Megacolon is a significant dilation of the colon. Toxic megacolon is the rapid nonobstructive dilation of the colon with infection or inflammation. Various forms of colitis such as ulcerative colitis, Crohn’s colitis, infectious colitis, ischemic colitis, radiation colitis and colitis associated with chemotherapy, and medications that affect motility of the bowel can all cause megacolon. The dilation may be segmental or include the entire colon. As nitric oxide increases and inhibits smooth muscle tone, inflammation progresses from the mucosa into smooth muscle layers and serosa, which causes the colon to expand. Radiologic evidence shows that the transverse colon may expand over 6 cm. This rapid widening may cause abdominal pain and tenderness, fever, perforation of the colon, rapid heart rate, shock, and sepsis.
Prognosis is best in the absence of perforation and when toxic megacolon is diagnosed and treated early. The distention must be reduced, electrolytes and fluids must be restored and any infection must be treated with antibiotics. Colectomy is recommended when dilation persists.