What is the general pathophysiology of a pseudoaneurysm?

General Pathophysiology of a Pseudoaneurysm

A pseudoaneurysm (false aneurysm) results from complete disruption of all three arterial wall layers (intima, media, and adventitia), with extravasated blood contained only by surrounding periarterial connective tissue rather than by intact vessel wall components. 1

Fundamental Structural Defect

• The defining pathophysiologic feature is full-thickness arterial wall disruption with blood leaking outside the vessel but remaining confined by adjacent soft tissue structures 1
• Unlike true aneurysms where all three arterial layers remain present (though attenuated), pseudoaneurysms lack intact vessel wall architecture at the site of injury 1
• The resulting extravascular hematoma maintains free communication with the intravascular space, creating what is also termed a "pulsating hematoma" 1
• Blood flows bidirectionally through the neck connecting the arterial lumen to the pseudoaneurysm sac 2, 3

Mechanism of Formation

Primary Etiologies

• Traumatic injury is the most common cause, particularly from blunt thoracic trauma with rapid deceleration (motor vehicle accidents, falls, sports injuries) 1
• Iatrogenic injury from arterial catheterization, surgical procedures, or catheter-based interventions accounts for significant cases 1
• Penetrating trauma from sharp objects or projectiles causes direct arterial wall disruption 4, 5
• Rare causes include arterial erosion from infection (mycotic aneurysms) and penetrating atherosclerotic ulcers 1

Containment Dynamics

• The periarterial connective tissue, surrounding organs, and anatomic compartments (pleura, pericardium, retroperitoneal space) provide temporary containment of the extravasated blood 1
• When pressure within the pseudoaneurysm exceeds the maximally tolerated wall tension of the surrounding tissue, fatal rupture occurs 1

Progressive Pathophysiologic Consequences

Local Complications

• Progressive enlargement occurs as the pseudoaneurysm sac expands under arterial pressure 1
• Fistula formation can develop between the pseudoaneurysm and adjacent structures 1
• Compression or erosion of surrounding structures (nerves, veins, airways) produces secondary pathology 1, 6
• Venous thrombosis results from compression of adjacent veins 6, 3
• Painful neuropathy develops from nerve compression 6, 3

Thrombotic and Embolic Sequelae

• Partial thrombosis within the pseudoaneurysm sac can occur 3
• Distal embolization of thrombus causes downstream ischemia 6, 3
• Complete thrombosis of the affected vessel with distal ischemia represents a limb-threatening complication 6

Rupture Pathophysiology

• Contained rupture maintains hemodynamic stability as periaortic structures temporarily seal the hemorrhage 1
• Free rupture leads to massive hemorrhage, internal bleeding, and rapid death 1
• Skin erosion in advanced cases precedes external hemorrhage 6

Size-Dependent Natural History

• Small pseudoaneurysms (<2.0 cm) demonstrate spontaneous thrombosis and resolution in 61% of cases within 7-52 days 7
• Larger pseudoaneurysms (≥2.0 cm) rarely resolve spontaneously and carry higher rupture risk 7
• The risk of complications increases proportionally with pseudoaneurysm size 7, 3

Clinical Pitfalls

• Physical examination alone misses more than 60% of pseudoaneurysms, making imaging essential for diagnosis 7, 6
• Pseudoaneurysms are easily confused with hematomas or abscesses on clinical examination, delaying appropriate treatment 7, 6
• Many present weeks to months after the initial injury when the original vascular trauma was missed 5
• The variable inflammatory response ranges from minimal to significant, further complicating clinical recognition 6