Extra-Articular Pigmented Villonodular Synovitis of the Deep Infrapatellar Bursa: A Case Report.

Abstract

Pigmented villonodular synovitis is a rare, benign, proliferative neoplastic condition affecting synovial-lined anatomic spaces1,2. It is characterized by hypertrophy of a synovial membrane by villous, nodular, and villonodular proliferation, with pigmentation secondary to hemosiderin deposition. These characteristics result in its typical imaging findings of low signal intensity on both T1 and T2-weighted images and typical “blooming artifact” with loss of signal foci on gradient echo sequences3-5. It is now well established in the pathology literature that pigmented villonodular synovitis is a neoplastic process on the basis of characteristic chromosomal changes6-9. Pigmented villonodular synovitis can be both localized and diffuse10 and can affect all synovial membranes, such as those of the joint or the bursa. For both forms of the disease, simple debridement with synovectomy is the most common treatment, although recurrence is common11—with rates as high as 25% to 50% in diffuse-type extra-articular disease12. Pigmented villonodular synovitis is usually monoarticular, affecting adults in the third or fourth decade of life; the knee is the most commonly involved anatomic location, followed by the hip, ankle, shoulder, and elbow13. Pigmented villonodular synovitis is usually intra-articular and only rarely extra-articular. In cases of extra-articular pigmented villonodular synovitis, there is usually evidence of extension from an intra-articular focus. As a result, the finding of pigmented villonodular synovitis in the deep infrapatellar bursa, which does not communicate with the knee joint14,15, is rare. Furthermore, to the best of our knowledge, there has never been a report of pigmented villonodular synovitis in the deep infrapatellar bursa. We present a case of extra-articular pigmented villonodular synovitis in a young patient with a painful slow-growing mass on the anterior aspect of the knee. The patient …