A 28-year-old man with a 3-day history of bloody diarrhea and severe abdominal pain is admitted with suspected fulminant ulcerative colitis. A supine abdominal X-ray is obtained as part of the acute abdomen series. The structures marked **A** in the diagram show loss of their normal appearance with associated colonic dilation measuring 8 cm. Which of the following best describes the significance of this radiological finding?

Question

Accepted Answer

B. Loss of haustra with dilation >6 cm indicates toxic megacolon, a surgical emergency with high mortality risk. The structure marked **A** represents colonic haustra — the incomplete folds that normally do NOT cross the entire lumen of the colon (unlike valvulae conniventes in small bowel). In fulminant ulcerative colitis, loss of haustra combined with colonic dilation >6 cm is pathognomonic for toxic megacolon, a life-threatening complication with mortality approaching 30%. The cecum is particularly at risk; dilation >9 cm (by Laplace law) predicts imminent perforation. This finding mandates urgent surgical consultation and typically requires colectomy. The normal "3-6-9 rule" for calibre (small bowel <3 cm, colon <6 cm, cecum <9 cm) is a cornerstone of acute abdomen interpretation on plain radiography. [Sutton Radiology 7e Ch 27]

Answer

A. Incomplete haustra crossing the lumen is a normal variant and does not require clinical correlation

Answer

C. Presence of haustra indicates normal colonic calibre and excludes any acute pathology

Answer

D. Haustra are incomplete folds that normally cross the entire colonic lumen, and their presence excludes obstruction

Explanation

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