What’s the life-threatening finding in this knee case?

This 57-year-old male presents with a large mass. What is it? But, more importantly, on these axial water-weighted MRI images, what is the potentially life-threatening finding?

Axial T2

Axial PD


The high signal mass is a gastrocnemius semimembranous bursal cyst (one of the many types of Baker’s cysts). The life-threatening finding is the absence of flow phenomena in the popliteal vein. This thrombosis (arrows) can eventually result in a pulmonary embolism. When a Baker’s cyst clinically simulates a popliteal thrombophlebitis, this is called pseudothrombophlebitis. But when it actually coexists with the thrombophlebitis due to compression (as in this case) it is called pseudo-pseudothrombophlebitis.

After you try to say pseudo-pseudothrombophlebitis five times fast, head to MRI Online for more knee case review.

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