The lateral knee x-ray shows a soft tissue swelling posterior to the distal femur with peripheral calcification. Further imaging revealed a popliteal artery aneurysm.

Popliteal artery aneurysm was an incidental finding in our patient.

Popliteal artery aneurysm:

• Uncommon with a median age of about 71 years.
• Bilateral in about 40-50% of patients.
• About 40-50 % of patients will have an associated aortic aneurysm.
• Main complication is acute leg ischemia related to thrombosis & embolization in up to  30-50% of patients.
• Less common complications are rupture & compression of adjacent structures.

Reference: Australian and New Zealand Society for Vascular Surgery. https://www.anzsvs.org.au/patient-information/popliteal-aneurysms/