Sarcoidosis presenting as prepatellar bursitis.

A 61-year-old woman complained of a subcutaneous mass in her right knee. MR images revealed a well-defined subcutaneous mass in the prepatellar region, containing some fluid and foci of short T2. The lesion showed some marginal contrast uptake after an administration of meglumine gadopentetate (Gd-DTPA), consistent with prepatellar bursitis. The pathological specimen, however, revealed subcutaneous sarcoidosis involving the bursa.