Review Question - QID 91

The history, MRI, and histology suggest pigmented villonodular synovitis of the knee. However, the question asks what is the analogous histologic disease process of PVNS when located away from the synovial lining of joints, which is giant cell tumor of tendon sheath. Features that help make the diagnosis of PVNS in this case include the intra-articular location, signal uptake on MRI, and the diagnostic hemosiderin laden macrophages on histology. The reference by Abdul-Karim et al. describes the histologic similarities between giant cell tumor of tendon sheath and PVNS. Fibrous dysplasia would show a fibrous histiocytic background with the characteristic chinese letters. Hemangiomas show vascular structures on histology. There is no cellular atypia or high nuclear to cytoplasmic ratio as would be seen with synovial sarcoma and the characteristic giant cell tumor of bone would show the spindle cell background with associated multinucleated giant cells. In addition, none these lesions "change" names with anatomic location. In the reference by McCarthy et al, they discuss the differential diagnosis and treatment of synovial based lesions including PVNS. They argue that because PVNS is a difficult disease to cure, if a patient is relatively asymptomatic treat first with observation followed by synovectomy if pain continues.