Schematic drawing: pre-treatment and during treatment. Schematic drawing of high-grade glioma, pre-treatment (A), and with anti-VEGF treatment (B). (A) Contrast leakage (white) occurs around leaky tumour vessels enhancing the tumour area on MRI. Capillaries in surrounding tissue are not leaky. (B) Contrast-enhanced area is strongly reduced under anti-VEGF treatment. Tumour cells migrate furtively into the surrounding tissue and co-opt existing vasculature.