bubble_chart Overview

Pigmented villonodular synovitis is relatively rare and has two types: villous and nodular. It predominantly affects young and middle-aged males, typically between the ages of 20 and 40. The disease most commonly occurs in the knee and ankle joints, followed by the hip, intertarsal, wrist, and elbow joints, and occasionally in bursae and tendon sheaths.

bubble_chart Pathological Changes

This disease may be a synovial membrane disorder that lies between inflammation and a benign tumor. The villous type is more similar to inflammation. Animal experiments have shown that repeated injections of blood into the joint cavity can produce pathological changes identical to those of the villous type. Athletes who experience repeated knee joint bleeding may also develop similar changes. The nodular type is composed of a large number of synovial membrane cells and is prone to recurrence if not completely excised, thus resembling a benign tumor.

In the villous type, the affected synovial membrane appears dark red or brownish-yellow, often significantly thickened, reaching over 1 cm in thickness. The surface of the synovial membrane is uneven, frequently exhibiting folds and villi. Some villi are slender, with the longest reaching 1–2 cm, floating in water like whiskers; others are shorter and fuse together to form nodular structures. The nodules vary in diameter from 1 cm to 4–5 cm. Smaller nodules are reddish-brown, while larger ones are yellowish-white with rust-colored spots. The nodules are slightly firm, and cross-sections reveal whorled fibrous tissue, occasionally with myxoid degeneration and fissures. Some cases exhibit both villous and nodular lesions.

Based on the distribution of lesions, the disease can also be classified into diffuse and localized forms. The diffuse form is more common, while the localized form is rarer. In diffuse sexually transmitted disease lesions, the villous and villonodular types predominate, whereas in localized sexually transmitted disease cases, the nodular type is generally observed.

Microscopically, the surface of the villi is covered by several layers of synovial membrane cells, with a core composed of sparse fibrous tissue, dilated capillaries, and a small number of inflammatory cells. Hemosiderin granules can be seen both intracellularly and extracellularly. The nodules consist of densely packed synovial membrane cells with scant cytoplasm, indistinct cell membranes, and deeply stained nuclei. Clefts and papillae are visible among the densely packed cells. Occasionally, multinucleated giant cells and foam cells are observed between the synovial membrane cells.

bubble_chart Clinical Manifestations

The disease does not present obvious systemic symptoms, with patients showing no fever, normal erythrocyte sedimentation rate, and unchanged blood counts. Local symptoms are also mild in the early stages, leading to delayed medical consultation and a prolonged course of illness, typically ranging from 1 to 5 years, with over half of the cases having a history of trauma.

The main symptoms of the disease include joint swelling, usually with mild pain, occasionally slightly elevated local skin temperature, and minimal joint function limitation. In cases of diffuse swelling, the thickened synovium feels spongy upon palpation, and fluctuation may be detected if there is significant effusion. Sometimes, nodules of varying sizes and slight mobility can be felt.

When the knee joint is affected, swelling of the suprapatellar bursa and patella is prominent, and a positive floating patella test may be observed if there is substantial effusion. Hyperplastic synovial tissue may sometimes rupture through the posterior joint capsule and extend into the popliteal fossa, spreading downward along the posterior muscle compartments of the lower leg, causing deep diffuse swelling. In cases of ankle joint involvement, swelling is most noticeable around the medial and lateral malleoli. For hip joint involvement, swelling is usually located anterior to the hip joint.

Regardless of whether the swelling is diffuse or localized, Grade I muscle atrophy is present in the affected limb. Joint aspiration may yield bloody or coffee-bean-colored fluid, which is highly characteristic and diagnostically significant.

bubble_chart Auxiliary Examination

In the early stages, diffuse or localized swelling may be observed, sometimes showing shadows of round soft tissue nodules. In the advanced stage, narrowing of the joint space, erosion of the joint margins, and proliferative changes can be seen, along with possible ligament calcification or intra-articular loose bodies.

bubble_chart Diagnosis

A careful analysis of clinical manifestations, combined with synovial fluid and X-ray examinations, usually makes the diagnosis straightforward.

bubble_chart Treatment Measures

The treatment of this disease includes surgical resection and radiation therapy. Surgical resection is more thorough and particularly suitable for nodular cases. Radiation therapy is more effective for villous types but less effective for nodular types. For diffuse sexually transmitted disease changes, complete removal of all synovial membrane tissue is necessary to avoid recurrence. For knee joint villous lesions with abundant synovial membrane that are difficult to completely remove, the synovial membrane tissue in the anterior and posterior aspects of the joint should be excised as much as possible, followed by postoperative radiation therapy, which can also achieve the goal of cure. For diffuse nodular lesions of the knee joint, the cruciate ligaments and collateral ligaments should be severed, and the joint should be dislocated before thoroughly removing the synovial membrane tissue in the anterior and posterior aspects. If nodular lesions are not completely excised, recurrence is highly likely, and a few cases may transform into synovial membrane fleshy tumors. For localized sexually transmitted disease changes, only the local synovial membrane tissue needs to be removed.

bubble_chart Differentiation

However, it must be differentiated from conditions such as subcutaneous synovial cyst, rheumatoid arthritis, hemophilic arthropathy, neuropathic arthropathy, intramuscular hemangioma, popliteal cyst, and meniscal cyst.