A pseudoaneurysm is a contained leak of blood that forms outside an artery wall after the wall has been damaged. Unlike a true aneurysm, where the artery balloons outward but its wall stays intact, a pseudoaneurysm involves a break in the vessel wall. Blood escapes through the break and pools in the surrounding tissue, held in place only by a thin layer of clotted blood and connective tissue rather than the artery’s own structure. This makes pseudoaneurysms inherently less stable and, in many cases, more dangerous than true aneurysms of the same size.
How It Differs From a True Aneurysm
The distinction comes down to what’s containing the blood. A true aneurysm is a widening of the artery itself. All three layers of the arterial wall (the inner lining, the muscular middle layer, and the outer covering) stretch outward but remain continuous. The artery is dilated, not ruptured.
A pseudoaneurysm, sometimes called a “false aneurysm,” has a fundamentally different structure. The arterial wall has an actual hole in it. Blood flows through this defect with each heartbeat and collects in a pocket outside the artery. That pocket is walled off only by compressed tissue and clot, not by the artery’s own muscular layers. Because this containment is improvised rather than structural, pseudoaneurysms can expand, rupture, or cause complications that a similarly sized true aneurysm might not.
Common Causes
The most frequent cause is medical procedures that involve puncturing an artery. Cardiac catheterization, where a thin tube is inserted through the femoral artery in the groin to access the heart, is the single most common trigger. Pseudoaneurysms develop at the puncture site in roughly 0.5% to 2% of these procedures, with the rate climbing higher when blood-thinning medications are used during or after the procedure, when larger catheter sizes are required, or when the puncture hits a difficult spot on the artery.
Beyond catheterization, pseudoaneurysms can result from:
- Trauma: Penetrating injuries like stab wounds or fractures that lacerate a nearby artery
- Surgery: Any operation near major blood vessels, including joint replacements and organ transplants
- Infection: Bacterial infections can weaken an artery wall enough to cause a breach, creating what’s called a mycotic pseudoaneurysm
- Inflammation: Conditions like pancreatitis can erode into arteries near the pancreas, forming pseudoaneurysms in the splenic or other abdominal arteries
IV drug use is another well-known cause. Repeated injections into the same area can damage arterial walls, and the non-sterile conditions increase the risk of infected pseudoaneurysms, which are particularly dangerous.
Where They Form
Location depends almost entirely on the cause. Procedure-related pseudoaneurysms overwhelmingly occur in the femoral artery in the groin, since that’s the most common access point for catheter-based heart and vascular procedures. The radial artery at the wrist is another access site that occasionally develops them.
Trauma-related pseudoaneurysms can form virtually anywhere. The arteries most commonly affected by non-procedural causes include the splenic artery (often from pancreatitis), the hepatic artery near the liver, and arteries in the extremities after fractures. Pseudoaneurysms of the aorta, the body’s largest artery, are rare but serious and typically result from major chest or abdominal trauma, or as a complication of aortic surgery.
Symptoms and How It’s Found
A small pseudoaneurysm may cause no symptoms at all. When symptoms do appear, they typically develop near the site of the damaged artery. The most common presentation after a groin catheterization is a pulsating lump at or near the puncture site, often accompanied by pain, swelling, or bruising that seems disproportionate to what you’d expect from a needle stick.
A doctor or nurse examining the area may feel a thrill (a vibration under the skin caused by turbulent blood flow) or hear a bruit (a whooshing sound) with a stethoscope. These are classic physical signs, though they’re not always present with smaller pseudoaneurysms.
More concerning symptoms suggest the pseudoaneurysm is growing or compressing nearby structures. These include increasing pain, numbness or tingling in the leg or hand below the site, skin color changes, or a rapidly expanding mass. If the pseudoaneurysm presses on a nerve, you might feel sharp or burning pain radiating down the limb.
Diagnosis is confirmed with ultrasound, which can show blood swirling in the pocket outside the artery and measure the size of both the pseudoaneurysm sac and the “neck,” the channel connecting it to the artery. CT scans with contrast dye provide more detailed imaging when ultrasound results are unclear or when the pseudoaneurysm is deep inside the abdomen or chest.
When They’re Dangerous
Not all pseudoaneurysms require urgent treatment. Small ones, generally under 2 centimeters, that aren’t growing and aren’t causing symptoms have a reasonable chance of clotting off and resolving on their own within a few weeks. Your doctor may recommend monitoring with repeat ultrasounds to confirm it’s shrinking rather than expanding.
The risk of complications rises with size, rapid growth, and certain locations. A pseudoaneurysm becomes dangerous when it ruptures, causing uncontrolled bleeding into the surrounding tissue or body cavity. Large pseudoaneurysms can also compress nearby veins (potentially causing leg swelling or blood clots), compress nerves, or become infected. An infected pseudoaneurysm is a surgical emergency because the combination of weakened tissue and active infection makes rupture far more likely.
Pseudoaneurysms in the abdomen, particularly those involving the splenic artery or arising from pancreatitis, carry a higher rupture risk than those in the groin. These are generally treated more aggressively regardless of size.
Treatment Options
Treatment depends on the size, location, and cause of the pseudoaneurysm, along with whether it’s growing or causing symptoms.
Ultrasound-Guided Compression
For femoral pseudoaneurysms, one of the simplest approaches involves a doctor using an ultrasound probe to apply firm, sustained pressure directly over the neck of the pseudoaneurysm. The goal is to stop blood flow into the pocket long enough for it to clot. Sessions typically last 10 to 30 minutes and succeed about 60% to 90% of the time for smaller pseudoaneurysms. The success rate drops significantly if you’re taking blood thinners, since those medications interfere with the clotting process the technique relies on.
Thrombin Injection
This has become the most widely used treatment for femoral pseudoaneurysms. Using ultrasound guidance, a doctor inserts a fine needle into the pseudoaneurysm sac and injects a small amount of thrombin, a protein that triggers rapid clot formation. The blood inside the sac clots almost immediately, sealing off the pseudoaneurysm. Success rates exceed 95% in most studies, and the procedure takes only minutes. The main risk is that thrombin could leak back into the artery and cause a clot there, though this is uncommon, especially when the neck of the pseudoaneurysm is narrow.
Endovascular Repair
For pseudoaneurysms in locations that aren’t accessible by compression or injection, or for larger and more complex cases, a catheter-based approach can place a covered stent inside the artery. The stent bridges the hole in the artery wall, sealing it from the inside while keeping the artery open. This avoids open surgery and works well for pseudoaneurysms in the limbs, pelvis, or certain abdominal arteries.
Surgical Repair
Open surgery is reserved for cases where less invasive options have failed, the pseudoaneurysm is infected, it’s compressing critical structures, or it has ruptured. The surgeon directly repairs the hole in the artery, sometimes using a patch or bypass graft. Recovery is longer than with catheter-based treatments, but surgery remains the definitive fix for complicated cases.
Recovery and Follow-Up
After thrombin injection or compression repair, most people go home the same day or the next morning. You’ll typically have a follow-up ultrasound within one to two weeks to confirm the pseudoaneurysm has stayed closed. Activity restrictions usually involve avoiding heavy lifting and strenuous exercise for a couple of weeks to prevent the repair from breaking down.
After surgical repair, recovery depends on the location and extent of the operation. Groin repairs generally mean a few days in the hospital and several weeks of limited activity. Abdominal or chest repairs involve longer hospital stays and a more gradual return to normal function.
Recurrence after successful treatment is uncommon. The main factor that increases the chance of a pseudoaneurysm coming back is if you continue to need blood-thinning medications or additional vascular procedures through the same access site.