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
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.
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. ¶