Coexisting sarcoidal granulomatous inflammation and diffuse tenosynovial giant cell tumor of the knee after a total knee replacement: a case report.

Sarcoidosis is a systemic inflammatory disorder characterized by non-caseating granulomas, predominantly involving lung, mediastinal lymph nodes and other organs. Synovium involvement is infrequent, and as far as we know, involvement of a periprosthetic membrane has not been reported in the English literature. Intra-articular diffuse tenosynovial giant cell tumor ("conventional diffuse pigmented villonodular synovitis") is an uncommon, locally aggressive neoplasm with few previous case reports in which it arose in periprosthetic tissues after knee arthroplasty. We describe a unique case of an intraarticular mass next to a total knee prosthesis implanted 6 years ago in a patient with a history of pulmonary sarcoidosis. Clinically, this 67-year-old gentleman presented with progressive left knee pain, effusion and marked instability. MRI showed a large complex effusion with synovial thickening in the supra patella recess and the medial and lateral gutters. In addition, a large multilobulated mass with mixed low and high signal intensity was present in the posterior joint space, extending into the popliteal area. A two-stage operation was performed. Histologically, the mass from the posterior joint space showed characteristic features of diffuse tenosynovial giant cell tumor, while the synovium from the anterior compartment demonstrated sarcoidal granulomatous inflammation. Orthopaedic wear debris was found within the giant cells of these sarcoidal granulomata. The histologic features are different from those "usual" macrophage reactions to the particles of debris. In this article, we also included two optional links (highlighted in blue in the figures) to digital whole slide image (WSI), which allow the readers to navigate the entire microscope slides.