Acute mesenteric ischaemia !

Acute mesenteric ischaemia is a sudden loss of blood flow to the intestine, usually in the superior mesenteric artery; the bowel can die within hours.

Updated 2026-10-29

Structures involved

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In the clinical exam

Acute abdomen and peritoneal irritation

In physiology

Splanchnic and portal circulation

Why it happens

What it is

A sudden loss of blood flow to the intestine, most often in the superior mesenteric artery, that can quickly lead to bowel necrosis. It is a surgical emergency with high mortality.

Who gets it

Uncommon but lethal; it mainly affects older adults with heart and vascular disease. Diagnosis is often delayed because early signs are subtle.

Causes

Arterial embolism to the superior mesenteric artery, usually from the heart (atrial fibrillation, recent myocardial infarction)
Arterial thrombosis on atherosclerotic narrowing at the origin of the vessel
Non-occlusive mesenteric ischaemia: low-flow states, shock, vasopressors, cardiac surgery, dialysis
Mesenteric venous thrombosis: thrombophilia, portal hypertension, pancreatitis, malignancy
Aortic dissection involving the mesenteric vessels

Risk factors

Atrial fibrillation, especially without anticoagulation
Atherosclerosis, smoking, diabetes; prior chronic mesenteric ischaemia (pain after meals, food fear, weight loss)
Heart failure and low cardiac output
Older age
Hypercoagulable states, oral contraceptives (venous form)

Pathophysiology

The mucosa is the layer most sensitive to ischaemia and starts to die within hours, releasing lactate and allowing bacteria to cross the bowel wall. Ischaemia then progresses to full-thickness necrosis, perforation, peritonitis and sepsis. Emboli usually lodge just beyond the origin of the middle colic artery, sparing the proximal jejunum; thrombosis occludes the ostium and affects more bowel.

Classification

Arterial embolic
Arterial thrombotic
Non-occlusive (NOMI)
Mesenteric venous thrombosis

Symptoms and signs

Severe abdominal pain out of proportion to the physical findings
Sudden bowel emptying: vomiting and diarrhoea
Blood in the stool (later)
Distension, then guarding and rigidity when the bowel has infarcted
Venous form: more gradual, less specific pain

Diagnosis

Clinical: High suspicion in an older patient with cardiovascular risk and severe pain with few signs; early examination may be nearly normal.
Tests: Lactate often rises but is non-specific, and a normal value does not rule out ischaemia. Leukocytosis, metabolic acidosis, D-dimer, raised amylase. ECG for atrial fibrillation.
Imaging: CT angiography (arterial and venous phases) is the first-line test: it shows the occlusion, bowel wall changes, pneumatosis and portal venous gas. It is not delayed for kidney function concerns. Plain X-ray is of little use.

Differential diagnosis

Perforated viscus
Acute pancreatitis
Small bowel obstruction or volvulus
Aortic dissection or ruptured abdominal aortic aneurysm
Ischaemic colitis
Myocardial infarction with abdominal pain

Goal of treatment

Restore blood flow to the bowel as fast as possible, remove dead bowel, and support the circulation, to save the patient and as much intestine as possible.

Treatment

Acute: Resuscitation with fluids, correction of acidosis, nasogastric decompression and broad-spectrum antibiotics.
Medical: Immediate anticoagulation with intravenous heparin unless contraindicated; it is the main treatment of mesenteric venous thrombosis.
Surgical: Laparotomy with embolectomy or bypass of the superior mesenteric artery, resection of non-viable bowel and often a planned second-look operation.
Procedure: Endovascular treatment (aspiration, thrombolysis, angioplasty and stenting) in selected patients, especially thrombotic occlusion, often in a hybrid setting.
Medical: Non-occlusive ischaemia: treatment of the cause, improvement of cardiac output, reduction of vasopressors and, in some centres, intra-arterial vasodilators.
Medical: Long-term anticoagulation for embolic or venous disease and antiplatelet and lipid-lowering therapy for atherosclerosis.

Complications

Bowel necrosis and perforation
Peritonitis, sepsis and multiorgan failure
Short bowel syndrome after extensive resection
Recurrent ischaemia or stricture

Prognosis

Mortality remains high, and it rises with every hour of delay. Early diagnosis with CT angiography and rapid revascularisation improve survival.

Prevention

Anticoagulation for atrial fibrillation when indicated
Control of vascular risk factors and stopping smoking
Revascularisation of symptomatic chronic mesenteric ischaemia

Test yourself

Think of the answer, then tap the question to see it.

What is the classic clinical feature of acute mesenteric ischaemia?

Severe abdominal pain out of proportion to the physical examination, often with sudden vomiting or diarrhoea.

What is the most common source of an embolus to the superior mesenteric artery?

The heart, usually a left atrial thrombus in atrial fibrillation, or a ventricular thrombus after myocardial infarction.

Which imaging test is first line when acute mesenteric ischaemia is suspected?

Biphasic CT angiography of the abdomen, done without delay.

Does a normal lactate exclude acute mesenteric ischaemia?

No. Lactate is non-specific and may stay normal early; a rising lactate is a late sign.

Why does an SMA embolus often spare the proximal jejunum?

Emboli usually lodge distal to the origin of the middle colic artery, so the first jejunal branches still receive blood.

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Educational information, not medical advice. For any symptom, see a health professional.

Sources: Acute Mesenteric Ischemia (StatPearls (NCBI Bookshelf), 2026).

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Representative model, for educational purposes only.

Superior mesenteric artery highlighted on the Durgical 3D model