MRI and 18F-FDG PET/CT findings of a giant cell tumor of the tendon sheath of the knee joint (pigmented villonodular synovitis): A case report and literature review.

We present a case of a 33-year-old female hospitalized with a 3-month history of right knee pain when squatting. Her physical examination showed no resting pain or local skin fever. Magnetic resonance imaging (MRI) showed multiple nodular long T1 and short T2 abnormal signal shadows in the popliteal fossa region. A patchy T2 high signal shadow was found in the soft tissue around the right knee.Fluorine-18-fluorodeoxyglucose positron emission tomography/computed tomography (¹⁸F-FDG PET/CT) revealed multiple soft tissue density nodules around and within the right knee joint (largest 20x13mm) with a maximum standardized uptake value (SUVmax) of 10.5 and a delayed SUVmax of 12.0. The subsequent histopathologic examination confirmed the diagnosis of a diffuse giant cell tumor of the tendon sheath (GCTTS) and pigmented villonodular synovitis(PVNS).