Pigmented nodular synovitis
The etiology of pigmented villonodular synovitis is controversial. The most common theory is that the disease is an inflammatory reaction of the synovium: however, some evidence exists that it is a benign neoplastic process. The incidence of pigmented villonodular synovitis is 1.8 cases per 1 million people per year Most studies show the disease to be equal between males and females. Pigmented villonodular synovitis (PVNS) generally occurs in patients between the ages of 20 and 45 years. The majority of patients with pigmented villonodular synovitis have monoarticular complaints of pain and swelling. In both the localized and diffuse subtypes, the knee is the most commonly affected joint (about 80 percent of patients), followed by the hip, ankle, small joints of the hands and feet, shoulder and elbow. Grossly, pigmented villonodular synovitis appears as a proliferative synovial process with brownish villonodular fronds in the affected joints. Diffuse disease is characterized by a mononuclear stromal cell infiltrate in the synovial membrane. Hemosiderin-laden macrophages give the characteristic brown color. Other cell populations include foam cells and multinucleated giant cells.
Diffuse pigmented villonodular synovitis of the knee can look like many other conditions. The two most common incorrect working diagnoses are patellofemoral syndrome and meniscal lesions. The disease is also confused with inflammatory arthritis, ligament instability and other conditions. Patients with diffuse pigmented villonodular synovitis of the knee complain of the insidious onset and slow progression of symptoms. One third of these patients report previous trauma to the knee. Patients also tend to complain of intermittent swelling and stiffness around the joint. The diagnosis of diffuse pigmented villonodular synovitis may be suggested by a clinical history of swelling that has an insidious onset, is not preceded by trauma and is out of proportion to the degree of discomfort. On physical examination, up to 96 percent of patients have distention of the suprapatellar pouch and a large effusion. As many as 40 percent of patients have a diffuse palpable synovial mass. Up to 90 percent of patients complain of mild to moderate tenderness, mainly over the medial knee. Arthrocentesis yields blood-tinged synovial fluid in 44 to 69 percent of patients.
In patients with pigmented villonodular synovitis of the knee, plain x-rays often appear normal. In general, bone and joint changes are less common in the knee than in the hip, because of the ability of the knee capsule to expand to accommodate the hyperplastic synovium. In patients with diffuse pigmented villonodular synovitis of the knee, magnetic resonance imaging (MRI) may show a large effusion, low signal intensity on both T1- and T2-weighted images (because of hemosiderin deposition), hyperplastic synovium and occasional bony erosions. The hip is the second most common location for pigmented villonodular synovitis. Like patients with knee disease, those with hip disease usually present with deep monoarticular pain of variable duration (a few months to a few years). The pain is often alleviated only by rest. Patients may localize the pain to the anterior groin or the lateral aspect of the hip. The pain is frequently intermittent. Patients occasionally report episodes of extreme pain, which may represent hemorrhage into the joint space. During these exacerbations, patients may be able to relieve the pain by positioning their hip in a flexed and externally rotated position. This positional relief of pain is typical of a joint effusion or inflammatory process of the synovium. Patients may also report decreased active and passive range of motion. In pigmented villonodular synovitis of the hip, x-rays show bony erosions in the head and neck of the femur and acetabulum in 95 percent of patients. These erosions are found early in the course of hip disease and appear as cyst-like structures.
Erosions are much more common in pigmented villonodular synovitis of the hip than the knee, primarily because the tight capsule of the hip joint does not allow the joint to expand to accommodate the hyperplastic synovium. As a result, intracapsular pressure increases, and bone erosion occurs.
MRI is highly sensitive and specific for the diagnosis of pigmented villonodular synovitis of the hip. Characteristic MRI findings include hip joint effusion, lifting of the joint capsule, low signal intensity on both T1- and T2-weighted images (because of hemosiderin deposition), hyperplastic synovium (that appears as a lobulated synovial mass), bony erosions and preservation of bone density. Pigmented villonodular synovitis should be considered in the differential diagnosis of patients aged 20 to 45 years who have monoarticular symptoms. Most patients with this disease have a long history of pain and disability. The presence of non-traumatic effusions of the hip or knee should raise the index of suspicion. Patients with nontraumatic knee effusions should then undergo arthrocentesis. The finding of blood-tinged fluid is highly suggestive. MRI should be performed to further suggest the diagnosis and define the extent of the disease process. In patients with hip lesions an MRI is usually performed to search for hip effusion and hypertrophic synovium before arthrocentesis is considered or attempted. The diagnosis of pigmented villonodular synovitis is confirmed by biopsy of the synovium. The treatment of choice is synovectomy. Associated bony lesions should be carefully curettaged, and bone grafting should be performed as necessary.
Diffuse pigmented villonodular synovitis has a high rate of local recurrence. The role of radiation therapy in the management of refractory disease is not clear. Radiotherapy can be considered in patients with previous adequate resection of disease who experience local relapse and in patients with a large amount of disease in whom complete resection is not possible. Synovectomy may not relieve all symptoms in patients with significant destructive changes in the joint. In these situations, arthrodesis or total joint replacement should be considered.
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