Toxic megacolon
Toxic megacolon is life-threatening, non-obstructive colonic dilation with systemic toxicity, most often complicating fulminant Clostridioides difficile colitis or a severe ulcerative colitis flare. Diagnosis requires colonic dilation over 6 cm on plain film plus systemic toxicity criteria; first-line treatment is bowel rest, correction of precipitants, targeted therapy of the underlying colitis, and urgent surgical consultation for colectomy if there is no rapid improvement.
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What this article covers
- Overview
Toxic megacolon is non-obstructive colonic dilation, most often of the transverse colon, in a patient with severe colitis who also meets systemic toxicity criteria: fever, tachycardia, leukocytosis…
- Epidemiology
Underlying disease: Toxic megacolon most often complicates fulminant Clostridioides difficile colitis or a severe ulcerative colitis flare, and less often Crohn colitis, ischemic colitis, radiation…
- Risk factors
Extent of colitis: Pancolitis with deep ulceration carries higher risk than left-sided or limited disease.
- Pathophysiology
Transmural extension of colonic inflammation, whether from C difficile toxin-mediated injury or an ulcerative colitis flare, damages the myenteric (Auerbach) plexus within the muscularis propria.
- Clinical features
Underlying colitis symptoms: Days of bloody diarrhea, crampy abdominal pain, and fever precede megacolon in most cases.
- Differential diagnosis
Acute colonic pseudo-obstruction (Ogilvie syndrome): Reaches the same dilation threshold on plain film, but without antecedent colitis, transmural inflammation, or systemic toxicity criteria; follows…
- Diagnosis
First, what establishes the diagnosis: A plain supine abdominal radiograph showing colonic dilation exceeding 6 cm (or cecal diameter exceeding 12 cm) in a patient who also meets systemic toxicity…
- Management
First, resuscitate and remove precipitants: Admit to an intensive care or high-acuity unit, keep the patient NPO with nasogastric decompression, give isotonic intravenous crystalloid, correct…
- Complications
Colonic perforation: The most feared complication, producing feculent peritonitis and septic shock; new peritoneal signs or free air on imaging demand immediate surgery.
- Prognosis
Mortality without perforation is roughly 2% to 8%, but rises to about 20% to 40% once perforation has occurred, so early recognition and timely surgery are the largest determinants of survival.
- Prevention
Avoid precipitants in active severe colitis: Do not use opioids, anticholinergic agents, antimotility agents, or barium enema; correct hypokalemia promptly, targeting a serum potassium of at least 4 mEq/L.
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Related articles
- Clostridioides difficile infection
Clostridioides difficile infection is toxin-mediated colitis that follows disruption of normal colonic flora, most often by antibiotics, and ranges from watery diarrhea to fulminant colitis with shock, ileus, or megacolon. Diagnosis rests on unformed stool testing (NAAT and/or toxin EIA) in a patient with three or more unformed stools in 24 hours, and treatment is chosen by IDSA/SHEA severity grade, oral vancomycin or fidaxomicin for 10 days, escalating to high-dose vancomycin plus IV metronidazole for fulminant disease.
- Ulcerative colitis
Ulcerative colitis is a chronic immune-mediated disease of continuous mucosal inflammation that begins in the rectum and extends proximally through the colon, presenting with bloody diarrhea and tenesmus and confirmed by colonoscopy with biopsy. Treatment is stepped by extent and severity from 5-aminosalicylates through corticosteroids, immunomodulators, and biologics, with acute severe disease requiring IV corticosteroids and medical or surgical rescue, and colectomy remains curative.
- Crohn disease
Crohn disease is a chronic transmural inflammatory bowel disease that can affect any segment from mouth to anus in skip lesions, most classically the terminal ileum, and is confirmed by ileocolonoscopy showing cobblestoning, skip areas, and non-caseating granulomas on biopsy. Management follows an ordered sequence of glucocorticoid or budesonide induction followed by immunomodulator or biologic maintenance, with surgery reserved for fixed complications rather than cure.
- Ischemic colitis
Ischemic colitis is the most common form of gastrointestinal ischemia, caused by a nonocclusive low-flow state in colonic microvessels that classically injures the watershed splenic flexure and rectosigmoid junction. Most cases are mild and self-limited with supportive care, but segmental CT thickening with peritoneal signs, pneumatosis, or gangrene demands emergent surgery rather than antibiotics alone.
- Viscus perforation
Viscus perforation is a breach through the wall of a hollow abdominal organ that spills luminal contents into the peritoneal cavity, producing sudden severe abdominal pain, peritonitis, and secondary bacterial peritonitis; free intraperitoneal air on imaging is the clinching finding, and management is emergent surgical source control paired with resuscitation and broad-spectrum antibiotics.
- Sepsis
Sepsis is life-threatening organ dysfunction caused by a dysregulated host response to infection, identified by an acute rise in SOFA score of 2 points or more in a patient with known or suspected infection. Survival depends on recognizing the pattern early and completing the hour-1 bundle: lactate, blood cultures before antibiotics, broad-spectrum antibiotics such as cefepime 2 g IV every 8 hours, and 30 mL/kg crystalloid for hypotension or a lactate of 4 mmol/L or higher.