A pseudoaneurysm, also known as a false aneurysm, is when there is a local hematoma being contained by the surrounding tissue around an artery. It is usually caused by a penetrating injury to the vessel, which then leads to a leakage of blood and causes this local hematoma. It may be pulsatile and can resemble a true aneurysm. A true aneurysm involves all three layers of the blood vessel. A dissecting aneurysm is when blood from the vessel lumen tracks between the two inner layers, the intima and the tunica media. This can cause blockage of the flow. A perivascular hematoma is a collection of blood that is external to the three vessel layers. Due to being close to the vessel, it can also be pulsatile, and can be mistaken for a pseudoaneurysm or aneurysm.

Femoral pseudoaneurysms may complicate up to 8% of vascular interventional procedures. Small pseudoaneurysms can spontaneously clot, while others need definitive treatment.

A pseudoaneurysm may also occur in a chamber of the heart following myocardial damage due to ischemia or trauma. A pseudoaneurysm of the left ventricle is a potentially lethal complication from a myocardial infarction.