Fig. 1

Imaging and histologic features of Patient #1. Preoperative MR imaging showing T2 FLAIR hyperintensity in the right temporal lobe (a) with minimal contrast enhancement in the T1 sequence with contrast (b). H&E-stained tumor tissue sections showing hypercellular brain parenchyma with microcalcifications. The brain parenchyma is infiltrated by monomorphic round glial cells with perinuclear clearing, resembling oligodendrocytes (c). Spindle cells in a perivascular distribution are noted (d). GFAP is positive in tumor cells (e), and Ki67 immunostaining shows a low proliferation index (f). Surveillance MR imaging showing T2 FLAIR hyperintensity around the surgical cavity (g) and new contrast enhancement along the resection cavity wall (h). H&E-stained tumor tissue sections show hypercellular brain parenchyma with oligo-like cells and perivascular pseudorosettes (i), and an endocrinoid (“chickenwire”) capillary network (j). The tumor cells are strongly positive for CD34 (k) and the Ki67 index is elevated (l) in comparison to the tumor resected in the first surgery (d)