Glioblastoma brain tumour. 3D diffusion tensor imaging (DTI) magnetic resonance imaging (MRI) scan of nerve pathways around a glioblastoma in the brain. Red pathways touch the tumour, yellow ones are dangerously close, and green ones are distant. The front of the brain is at right. Glioblastoma is the most common malignant primary brain tumour. Symptoms depend on the region of the brain affected, and include seizures, headaches, and memory and personality changes due to the growth of the cancer. Diffusion tensor imaging (tractography) measures the direction of water diffusion, which in the brain reveals the orientation of nerve fibres.