A pseudoaneurysm, also known as a false aneurysm, is a locally-contained hematoma outside an artery or the heart due to damage to the vessel wall. The injury passes through all three layers of the arterial wall, causing a leak, which is contained by a new, weak, "wall" formed by the products of the clotting cascade. A pseudoaneurysm does not contain any layer of the vessel wall. This differentiates it from an true aneurysm, which has all the three layers of the vessel wall, and a dissecting aneurysm, where there is a breach in the innermost layer of an artery and subsequent dissection/separation between the tunica intima and the tunica media. Pseudoaneurysm, being close to the vessel, can be pulsatile; it may be mistaken for a true aneurysm or dissecting aneurysm, or vice versa. The most common presentation of pseudoaneurysm is femoral artery pseudoaneurysm following access for an endovascular procedure, and this event may complicate up to 8% of vascular interventional procedures. Small pseudoaneurysms are capable of spontaneous clotting, 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 of a heart attack. Signs and symptoms Pseudoaneurysms usually present as a painful, tender, pulsatile mass. The overlying skin is sometimes erythematous (red). They can sometimes be confused with abscesses. The patient may describe a history of catheterization or trauma, and they may note that the pulsatile mass is gradually expanding. Diagnosis The diagnosis should be suspected if the patient has a history of arterial trauma. This can include arterial access for catheterization (i.e. the common femoral artery), blunt trauma (i.e. to an extremity), or penetrating trauma (i.e. gunshot or blast injury). Blunt or penetrating trauma can cause a disruption in the arterial wall, leading to a pseudoaneurysm. A patient with such a history who presents with a painful, pulsatile, tender mass at the site of catheterization or trauma should be suspected to have a pseudoaneurysm. The diagnosis should be confirmed using Duplex ultrasonography, which will reveal arterial blood flow into the pseudoaneurysm. A CT angiogram or conventional angiogram can also diagnose a pseudoaneurysm. It is important that the diagnosis be confirmed before any procedures are performed. Incision and drainage of a suspected abscess, which is instead a pseudoaneurysm, could lead to extensive hemorrhage. Locations A pseudoaneurysm