Introduction: Intraoperative magnetic resonance imaging (iMRI) can be used to enhance and confirm resection of high-grade gliomas. Effective use of iMRI in the assessment of high-grade glioma resection depends on accurate identification of contrast-enhancing residual tumor. The authors systematically analyzed findings in patients undergoing iMRI to identify factors that could confound the assessment of residual tumor.
Methods: A single-center analysis included consecutive high-grade glioma patients undergoing their first resection surgery with the goal of gross total resection using iMRI guidance (3T, T1-weighted with and without contrast). Preoperative, intraoperative and postoperative imaging, as well as pathologic findings were assessed.
Results: Forty-four consecutive iMRI high-grade glioma resection patients were included (24 male, 20 female). Eighteen of 44 cases (41%) demonstrated contrast enhancement on iMRI that prompted inspection and/or additional resection. While enhancement corresponding to residual glioma was identified and removed in 14 cases (78% of cases with iMRI enhancement), there was no tumor found in 4 cases of iMRI enhancement (22%, false positives). There were no cases of false negatives. All false positive cases were the result of contrast extravasation pooling in dependent portions of the resection site (Figure 1) that appeared as enhancing tumor; the contrast medium mixed with fluid in the surgical cavity and was removed by aspiration. Prone position was associated with false positives (P=0.04). Gross total resection was confirmed in all 44 cases on postoperative imaging.
Conclusions: False-positive iMRI findings can confound assessment of residual high-grade glioma and are the result of contrast extravasation into resection cavity fluid. Imaging features associated with iMRI false positives include contrast enhancement in the dependent portion of the resection cavity. Further investigation of the mechanism for increased risk of false positives with prone position is warranted. Identification and avoidance of false positive errors can prevent unnecessary additional resection and reduce potential morbidity.
Patient Care: Understanding that false positive enhancement can occur on intraoperative MRI during glioma resection can both prevent further unnecessary resection and inform future efforts to improve imaging accuracy.
Learning Objectives: By the conclusion of this session, participants should: 1) Be aware that false positive enhancement can occur on iMRI for glioma resection, especially with prone positioning 2) Recognize iMRI images worrisome for false positives 3) Decide upon need for further glioma resection based upon these findings
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