What are the differences between a pseudoaneurysm and a true aneurysm in terms of definition, etiology, clinical presentation, diagnosis, and management?

Pseudoaneurysm versus True Aneurysm

A pseudoaneurysm is a contained rupture of the arterial wall where blood leaks outside the vessel but remains confined by surrounding soft tissue, lacking the normal three-layer arterial wall structure, whereas a true aneurysm is a dilatation involving all three intact layers of the vessel wall (intima, media, and adventitia). 1, 2

Definition and Structural Differences

The fundamental distinction lies in wall architecture:

• True aneurysm: The wall contains all three normal histological components of the arterial wall—intima, media, and adventitia—in a dilated configuration 2, 3
• Pseudoaneurysm: Represents a full-thickness arterial wall disruption where the "wall" consists only of fibrous peel, adventitia, and perivascular connective tissue that has formed around the perforation 1, 2, 4
• The pseudoaneurysm creates a "pulsating hematoma" that maintains free communication with the intravascular space through the arterial defect 1, 5

Etiology

True aneurysms develop from:

• Degenerative atherosclerotic disease 6
• Genetic connective tissue disorders 6
• Chronic hypertension 6
• Inflammatory arteritis 6

Pseudoaneurysms arise from:

• Traumatic injury: Blunt deceleration trauma (motor vehicle accidents, falls) is the most common cause, particularly affecting the thoracic aorta at the isthmus in 45% of cases 6, 1
• Iatrogenic injury: Arterial catheterization (0.1-0.2% after diagnostic angiography, 3.5-5.5% after interventional procedures), surgical procedures, or catheter-based interventions 6, 1
• Penetrating atherosclerotic ulcers: Erosion through the arterial wall in elderly patients with diffuse atherosclerosis 6, 1
• Infection: Mycotic aneurysms or arterial erosion from adjacent infection 6, 1

Clinical Presentation

True aneurysms typically present as:

• Asymptomatic incidental findings on imaging 6
• Symptoms from mass effect on adjacent structures 6
• Acute rupture with hemodynamic collapse 7

Pseudoaneurysms present as:

• Pulsatile, painful mass at the site of injury 5, 8
• Symptoms mimicking coarctation (arm BP > leg BP, interscapular murmur) in thoracic aortic pseudoaneurysms 6
• Compression syndromes: Venous thrombosis, painful neuropathy from femoral nerve compression, or soft tissue erosion 6
• Critical pitfall: Physical examination alone misses more than 60% of pseudoaneurysms, making them easily confused with hematomas or abscesses 1

Diagnosis

Imaging approach differs by location and stability:

Femoral/Peripheral Pseudoaneurysms

• Duplex ultrasound is the first-line diagnostic test, showing a hypoechoic image communicating with the arterial lumen 6, 5
• Color Doppler demonstrates characteristic "to-and-fro" flow pattern in the neck 6, 4

Thoracic/Abdominal Aortic Pseudoaneurysms

• CT angiography is the gold standard (91.4% sensitivity, 93.6% specificity), showing contrast extravasation, periaortic hematoma, and the characteristic "mushroom-like outpouching with overhanging edges" 6, 7, 3
• Transesophageal echocardiography (TEE) provides high accuracy for bedside diagnosis in unstable patients 6, 7
• Chest radiograph may show mediastinal widening or nasogastric tube displacement (80% sensitivity) but is neither sensitive nor specific 6, 7

Key imaging distinction: True aneurysms show smooth, symmetric dilatation with intact wall layers, while pseudoaneurysms demonstrate focal outpouching with a narrow "neck" corresponding to the point of arterial penetration 6, 3

Management

Small Femoral Pseudoaneurysms (<2.0 cm)

Conservative management is appropriate for asymptomatic lesions: 6, 1

• 61% resolve spontaneously within 7-52 days without antithrombotic therapy 6, 1
• Re-evaluate with duplex ultrasound at 1 month (Class IIa, Level B) 6
• Only 11% ultimately require surgical intervention 6

Larger Femoral Pseudoaneurysms (≥2.0 cm)

Active intervention is indicated: 6, 1

• Ultrasound-guided thrombin injection is first-line therapy for uncomplicated pseudoaneurysms 6
• Ultrasound-guided compression therapy is an alternative but causes more pain and has longer compression times 6
• Surgical repair is reasonable for pseudoaneurysms ≥2.0 cm that persist or recur after thrombin injection (Class IIa, Level B) 6

Thoracic Aortic Pseudoaneurysms

Urgent repair is mandatory due to high rupture risk: 6, 1

• Pseudoaneurysms rarely resolve spontaneously and inevitably enlarge if left untreated 6, 1
• Endovascular stent-graft repair is preferred when anatomically suitable 6
• Open surgical repair for lesions not amenable to endovascular approach 6

Critical Management Pitfalls

• Never insert a chest tube blindly in suspected thoracic aortic pseudoaneurysm—this can precipitate catastrophic exsanguination; obtain CTA first and achieve definitive aortic control before pleural drainage 9
• Infected femoral pseudoaneurysms require extensive operative debridement with autogenous reconstruction or extra-anatomic bypass 6
• Skin erosion or expanding rupture into soft tissue mandates urgent surgical repair regardless of size 6

Natural History and Prognosis

Size-dependent outcomes for pseudoaneurysms:

• Small lesions (<2.0 cm): 90% spontaneous closure within 2 months 6, 1
• Large lesions (≥2.0 cm): Progressive enlargement under arterial pressure with high rupture risk 1
• When pressure within the pseudoaneurysm exceeds wall tension of surrounding tissue, fatal rupture occurs 1

True aneurysms: Rupture risk correlates with size and growth rate, with abdominal aortic aneurysms >5.5 cm carrying significant annual rupture risk 7