole allowed for resection. For most tumors of the uncus and those extending into the hippocampus/parahippocampus, a corticectomy was performed within the middle and/or inferior temporal gyri to approach the lesion. To locate the safest corridor for the corticectomy, language mapping was performed in 96.9% of the left-sided tumor cases, and subcortical motor mapping was performed in 52% of all cases. The mean volumetric extent of resection of low- and high-grade tumors was 89.5% and 96.0%, respectively, and did not differ by tumor location or Schramm type. By 3 months' follow-up, 12 patients (24%) had residual deficits, most of which were visual field deficits. Three patients with left-sided tumors (9.4% of dominant-cortex lesions) experienced word-finding difficulty at 3 months after resection, but 2 of these patients demonstrated complete resolution of symptoms by 1 year.CONCLUSIONSMesial temporal lobe gliomas, including larger Schramm type C and D tumors, can be safely and aggressively resected via a transcortical equatorial approach when used in conjunction with cortical and subcortical mapping.

Combined Motor Evoked Potential Monitoring and Subcortical Dynamic Mapping in Motor Eloquent Tumors Allows Safer and Extended Resections

Subcortical motor mapping is crucial to ensure preservation of motor tracts during resections of tumors. Continuous dynamic mapping using a modified monopolar suction probe is a novel and effective way of achieving this goal. We describe our experience using this technique. Forty patients were operated on between June 2017 and February 2018. Transcranial electric stimulation (TES) and direct cortical strip (DCS) motor evoked potentials (MEPs) were monitored. Subcortical stimulation (SCS) mapping was attempted in all cases by adapting the technique using a monopolar suction stimulator. Neurologic outcomes and extent of resection were analyzed. Motor fibers were between 0 and 7.6 mm away from the tumor boundaries in 26 patients. TES MEP were monitored in all patients. DCS MEPs were attempted in 31 and successfully monitored in 26 patients. SCS using the monopolar suction probe worked in all patients except one. SCS elicited no responses at 15-mA motor thresholds in 16 patients. The motor threshold ranged from 3 to 10 mA in the remainder. Overall, MEP changes were noted in 5 patients. Ten patients experienced neurologic worsening (6transient, 3 prolonged, and 1 delayed). There was no permanent deficit at 3 months. DCS MEPs predicted neurologic worsening better than did TES MEPs. Radical resections were achieved in 68%. Neuromonitoring inputs resulted in premature termination of resection in 14 patients (35%). Radical resections (near-total resections) were still achieved in 8 of the 14 patients. Continuous dynamic subcortical mapping is a reliable method to map the motor tracts. This process is crucial to correctly identify truly eloquent tumors and tailor the surgical procedure as per planned goals, maximizing the resections with acceptable morbidity.

LP10: The warning sign hierarchy between quantitative subcortical motor mapping and continuous motor evoked potential monitoring during surgery of supratentorial brain tumors

LP10: The warning sign hierarchy between quantitative subcortical motor mapping and continuous motor evoked potential monitoring during surgery of supratentorial brain tumors

22. Implementation of multimodal intraoperative neuromonitoring into an established setting of awake craniotomy

Bipolar 60 Hz-stimulation-mapping and clinical evaluation are commonly used for patient assessment in awake neurosurgical procedures. Stimulation related seizures, afterdischarges, delayed wake-up or malcompliance interfere with successful testing. Somatosensory (SEPs) and motor evoked potentials (MEPs) are objective tools for mapping and monitoring independent of patients’ compliance. Their introduction into an established ‘awake setting’ were prospectively analysed for feasibility, reliability and effect on surgical strategy. Multimodal intraoperative neuromonitoring consisting of contralateral SEPs, transcranially (TES) and direct cortically (DCS) elicited MEPs (monopolar, train-of-five-technique with 250 Hz) were implemented in a 13 month period. 105 patients (53 ± 14 years, 60 male) with frontal/precentral (48), postcentral/parietal (33), temporal (16) and trigonal (8) located lesions (glioma (81), metastasis (18), others (6)) were analysed. SEPs and TES-MEPs were present in all 105 patients, as well as DCS for cortical and subcortical motor mapping. There were no serious side effects despite the description of tingling pain during direct cortical stimulation. After 5 months, a bias towards motor mapping with the monopolar stimulation was seen, such monopolar vs. bipolar stimulation was only compared in the first 70 patients: DCS-MEPs were elicited in all 70 patients, whereas the 60 Hz-stimulation elicited motor responses in 60/70 patients (p = 0.0016; Fisher’̃s-test). 90/105 patients (86%) were cooperative for the awake setting. In 4 of the 15 remaining patients (4%) language testing was considered essential and surgery was prematurely terminated. In the other 11 patients (10%), surgery was continued asleep with monopolar cortical and subcortical mapping and continuous monitoring of SEPs and MEPs. Multimodal monitoring is feasible in awake craniotomies and was well tolerated. Despite malcompliance and clinical deterioration it allows for objective assessment of somatosensory and motor pathways and proceeding with the surgical tumour resection. In conclusion, the inclusion of multimodal monitoring might be essential for pericentral surgery.

Continuous dynamic mapping of the corticospinal tract during surgery of motor eloquent brain tumors: evaluation of a new method

The authors developed a new mapping technique to overcome the temporal and spatial limitations of classic subcortical mapping of the corticospinal tract (CST). The feasibility and safety of continuous (0.4-2 Hz) and dynamic (at the site of and synchronized with tissue resection) subcortical motor mapping was evaluated. The authors prospectively studied 69 patients who underwent tumor surgery adjacent to the CST (< 1 cm using diffusion tensor imaging and fiber tracking) with simultaneous subcortical monopolar motor mapping (short train, interstimulus interval 4 msec, pulse duration 500 μsec) and a new acoustic motor evoked potential alarm. Continuous (temporal coverage) and dynamic (spatial coverage) mapping was technically realized by integrating the mapping probe at the tip of a new suction device, with the concept that this device will be in contact with the tissue where the resection is performed. Motor function was assessed 1 day after surgery, at discharge, and at 3 months. All procedures were technically successful. There was a 1:1 correlation of motor thresholds for stimulation sites simultaneously mapped with the new suction mapping device and the classic fingerstick probe (24 patients, 74 stimulation points; r(2) = 0.98, p < 0.001). The lowest individual motor thresholds were as follows: > 20 mA, 7 patients; 11-20 mA, 13 patients; 6-10 mA, 8 patients; 4-5 mA, 17 patients; and 1-3 mA, 24 patients. At 3 months, 2 patients (3%) had a persistent postoperative motor deficit, both of which were caused by a vascular injury. No patient had a permanent motor deficit caused by a mechanical injury of the CST. 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. The acoustic feedback and the ability to stimulate the tissue continuously and exactly at the site of tissue removal improves the accuracy of mapping, especially at low (< 5 mA) stimulation intensities. This new technique may increase the safety of motor eloquent tumor surgery.

Simultaneous Direct Cortical Motor Evoked Potential Monitoring and Subcortical Mapping for Motor Pathway Preservation During Brain Tumor Surgery

The warning-sign hierarchy between quantitative subcortical motor mapping and continuous motor evoked potential monitoring during resection of supratentorial brain tumors: clinical article.Seidel K, Beck J, Steiglitz L, Schucht P, Raabe A.J Neurosurg 2013; 118:287-296. Mapping and monitoring are believed to provide an early warning sign to determine when to stop tumor removal to avoid mechanical damage to the corticospinal tract (CST). The objective of this study was to systematically compare subcortical monopolar stimulation thresholds (1-20 mA) with direct cortical stimulation (DCS)-motor evoked potential (MEP) monitoring signal abnormalities and to correlate both with new postoperative motor deficits. The authors sought to define a mapping threshold and DCS-MEP monitoring signal changes indicating a minimal safe distance from the CST. A consecutive cohort of 100 patients underwent tumor surgery adjacent to the CST while simultaneous subcortical motor mapping and DCS-MEP monitoring were used. Evaluation was performed regarding the lowest subcortical mapping threshold (monopolar stimulation, train of 5 stimuli, interstimulus interval 4.0 milliseconds, pulse duration 500 microseconds) and signal changes in DCS-MEPs (same parameters, 4 contact strip electrode). Motor function was assessed 1 day after the surgery, at discharge, and at 3 months postoperatively. The lowest individual motor thresholds (MTs) were as follows (MT in mA, number of patients): >20 mA, n = 12; 11 to 20 mA, n = 13; 6 to 10 mA, n = 20; 4 to 5 mA, n = 30; and 1 to 3 mA, n = 25. Direct cortical stimulation showed stable signals in 70 patients, unspecific changes in 18, irreversible alterations in 8, and irreversible loss in 4 patients. At 3 months, 5 patients had a postoperative new or worsened motor deficit (lowest mapping MT 20 mA, 13 mA, 6 mA, 3 mA, and 1 mA). In all 5 patients, DCS-MEP monitoring alterations were documented (2 sudden irreversible threshold increases and 3 sudden irreversible MEP losses). Of these 5 patients, 2 had vascular ischemic lesions (MT 20 mA, 13 mA) and 3 had mechanical CST damage (MT: 1 mA, 3 mA, and 6 mA; in the latter 2 cases, the resection continued after mapping and severe DCS-MEP alterations occurred thereafter). In 80% of patients with a mapping MT of 1 to 3 mA and in 75% of patients with a mapping MT of 1 mA, DCS-MEPs were stable or showed unspecific reversible changes, and none had a permanent motor worsening at 3 months. In contrast, 25% of patients with irreversible DCS-MEP changes and 75% of patients with irreversible DCS-MEP loss had permanent motor deficits. Mapping should primarily guide tumor resection adjacent to the CST. Direct cortical stimulation-motor evoked potential is a useful predictor of deficits, but its value as a warning sign is limited because signal alterations were reversible in only approximately 60% of the present cases and irreversibility is a post hoc definition. The true safe mapping MT is lower than previously thought. The authors postulate a mapping MT of 1 mA or less where irreversible DCS-MEP changes and motor deficits regularly occur. Therefore, they recommend stopping tumor resection at an MT of 2 mA at the latest. The limited spatial and temporal coverage of contemporary mapping may increase error and may contribute to false, higher MTs.

The warning-sign hierarchy between quantitative subcortical motor mapping and continuous motor evoked potential monitoring during resection of supratentorial brain tumors

Mapping and monitoring are believed to provide an early warning sign to determine when to stop tumor removal to avoid mechanical damage to the corticospinal tract (CST). The objective of this study was to systematically compare subcortical monopolar stimulation thresholds (1-20 mA) with direct cortical stimulation (DCS)-motor evoked potential (MEP) monitoring signal abnormalities and to correlate both with new postoperative motor deficits. The authors sought to define a mapping threshold and DCS-MEP monitoring signal changes indicating a minimal safe distance from the CST. A consecutive cohort of 100 patients underwent tumor surgery adjacent to the CST while simultaneous subcortical motor mapping and DCS-MEP monitoring was used. Evaluation was done regarding the lowest subcortical mapping threshold (monopolar stimulation, train of 5 stimuli, interstimulus interval 4.0 msec, pulse duration 500 μsec) and signal changes in DCS-MEPs (same parameters, 4 contact strip electrode). Motor function was assessed 1 day after surgery, at discharge, and at 3 months postoperatively. The lowest individual motor thresholds (MTs) were as follows (MT in mA, number of patients): > 20 mA, n = 12; 11-20 mA, n = 13; 6-10 mA, n = 20; 4-5 mA, n = 30; and 1-3 mA, n = 25. Direct cortical stimulation showed stable signals in 70 patients, unspecific changes in 18, irreversible alterations in 8, and irreversible loss in 4 patients. At 3 months, 5 patients had a postoperative new or worsened motor deficit (lowest mapping MT 20 mA, 13 mA, 6 mA, 3 mA, and 1 mA). In all 5 patients DCS-MEP monitoring alterations were documented (2 sudden irreversible threshold increases and 3 sudden irreversible MEP losses). Of these 5 patients, 2 had vascular ischemic lesions (MT 20 mA, 13 mA) and 3 had mechanical CST damage (MT 1 mA, 3 mA, and 6 mA; in the latter 2 cases the resection continued after mapping and severe DCS-MEP alterations occurred thereafter). In 80% of patients with a mapping MT of 1-3 mA and in 75% of patients with a mapping MT of 1 mA, DCS-MEPs were stable or showed unspecific reversible changes, and none had a permanent motor worsening at 3 months. In contrast, 25% of patients with irreversible DCS-MEP changes and 75% of patients with irreversible DCS-MEP loss had permanent motor deficits. Mapping should primarily guide tumor resection adjacent to the CST. DCS-MEP is a useful predictor of deficits, but its value as a warning sign is limited because signal alterations were reversible in only approximately 60% of the present cases and irreversibility is a post hoc definition. The true safe mapping MT is lower than previously thought. The authors postulate a mapping MT of 1 mA or less where irreversible DCS-MEP changes and motor deficits regularly occur. Therefore, they recommend stopping tumor resection at an MT of 2 mA at the latest. The limited spatial and temporal coverage of contemporary mapping may increase error and may contribute to false, higher MTs.