Superior Mesenteric Artery Thrombosis

Superior mesenteric artery thrombosis is acute occlusion of the superior mesenteric artery by thrombus forming on an atherosclerotic plaque, usually at its origin. It causes extensive bowel ischaemia, often from the proximal jejunum to the transverse colon.

It accounts for 25% to 30% of acute mesenteric ischaemia, with mortality of 60% to 80%. Patients are older, have widespread atherosclerosis, and often report weeks of postprandial pain and weight loss (chronic mesenteric ischaemia). Other causes are aortic dissection, vasculitis, hypercoagulable states and low flow with a fixed stenosis.

Pathophysiology.

Plaque rupture or low flow causes thrombosis of a stenosis that already limits flow. Collateral vessels have often developed, so severe disease can be well tolerated until the final occlusion.

Acute severe abdominal pain out of proportion to findings, with a previous history of postprandial pain, food fear and weight loss. Vomiting, diarrhoea, bloody stools, distension and peritonitis follow, with shock in late disease.

Red flags.

• Peritonitis.
• Rising lactate or acidosis.
• Shock.
• Aortic dissection signs.

Multiphase CT angiography shows occlusion at the origin or proximal superior mesenteric artery with calcified plaque, and bowel wall changes. Lactate, full blood count, creatinine and D-dimer are sent. Do not delay treatment for tests. Echocardiography and lipid profile follow.

Differential diagnosis.

• Mesenteric arterial embolism.
• Nonocclusive mesenteric ischaemia.
• Mesenteric venous thrombosis.
• Aortic dissection.
• Perforated viscus.
• Acute pancreatitis.

Resuscitate and give heparin. Revascularise by endovascular recanalisation (aspiration, angioplasty and stent) or by open bypass or endarterectomy, and resect non-viable bowel, with second look surgery within 24 to 48 hours. Endovascular treatment is preferred when there is no peritonitis.

• Heparin (unfractionated): 80 units/kg IV bolus (maximum 5,000 units) then 18 units/kg/h, adjusted to an activated partial thromboplastin time of 1.5 to 2.5 times control; maximum bolus 5,000 units; monitor aPTT every 6 hours, platelets and bleeding; reduce with hepatic impairment and thrombocytopenia.
• Piperacillin-tazobactam: 4.5 g IV every 6 hours for 5 to 7 days (up to 14 days after resection with contamination); maximum 18 g daily; monitor renal function and counts; reduce for creatinine clearance under 40 mL/min.
• Aspirin after revascularisation: 75 to 100 mg orally once daily long term; maximum 100 mg daily; monitor bleeding; avoid with active bleeding and peptic ulcer.
• Atorvastatin: 40 to 80 mg orally once daily at night long term; maximum 80 mg daily; monitor liver tests, creatine kinase and lipids; reduce to 20 mg with strong CYP3A4 inhibitors, and avoid in active liver disease.

Clopidogrel 75 mg daily for 1 to 3 months is added after stenting by vascular decision. Control blood pressure, stop smoking and treat diabetes.

Monitoring. Lactate, haemoglobin and abdominal examination every 4 to 6 hours for 48 hours; duplex or CT angiography at 1, 6 and 12 months after stenting.

Referral and escalation. Vascular surgery and interventional radiology urgently; critical care; intestinal failure team for short bowel.