Pigmented Villonodular Synovitis Presenting at an Atypical Site: A Case Report.

Pigmented villonodular synovitis (PVNS) is an idiopathic villous overgrowth and pigmentation of the synovial membrane of a single joint. It is an uncommon condition characterized by yellow or yellowish-brown colour due to deposits of cholesterol and hemosiderin, excessive secretion of yellowish-brown synovial fluid, and the formation of brownish chocolate synovial tissue. This condition commonly occurs at the knee joint at the age of 20-50 years. Here we present a case of a 75-year-old male with PVNS involving the lower third of the right thigh who came to the surgery department and was eventually referred to the orthopedic department on the basis of investigations performed. It is a case of PVNS at a unique location on the lower third of the right thigh. The swelling was painless initially, but the pain increased over a duration of 10 months. Clinically, the mass was suspected to be bursitis or lipoma with features of mild inflammation in the overlying skin. Magnetic resonance imaging (MRI) suggested a swelling of 100*70*40 mm in dimension with the possibility of PVNS. Ultrasonography (USG) of the mass and fine needle aspiration cytology (FNAC) supported the diagnosis of PVNS. An excisional biopsy of the swelling was submitted. Per-operatively, there were typical features of PVNS. The swelling was situated superficial to the iliotibial band. There was no defect or gap in the iliotibial tract, and the swelling didn't have any continuity to the knee joint. The occurrence of synovial tissue without any attachment to the joint or tendon is rare and hence reported.