Twisted sigmoid colon. Coloured barium X-ray of the abdomen of a 68 year old patient with a twisted sigmoid colon (known as sigmoidal volvulus). The sigmoid colon is the last part of the large intestine before the rectum. The patient was given an enema containing radio-opaque barium prior to the X-ray, and the irregular build up of barium (bottom, white) reveals the twist (upper centre). Twisting of the intestine can lead to its partial or full obstruction, limiting the intestine's blood supply and the passage of food. Cutting off of the blood supply can lead to tissue death and gangrene, therefore requiring emergency surgery.