Abstract
ales and females and also in animals, it could lead to severe pain, joint deformity and decrease of joint function with a consequent lowering of the productivity. Moreover it is a diagnostic challenge, the difficulty stems from the insidious onset and nonspecific presentation of the disease, as well as its subtle radiographic findings. In addition, the disease is difficult to be differentiated from conditions such as rheumatoid arthritis, osteoarthritis and other inflammatory and neoplastic processes of the synovial lining. PVNS comes in two forms: localized and diffuse. Diffuse PVNS affects the entire synovium and typically occurs in large joints such as the knee or hip. Localized or nodular, PVNS is less common than the diffuse form and typically occurs in smaller joints such as the hands and feet. Involvement of bursa (PVNB, pigmented villonodular bursitis) is the least common. The incidence of pigmented villonodular synovitis is 1.8 cases per 1 million people per year. It is equally affect males and females. Animals are less commonly affected and the condition mostly misdiagnosed. Histopathologically, diffuse disease is characterized by a mononuclear stromal cell infiltrate in the synovial membrane.