A 30-year-old woman with acute severe ulcerative colitis on intravenous hydrocortisone develops abdominal distension, fever of 39 degrees C, and a heart rate of 128/min over 24 hours. Abdominal radiograph shows a transverse colon diameter of 7.5 cm with no free air. What is the defining radiological criterion for the complication she has developed?
- A Colonic diameter greater than 10 cm at any point with mucosal islands
- B Caecal diameter greater than 12 cm with caecal wall thickening
- C Transverse colon diameter greater than 6 cm in a patient with systemic toxicity ✓
- D Diffuse colonic dilatation greater than 8 cm limited to the sigmoid colon
Correct answer: C. Transverse colon diameter greater than 6 cm in a patient with systemic toxicity
Explanation
Toxic megacolon is defined as systemic toxicity with colonic dilatation exceeding 6 cm, measured at the transverse colon on plain radiograph. Caecal dilatation above 9 to 12 cm defines Ogilvie syndrome rather than toxic megacolon. Management includes intravenous steroids, antibiotics, decompression, and serial radiographs; full-thickness colonoscopy and barium enema are contraindicated because of perforation risk. Colectomy is indicated for free perforation, uncontrolled sepsis, or failure to improve within 48 to 72 hours.
Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.
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Written and medically reviewed by the StethoPrep medical team.