A transverse colon over 6 cm with loss of haustra and nodular, thinned wall in a systemically unwell patient with colitis — reported with the maximal diameter and a direct search for free gas.
Orient first
- Complication of severe colitis: ulcerative colitis, C. difficile, infective and ischaemic colitis.
- The transverse colon is the usual site because it is non-dependent in a supine patient.
- Perforation is the event that kills; its signs are sought on every study.
Acquire the study
- Supine abdominal radiograph and an erect chest radiograph (or left lateral decubitus) for free gas.
The manoeuvre
- Supine radiograph: maximal transverse colon diameter in cm — over 6 cm is dilated.
- Haustra: absent, or thickened pseudopolypoid "thumbprinting" along the wall.
- Erect chest radiograph: subdiaphragmatic free gas; supine signs — Rigler sign, football sign.
What confirms it
- Colonic dilatation over 6 cm with loss of haustra in a patient with colitis and systemic toxicity (the clinical criteria complete it).
What licenses you to exclude it
- A normal-calibre colon with preserved haustra excludes megacolon; it does not exclude severe colitis.
The classic misread
- Measuring a redundant sigmoid loop and calling it megacolon — use the transverse colon on the supine film.
- Missing contained perforation that is only visible on CT.