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Giant synovial chondromatosis

Summary

Giant synovial chondromatosis is a variant of synovial chondromatosis, where one or multiple chondromas enlarge to greater than 1 cm and may be as large as 20 cm.

These lesions are so rare that data on age distribution are lacking. The author has encountered several of these lesions in patients in their 20's, 30's and 40's.
These tumors may be totally asymptomatic, or may present as a painful mass near a tendon or a joint.
A mass is seen in the soft tissues near the joint which has features of chondroid matrix.
Simple excision is curative. Recurrence is rare.
Complete Information on this Tumor
Introduction and Definition: 

When one or a multitude of synovial chondromas enlarge to significant size, they are termed giant synovial chondroma or giant synovial chondromatosis. The cause if these tumors is unknown. The tumor can be so large that it may be confused with a chondrosarcoma.

Incidence and Demographics: 
Data are very scarce for this tumor. In the author's series, it appears to occur more commonly in women than men, and persons in their 20's 30's, and 40's are affected. Isolated cases of children having this tumor have also been reported.
Symptoms and Presentation: 

In the author's series, the tumor has been found as an incidental lesion in the ankle, a painful mass in the ankle or knee, or as a snapping sensation in the hip. Lesions have been reported in most large joints, including the elbow, shoulder, and the lower extremity. Some tumors in the author's series have been located in a tendon sheath outside the joint entirely, but not anatomically very far from a large joint.

X-Ray Appearance and Advanced Imaging Findings: 
The tumor is well defined, and on close analysis, has features consistent with cartilage. These include the usual "popcorn" or "rings and arcs" appearance on the plain radiographs. On MRI, the lesion is well circumscribed, dark on T1 and bright on T2, and a lobular or nodular appearance is often clearly seen. The CT scan will show the lesion clearly and its cartilage nature will be apparent. Bone scan will show moderate uptake. Plain xrays and MRI are adequate to identify the lesion, but suspicious tumors still need to be carefully biopsied to rule out malignancy.
Differential Diagnosis: 
Chondrosarcoma, parosteal osteosarcoma, osteochondroma, periosteal chondroma. Synovial sarcoma occurs very rarely in joints. However, at least one case of calcified synovial sarcoma which was misdiagnosed as synovial chondromatosis has been reported.
Preferred Biopsy Technique for this Tumor: 
Open, incisional
Histopathology findings: 
See synovial chondromatosis
Treatment Options for this Tumor: 
Once the diagnosis has been confirmed, simple excision is curative.
Preferred Margin for this Tumor: 
Marginal, intralesional is acceptable as well
Outcomes of Treatment and Prognosis: 
Recurrence is rare. Large lesions can cause minor local joint dysfunction that may persist following excision. Very rarely, the tumor may be very difficult to eradicate and recur aggressively, leading to complete destruction of the joint.
Special and Unusual Features: 
Arthroscopic surgical removal of multiple small synovial chondromatosis tumors has been reported, but the large tumors presented here are not amenable to arthroscopic removal and as such it is not recommended.