Schematic representation of the growth pattern of a GBM (a), including the following secondary structures of Scherer: perivascular accumulation of tumor cells (example in area indicated by b; vessels in red, tumor cells in blue), perineuronal satellitosis (b; neurons in green), subpial growth of tumor cells (b), and intrafascicular growth in the corpus callosum (c). Mitotic tumor cells are depicted in black. Furthermore, in GBMs necrosis (dark grey area) surrounded by pseudopalisading tumor cells and adjacent florid/glomeruloid microvascular proliferation (d) are often present. Images b–d on the right represent the histology of these features: in basterisk indicates subpial growth, arrow indicates perineuronal satellitosis, arrowhead indicates perivascular accumulation of tumor cells; image c shows increased cellularity with diffuse infiltration of tumor cells in the relatively well preserved myelinated tracts of the corpus callosum; in image dasterisk indicates area of necrosis, arrow indicates peri-necrotic pseudopalisading tumor cells, arrowheads indicate glomeruloid microvascular proliferation [b, d: H&E staining, c: combined Luxol Fast Blue and H&E staining; original magnification ×200 (b, c) and ×100 (c)]