Magnetic resonance imaging and thallium-201 scintigraphy for the diagnosis of localized pigmented villonodular synovitis arising from the elbow: A case report and review of the literature.

Pigmented villonodular synovitis (PVNS) arising from the elbow joint is extremely rare; only 24 cases have been reported. It is extremely difficult to differentiate PVNS from other soft tissue tumors on the basis of imaging findings alone. Therefore, a biopsy is required for definitive diagnosis. A 20-year-old female reported a mass on her right elbow. Physical examination revealed a tumor measuring 3.0x3.0 cm. Magnetic resonance imaging (MRI) revealed that the signal intensity of the tumor was isointense to muscle on T1-weighted images; however, it was hyper- or isointense to muscle on T2-weighted images. In images obtained by gadolinium-enhanced MRI, the margin of the tumor was well-contrasted. Thallium (Tl)-201 scintigrams revealed an abnormal accumulation in the area of the mass in the early and delayed phases. On the basis of clinical findings, imaging characteristics and incision biopsy results, localized PVNS was diagnosed and marginal excision was performed. We thus identified an extremely rare case of PVNS arising from the elbow joint. When interpreting Tl-201 images for the assessment of bone and soft tissue lesions, it is important to recognize PVNS as a condition that simulates malignant tumors. Furthermore, PVNS should be considered in the differential diagnosis when increased Tl-201 activity is closely related to the joint. MRI aids in the differentiation by demonstrating features of hemosiderin degradation products. These findings are likely to be extremely helpful in the differential diagnosis of bone and soft tissue tumors.