A 47-year-old woman with a swollen leg.

This case illustrates the importance of expanding the differential diagnosis beyond ruling out a DVT in a patient presenting with calf swelling. A good history and examination and a compulsive search for an etiology are necessary in the pursuit of the correct diagnosis. In this patient, only after identifying the popliteal cyst and recognizing that it represented an inflammatory synovitis could the cause be determined and the proper treatment instituted.