A 68-year-old man with atrial fibrillation develops sudden left-sided abdominal pain and bloody diarrhoea. Contrast CT shows segmental wall thickening of the descending colon and splenic flexure with a patent superior and inferior mesenteric artery. Colonoscopy shows oedematous, bluish mucosa that spares the rectum. Which feature best explains the distribution of injury seen here?

• A Watershed zones at the splenic flexure and rectosigmoid junction receive tenuous collateral supply ✓
• B The rectum is supplied solely by the inferior mesenteric artery and is the first territory lost when flow falls
• C Emboli preferentially lodge at branch points of the middle colic artery
• D The caecum has the thinnest wall and lowest perfusion pressure in the colon

Explanation

Ischaemic colitis is usually non-occlusive and targets watershed areas with poor collateral circulation: Griffiths point at the splenic flexure and Sudeck point at the rectosigmoid junction. The rectum is characteristically spared because it enjoys a rich dual blood supply from the inferior mesenteric and internal iliac arteries via the superior rectal and middle and inferior rectal arteries, which kills option B. Caecal involvement relates to embolic occlusion, not typical non-occlusive ischaemia.

Reference: Schwartz's Principles of Surgery, 11th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.