Patterns of radiation-induced subependymal enhancement in patients with high-grade glioma

Background and purpose Interpretation of imaging findings after radiation can be challenging in patients with high-grade glioma. Appearance of contrast-enhancing lesions during follow-up imaging poses difficulty in differentiating true progression from treatment-related changes. In the current study, we report patterns and clinical outcomes of radiation-induced subependymal enhancement. Materials and methods Patients with histopathological diagnosis of HGG developing radiation-induced contrast enhancement in the subependymal region were considered in the retrospective study. The subependymal enhancement was required to be in the high-dose region of radiotherapy. Patients underwent multiparametric magnetic resonance imaging (MRI), which included T1-contrast, T2-weighted, perfusion, and spectroscopy. Confirmation of radiation changes rather than disease progression was decided based on regression or stability of concerned findings on follow-up imaging. Results Thirty-four patients were included in the analysis. The median time from radiotherapy to onset of subependymal enhancement was 15 months. The enhancement pattern was feathery, nodular, and linear in 53%, 35%, and 3% of patients, respectively. A T2-hyperintense signal with a hypointense rim was seen in 74% of patients. Majority of these lesions were isoperfused (26%) or hypoperfused (47%). The median radiological follow-up after onset of subependymal enhancement was 7 months (range 1–61 months). At final follow-up, complete resolution, partial regression, and stable findings of the concerned enhancement were seen in 18%, 38%, and 44%, respectively. Conclusion Subependymal enhancement can be seen following radiation, which should be considered during the evaluation of follow-up imaging. Multiparametric MRI with specific contrast patterns, T2-weighted findings, and perfusion imaging can help identify radiation-induced enhancement.