Localized pigmented villonodular synovitis of the knee: a report of two cases

Two cases of localized pigmented villonodular synovitis (PVNS) are reported, both having received surgery. Localized PVNS and diffuse PVNS have not been clearly separated in the literature. Although the clinicopathologic features of the former lesions are similar to diffuse PVNS involving the synovium of the knee joint, the villous component with brownish red color, brownish-stained bloody fluid, and the hemosiderin in the surface-lining cells were lacking in these two cases. Localized PVNS can be treated with simple excision arthroscopically, but it tends to recur as diffuse PVNS if it is excised inadequately. It is suggested that attention must be paid to a soft tissue mass within the knee joint by doing comprehensive pre-operative evaluations which include history taking, computed tomography, and/or magnetic resonance imaging. Intra-operative findings focused on the morphology including the proliferated synovial membrane, gross appearance of the lesion and the pattern of effusion which are all important for distinguishing between localized PVNS and diffuse PVNS. There was no evidence of recurrence in these two cases during the 18 months' follow-up.