Internal bleeding. Coloured X-ray angiogram of internal abdominal bleeding (upper right). Blood vessels (yellow-purple) are visible on the X-ray because they have been injected with a contrast medium by a catheter (thin tube, far left). The bleeding (red/white area, upper right) is into the descending colon (part of the large intestine, not seen). These blood vessels are branches from the superior mesenteric artery, an artery bringing blood to this region of the abdomen. Such internal bleeding would show in bloody faeces. In severe cases it is potentially fatal. Treatment will be to stem the blood flow and diagnose the cause.