Primary synovial chondromatosis is a relatively uncommon condition. Synovial chondrosarcoma is considered to be very rare and it is not always clear whether the sarcoma develops by malignant transformation of synovial chondromatosis or whether it arises de novo. Differentiation of the two conditions on clinical and radiographic features is not possible and on histological criteria can be difficult. We report the case of a 59-year-old man who, 4 years after a synovectomy for synovial chondromatosis, developed a synovial chondrosarcoma of the hip. The literature is reviewed.

Desmoplastic fibroma is a rare benign primary bone tumor, histologically identical to the extra-abdominal desmoid tumor of soft tissues. The incidence in major series of bone tumors is 0.1%-0.3%. In the present study 18 cases from the files of the Netherlands Committee on Bone Tumors are reported, with an emphasis on the radiographic features. Eight female and ten male subjects were affected, with a fairly even age distribution from the second to the seventh decade of life. The most frequent sites of involvement were the femur and the pelvis. Radiographically the lesions nearly always demonstrated benign features with respect to pattern of destruction, margins, and reactive bone formation; however, soft tissue extension was sometimes present. Although desmoplastic fibroma usually presents with pain or swelling, in 5 of the 18 cases the existence of the lesion was an accidental finding, and in 2 cases the patient had long-standing, vague complaints of pain. Though overall benign radiographic features may support the final diagnosis, the main and often troublesome histological differential diagnosis is of a low-grade fibrosoma. En bloc resection is the treatment of choice in view of the high incidence of recurrence after curettage.

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