Subcortical stimulation mapping of descending motor pathways for perirolandic gliomas: Assessment of morbidity and functional outcome in 702 cases

OBJECTIVE Herein, the authors report their experience with intraoperative stimulation mapping to locate the descending subcortical motor pathways in patients undergoing surgery for hemispheric gliomas within or adjacent to the rolandic cortex, with particular description of the morbidity and functional outcomes associated with this technique. METHODS This is a retrospective analysis of patients who, in the period between 1997 and 2016, had undergone resection of hemispheric perirolandic gliomas within or adjacent to descending motor pathways. Data regarding intraoperative stimulation mapping and patient postoperative neurological status were collected. RESULTS Of 702 patients, stimulation mapping identified the descending motor pathways in 300 cases (43%). A new or worsened motor deficit was seen postoperatively in 210 cases (30%). Among these 210 cases, there was improvement in motor function to baseline levels by 3 months postoperatively in 161 cases (77%), whereas the deficit remained in 49 cases (23%). The majority (65%) of long-term deficits (persisting beyond 3 months) were mild or moderate (antigravity strength or better). On multivariate analysis, patients in whom the subcortical motor pathways had been identified with stimulation mapping during surgery were more likely to develop an additional and/or worsened motor deficit postoperatively than were those in whom the subcortical pathways had not been found (45% vs 19%, respectively, p < 0.001). This difference remained when considering the likelihood of a long-term deficit (i.e., persisting > 3 months; 12% vs 3.2%, p < 0.001). A higher tumor grade and the presence of a preoperative motor deficit were also associated with higher rates of motor deficits persisting long-term. A region of restricted diffusion adjacent to the resection cavity was seen in 20 patients with long-term deficits (41%) and was more common in cases in which the motor pathways were not identified (69%). Long-term deficits that occur in settings in which the subcortical motor pathways are not identified seem in large part due to ischemic injury to descending tracts. CONCLUSIONS Stimulation mapping allows surgeons to identify the descending motor pathways during resection of tumors in perirolandic regions and to attain an acceptable rate of morbidity in these high-risk cases.