Colonic gas distribution in toxic megacolon.

To determine whether dilation of the transverse colon is a specific pathophysiologic feature in toxic megacolon, plain films of the abdomen in different positions were obtained of 6 patients with ulcerative colitis complicated by toxic megacolon. All patients were examined initially in the supine position and subsequently in the prone position. Redistribution of gas in the colon occurred in all patients when the prone position was assumed. The shift of gas was largely from the transverse colon to the descending colon. Pathological examination of the colon in 5 patients revealed the transverse colon to be no more severely involved than the remainder of the colon. The findings suggest that distribution of colonic gas in toxic megacolon is largely governed by the influence of gravity and the anatomic position of the colon in the peritoneal cavity.