Chondromyxoid Fibroma

     Chondromyxoid fibroma (CMF) is a benign cartilage tumor that also has myxoid and fibrous elements. It is extremely rare and accounts for less that 1% of all bone tumors.i CMF is found most often in the metaphysis around the knee in the proximal tibia, proximal fibula, or distal femur. It presents in the second to third decade and has a male to female ratio of 2 to 1. The clinical presentation is usually chronic pain, swelling and possibly a palpable soft tissue mass or restriction of movement. Only 5% of patients with CMF present with a pathological fracture."
     Radiological findings demonstrate an eccentrically placed Iytic lesion with well defined margins in the metaphysis of the lower extremity. The lesion usually has a sclerotic margin of bone and a lobulated contour. Ridges and grooves that appear in the margins secondary to scalloping falsely appear to be trabeculae. CT helps define cortical integrity and confirms that there is no mineralization of the matrix, unlike other cartilage tumors. CMF has the same appearance on MRI as other cartilage tumors which is decreased signal on T 1 weighted images and increased signal on T2 weighted images. MRI is helpful in preoperative planning and staging. The radiologic differential diagnosis includes giant cell tumor, aneurysmal bone cyst, unicameral bone cyst, chondroblastoma and fibrous dysplasia.
     CMF resembles fibrocartilage grossly. It has a sharp border often with an outer surface of thin bone or periosteum. The glistening grayish white lesion is firm and lobulated. It may also have small cystic foci or areas of hemorrhage.
     Histologically, CMF appears very similar to chondrosarcoma. They are so close in histology that often radiology helps to make the final diagnosis. The predominant features of CMF are the zonal architecture and lobular pattern. Nodules of cartilage are found in between fibromyxoid areas. In some fields the loose myxoid dominates and in other the dense chondroid dominates. The chondrocytes are plump to spindly in shape and have indistinct cell borders in sparsely cellular lobules of myxoid or chondroid matrix. There are also more cellular zones of the tumor with some giant cells at the edges. The sharp borders of each lobule and the lesion itself help to differentiate it from chondrosarcoma.
     Treatment of CMF is en bloc excision. Recurrences after curettage are common.

References
Giudici, M. et al, Cartilaginous Rone Tumors, Radiologic Clinics of North America, 31(2):237-259, March 1993. UGiudici et al.

Bulloughs, Peter, Orthopedic Pathologv (third edition), Times Mirror International Publishers Limited, London, 1997.

Huvos, Andrew, Bone Tumors:Diagnosis. Treatment and Prognosis, W.B. Saunders, Co., 1991. ¶