Blood vessel tumour. Coloured magnetic resonance imaging (MRI) head scan showing an arteriovenous malformation (AVM, red, upper left). The AVM is in the brain (pink & yellow) of a 20-year-old patient in this sagittal (vertical) image. This benign (non-cancerous) tumour, also known as an arteriovenous angioma, is formed from a clump of distended blood vessels. It may compress the brain, resulting in epilepsy, or cause a haemorrhage if a vessel bursts. AVMs are surgically removed or destroyed by radiotherapy. MRI scans produce slice images through tissues using a powerful magnet and pulses of radio waves.