pigmented villonodular synovitis

Pigmented villonodular synovitis (PVNS) is a condition that causes the synovium—the thin layer of tissue that lines the joints and tendons—to thicken and overgrow. PVNS usually affects the knee although it can affect other joints as well. In most cases, surgery is needed to remove the damaged joint lining and the mass.

When the tumor involves the tendons that support the joint, or occurs in just one area of the joint, it is called localized PVNS. This type usually responds well to treatment.

When the condition is more widespread and involves an entire joint, it is called diffuse PVNS. It tends to be more destructive and is more difficult to treat.

Images

 https://www.webpathology.com/case.asp?case=357

See also

 giant-cell tumor of tendon sheaths