Pigmented villous nodular synovitis is relatively rare, and there are two types: villous and nodular. Patients are mostly young and middle-aged men. They are mostly between the ages of 20 and 40. The disease is more common in the knee and ankle joints, followed by the hip, intertarsal, wrist, elbow, and occasionally the bursa and tendon sheath. This disease may be a synovial disease between inflammation and benign tumor. The villous form is more similar to an inflammatory disease. Animal studies have demonstrated that repeated injections of blood into the joint cavity can produce the same pathological changes as the villous form. Similar changes may be seen in athletes with repeated knee bleeding. The nodular type is composed of a large number of synovial cells and is prone to recurrence if not completely excised, thus resembling a benign tumor. In the villous type, the synovial membrane is dark red or brownish yellow and often thickens significantly, up to 1 cm or more. The synovial surface is uneven and often has folds and villi. Some of the villi are long and thin, up to 1-2 cm long, and float in the water like whiskers; others are short and fuse with each other to form nodules. The diameter of the nodules ranged from 1 cm to 4-5 cm. Smaller nodules were reddish brown, while larger nodules were yellowish white with rusty spots. The nodules are slightly stiff and tough, and swirling fibrous tissue is seen on section, with occasional mucus degeneration and fissures. In some cases, there are both villous and nodular lesions. The distribution of lesions can be classified as diffuse or limited. Diffuse lesions are more common, and a few are limited. In diffuse lesions, the villi and villi nodules are usually of the nodular type, and in limited cases, they are usually of the nodular type. Microscopically, the surface of the villi is composed of several layers of synovial cells with a little fibrous tissue, dilated capillaries and a few inflammatory cells in the center. Iron-containing haematoxylin granules are visible inside and outside the cells. The nodules consisted of dense synovial cells with little cytoplasm, indistinct cytosol, and dark nuclear staining. Fissures and papillae were seen in the dense cells. Multinucleated giant cells and foam cells are occasionally seen between the synovial cells. Clinical manifestations of chromophobe nodular synovitis There are no obvious systemic symptoms, the patient does not have a high temperature, the blood sedimentation is not rapid, and the blood picture is unchanged. Local symptoms are also mild in the early stages, so patients are seen late and have a long duration of illness, and most have a history of trauma. The main symptom of the disease is joint swelling, pain is relatively mild, local skin temperature is sometimes slightly high, and joint function is not significantly limited. In diffusely swollen joints, the thickened synovial membrane is spongy to the touch, and fluctuating sensations can be palpated in cases of fluid accumulation. Sometimes nodules of varying size and slightly mobile can be palpated. The suprapatellar bursa and patella are obviously swollen when the knee is involved, and the patella test is positive if there is a lot of fluid. The hyperplastic synovial tissue may sometimes penetrate the posterior joint capsule and enter the N fossa and spread down the posterior calf muscle space, producing a deep diffuse swelling. Swelling is most pronounced around the inner and outer ankles in ankle involvement. In hip involvement, the swelling is mostly located anterior to the hip joint. Whether diffuse or limited, there is mild muscle atrophy in the affected limb. Joint puncture may draw out bloody or coffee-colored fluid, and this joint fluid is very specific and has diagnostic value.