NIMG-73. FALSE POSITIVE INTRA-OPERATIVE MAGNETIC RESONANCE IMAGING DURING HIGH GRADE GLIOMA RESECTION

Abstract Intraoperative magnetic resonance imaging (iMRI) allows assessment of extent of resection during surgery for high-grade glioma (HGG). In most cases, contrast-enhancing areas noted on iMRI indicate residual tumor. However, false positives may occur, leading to inappropriate additional resection and patient morbidity. The rate and pattern of false positive findings in iMRI have not been fully described. We analyzed surgical and imaging findings in patients undergoing iMRI during resection of HGG to determine factors linked with potential false positive contrast enhancement. A single-center analysis retrospectively assessed consecutive patients undergoing resection of newly diagnosed high-grade glioma using iMRI guidance. Preoperative, intraoperative and postoperative imaging, as well as pathologic findings were assessed. One hundred seventy-four consecutive patients who underwent surgery from 2016-2023 were included. All patients had preoperative MRI showing contrast-enhancing tumor and all underwent one iMRI during surgery to assess extent of resection. 124/174 cases (71.3%) demonstrated contrast enhancement on iMRI that prompted inspection and additional resection using updated neuronavigation. Enhancement corresponding to residual tumor was identified with or without additional removal in 120/124 cases (96.8%). No residual tumor was found in 4/124 cases (3.2%, false positives). All false positive cases were the result of contrast accumulation in hematomas (2), hemostatic agents (1) or dependent portions of the resection cavity (1). Both hematomas were located in the walls of the resection cavity and confirmed as hematoma, rather than tumor, by separate pathology analysis. False positives were not associated with patient positioning, tumor sub-type, anatomic location of tumor or extent of resection. Gross total resection (GTR) was confirmed in 163/174 (93.7%) cases on postoperative imaging. False-positive iMRI during HGG surgery can mimic residual tumor. This occurs at a low rate due to contrast pooling in the cavity or accumulation within hemostatic agents or hematomas along the cavity wall. Meticulous hemostasis when preparing the patient for iMRI may help prevent false positives and prevent unnecessary additional resection.