Aortic Mural Thrombus

A thrombus attached to the aortic wall that does not arise in an aneurysm. It is a rare but important source of arterial embolism, and it is found in the aortic arch, the descending thoracic aorta and, less often, the abdominal aorta.

• Causes:
  • Atherosclerosis with ulcerated or complex plaque (the commonest cause in older patients).
  • Hypercoagulable states in younger patients with a normal looking aorta: malignancy, antiphospholipid syndrome, heparin induced thrombocytopenia, myeloproliferative neoplasms (including JAK2 mutation), factor V Leiden, prothrombin gene mutation, protein C or S deficiency, nephrotic syndrome, oral contraceptives, and severe infection.
  • Other: aortic aneurysm, trauma, aortitis, previous aortic surgery or stents, and catheter injury.
• Consequences: embolic stroke, mesenteric ischaemia, renal and splenic infarction, acute limb ischaemia and blue toe syndrome. Thrombus can recur after anticoagulation fails in about 10%. Larger, pedunculated and mobile thrombi embolise more often.

• Often discovered after an embolic event: transient ischaemic attack or stroke with no cardiac or carotid source, abdominal pain with mesenteric ischaemia, flank pain and haematuria from renal infarction, left upper quadrant pain from splenic infarction, acute limb ischaemia (pain, pallor, pulselessness, paraesthesia, paralysis), blue toes and livedo reticularis. Some are asymptomatic.
• Differential diagnosis: cardiac source (atrial fibrillation, left ventricular thrombus, infective endocarditis, myxoma), carotid disease, cholesterol atheroembolism, aortic dissection, aortic tumour (sarcoma), vasculitis, and heparin induced thrombocytopenia.
• Complications: stroke, bowel infarction, acute kidney injury, limb loss, recurrent embolism, and bleeding on anticoagulation.

• Transoesophageal echocardiography (arch and descending aorta) shows the mobile or sessile mass; CT angiography shows a low attenuation, non-enhancing filling defect along the wall; MRI for tissue characterisation.
• Exclude a cardiac source: ECG, prolonged rhythm monitoring (14 to 30 days), transthoracic and transoesophageal echocardiography, and blood cultures if infection is suspected. Carotid imaging, brain MRI and abdominal CT for embolic sites.
• Blood tests: full blood count (platelets, haemoglobin), prothrombin time and aPTT, D-dimer, creatinine, urinalysis, lipids.
• Thrombophilia testing, ideally before or off anticoagulants where possible: lupus anticoagulant, anticardiolipin and beta-2 glycoprotein I antibodies (repeat at 12 weeks), factor V Leiden, prothrombin gene mutation, protein C, protein S and antithrombin levels, JAK2 V617F, and a heparin induced thrombocytopenia assessment if heparin exposure. Screen for cancer by examination, chest, abdominal and pelvic imaging.

• Anticoagulation is the first line treatment (evidence is observational and limited):
  • Enoxaparin 1 mg/kg SC every 12 hours (1 mg/kg once daily if creatinine clearance is less than 30 mL/min), or IV unfractionated heparin 80 units/kg bolus then 18 units/kg/h (aPTT 1.5 to 2.5 times control).
  • Then warfarin to INR 2.0 to 3.0 for at least 3 to 6 months; continue indefinitely if the cause persists (antiphospholipid syndrome, cancer, thrombophilia) or events recur. Triple positive antiphospholipid syndrome: warfarin to INR 2.0 to 3.0 (higher intensity (INR 3.0 to 4.0, or 2.5 to 3.5 per local protocol) if arterial events occur or recur despite INR 2.0 to 3.0), and avoid direct oral anticoagulants.
  • A direct oral anticoagulant can be used in the absence of antiphospholipid syndrome and cancer: apixaban 10 mg twice daily for 7 days then 5 mg twice daily, or rivaroxaban 15 mg twice daily for 21 days then 20 mg daily; evidence is limited.
  • Cancer associated thrombus: enoxaparin 1 mg/kg every 12 hours (or 1.5 mg/kg once daily) for at least 6 months and while cancer is active.
  • Add aspirin 75 to 100 mg daily for atherosclerotic disease when bleeding risk is low, and atorvastatin 40 to 80 mg daily.
  • Repeat CT angiography or transoesophageal echocardiography at 3 months; resolution occurs in about two thirds of patients.
• Heparin induced thrombocytopenia: stop all heparin, start argatroban 2 micrograms/kg/min IV (0.5 to 1 microgram/kg/min in hepatic impairment) or fondaparinux 7.5 mg SC daily (5 mg if under 50 kg, 10 mg if over 100 kg); begin warfarin only after platelets exceed 150 x 10^9/L, with at least 5 days of overlap.
• Intervention for failure of therapeutic anticoagulation (recurrent emboli), a large (greater than 10 mm) pedunculated or mobile thrombus, or a contraindication to anticoagulation:
  • Thromboendarterectomy or resection with graft replacement of the involved segment.
  • Thoracic endovascular aortic repair with a covered stent to exclude the thrombus (avoid in aortic arch branch vessels without protection).
  • Thrombolysis is avoided because it can fragment the thrombus and cause further embolism.
• Treat embolic complications: embolectomy or thrombolysis free revascularisation for acute limb ischaemia; mesenteric revascularisation and bowel resection for infarction; mechanical thrombectomy for large vessel stroke; supportive care for acute kidney injury.
• Treat the cause: cancer therapy, hydroxyurea or ruxolitinib for myeloproliferative neoplasms under specialist care (hydroxyurea 15 to 30 mg/kg/day), withdrawal of oestrogens, treatment of nephrotic syndrome.
• Special groups:
  • Pregnancy: therapeutic enoxaparin 1 mg/kg every 12 hours throughout pregnancy and for 6 weeks after delivery; avoid warfarin and direct oral anticoagulants.
  • Children: rare; use weight based enoxaparin (1 mg/kg every 12 hours) with specialist advice.
  • Renal impairment: reduce enoxaparin; use unfractionated heparin when creatinine clearance is less than 15 mL/min.
  • Elderly: balance bleeding risk and use apixaban or warfarin with close monitoring.
• Red flags: new neurological deficit, abdominal pain with lactate rise, cold painful limb, haematuria with flank pain, bleeding on anticoagulation, falling platelets on heparin.
• Follow up: imaging at 3 months and 12 months; INR monthly on warfarin; yearly review of the cause; repeat thrombophilia tests (antiphospholipid antibodies at 12 weeks).