Localized pigmented villonodular synovitis of the knee: acute onset in pregnancy.

A pregnant patient in the first trimester presented with acute onset knee pain and effusion. As the clinical status was mimicking septic arthritis, surgery was performed. Arthroscopy demonstrated a local synovial tumor and excision was performed with arthrotomy. Microscopic evaluation revealed localized pigmented villonodular synovitis. Due to the presence of necrosis and hematoma in the tumor, we hypothesize that, that torsion or bleeding of the tumor in the presence of physiological pregnancy- related metabolic changes might have been the cause of acute presentation.