Ogilvie syndrome is the acute dilatation of the colon in the absence of any mechanical obstruction in severely ill patients. Acute colonic pseudo-obstruction is characterized by massive dilatation of the cecum (diameter > 10 cm) and right colon on abdominal X-ray. It is a type of megacolon, sometimes referred to as "acute megacolon," to distinguish it from toxic megacolon. The condition carries the name of the British surgeon Sir William Heneage Ogilvie (1887–1971), who first reported it in 1948.