Multiple nodular form of localized pigmented villonodular synovitis in the infrapatellar fat pad: A case report

Pigmented villonodular synovitis (PVNS) is a rare, benign, proliferative disease of the synovial membrane of joints, tendon sheaths, and bursas. It usually presents in two forms, diffuse and localized. A 35-year-old male, since adolescence, presented left knee pain with palpable, multiple nodular tumorous lesions in the infrapatellar fat pad. An arthroscopic excisional biopsy was performed. Multiple brown-colored pedunculated synovial nodules were limited to the infrapatellar fat pad area. The histology of the resected specimens showed proliferation of mononuclear histiocytes with multinucleated giant cells and hyperplasia of the synovium, diagnosed as PVNS. LPVNS is usually a single mass with a pedunculated or, less frequently, a sessile appearance. This report describes a rare case of a multiple nodular form of LPVNS, localized at the infrapatellar fat pad. This case highlights the need to consider LPVNS one of the causes of vague and long-lasting knee pain. Abbreviations: PVNS: Pigmented Villonodular Synovitis; DPVNS: Diffuse Pigmented Villonodular Synovitis; LPVNS: Localized Pigmented Villonodular Synovitis; MRI: Magnetic Resonance Imaging Introduction Pigmented villonodular synovitis (PVNS), also known as pigmented villonodular bursitis and pigmented villonodular tenosynovitis, is a benign, proliferative disease that occurs at the synovial membrane of joints, bursas, and tendon sheaths. There are two distinct forms: diffuse (DPVNS) and localized (LPVNS) pigmented villonodular synovitis [1]. The diffuse form affects the whole synovium of the joint, while the localized form is characterized by focal involvement of the synovium [2]. The localized form is usually a single pedunculated mass or, less frequently, two or three nodules. Finding multiple nodules in LPVNS is extremely rare. To the best of our knowledge, there are only two reported cases [3]. Here, we describe a case of the multiple nodular form of LPVNS in the knee joint. It should be included as an atypical form of LPVNS in the differential diagnosis of knee problems. Case report A 35-year-old male visited our hospital with left knee pain and a palpable mass which developed since adolescence. Physical examination revealed neither effusion nor restriction of knee motion. Modest swelling was palpable over the infrapatellar area of the left knee versus the right side. He had tenderness around the patella tendon and tibial tuberosity. Laboratory studies revealed no abnormal findings. Plain radiographs showed a slightly increased radiopacity in the infrapatellar area and soft tissue swelling versus the contralateral side (Figure 1). Magnetic resonance imaging (MRI) showed multiple well-demarcated masses, with intermediate to low signal intensity on T1and T2-weighted images, surrounded by fluid signals in the anterior compartment of the knee joint (Figure 2). He underwent an arthroscopic excisional biopsy to remove the mass. Multiple brown-colored pedunculated nodules were found; they were limited to the infrapatellar fat pad (Figure 3). No other lesion was found throughout the knee joint. A pathology examination revealed the nodules surrounded by fibrous septa and foci of hemosiderin-laden macrophages and the proliferation of polyhedral mononuclear histiocytic cells, some of which had formed multinucleated giant cells. There was mild hyperplasia of the synovium, with focal layers of fibrin consistent with pigmented PVNS (Figure 4). Three years later, he had neither pain nor a mass on palpation over the lesion. On follow-up MRI, no sign of recurrence was noted (Figure 5). Discussion The incidence of PVNS is ~1.8 cases per million people [4]. The etiology of PVNS is still uncertain: chronic inflammation, trauma, hemarthrosis, neoplastic origin, and chromosomal disorders have been Correspondence to: Yong-Geun Park, Department of Orthopedic Surgery, Jeju National University Hospital, Jeju National University School of Medicine, Aran 13gil 15, Jeju 690-767, South Korea, Tel: +82-64-754-8116; Fax: +82-64-7171131; E-mail: [email protected]