Management of Mural Thrombus in Abdominal Aortic Aneurysm
The presence of mural thrombus in an abdominal aortic aneurysm does not change the fundamental treatment approach: repair is indicated when the AAA reaches ≥55 mm in men or ≥50 mm in women, with EVAR preferred when anatomically suitable, though extensive thrombus (>90% circumference) in the proximal neck increases technical complexity and endoleak risk. 1
Surveillance and Monitoring Strategy
The surveillance protocol is determined by maximum aneurysm diameter, not by thrombus presence 1:
- AAA 25-29 mm: Duplex ultrasound every 4 years 1
- AAA 30-39 mm: Duplex ultrasound every 3 years 1
- AAA 40-44 mm (women) or 40-49 mm (men): Annual duplex ultrasound 1
- AAA 45-50 mm (women) or 50-55 mm (men): Duplex ultrasound every 6 months 1
Contrast-enhanced CT angiography is mandatory for pre-operative planning to assess thrombus burden, measure true aneurysm diameter, and determine EVAR feasibility 1. Multiplanar reformatted images with centerline 3-D software should be used for accurate diameter measurement in tortuous aneurysms 1.
Indications for Intervention
Repair is recommended when 1:
- AAA diameter ≥55 mm in men or ≥50 mm in women (regardless of thrombus configuration)
- Rapid growth ≥10 mm per year or ≥5 mm in 6 months
- Saccular morphology ≥45 mm (higher rupture risk)
The presence of mural thrombus does not lower these thresholds, as size remains the primary determinant of rupture risk 1.
Choice of Repair Technique
EVAR should be considered as the preferred approach for patients with suitable anatomy and reasonable life expectancy (>2 years), as it reduces peri-operative mortality to <1% compared to open repair 1. However, extensive mural thrombus covering >90% of the proximal neck circumference requires careful evaluation due to increased risk of type I endoleak and stent graft migration 1.
Technical Considerations for EVAR with Mural Thrombus:
- Stent-graft diameter should be oversized by 10-20% relative to the aortic diameter at the proximal neck 2
- Bifurcated stent-grafts are used in most cases 2
- Fixation may be suprarenal or infrarenal depending on device and thrombus location 2
- Completion angiography must confirm absence of endoleak and patency of all components 2
Open surgical repair remains appropriate for patients with unsuitable anatomy for EVAR (particularly those with extensive proximal neck thrombus) or those with failed prior EVAR 1.
In ruptured AAA with suitable anatomy, endovascular repair is recommended over open repair to reduce peri-operative morbidity and mortality 1.
Medical Management
All AAA patients require optimal cardiovascular risk management to reduce major adverse cardiovascular events 1. Fluoroquinolones should be avoided unless there is a compelling indication with no alternative 1.
Anticoagulation Considerations:
While historically anticoagulation was proposed for isolated aortic mural thrombus without aneurysm, this approach is not recommended for AAA with mural thrombus as it is associated with 25-50% embolic recurrence rate, thrombus persistence in 35%, and need for secondary aortic surgery in up to 31% of cases 3. The definitive treatment remains aneurysm repair, not anticoagulation alone.
Post-Intervention Surveillance
Following repair, the European Society of Cardiology recommends 1:
- 30-day imaging with contrast-enhanced CT plus duplex ultrasound to assess intervention success
- Follow-up at 1 and 12 months post-operatively
- Yearly surveillance until the fifth post-operative year
- Re-intervention for type I or type III endoleaks to achieve seal
Critical Pitfalls to Avoid
Do not delay repair based on thrombus presence—size criteria remain paramount 1. Do not attempt anticoagulation alone as primary therapy for AAA with mural thrombus, as this increases embolic complications without addressing the underlying aneurysm 3. Do not underestimate technical challenges when extensive thrombus (>90% circumference) involves the proximal neck, as this significantly increases endoleak and migration risk with EVAR 1.