Chondromyxoid fibroma is a rare, benign bone tumour, characterised by lobulated, myxoid and chondroid tissue with a scalloped border and radiolucent areas on imaging.
Description
Chondromyxoid fibroma (CMF) is a rare benign bone tumour of the cartilage, accounting for less than 1% of all bone tumours. It most commonly affects adolescents and young adults, with a slight male predominance. CMF is characterised by a mixture of chondroid, myxoid, and fibrous tissue. It typically occurs in the metaphysis of long tubular bones, especially around the knee, and less frequently in the pelvis and small bones of the hands and feet. Despite its benign nature, CMF can be locally aggressive and cause significant pain and swelling. The term “chondromyxoid fibroma” reflects the tumour’s histological composition, with “chondro-” indicating cartilage, “myxoid” referring to the gelatinous matrix, and “fibroma” denoting fibrous tissue.
Pathogenesis
The exact pathogenesis of CMF is unclear. However, it is thought to originate from primitive mesenchymal cells that differentiate along the chondroid lineage. Aberrations on chromosomes 6 and 11 have been identified in some tumours.
The exact pathogenesis of CMF is unknown, but it is thought to arise from primitive mesenchymal cells capable of differentiating into chondroid, myxoid, and fibrous tissues. Genetic mutations or aberrations, such as those involving the IDH1 gene, have been implicated in the development of CMF, although they are not present in all cases. The tumour is typically well-circumscribed and lobulated, with a propensity to expand and cause cortical thinning and disruption.
Subtypes
There are no recognised subtypes of chondromyxoid fibroma.
Epidemiology, Risk Factors & Associations
- Typically presents in the second or third decade of life.
- There is a slight male predominance.
Clinical Features
- Patients typically present with long-standing pain, swelling, and occasionally a palpable mass.
- The proximal tibia and the distal femur are the most frequently involved sites. Other less common locations include the bones of the foot and the flat bones such as the pelvis and the ribs.
Complications
- There is a low risk of local recurrence after curettage (10-25%).
- Malignant transformation is rare but has been reported.
Pathological Features
Histopathology
- Macroscopic: The tumour is well-circumscribed with a lobulated appearance, and is grey-white to yellow in colour.
- Microscopic: Characterised by lobulated myxoid and chondroid tissue, separated by fibrous septa containing spindle-shaped cells.
Serology
Not typically applicable to this condition.
Biochemistry
Not typically applicable to this condition.
Radiological Features
General Features
- Most commonly affects the long bones, particularly the metaphyseal region.
- The proximal tibia and the distal femur are the most frequently involved sites. Other less common locations include the bones of the foot and the flat bones such as the pelvis and the ribs.
- Characteristically demonstrates a well-defined lytic lesion with a scalloped border.
- The tumour has a lobulated appearance with occasional internal septations.
XR
- Shows a well-circumscribed lytic lesion in the metaphysis of a long bone.
- A scalloped, multilobulated appearance is often seen.
CT
- Non-contrast: Shows a well-defined lytic lesion with a lobulated appearance. The cortex may be thinned but is not usually breached.
- Contrast-enhanced: Enhancement is usually heterogeneous.
MRI
- T1WI: The tumour appears low to intermediate signal.
- T2WI: High signal intensity due to myxoid matrix.
- T1 C+: Enhancement is usually heterogeneous.
US
- Not typically used in the evaluation of this condition.
NM
- Not typically used in the evaluation of this condition.
Grading and Staging
Grading and staging are not typically relevant to CMF as it is a benign condition.
Diagnosis
Diagnosis is based on the characteristic imaging findings in conjunction with histological confirmation.
Differential Diagnosis
- Chondrosarcoma: Typically occurs in older patients and demonstrates more aggressive features on imaging such as cortical destruction.
- Simple bone cyst: Typically presents in a younger age group and lacks the scalloped, lobulated appearance of CMF.
Management
Surgical curettage is the treatment of choice, with resection reserved for recurrent or larger lesions. Patients should be followed up due to the risk of recurrence.