Clinical History
A patient presented with a swelling of the left knee, which developed slowly.
Imaging Findings
The patient complained of a swelling in the left knee over the past eight months. A plain film radiograph showed a slightly expansile lytic lesion with lobulated and well-defined margins involving
eccentrically the proximal metaphysis of the tibia (Fig. 1). On MR imaging, the lesion showed an intermediate signal on T1-weighted images (Fig. 2a), which became homogeneously hyperintense on
T2-weighted images (Fig. 2b). After an intravenous injection of Gd-DOTA was given, heterogeneous enhancement could be seen (Fig. 2c). The lesion was surgically removed and a bone allograft was
required.
Discussion
A chondromyxoid fibroma (CMF) is the least common of the benign cartilaginous skeletal neoplasms. It is most common in the second and third decades of life. A slowly progressive pain, tenderness and
swelling, taking anywhere from 1 week to several years to develop, are the most frequent clinical abnormalities. The typical radiographic findings include an eccentric lytic lesion with a
well-defined and often sclerotic margin in the metaphysis of a long tubular bone, especially those in the lower extremities (as seen in 80% of the cases). However, a CMF can have a protean
radiographic presentation and can occur anywhere in the skeleton as a benign slow-growing tumour. Extensive periosteal reaction and pathologic fractures are unusual, and calcification is rare. On MR
imaging, a CMF has a decreased signal on T1-weighted images and an increased signal on T2-weighted images. A lobular pattern of high signal intensity has been described for a CMF, as in other
cartilaginous tumours, although the signal intensity of a CMF will depend on the proportion of the chondroid, myxoid and fibrous tissues. The classical histological feature of this tumour is the
presence of stellate or spindle-shaped cells arranged in lobules against a background of myxoid or chondroid tissues. The differential diagnosis of a CMF includes, the possibility of a giant cell
tumour, an aneurysmal bone cyst and a nonossifying fibroma. The presence of calcification within the tumour suggests other possibilities such as a chondroblastoma and an enchondroma. A surgical
resection is the treatment of choice. Because these neoplasms are locally aggressive, wide resection and bone grafting are usually required.
Differential Diagnosis List