Why does pseudoaneurysm occur?

What Causes a Pseudoaneurysm?

Unlike a true aneurysm, which involves a weakening and bulging of all three layers of a blood vessel wall, a pseudoaneurysm—sometimes referred to as a "false aneurysm"—develops after the wall has been damaged. When an injury occurs, such as from a surgical procedure, trauma, or even a violent impact, blood can leak out of the vessel. However, instead of flowing freely into surrounding tissues, the escaping blood gets contained by the surrounding connective tissue, forming a sac.

This blood-filled sac pulses with each heartbeat, mimicking the appearance of a true aneurysm on imaging tests, but without the actual structural integrity of a normal vessel wall. Common causes include complications from arterial catheterization—like after cardiac catheterization or angiography—blunt or penetrating trauma, and infections that erode vessel walls. In some cases, even severe hypertension or underlying vascular disease can contribute.

The body often seals small pseudoaneurysms on its own, but larger or persistent ones can be dangerous. Left untreated, they may rupture, cause clot formation, or compress nearby structures. Symptoms can include localized pain, swelling, a pulsating mass, or even a noticeable bruit (an abnormal sound heard with a stethoscope).

Diagnosis is typically made with ultrasound, which can visualize the flow of blood in and out of the sac. Treatment varies depending on size and risk, ranging from ultrasound-guided compression and thrombin injections to surgical repair in more serious cases.

While relatively uncommon, understanding how a pseudoaneurysm forms helps emphasize the importance of careful monitoring after procedures involving blood vessels. Early detection can prevent potentially life-threatening complications.