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Megacolon

Last updated: February 5, 2021

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Megacolon is the dilation of the colon in the absence of a mechanical obstruction (e.g., colonic tumor/stricture). There are three etiological types of megacolon: acute, chronic, and toxic megacolon. Acute megacolon (Ogilvie's syndrome) is the acute dilation of the colon, characteristically seen in severely medically/surgically ill patients, probably secondary to an electrolyte/metabolic imbalance. Chronic megacolon is the permanent dilation of the colon caused by chronic colonic dysmotility due to an underlying neuropathic (Hirschsprung's disease, chronic Chagas disease) or myopathic (Duchenne's muscular dystrophy) disorder. Patients with acute/chronic megacolon typically present with abdominal pain, bloating, and constipation. Toxic megacolon is a life-threatening dilation of the colon associated with systemic toxicity due to infectious colitis (C. difficile pseudomembranous colitis, Salmonella enterocolitis) or inflammatory colitis (inflammatory bowel disease). Patients typically present with signs of sepsis (tachycardia, hypotension) and a history of abdominal pain and bloody diarrhea. Abdominal x-rays demonstrate a colonic dilation, with/without air-fluid levels, and preserved haustrae. Contrast-enhanced CT scans can identify/rule out a mechanical colonic obstruction and possible complications (colonic ischemia/perforation). Patients with acute/chronic megacolon can often be treated conservatively with bowel rest, dietary modifications, prokinetic drugs, and/or neostigmine. Colonoscopic decompression is often successful in patients with acute megacolon. Surgical intervention for acute/chronic megacolon (colectomy and ileorectal anastomosis) is indicated if conservative treatment fails. Conservative management of toxic megacolon includes bowel rest, IV antibiotics (for infectious colitis), IV steroids (for inflammatory bowel disease). There is a high risk of colonic perforation in patients with toxic megacolon. Hence, no improvement to medical therapy within 48–72 hours is an indication to perform surgery (subtotal colectomy and end ileostomy).

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Colonoscopy should be avoided in patients with suspected toxic megacolon since it increases the risk of colonic perforation.
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