P27.25.A THE UTILITY OF INTRAOPERATIVE MRI IN THE RESECTION OF RECURRENT GBM: A SINGLE-CENTER RETROSPECTIVE ANALYSIS

Abstract BACKGROUD Intraoperative magnetic resonance imaging (iMRI) guidance for the resection of newly diagnosed glioblastoma (GBM) has been shown to be comparable to fluorescence guidance. However, the role of iMRI-guided resection in the recurrent setting remains unclear. In this study, we aimed to examine the utility of iMRI in the resection of recurrent GBM. METHODS Patients undergoing re-resection for the first recurrence of WHO grade 4 IDH-wildtype GBM were retrospectively analyzed. The utility of iMRI (1.5T) guidance with respect to intraoperative decision-making for additional tumor resection and residual nodular contrast enhancing (CE) tumor on early postoperative MRI (epMRI, within 48 hours, 3T) scans was assessed. RESULTS 103 consecutive patients (mean age: 59 years; 64 males and 39 females) undergoing re-resection for first GBM recurrence in the years 2018 to 2022 were included. iMRI-guided resection was performed in 84 (81%) cases and 5-ALA was applied in 8 (8%) cases. In 11 cases (11%), neither was applied. In 77/84 (92%) patients of the iMRI group, a gross total resection (GTR; defined as no residual nodular CE tumor) was intended. After iMRI, additional resection was carried out in 53/84 cases (63%) while a GTR was already achieved in 28/84 cases (33%). In the remaining 3 cases, additional resection was not possible due to functional reasons. On epMRI, a GTR was achieved in 63/84 (75%) cases. In 17 cases (20%), residual CE was detected on epMRI (GTR not intended in 3 cases). In 28 cases with intraoperatively assumed GTR, epMRI confirmed GTR in 25 cases (89%, mismatch in 3 cases, 11%), which was higher than in cases with additional intraoperative resection after iMRI (GTR in 42 out of 53 cases, 82%, p=0.07). In the remaining 11/53 cases, residual CE tumor was detected despite additional intraoperative resection (18%). Hence, GTR was achieved in 63 out of intended 77 patients (81%). Postoperative neurological deficits were noted in 11/53 patients with additional resection (20%) compared to 3/28 patients without additional resection (10%, p=0.126) and were mostly transient (permanent deficits 3/53 and 1/28 patients, respectively). In this cohort, median survival after repeat surgery was 220 days. CONCLUSION iMRI provides valuable information on residual CE tumor for intraoperative decision making concerning additional tumor resection in the setting of recurrent GBM. A mismatch between GTR assessed on iMRI and epMRI could be attributed to diff