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Chondromyxoid Fibroma

Definition

  • A rare benign tumour derived from cartilage forming connective tissue.
  • Jaffe & Lichtenstein originally described the tumour in 1948

Aetiology

  • May arise from the epiphyseal cartilaginous plate.
  • Has a characteristic rearrangement on at 6q13

Incidence

  • 1.8% of all benign tumours
  • Chondroblastoma is 2.5 times more common than CMF
  • There is a slight male preponderance
  • Most common in the second & third decades

Localization

  • Typically in the metaphyseal region of a long bone. 
  • The lower limb is affected in 70%
  • Rarely, involves both metaphysis & epiphysis
  • Proximal tibial metaphysis is the commonest site.
  • small bones of the foot are commonly involved

Symptoms

  • Pain
  • Local swelling is found, rarely.
  • Occasionally asymptomatic finding on XR

Physical findings

  • May be swelling & tenderness

Radiology

  • Xray
    • Characteristically an eccentric, sharply circumscribed zone of rarefaction that occasionally expands the bone.
    • defect can be round or oval. 
    • It frequently has a scalloped appearance, caused by the lobulated nature of the tumour.
    • In many cases trabeculae appear to traverse the defect.  These are actually corrugations on the surface of the cavity that contains the tumour.
    • Chondromyxoid fibroma involving the surface of a bone tends to have extensive mineralization
  • Bone scan
    • hot
  • MRI
    • typically shows low intensity on T1 & high intensity on T2

Pathology

Macroscopic

  • Usually small; in the Mayo data the largest tumour was 5cm.
  • Fragments appear firm, fibrous & semi translucent.
  • If it is removed intact it appears lobulated & sharply demarcated

Microscopic

  • Mixture of myxomatous zones, fibrous zones & zones with chondroid appearance.
  • There is a characteristic lobular pattern of growth, with a hypocellular appearance centrally & a hypercellular periphery.
  • At the edge of the periphery around 50% of tumours have scattered giant cells.
  • May be foci of cellular atypia.
  • most important differential diagnosis is of a myxoid chondrosarcoma. 
  • These typically show liquefactive changes in the matrix, clear permeation of the surrounding bone, malignant XR features & most importantly hypercellularity throughout

Treatment

  • En bloc resection is the best treatment
  • Curettage has around a 25% risk of recurrence, & bone grafting is often necessary. 
  • Bone grafting may reduce the risk of recurrence.
  • Radiotherapy is not indicated except in the very rare surgically inaccessible region

Prognosis

  • Recurrence rate of around 25%
  • Sarcomatous change has not been convincingly demonstrated.  It may occur after radiotherapy.

 

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