NIMG-73. RADIOGRAPHIC CHANGES AFTER RADIATION THERAPY IN SUBTOTALLY RESECTED ATYPICAL MENINGIOMAS

Abstract

Abstract BACKGROUND Adjuvant radiotherapy (RT) has been shown to improve outcomes after subtotal resection (STR) of atypical meningioma, but little is known about how tumors evolve on magnetic resonance imaging (MRI) and whether this correlates with RT response. METHODS We retrospectively identified histologically confirmed cases of WHO Grade II atypical meningioma at a large academic institution from 2004-2020 who underwent subtotal resection and received radiation. Clinicodemographic, surgical, RT, and histopathologic data were collected, as well as clinical outcomes, with a median follow-up time of 69 months (IQR 61). Patients were stratified by external beam RT (EBRT) and stereotactic radiosurgery (SRS). Radiographic data included tumor location, cerebral edema, susceptibility changes, leptomeningeal enhancement, calcification, necrosis, and time to recurrence. Progression was defined by radiology report. RESULTS Of 31 patients with STR for newly diagnosed atypical meningioma, 65% (20 of 31) received RT and 11 of 20 (55%) received EBRT while nine received SRS. Of the convexity/parasagittal meningiomas (N=10), 40% demonstrated venous sinus invasion. 65% (N=13) of cases were treated upfront; the other seven progressed at a median 9.4 months before undergoing RT. Post-RT, 74% decreased in size (N=5) or stabilized (N=9); imaging was not available for one case. Recurrence after RT was observed in five cases. 11 cases developed restricted diffusion at median onset of 24.9 months; 7 developed adjacent leptomeningeal enhancement at median onset of 14.7 months, of which 86% (6 of 7) received SRS. Other patterns included adjacent nodular (N=3) and linear (N=2) enhancement, and adjacent confluent T2 signal (N=4); these could potentially represent radiation-related changes. Only one case developed calcification after 70 months. CONCLUSIONS Atypical meningiomas exhibit variable patterns of evolution after RT which may predict treatment outcomes. Multivariate analysis is planned to correlate radiographic changes with pathology characteristics, RT modality, and time to recurrence.