A pseudoaneurysm, often called a false aneurysm, is a collection of blood that forms outside an injured blood vessel, most commonly an artery. It occurs when an injury pierces the vessel wall, allowing blood to leak into the surrounding tissue where it is contained, forming a sac-like structure. The wall of this sac is not made up of the artery’s own layers, but is composed of fibrous tissue from the body’s clotting process.
Differentiating from a True Aneurysm
The distinction between a pseudoaneurysm and a true aneurysm lies in the composition of their walls. A true aneurysm involves all three layers of the artery wall—the intima, media, and adventitia—bulging outwards together. This creates a weakened, balloon-like swelling within the vessel itself where the artery’s structural integrity is compromised.
In contrast, a pseudoaneurysm is a breach in the arterial wall. Blood escapes through this hole and is walled off by the surrounding tissues, which form a fibrous capsule. This capsule prevents the blood from leaking further but does not have the structural components of an actual artery wall. The difference can be visualized by comparing a true aneurysm to a weak spot on a tire’s sidewall, while a pseudoaneurysm is more like a patch covering a puncture.
The connection between the artery and the pseudoaneurysm is a narrow channel called the “neck”. Through this neck, blood flows in and out of the contained sac, which is why a pseudoaneurysm feels like it is pulsating. The wall of a pseudoaneurysm is weaker than the stretched wall of a true aneurysm, which influences its risk of rupture.
Causes and Symptoms
The most frequent cause is an iatrogenic injury, meaning it results from a medical procedure. Procedures that require puncturing an artery, such as cardiac catheterization or angiography, are common causes. If the puncture site does not seal properly after a catheter is removed, blood can leak and form a pseudoaneurysm.
Other causes include direct trauma that damages a blood vessel and certain surgical procedures. Infections can also weaken an artery wall, leading to the formation of a pseudoaneurysm. Risk factors after a procedure include high blood pressure, obesity, and the use of anticoagulant medications.
The most common symptom is a painful, tender, and pulsating lump under the skin near the site of a recent injury or procedure. This area may also show swelling, bruising, or skin discoloration. If large enough to press on a nearby nerve, it can cause numbness, tingling, or weakness in the affected limb. Smaller pseudoaneurysms may not produce any symptoms and might be discovered incidentally.
Diagnosis and Treatment Options
Diagnosis begins with a physical examination, where a healthcare provider may feel for a pulsating mass at the suspected site. The primary diagnostic tool is a duplex ultrasound. This non-invasive imaging test uses sound waves to visualize blood flow and can confirm the presence of the pseudoaneurysm, identify its size, and show its connection to the parent artery. A CT angiography (CTA) may be used for a more detailed image.
Treatment decisions are based on the pseudoaneurysm’s size, location, and whether it is causing symptoms. For very small, stable pseudoaneurysms, “watchful waiting” may be recommended, as some can close on their own. This involves regular monitoring with ultrasound to ensure it is not enlarging.
A common, minimally invasive treatment is an ultrasound-guided thrombin injection. Using ultrasound for guidance, a physician injects a clotting agent called thrombin directly into the pseudoaneurysm sac. This causes the blood within the sac to clot rapidly, sealing the leak. Another non-invasive option is ultrasound-guided compression, where a healthcare professional applies firm pressure over the neck of the pseudoaneurysm to help it close, though this method is used less frequently now.
For larger, more complex cases, or when other methods are unsuccessful, surgical repair may be necessary. This involves an open procedure where a surgeon directly stitches the hole in the artery closed or uses a patch to repair it. A less invasive surgical alternative is endovascular repair, where a covered stent is placed inside the artery to cover the hole from within.