PIGMENTED VILLONODULAR SYNOVITIS AND MENISCAL CYSTS
This diffuse or localized lesion develops in synovial tissue and involves the joints, bursae, and tendon sheaths. Although its etiology remains unclear, it does appear to be an idiopathic condition.
Diffuse Villonodular Synovitis
This condition typically occurs in adults between 20 and 40 years of age. A single joint of the lower limb, most frequently the knee, is the most common site of involvement. The synovial membrane becomes thickened and diffusely covered with long, tangled, reddish and yellow-brown villi, which may mat together to form plaques. Later, both sessile and pedunculated rubbery nodules appear. Hemosiderin-bearing stromal cells, lipid-bearing foam cells, and multinucleated giant cells are seen on microscopic examination.
Late in the disease, the pathologic changes may cause pressure indentation of bone and sometimes actual invasion of bone at the articular margins with subsequent bone destruction.
The predominant symptom is a chronic, slowly increasing swelling of the joint that is associated with mild aching. Acute episodes of pain with increased joint swelling may occur intermittently and are attributed to pinching of villi between the joint surfaces, with subsequent hemorrhage. Because the course of the disease is usually benign, diagnosis and treatment are often delayed. Examination of a palpable joint often shows a diffuse, slightly warm and tender, boggy swelling. A valuable diagnostic finding is the aspiration of bloody, brown, or serosanguineous fluid from a chronically swollen, uninjured joint.
Early on, radiographic examination may reveal an increase in joint fluid and a thickened synovial membrane. However, MRI remains the diagnostic imaging modality that is most beneficial. Late in the disease, superficial erosions of cortical bone near the joint margin and irregular areas of bone destruction may be present. Surgical treatment options range from arthroscopic synovectomy for more mild or inactive forms to complete open synovectomy for active diffuse forms. If the entire synovial membrane cannot be excised, localized disease can recur and radiation therapy may be indicated. If bone destruction is present, a total joint arthroplasty can be performed.
Localized Villonodular Synovitis
This more common form occurs in small joints, bursae, and tendon sheaths. The characteristic lesion is a sessile or pedunculated, yellow to reddish brown nodule with localized villous proliferation around its base. Symptoms are mild, consisting of intermittent swelling and aching. Slight swelling and a localized nodule may be noted on examination. The tenosynovitis, also called a xanthomatous giant cell tumor of the tendon sheath, is the most common manifestation of localized villonodular synovitis, occurring primarily in the hand or foot, where it presents as a discrete, firm, slowly enlarging nodule.
Treatment is complete excision of the nodular lesions in joints, tendon sheaths, and bursae.
Cysts of the meniscus of the knee are one of the most frequent causes of swelling at the lateral or medial joint line. The lateral meniscus is involved much more
frequently than the medial meniscus. Although the etiology of these cysts is unknown, they may be due to trauma that causes cystic or mucoid degeneration in fibrocartilage and fibrous tissue and are often associated with tears of the meniscus. Patients vary in age from adolescence to middle age.
The cysts normally develop in the periphery of the middle third of the meniscus and in the adjacent soft tissues within the joint capsule. Usually multilocular and lined with endothelium, they contain a clear, gelatinous material.
Persistent aching in the cyst area is the main symptom. Examination reveals a tense, palpable, and often visible swelling at the joint line over the middle third of the meniscus, usually just anterior to the LCL. The cyst, which moves with the tibia, is most prominent on extension of the knee and tends to disappear on flexion. Arthroscopic examination and decompression of the cyst, while addressing any meniscal pathology, is indicated if pain and disability are significant.