This patient is suspected to have a ruptured popliteal cyst, or Baker cyst. The cyst presents as a swelling in the popliteal fossa, and its rupture can produce ecchymoses involving the posterior calf. Bruising below the medial malleolus, termed the crescent sign, helps differentiate this from other conditions, such as a deep vein thrombosis. Imaging can help to confirm the diagnosis. Learn more about this case and join the conversation on Figure 1.
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