Upper left image shows a 5 cm groin lesion with swirling blood, consistent with a pseudoaneurysm.
Upper right image shows the classic "yin-yang" flow pattern in a pseudoaneurysm.
Bottom images show the neck of the pseudoaneurysm, with the classic to-and-fro flow.
An aneurysm is a dilated vessel where all three layers of the vessel wall (intima, media, and adventia) are intact. A pseudoaneurysm is an eccentric outpouching / contained perforation that is only surrounded by adventitia or surrounding tissues.
Small groin pseudoaneurysms can be treated by ultrasound guided compression, or by ultrasound guided thrombin injection. In both cases, pressure is applied using the ultrasound probe until the flow in the neck of the pseudoaneurysm is eliminated. Pseudoaneurysms can also be resected.