A 21-year-old woman with left leg pain.
Radiograph of the left femur revealed a mixed lucent, sclerotic and slightly expansile lesion, eccentrically located within the distal femoral metaphysis and diametaphysis. A periosteal reaction with chronic appearance was noted along the medial aspect of the distal femoral metaphysis. A fracture was not identified.
CT images demonstrated an expansile, lytic lesion eccentrically located within the distal femoral metaphysis and diametaphysis. The most inferior component of the lesion extendws to the distal epiphysis. Cortical thickening was present along the superior aspect of the lesion, while cortical thinning was noted along the inferior aspect of the lesion. Mild periosteal reaction was noted. Bony septations were noted inferiorly within the lesion.
The MR examination included axial SE T1 -, axial SE T2-, coronal STIR-, and sagittal GR- weighted sequences. The MR images demonstrated an eccentric, lobulated mass within the distal femoral metaphysis and diametaphysis, measuring up to 7.5cm in the largest dimension. The lesion demonstrated T2 hyperintensity and T1 hypointensity relative to skeletal muscle. Foci of susceptibility artifact were identified at the peripheral aspect of the lesion likely representing calcifications. Adjacent cortical thickening and thinning of the medial femoral metaphysis was identified. A moderate amount of bone marrow oedema was noted.
CT guided core biopsy of the lesion was performed, returning a pathologic diagnosis of chondromyxoid fibroma.
Chondromyxoid fibroma (CMF) is a rare benign tumour of bone with chondroid, myxoid and fibrous elements. It represents approximately 2% of all benign bone tumours and less than 1% of all primary bone tumours [1]. CMF presents in the second or third decade of life and occurs more commonly in the metaphysis of long bones, particularly around the knee [2]. However, CMF has been reported to involve the skull base, facial and calvarial bones [1,3].
Patients often present with pain and swelling. CMF may be an incidental finding in a small number of patients. Approximately 2-5% of patients present with a pathological fracture. [2,4]
CMF is a well circumscribed, slightly expansile, mixed lytic and sclerotic bone lesion, in which the margins are typically lobulated and sclerotic. Septations with cortical thickening have also been reported. Calcification of the matrix is rare. The average size at diagnosis is 3-4 cm [1].
On MR imaging, CMF is hypointense on T1 and heterogeneously hyperintense on T2. Chondroid, myxoid and fibrous components contribute to the T2 heterogeneity. These lesions enhance with gadolinium.
The differential diagnosis for this lesion in this case includes nonossifying fibroma (NOF) and aneurismal bone cyst (ABC).
NOF is a common, expansile, cortically based lytic lesion with subendosteal scalloping often involving the metaphysis of the long bones. It is seen in patients less than 30 years of age. In this case, the absence of fluid-fluid levels on MRI makes aneurysmal bone cyst less likely.
Treatment of CMF involves curettage and bone grafting. However curettage is associated with recurrence rates of up to 25%. En bloc excision is favored as it is associated with fewer recurrence rates. Malignant degeneration is rare and felt to be misclassified as low grade chondrosarcomas [5].
Chondromyxoid fibroma
The patient is a 21-year-old female presenting with left leg pain.
On the X-ray, a localized expansile radiolucent lesion is observed in the metaphyseal region of the distal left femur, with relatively clear margins and partial septation or sclerotic rim. The lesion shows mixed osteolytic destruction, and there may be some cortical thickening or mild outward bulge in the surrounding bone cortex.
CT images reveal an irregular expansile low-density lesion with multiple septations and scant obvious calcification. The lesion margins often show sclerosis or enhancement along the boundary.
On MRI, T1-weighted images present relatively low signal, while T2-weighted images show predominantly high signal with some degree of heterogeneous mixed signal, suggesting possible cartilaginous, myxoid, and fibrous components within the lesion. Contrast enhancement demonstrates pronounced enhancement of the lesion, which aligns with the features of cartilaginous and myxoid tissue.
No significant extensive soft tissue involvement is noted, and there is no apparent evidence of pathological fracture. However, the lesion is relatively large, with notable local expansion.
Considering the patient’s age, clinical symptoms, and imaging findings, the most likely diagnosis is
Chondromyxoid Fibroma (CMF).
For definitive confirmation, a biopsy (core needle biopsy) or surgical resection with pathological examination is recommended to exclude other rare bone tumors or malignant lesions.
During and after surgery, it is advised to perform functional exercises under the guidance of specialists and rehabilitation therapists, following the general principles of FITT-VP:
If the patient experiences significant pain, swelling, or other adverse symptoms during rehabilitation, immediate medical evaluation is necessary, and the plan should be adjusted accordingly. Given the risk of recurrence after curettage of such bone tumors, periodic imaging follow-ups and continuous monitoring of rehabilitation progress are crucial.
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Chondromyxoid fibroma
