Rare common femoral vein adventitial cystic disease presenting with lower-extremity swelling.

Adventitial cystic disease (ACD) is a rare, nonatherosclerotic disorder caused by mucin-filled cysts within the vessel wall that produce luminal compression. Venous ACD is uncommon and may mimic deep vein thrombosis. A 24-year-old woman presented with right leg pain and swelling from a 2.8-cm common femoral vein cyst. The patient underwent cyst excision and bovine patch venoplasty but developed postoperative thrombosis from venoplasty-site stenosis and hematoma compression. Thrombectomy and angioplasty failed, requiring venous stenting. Pathology confirmed ACD. The patient recovered on enoxaparin and clopidogrel. This case emphasizes confirming durable venous outflow after cyst excision.