Sigmoid volvulus is a closed-loop colonic obstruction due to twisting along the mesenteric or long axis of the bowel. Although colonic volvulus is not common, about 90% of cases occur in the sigmoid colon. On plain abdominal films, the sigmoid volvulus forms an inveed U-shaped structure with the twisted sigmoid loops lying adjacent and having an oval appearance called the "coffee bean" sign. On barium enema examination, tapered obstruction of the sigmoid colon is found. Ref: Ott D.J. (2011). Chapter 10. Gastrointestinal Tract. In M.Y. Chen, T.L. Pope, D.J. Ott (Eds), Basic Radiology, 2e.