 A false aneurysm, or pseudoaneurysm, is a collection of blood leaking completely out of an artery or vein, but confined next to the vessel by the surrounding tissue.This blood-filled cavity will eventually either thrombose (clot) enough to seal the leak, or rupture out of the surrounding tissue.Pseudoaneurysms can be caused by trauma that punctures the artery, such as knife and bullet wounds, as a result of percutaneous surgical procedures such as coronary angiography or arterial grafting, or use of an artery for injection.