Blood vessel tumour. Coloured angiogram (X-ray) of an arteriovenous malformation (red and black mass, lower centre) in the lung of a 72-year-old man. This is a type of angioma, a benign tumour that is formed from a clump of distended blood vessels. It may cause internal bleeding if a vessel bursts. Surgical treatment may be required. In this case, treatment was with embolization coils to reduce or occlude blood flow to the affected area. The blood vessels have been highlighted with a contrast medium so that they can be seen on the X-ray. The contrast medium has been injected with a catheter, seen as the loop at upper left.