Infected Ruptured Baker’s Cyst Mimicking Deep Vein Thrombosis: A case report

Acute unilateral calf erythema and swelling frequently prompt empirical treatment for cellulitis and urgent investigation for deep vein thrombosis (DVT). Rupture of a Baker's cyst is an uncommon but important mimic. A 60-year-old patient presented with a one-week history of progressive swelling of the left lower limb despite treatment with amoxicillin-clavulanate. Examination showed an ill-defined erythematous, edematous, and warm plaque over the left calf with overlying ecchymosis. DVT was initially suspected; however, the D-dimer assay was negative and venous duplex ultrasonography showed no thrombosis. The examination instead demonstrated a complex left Baker's cyst considered dissected and ruptured. Surgical drainage and adjusted antibiotic therapy were followed by a favorable clinical course. This case highlights the need to consider a ruptured Baker's cyst in patients with unilateral inflammatory calf swelling, particularly when ecchymosis is present and presumed cellulitis does not improve with antibiotics. Duplex ultrasonography is valuable because it can both exclude DVT and identify an alternative popliteal or calf process.