Pigmented villonodular synovitis

Pigmented villonodular synovitis (PVNS) is a rare, benign condition that affects the synovium of joints, bursae, and tendon sheaths. The etiology, or cause, of this proliferative disorder is unknown. Two forms of the disorder exist: localized and diffuse, the latter being more common.

Classification
Pigmented villonodular synovitis, described distinctly in 1941, comes in two forms: localized and diffuse. Diffuse PVNS effects the entire synovium and typically occurs in large joints such as the knee or hip. Localized, or nodular, PVNS is less common than the diffuse form and typically occurs in smaller joints such as the hands and feet. It often arises in the form of a benign giant cell tumor on the tendon sheaths of the joint. As the tumor grows in the joint, it damages the surrounding bone and tissues. Localized PVNS is predominantly found in females and is frequently found in the fingers. Although rare, localized PVNS may develop in large joints. In either case, the knee is the most commonly affected joint (80% of cases), followed by the hip, and less commonly the ankles and shoulders. PVNS is generally found more in men than women.

Clinical presentation
In general, pigmented villonodular synovitis often manifests initially as sudden onset, unexplained joint swelling and pain; the joint swelling is disproportionate to the amount of pain the patient feels at first. Decreased motion and increased pain occur as the disorder progresses as well as locking of the joint. The localized form often manifests initially as a painless, slow-growing mass and progresses to the other common symptoms of PVNS. The swelling often feels warm to the touch. Diffuse PVNS symptoms are often confused with those of Rheumatoid arthritis. While pigmented villonodular synovitis can occur in both pediatric and geriatric patients, it is more common with ages 20-50.

Complications
PVNS is locally aggressive and can spread to surrounding tissues, causing bone erosion and tissue damage. If not treated early, it can spread to areas outside the joint. The disorder also has, on average, a 45% rate of recurrence.

Diagnosis
PVNS is radiologically diagnosed by Magnetic Resonance Imaging (MRI). The disorder is difficult to identify and is often not diagnosed for four years or more after presentation due to nonspecific symptoms or a general paucity of symptoms.

Diagnostic Findings

 * Conventional radiographs of joints affected by PVNS may appear normal or may demonstrate periarticular soft-tissue swelling. Joint spaces and bone mineralization are characteristically preserved until late in the disease. Bone erosions are common in joints with a tight capsule, such as the hip and ankle.
 * On MR images, the masslike proliferative synovium has a lobulated margin, and it may be extensive in diffuse PVNS or limited to a single nodule in the focal form.
 * The lesions tend to bleed, causing hemosiderin deposition and a characteristic blooming on gradient echo imaging.
 * Areas of high signal intensity on T2-weighted images may be present and are likely caused by inflamed synovium or joint effusions.

(Images courtesy of WikiDoc)

Patient #1: MR images demonstrate PVNS

Treatment
Once PVNS is confirmed by biopsy of the synovium of an affected joint, a synovectomy of the affected area is most common treatment. Bone lesions caused by the disorder are removed and bone grafting is performed as needed. Because diffuse PVNS has a relatively high rate of recurrence, radiation therapy may be considered as a treatment option. In some cases, a total joint replacement is needed to relieve symptoms when PVNS causes significant joint destruction.

Summary

 * Pigmented Villonodular Synovitis (PVNS) is a benign proliferative disorder of the synovium that may affect the joints, bursae, or tendon sheaths.
 * It can appear in either a diffuse or, less commonly, a focal form within the joint.
 * PVNS most often occurs in young to middle-aged adults.
 * The knee is the most frequently involved joint, followed by the hip, ankle, and shoulder.
 * Polyarticular involvement is extremely rare.
 * Local recurrence following surgical or arthroscopic synovectomy occurs in almost 50% of case.