Synovial osteochondromatosis

A 66-year-old man presented with a 2-year history of a left-sided preauricular mass that was associated with mild trismus and difficulty chewing. He was otherwise asymptomatic. Computed tomography (CT) and magnetic resonance imaging (MRI) of the mass demonstrated discrete areas of calcification arising from the condyle of the left mandible, with extension along the skull base and the medial pterygoid muscles (figure). No evidence of parotid extension was observed. After several fine-needle aspiration biopsies were nondiagnostic, an incisional biopsy was performed. Intraoperatively, the tumor was identified as a cystic mass in the temporomandibular joint (TMJ) space; multiple calcified nodules were also noted. Findings on histopathologic evaluation were consistent with synovial chondromatosis.

Osteochondromatosis (synovial chondromatosis) is generally a benign, self-limited pathologic condition that affects synovial tissue. (1) Its onset is insidious, and it usually arises in the larger joints such as the knee, hip, shoulder, elbow, and ankle; it rarely affects the TMJ. It typically occurs during the third through fifth decades of life, and the ratio of male to female patients is 2:1. (2)

Synovial chondromatosis is not a true neoplasm; rather, it represents a metaplastic process. Metaplastic zones develop within the synovial intima, which organizes into small bodies within the joint spaces. This occurs in three progressive stages. (3)

* During stage 1, metaplasia of the synovial intima results in the formation of small cartilaginous nodules.

* During stage 2, the small nodules are released into the joint.

* During stage 3, the nodules begin to ossify centrally, and the synovium becomes inactive.

Most patients do not present until their disease has reached the third stage. As a result, making a definitive diagnosis is difficult because by then, synovial tissue is inactive on biopsy analysis.

The etiology of synovial chondromatosis is unknown. The disease is classified as primary or secondary. Primary disease occurs de novo in an otherwise normal joint, and it is more likely to recur. (4) Secondary disease is caused by irritation of the synovial tissue that surrounds the involved joint. The most common irritants are believed to be trauma and infection, although neither has been proven to be so. (5) Secondary synovial chondromatosis is usually associated with a history of trauma or osteoarthritis.

Patients with synovial chondromatosis of the TMJ space typically present with preauricular swelling, sometimes with a history of trauma to the joint. In view of its rarity and close proximity to the parotid, synovial chondromatosis of the TMJ space must be distinguished from parotid tumors. CT and MRI studies can be helpful in detecting the loose bodies, delineating extension, and identifying associated articular and extraarticular disease. In addition to synovial chondromatosis, the differential diagnosis of loose joint bodies in the TMJ includes osteochondral fracture fragments, condylar fracture, rheumatoid arthritis, degenerative arthritis, and avascular necrosis. Lesions should be resected to establish a definitive diagnosis and to relieve symptoms.

Although synovial chondromatosis is generally benign, rare cases of malignant transformation to synovial chondrosarcoma are known to have occurred. Also, postsurgical recurrence is possible. Regular follow-up examinations should be performed to monitor joint function.

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References

(1.) Henderson MS, Jones HT. Loose bodies in joints and bursae due to synovial osteochondromatosis. J Bone Joint Surg 1923;5:400-24.

(2.) Yu GV, Zema RL, Johnson RW. Synovial osteochondromatosis: A case report and review of the literature J Am Podiatr Med Assoc 2002;92:247-54.

(3.) Milgram JW. Synovial osteochondromatosis: A histopathological study of thirty cases. J Bone Joint Surg Am 1977;59:792-801.

(4.) Jeffreys TE. Synovial chondromatosis. J Bone Joint Surg Br 1967;49:530-4.

(5.) Crony JM, Monu JU, Pope TL, Jr. Synovial osteochondromatosis. Radiol Clin North Am 1996;34:327-42.

From the Head and Neck Cancer Center, Cedars-Sinai Medical Center, Los Angeles

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