Chondromyxoid fibroma

Case contributed by Dr Naim K

Presentation

Long-standing right knee pain.

Patient Data

Age: 6 years
Gender: Male

Right knee

X-ray

There is a large multilobulated expansile lucent bone lesion located at proximal tibial diaphysis and metaphysis measures around six by two and half by two centimeters in maximal craniocaudal, anteroposterior and transverse dimensions respectively.

The previously described lesion shows well defined sclerotic margins and a narrow zone of transition with its long axis parallel to the long axis of the long bone.

There is an ill-definition of the cortex in the medial aspect of the lesion, suspicious for a cortical breakthrough. No obvious soft tissue component.

No suspicious periosteal reaction or pathological fracture.

A biopsy is advised to rule out a bone tumor.

Right knee and proximal tibia

MRI

There is a large well-defined proximal tibial diaphysis and metaphysis heterogeneous signal intensity mass lesion. Appears hypointense on T1WI and hyperintense on T2WI associated with bone marrow edema more distally in the diaphysis.

Bone expansion is noted more on the lateral side, with remarkable cortical thinning is seen posteriorly, laterally, and proximally with interruption seen anteriorly extending into the chondral tissue of tibial tuberosity without soft tissue component.

A small linear signal is seen arising from the upper part of the mass lesion extending close to the growth plate, better seen on sagittal gradient-echo images.

It measures around six by three by three centimeters respectively in maximal craniocaudal, transverse, and anteroposterior dimensions.

Soft tissue edema is noted also more distally.

The fibular, tibial epiphysis, and distal femur appear normal.

No significant knee joint fluid.

No evidence of neurovascular bundle invasion.

Impression:

  • MRI findings are due to the known bone tumor (Chondromyxoid fibroma).

Case Discussion

A 6-year-old boy with long-standing right knee pain was initially investigated by x-ray depicting a lytic lesion involving the proximal tibia. A biopsy of the lesion was done and the results were shown below.

Histopathology report:

Biopsy of the right upper tibia bone lesion shows a lobulated tumor formed of hypo and hypercellular areas with myxochondroid islands alternating with cellular fibrous areas containing many osteoclastic giant cells. Scanty mitotic figures are seen. No tumor necrosis is seen. Features are consistent with chondromyxoid fibroma. Radiopathological correlation is recommended.

As the histopathology report recommended further evaluation of the bone lesion. MRI was done and show findings compatible with Chondromyxoid fibroma.

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