Segmental colonic wall thickening in a watershed territory (splenic flexure, rectosigmoid) in an older patient with pain and bloody stool — CT separates non-occlusive colitis from transmural infarction that needs surgery.
Orient first
- Most colonic ischaemia is non-occlusive (low flow); arterial occlusion is less common in the colon than in the small bowel.
- Watershed areas: Griffiths point (splenic flexure) and Sudeck point (rectosigmoid); the rectum is usually spared.
- Right-sided colonic ischaemia carries a worse prognosis and may reflect SMA disease.
Acquire the study
- CT abdomen-pelvis with IV contrast (arterial and portal venous phases if mesenteric vessel disease is a question); coronal reformats; lung window for pneumatosis.
The manoeuvre
- Map the thickened segment on coronal images and relate it to a vascular territory (SMA vs IMA).
- Wall pattern on portal venous phase: target/halo (oedema, reversible) vs thin, non-enhancing wall (transmural infarction).
- Lung window: pneumatosis and portal venous gas.
- Arterial phase: SMA and IMA origins; embolus or occlusion.
- Pericolic fluid and fat stranding; free gas = perforation.
What confirms it
- Segmental colonic wall thickening in a watershed territory with a compatible clinical setting, and no alternative cause.
What licenses you to exclude it
- Normal colonic wall and enhancement excludes established ischaemic colitis; early mucosal ischaemia may still be seen only on colonoscopy.
The classic misread
- Calling it infectious or inflammatory colitis by pattern alone — the distribution and age decide.
- Missing a thin, paper-like wall that is the worst sign, not a normal one.