[Synovial metastases from colonic cancer presenting as arthritis of the knee. Characterization by 18FDG PET scan]

A case of carcinomatous monoarthritis involving the left knee due to colonic adenocarcinoma is described. Large recurrent synovial effusion, that will be later hematic, lytic lesion of the bones and chondrolysis were noted. Knee positron emitting tomography scan using FDG (FDG-PET) revealed a diffuse increased uptake in soft tissues assumed to be synovium, the hypertrophy of which was identified by ultrasonography. Whole body PET scan showed extensive lymph node, visceral and bone metastases, suggesting that the increase in the synovium could also be of metastatic origin. The final diagnosis of synovial carcinomatosis secondary to the known colonic adenocarcinoma was confirmed by histological analysis of biopsies obtained by arthroscopy. A review of the literature is realised. To our knowledge, this is the first synovial metastasis studied by FDG-PET.