Most common site of pseudoaneurysm in I.V. drug abusers is:

In the IDU, frequent direct trauma to peripheral vessels produces damage to the vessel wall and an initial sterile perivascular hematoma. Injection of chemical agents in illicit drugs also causes tissue necrosis. The vascular wall usually becomes infected by contiguous spread from adjacent subcutaneous abscesses or areas of cellulitis. The infection causes liquefaction of the central poion of the hematoma in communication with the aerial or, less commonly, the venous wall, forming a secondary (false) pseudoaneurysm. The common femoral aery is the most frequent location, followed by the deep femoral and superficial femoral aeries. Because most IDUs are right handed, left-sided groin infections and aneurysms are more common. Primary mycotic aneurysms in which the damaged vessel wall is infected secondary to unrelated bacteremia are rare and are more likely to involve cerebral vessels as a complication of endocarditis. Pathogenesis includes septic embolization from valvular vegetations to the vasa vasorum of smaller vessels, such as the middle or posterior cerebral and visceral infra-abdominal aeries, which are more frequently involved than the aoa.