Case report 651: Thrombosed, leaking popliteal aneurysm.

A thrombosed, leaking aneurysm of the popliteal artery, mimicking a soft tissue sarcoma both clinically and by MRI examination, is described. It may be difficult to separate a leaking, thrombosed aneurysm from an inflammatory response secondary to a sarcoma with intralesional hemorrhage. An aneurysm should, however, be considered in the differential diagnosis if the mass is present in a well-recognized location for aneurysm and is associated with vascular engulfment and signs of subacute or chronic hemorrhage.