Chondromyxoid fibroma (CMF) is a rare, benign tumor of the bone that was described by Jaffe and Lichenstein in 1948.  CMF is most often found in the long tubular bones, especially the tibia and femur near the knee joint. CMF occurs predominantly in younger patients in the second or third decade of life. [2, 3]
The tumor arises from the cartilage-forming connective tissue of the marrow space. As its name implies, this benign cartilaginous neoplasm consists of chondroid, myxoid, and fibrous tissue in variable amounts, and microscopic evaluation of a wide area of the tumor may be necessary to identify all of the tissue subtypes. The radiographic characteristics of CMF are depicted in the images below.
Osteoclast-like giant cells may also be present, as may small cysts and hemorrhagic zones. Focal calcification is found microscopically in approximately one fourth of patients, although any gross evidence of calcification is rare.
Most CMFs (75%) occur in the bones of the lower extremity, particularly around the knee joint. CMF is localized to the femur and tibia (as seen in the images below) in 50% of patients. The most common site is the proximal tibia, which accounts for approximately 30% of cases. The humerus, radius, and ulna also are affected, although reported percentages vary widely from study to study because of the rarity of the lesion.
In addition, the small bones of the foot are relatively common sites, and lesions of the hands, skull, spine, and pelvis (see the image below) have been reported. 
Within the bone, the tumor typically originates in the metaphysis close to the physis. The tumor may extend into the epiphysis, the diaphysis, or both. Apophyses also may be affected (eg, the greater trochanter of the femur). In the long bones, the tumor is usually eccentric and ovoid in shape (as seen in the image below), with the long axis paralleling the length of the bone. In smaller bones, the tumor may occupy the entire volume of bone.
Conventional radiography provides the most useful diagnostic information of any imaging modality; however, definitive diagnosis can only be made using analysis of biopsy specimens. Unless contraindicated, magnetic resonance imaging (MRI) is recommended over computed tomography (CT) scanning for delineation of tumor extent before surgery. (See the images below). [5, 6]
Limitations of techniques
Although findings on conventional radiographs may suggest the diagnosis of CMF, definitive diagnosis requires an analysis of biopsy specimens.
On conventional radiographs, such as the 2 images below, a CMF usually appears as a well-marginated, expansile, eccentric, lucent medullary lesion in the metaphysis of a long bone, ranging in length from 3-10 cm.
The tumor may extend into the diaphysis (see the first image below) or, uncommonly, into the epiphysis (see the second and third images below). CMF may rarely be purely diaphyseal (see the fourth image below), but it is never solely epiphyseal. The tumor may replace the bulk of a smaller bone. Smaller CMFs may appear to arise from the cortex of bone, and juxtacortical (exophytic) tumors have been reported.
Smaller tumors are usually round with a thin, sclerotic margin (as in the image below) and uncommonly contain visible calcification or trabeculation. In larger lesions, remnants of cortical bone reinforcing the tumor at the periphery can appear on radiographs as trabeculation.
These osseous ridges along the periphery are also responsible for the bubbly, cystic radiographic appearance of CMF (see the first 2 images below). A sclerotic, scalloped border is typical. Compared with other cartilaginous tumors, the matrix of CMF uncommonly appears calcified on conventional radiographs.
Degree of confidence
An eccentric, medullary, bubbly-appearing, metaphyseal lesion with scalloped, sclerotic borders should prompt the radiologist to consider CMF in the differential diagnosis, particularly if the lesion is found in the proximal tibia. However, diagnosing CMF with a high degree of confidence by using imaging studies may be difficult because of the rarity of the tumor. An analysis of a biopsy specimen is always necessary for a definitive diagnosis.
After conventional radiography, CT scans may be used to further study the nature and extent of the suspected CMF. (See the images below.)
CT scanning is the best imaging modality for detecting sclerotic margins and ridges and matrix mineralization, and CT findings can depict the cortical integrity of the lesion. CT scans may show calcification within the tumor that is not visible on conventional radiographs.
Degree of confidence
CT findings may reveal calcifications within the lesion that are not apparent on conventional radiographs; therefore, CT findings may increase the suspicion that a lesion is cartilaginous. Otherwise, CT scans add little to the diagnosis.
Magnetic Resonance Imaging
MRI findings of CMF are nonspecific. The tumor typically demonstrates low signal intensity on T1-weighted images (as in the first 3 images below) and heterogeneous, high signal intensity on T2-weighted images (as in the fourth image below).
Smaller lesions, as well as some larger lesions, may demonstrate a homogeneously bright signal on T2-weighted images, often with a hypointense rim (see the first image below). Enhancement following intravenous administration of gadolinium is typically heterogeneous (see the second image below), often most prominent along the vascular borders of the tumor. Heterogeneity is believed to be the result of varying amounts of chondroid, myxoid, and fibrous tissues in the tumor, as well as any underlying cystic and/or hemorrhagic components.
Gadolinium-based contrast agents (gadopentetate dimeglumine [Magnevist], gadobenate dimeglumine [MultiHance], gadodiamide [Omniscan], gadoversetamide [OptiMARK], gadoteridol [ProHance]) have been linked to the development of nephrogenic systemic fibrosis (NSF) or nephrogenic fibrosing dermopathy (NFD). The disease has occurred in patients with moderate to end-stage renal disease after being given a gadolinium-based contrast agent to enhance MRI or MRA scans.
NSF/NFD is a debilitating and sometimes fatal disease. Characteristics include red or dark patches on the skin; burning, itching, swelling, hardening, and tightening of the skin; yellow spots on the whites of the eyes; joint stiffness with trouble moving or straightening the arms, hands, legs, or feet; pain deep in the hip bones or ribs; and muscle weakness.
Degree of confidence
MRI findings of CMF are nonspecific and typically do not alter the degree of confidence in the diagnosis. The primary role of MRI is in preoperative planning (ie, evaluation of the extent of the tumor).
Although increased radionuclide activity is demonstrated in CMFs on bone scans (as in the image below), nuclear medicine procedures are of limited use in the diagnosis or management of these lesions.
The typically eccentric location of a CMF may be evident if the lesion is relatively small (see the first image below). Smaller lesions may be subtle if located adjacent to a growing physis or joint that typically accumulates radiotracer (eg, the sacroiliac joint) (see the second image below).
Increased flow may be apparent on the angiographic portion of a 3-phase study (see the first image below). Bone scintigraphy may be used to exclude the possibility of multiple lesions, which are highly uncharacteristic of CMF (see the second image below).
Degree of confidence
Nuclear medicine studies add little to the degree of confidence in the diagnosis, although finding multiple lesions on a bone scan is highly uncharacteristic in CMF.
Angiography is of limited use in the diagnosis of CMF. Angiographic appearances are nonspecific, with the tumor demonstrating either minimal neovascularity or no internal vascularity, with or without surrounding vascular tissue. Angiography may be used to define surrounding vasculature or for planning embolization (uncommon).
Degree of confidence
Angiography typically does not alter the degree of confidence in the diagnosis, but it may be used as a preoperative study.