pseudo aneurysm of popliteal artery

This patient was a drug addict with history of injecting into the popliteal vessels. He presented with a pulsatile swelling in the Lt. popliteal region. Color Doppler study shows the typical cystic structure, in close relation to the Lt. popliteal artery, with swirling blood flow within it. This produces what is typically called the yin -yang sign on color doppler. (The picture below shows the typical yin yang symbol).
Pseudoaneurysms are formed by trauma to the artery, usually iatrogenic, resulting in a perfused sac surrounding the vessel. It is lined either by the media or the adventitia or even by the soft tissue surrounding the injured vessel.
CT or MR imaging can help by locating the lesion and the feeding vessel (especially on 3D reconstruction).
Case and images courtesy of Dr. Vikas Arora, MD, Ferozepur, India.


References: 1) http://www.jultrasoundmed.org/cgi/content/full/25/9/1211#SEC1
2) http://findarticles.com/p/articles/mi_qa3794/is_200508/ai_n15846548