Colonic bleeding. Endoscope view of bleeding in the sigmoid colon (part of the large intestine) from a Dieulafoy's lesion. The colon has been flooded with water to improve the view of the source of the bleeding. Dieulafoy's lesion is a pinpoint eroded patch in an artery in the lining of the colon. It causes heavy bleeding and blood in the faeces (melaena). Once identified it can be treated in several ways. The blood vessel can be sealed by an electric current (electrocoagul- ation), the injection of a sclerosant (an irritant chemical which blocks the vessel), laser or by the application of a tight band.