Pigmented Villonodular Synovitis

Pigmented villonodular synovitis is a slow growing, benign, and locally invasive tumor of the synovium which affects synovial lined joints, bursae, and tendon sheaths. It commonly occurs in knee followed by hip, ankle, and elbow. In this disease, the synovial membrane proliferates and its surface develops nodules and villi. It also turns into brown color.

Two primary forms are described

• Diffuse form that affects the entire synovial lining of a joint, bursa, or tendon sheath, and a rare focal, or localized, form. The diffuse form typically involves the large joints.

• Typically occurs around the small joints of the hands and feet. Often it appears around tendon sheaths, in which case it is termed giant cell tumor of the tendon sheath. Rarely, the localized form may develop around large joints.

The term pigmented villonodular synovitis is used when the condition, in either diffuse or localized form, affects a joint.

Etiology

The cause of pigmented villonodular synovitis is not clear. Inflammation, response to antecedent trauma, repeated hemorrhage into the joint, and disorders of lipid metabolism have been proposed to be possible causes.

Presently, neoplasia is accepted underlying etiology.

About 10 cases per million have been reported to occur in extra-articular locations and about 2 per million occur in intraarticular locations

Diagnosis is more common between ages 20 and 50 years, with a median age of 30 years.

The disease is monoarticular mostly i.e. it confines to a single joint. The knee joint is the most common site of affliction. It is followed in decreasing order of frequency in the fingers, feet, ankles, hips, wrists, and shoulders.

Pathology

Gross features are thickened synovium, with a combination of villous and nodular proliferation. Microscopically Pigmented Villonodular Synovitis is characterized by the presence of hemosiderin-laden, multinucleated, giant cells. Lipid-laden macrophages, fibroblasts, and other large, polyhedral-shaped, mononuclear cells may also be seen. The lesion is very vascular and shows synovial hyperplasia.

The presence of hemosiderin is responsible for pigmentation.

The lesion can invade local tissues including the invasion of the subchondral bone, with resultant cyst formation which is a characteristic finding.

Presentation of Pigemented Villonodular Synovitis

The disease is characterized by acute attacks of pain and swelling, usually in a single joint. The patients may have mechanical symptoms like locking and catching in the knee.   It usually presents as a monoarticular hemarthrosis, and may exist in a nodular or a diffuse form. Swelling is disproportionate to the degree of pain.

On examniation, there might be nodular or diffuse joint swelling. Swelling may be warm and  tender to palpation. On aspiration of the affected joint, a dark brown or frankly serosanguinous fluid is obtained

Imaging

X-rays

Findings on plain xrays  are not specific. In pigmented villonodular synovitis of the knee findings of the knee apparently are normal except for the curvilinear calcification seen peripherally to the medial femoral condyle.

Saucer shaped lesions due to pressure erosions  and cysts may occur on either side or both sides of the joint. Secondary degenerative changes may occur in the affected joint in long-standing disease.

Computed Tomography

The lesions appear hyperdense . CT scanning is also valuable in delineating bone cysts and erosions and is also useful for needle biopsy guidance for a histologic diagnosis.

Magnetic Resonance Imaging

MRI demonstrates variable appearance  depending on the composition of the lesion [relative proportions of hemosiderin, lipid, fibrous tissue, cyst formation, and cellular element].

Nodular intra-articular masses that demonstrate low signal intensity are visible [due to hemosiderin deposits]. Hyperplastic and hypervascular synovium enhancement occur following gadolinium enhancement.

Bony erosions (when present) and extra-articular extension of the lesion are well demonstrated on MRI.

Nuclear Imaging

Bone scans do not play a significant or routine role in the diagnosis of pigmented villonodular synovitis. Hypervascularity and areas of erosion may result in increased radionuclide uptake.

Differential Diagnoses

• Chronic monarticular rheumatoid arthritis
• Synovial hemangiomatosis
• Low-grade infectious arthritis
• Tuberculosis
• Gout
• Hemochromatosis
• Synovial Osteochondromatosis
• Synovial Sarcoma

Treatment

Though it is a  benign condition, pigmented villonodular synovitis may result in significant morbidity if left untreated.
The primary treatment options include surgical resection via synovectomy or radiation therapy.

Radiation therapy may be used as the primary treatment method or in addition to surgical excision.

Open synovectomy is the treatment of choice for pigmented villonodular synovitis with the active form of the disease. Recurrence rate is relatively high.

Total knee arthroplasty id done in the patient of pigmented villonodular synovitis with joint destruction.

A long course of the disease and numerous recurrences may necessitate amputation.