Primary synovial epithelioid sarcoma of the knee: distinctly unusual location leading to its confusion with XXXX .

@entity1 @entity4166 @entity242 @entity39 @entity8650 @entity1362 @entity5 @entity158 @entity2280 @entity378 @entity6195
@entity242 ( @entity242 ) is a rare @entity8650 occurring in the distal extremities of young adults and is characterized histologically by nodules of epithelioid cells showing central @entity39 . Intra-articular @entity242 is extremely rare; only four cases have been reported, but their radiologic and histologic documentation of intra-articular origin have been imprecise. We report the first radiologically and histologically well-documented case of primary synovial @entity242 . A 59-year-old @entity1 presented with @entity158 followed by swelling of her right knee for 6  months. MRI revealed an entirely intra-articular nodular synovial mass in the lateral part of the right knee joint in a background of diffusely thickened synovium. Synovectomy was performed under the clinical impression of @entity1362 ( @entity1362 ), a diagnosis erroneously confirmed by the reporting pathologist. The @entity5 rapidly recurred 3  months afterward and the diagnosis of primary synovial @entity242 was made. Despite above-knee amputation, the @entity5 continued to spread proximally to the retroperitoneum. She developed multiple lung metastases and died 20  months after initial presentation. The nodular aggregates of @entity5 cells with central @entity39 resulted in diffuse polypoid synovial thickening mimicking @entity378 and @entity1362 . The @entity5 cells showed positive staining for EMA, @entity4166 , @entity2280 , and complete loss of @entity6195 staining, establishing the diagnosis of primary synovial @entity242 . The @entity242 spread from the synovium to and along the joint capsule, and then extra-articularly into the soft tissue surrounding the knee joint, with lymphovascular permeation. Such pattern of spread calls for radical surgical excision as the treatment of choice.
