Localized Pigmented Villonodular Synovitis of the Knee Joint: A Case Report

BACKGROUND: The localized form is characterized by local participation of the synovium as a nodule or pedunculated mass. The incidence rate of PVNS is estimated to be 1.8 per million people – the localized type is just one-quarter of that. The aim of this study is to remind orthopedic surgeons about the unusual properties of LPVNS located in the knee. CASE REPORT: A 39-year-old man presented to our clinic with pain and discomfort in his right knee. Magnetic resonance imaging showed an intra-articular mass in the infrapatellar region of the knee adjacent to the Hoffa fat pad. The mass was hypointense in the T1 sequence and heterogeneously hyperintense in the T2 sequence, which may be considered a local type of tenosynovial giant cell tumor (LPVNS). Excision was carefully performed without penetrating the tumor. The macroscopic appearance of the tumor was yellow-reddish and brown in color. Histopathologic examination revealed pigmented villonodular synovitis of the local type. CONCLUSION: Even though the LPVNS of the knee is an uncommon intra-articular phenomenon, orthopedic surgeons should not overlook this lesion based on imaging findings, and open excision should be regarded as a reliable treatment option.