the patient is obese, since there is more fatty tissue between the skin and the neck of the pseudoaneurysm. It also is less successful if the neck of the pseudoaneurysm is wider, since it is less likely to clot off during the period of compression. Finally, it is also much less successful if the patient is taking aspirin, warfarin (Coumadin), or another anticoagulant, since these would prevent clotting of blood within the pseudoaneurysm. Advantages are that this is the least invasive method of stopping arterial blood flow into a pseudoaneurysm. Ultrasound-guided thrombin injection In addition to covered stent placement, another popular, minimally-invasive technique used today is ultrasound-guided thrombin injection. Thrombin (factor IIa in the coagulation cascade) is a clotting factor that converts fibrinogen into fibrin, which then polymerizes to form a blood clot. Under ultrasound guidance, thrombin can be injected directly into a pseudoaneurysm, causing it to clot. Advantages are that the technique is relatively easy to perform, is successful, and is minimally invasive. One contraindication to this procedure is if there is an arteriovenous fistula (communication between an artery and vein), in addition to the pseudoaneurysm. This occurs with about 10% of pseudoaneurysms. If this is present, thrombin injected into the pseudoaneurysm could then enter the venous circulation and possibly lead to distant thrombosis. Surgical ligation (with or without distal bypass) Open surgery may also be performed to remove pseudoaneurysms or prevent them from expanding. If the artery is small and "expendable" - the tissues it supplies have adequate collateral blood flow - then the artery supplying the pseudoaneurysm may be ligated both proximally and distally to the pseudoaneurysm. The pseudoaneurysm may or may not be removed. If the tissues supplied by the artery do not have sufficient collateral flow (the artery is not expendable), then a vein or synthetic graft would have to be anastomosed proximally and distally to allow for continued blood flow around the pseudoaneurysm. Advantages are that the technique has been successful in the treatment of pseudoaneurysms for many years. However, it is more invasive (a large skin incision is necessary), and there is more postoperative pain and a risk for wound infection. One of the less invasive options may be preferred in a patient with many comorbidities, who is at high risk for surgery. See also Intradural pseudoaneurysm References External links Gross pathology