Yesterday, we received 3 consecutive patients with pigmented villous nodular synovitis, all of whom were women. The patient has a lot of doubts about this disease, so today we will introduce: 1. What is pigmented villous nodular synovitis Pigmented villous nodular synovitis is a specific type of synovitis that occurs mainly in the joints, tendon sheaths and bursa tissue. It is called hyperpigmented villous nodular synovitis because of the presence of villous and/or nodular fibrous connective tissue protrusions at the site of the lesion and the large number of mononuclear macrophage-like cells that can be seen proliferating microscopically, along with iron-containing hemoglobin deposits. The clinical manifestations are mainly recurrent swelling and pain in the joints, which gradually worsen with time. The disease is divided into two types: (1) limited type. (2) Diffuse type. These two types of lesions differ in their general pathology and clinical treatment. Most of the lesions in the limited type are single nodules, ranging from a few millimeters to a few centimeters in diameter, and are brownish-red or reddish-brown, tough masses. There is no abnormal change in the synovial membrane surrounding the nodule or it is yellow in color with hyperpigmentation. These lesions can be satisfactorily resected alone. In diffuse lesions, the entire synovial membrane is affected by the villi and nodules and the lesion is yellow, brown or reddish-brown in color. These lesions have a high recurrence rate after treatment. The pathogenesis of this disease is not yet clear, and the lack of specific clinical manifestations and the ease of recurrence of the diffuse type make the clinical diagnosis and treatment problematic. For limited lesions, the main problem is the difficulty of diagnosis. Larger lesion nodules (more than 5-10 mm in diameter) can be detected by MRI and further clarified by arthroscopic exploration and removal of the nodules with good results and low recurrence rate. Treatment of diffuse lesions is more difficult, and total synovectomy is currently advocated. However, neither open surgery nor arthroscopic total synovectomy can completely remove 100% of the diseased synovium. Therefore, local radiation therapy (similar to the treatment of certain malignant tumors, but at a lower dose) is usually required after surgery. Local radiation therapy can kill the residual synovial membrane, but has the disadvantage of causing joint stiffness and slow wound growth and healing. Postoperative functional exercises should be carried out under the guidance of a rehabilitator, and daily activities can usually be resumed 1-3 months after surgery. In conclusion, MRI has a high diagnostic value in the diagnosis of pigmented villonodular synovitis. The use of total synovectomy under knee arthroscopy supplemented with postoperative radiation therapy can achieve satisfactory results in the treatment of diffuse hyperpigmented villous nodular synovitis. Of course, early diagnosis and treatment are crucial. Long-term, chronic lesions have a poor prognosis because of the heavy synovial erosion of the articular cartilage.