Diffuse low-grade oligodendrogliomas extend beyond MRI-defined abnormalities

Background: Imaging determinations of the spatial extent of diffuse low-grade gliomas (DLGGs) are of paramount importance in evaluating the risk-to-benefit ratio of surgical resection. However, it is not clear how accurately preoperative conventional MRI can delineate DLGGs. Methods: We report a retrospective histologic and imaging correlation study in 16 adult patients who underwent serial stereotactic biopsies for the diagnosis of untreated supratentorial well-defined and non–contrast-enhanced DLGG, in whom biopsy samples were taken within and beyond (OutBSs) MRI-defined abnormalities. Results: Thirty-seven OutBSs that extended from 10 to 26 mm beyond MRI-defined abnormalities were studied. Immunostaining revealed MIB-1–positive cells (i.e., cycling cells) in all but 2 of the OutBSs. None of the MIB-1–positive cells coexpressed glial fibrillary acidic protein, and all of them coexpressed OLIG2. MIB-1–positive cells were cycling isolated tumor cells, because 1) their morphologic characteristics reflected those of tumor cells, 2) the number of MIB-1–positive cells per square centimeter was significantly higher than that of controls, 3) the number of MIB-1–positive cells per square centimeter was positively correlated with the tumor growth fraction (p = 0.012), and 4) the number of MIB-1–positive cells per square centimeter in OutBSs decreased with distance from the tumor (p = 0.003). Conclusions: This study demonstrates, using a multiscale correlative approach, that conventional MRI underestimates the actual spatial extent of diffuse low-grade gliomas (DLGGs), even when they are well delineated. These results suggest that an extended resection of a margin beyond MRI-defined abnormalities, whenever feasible in noneloquent brain areas, might improve the outcome of DLGGs.