# Mesenteric Ischaemia and Ischaemic Colitis

> Mesenteric ischaemia and ischaemic colitis for NEET-PG Medicine covering pain out of proportion, watershed areas and embolic versus thrombotic causes.

- Canonical URL: https://prepelephant.com/topics/neet-pg/medicine/mesenteric-ischaemia-and-ischaemic-colitis
- Exam / course: NEET-PG · Subject: Medicine
- Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team
- First published: 2026-10-14
- Last updated: 2026-10-14
- Reference basis: Harrison's Principles of Internal Medicine; Bailey and Love's Short Practice of Surgery; Sleisenger and Fordtran's Gastrointestinal and Liver Disease
- How to cite: "Mesenteric Ischaemia and Ischaemic Colitis", PrepElephant, https://prepelephant.com/topics/neet-pg/medicine/mesenteric-ischaemia-and-ischaemic-colitis

## Direct answer

Mesenteric ischaemia is reduced intestinal blood flow, most dangerously from acute occlusion of the superior mesenteric artery, which can cause transmural bowel necrosis. Its classic clue is pain out of proportion to the abdominal examination, often with a soft abdomen early on. Ischaemic colitis is a milder colonic form that usually affects the mucosa and watershed areas, and it often settles with supportive care.

## What you must remember

- **Pain out of proportion:** severe periumbilical pain with a soft abdomen early on; peritonism appears late, once necrosis develops.
- **Embolic occlusion:** sudden, usually from atrial fibrillation or a left ventricular thrombus after myocardial infarction.
- **Thrombotic occlusion:** develops on atherosclerotic plaque, often after a period of postprandial pain.
- **Non-occlusive ischaemia:** low splanchnic flow from shock, vasopressors, digoxin or heart failure.
- **Watershed areas:** the splenic flexure (Griffiths point) and rectosigmoid junction (Sudeck point), where ischaemic colitis usually strikes.
- **Ischaemic colitis:** commonly affects the left colon with rectal bleeding, and most cases are self-limiting.
- **Diagnosis:** CT angiography is first line in suspected acute mesenteric ischaemia, and a raised lactate suggests established necrosis.

## Embolic, thrombotic or non-occlusive: a clinical comparison

A 71-year-old man with atrial fibrillation has sudden periumbilical pain out of proportion to a soft abdomen, with a raised lactate. The examiner asks which cause fits and how it is confirmed. Each cause is distinguished by its tempo of onset and by the cardiac or vascular background.

| Feature | Embolic | Thrombotic | Non-occlusive |
|---|---|---|---|
| Onset | Sudden | Gradual, after prior pain | Gradual, in shock |
| Typical source | Atrial fibrillation or LV thrombus | Atherosclerotic plaque | Low flow, vasopressors |
| Key treatment | Anticoagulation and embolectomy | Revascularisation | Restore flow, stop vasoconstrictors |

The history and the tempo of onset usually separate the three causes, and CT angiography confirms the site of occlusion. A patient with atrial fibrillation who develops sudden pain is an embolic cause until proved otherwise.

Mesenteric ischaemia is a surgical and vascular emergency, so bowel salvage depends on speed, and delayed diagnosis is the main avoidable cause of death. Heparin is usually started early in suspected embolic or thrombotic disease while imaging is arranged, unless contraindicated. Lactate and clinical signs of bowel viability then guide the timing of revascularisation and any resection.

## Where the exam tests the reassurance trap

Mesenteric ischaemia is tested through findings that look reassuring but are not.

- **Trap:** reassuring a patient whose abdomen is soft — **Correct:** pain out of proportion to examination is the hallmark of acute mesenteric ischaemia, and peritonism comes later.
- **Trap:** choosing colonoscopy for suspected acute mesenteric ischaemia — **Correct:** CT angiography is first line, since endoscopy cannot assess the mesenteric vessels.
- **Trap:** assuming ischaemic colitis always needs surgery — **Correct:** most cases are mild and settle with fluids and bowel rest, while gangrene or peritonitis needs surgery.

## Frequently asked questions

### Why does pain out of proportion suggest acute mesenteric ischaemia?

Pain out of proportion to abdominal findings is the hallmark of acute mesenteric ischaemia, because the bowel is in pain before it becomes inflamed. A soft abdomen with severe pain should prompt urgent CT angiography, even before peritoneal signs appear.

### Which parts of the colon are watershed zones prone to ischaemic colitis?

The splenic flexure, known as Griffiths point, and the rectosigmoid junction, known as Sudeck point, are the watershed zones prone to ischaemic colitis. Griffiths point lies between the superior and inferior mesenteric artery territories, and Sudeck point lies between the lowest sigmoid branches and the superior rectal artery, so reduced flow affects them first.

### How does an embolic mesenteric occlusion differ from a thrombotic one?

An embolic occlusion arises suddenly from a cardiac source, most often atrial fibrillation, and causes severe pain without a prior history. A thrombotic occlusion develops on atherosclerotic plaque, so it is often preceded by postprandial pain and has a more gradual course.

### Which test is first line for suspected acute mesenteric ischaemia?

CT angiography of the abdomen is the first-line test for suspected acute mesenteric ischaemia, showing vessel occlusion and bowel wall changes. Endoscopy is not used for this diagnosis, and a raised lactate supports the clinical suspicion.