PassFinals
Colorectal Surgery

Ischaemic Colitis

A fall in colonic perfusion below what the mucosa needs, striking hardest at the watershed zones where two arterial territories barely overlap, so the splenic flexure suffers first and the resulting mucosal injury produces the classic pairing of left-sided pain and bloody diarrhoea.

In a nutshell

Ischaemic colitis is usually a low-flow state, not an occluded artery, striking hardest at watershed zones (splenic flexure, rectosigmoid junction) where collateral supply is sparsest. Mucosal injury there produces crampy left-sided pain with bloody diarrhoea, and management is supportive unless transmural infarction develops.

Classic presentation

An older patient with vascular risk factors or recent hypotension develops sudden crampy left iliac fossa pain followed within hours by bloody diarrhoea.

Key points

  • The splenic flexure (Griffiths' point) and rectosigmoid junction (Sudek's point) are watershed zones between the SMA and IMA territories, and are hit first whenever perfusion falls.
  • Ischaemic colitis is typically caused by global hypoperfusion (hypotension, arrhythmia, low cardiac output), unlike acute mesenteric ischaemia, which is usually embolic or thrombotic occlusion of a named vessel.
  • The pain-then-bloody-diarrhoea sequence follows directly from mucosal sloughing and ulceration in the ischaemic segment.
  • Most cases are mucosal/submucosal and self-limiting with supportive care; peritonism or a rising lactate signals transmural infarction requiring surgery.
  • Isolated right-sided ischaemic colitis carries a worse prognosis because the right colon shares watershed vulnerability with the SMA territory supplying the small bowel.

First-line investigation

CT abdomen and pelvis with contrast to define the affected segment and look for signs of transmural involvement.

Management

Resuscitate and involve specialists

  • Admit for urgent senior gastroenterology and colorectal-surgical review; resuscitate, monitor perfusion and correct the precipitating low-flow state.1,2

Confirm extent and severity

  • Use urgent contrast CT; add arterial and portal-venous phase angiography when acute mesenteric ischaemia or right-sided disease is possible, and use limited endoscopy within 48 hours only if stable and safe.1,2

Support uncomplicated disease

  • Provide bowel rest initially, early enteral nutrition when safe, VTE prophylaxis when indicated, and antibiotics only when disease severity or systemic toxicity justifies them under local policy.1,3,4

Operate for transmural injury

  • Peritonitis, perforation, gangrene, uncontrolled haemorrhage or deterioration despite resuscitation require urgent operative assessment and resection of non-viable bowel.1

Prevent recurrence and detect stricture

  • Review cardiovascular and medication contributors after recovery, and investigate recurrent bleeding, anaemia, diarrhoea or obstructive symptoms for chronic colitis or a post-ischaemic stricture.1

Exam traps

  • Do not confuse ischaemic colitis (low-flow, watershed, usually self-limiting) with acute mesenteric ischaemia (embolic/thrombotic occlusion, small bowel, high mortality): the mechanisms and urgency differ.
  • A rigid, peritonitic abdomen changes this from a medical to a surgical emergency: supportive management alone is inappropriate once transmural signs appear.
  • The splenic flexure is the classic exam location because it is a watershed zone, not because of any local pathology there specifically.
  • Bloody diarrhoea in an older patient with cardiovascular disease is ischaemic colitis until proven otherwise, but colonoscopy should be performed cautiously without full insufflation given the compromised bowel wall.

Illustrations

Colonic watershed zonesDiagram of the colonic arterial supply showing the SMA and IMA territories meeting at the splenic flexure (Griffiths' point) and rectosigmoid junction (Sudek's point), highlighting these as areas of sparse collateral supply.PassFinals · original
CT appearance of ischaemic colitisAxial contrast CT image showing segmental thickening of the splenic flexure with surrounding fat stranding, sparing adjacent bowel.Hellerhoff, Wikimedia Commons · CC-BY-SA-4.0
Endoscopic appearance of mucosal ischaemiaColonoscopic image showing pale, oedematous mucosa with petechial haemorrhage and patchy ulceration in a segmental distribution.melvil, Wikimedia Commons · CC-BY-SA-4.0

Key sources

  1. BMJ clinical update: Ischaemic colitis (UK clinical update covering urgent assessment, contrast CT, endoscopic confirmation, supportive care, surgical indications, antimicrobial uncertainty, VTE prophylaxis and follow-up. It notes that there is no dedicated UK national ischaemic-colitis guideline and cites the relevant specialist evidence available at publication.)
  2. ESVS 2025 Guidelines on Diseases of the Mesenteric and Renal Arteries and Veins (Current specialist vascular guideline for acute and chronic mesenteric ischaemia, including urgent biphasic CT angiography, specialist-centre care and exclusion of acute mesenteric arterial or venous disease when the colonic presentation is severe or atypical.)
  3. NICE NG89: Venous thromboembolism in over 16s (NICE VTE-prevention guidance used for risk assessment and mechanical or pharmacological prophylaxis when indicated and safe; it does not provide disease-specific treatment for ischaemic colitis.)
  4. BNF online: current antibacterial prescribing (Use the current BNF and local antimicrobial policy for agent choice, dosing, route, renal adjustment, interactions, duration and review; no fixed antibiotic regimen is reproduced here.)

This page is exam revision material, not medical advice, and must not be used for patient care. Always check drug doses against the BNF and current guidance. Full disclaimer.