Learning Radiology xray montage

Giant Bone Island

General Considerations

  • Bone islands (enostoses) are areas of mature compact bone in cancellous bone in the medullary cavity
  • Usually oriented with its long axis parallel to the cortex
  • Most common in pelvis, proximal femurs and ribs
  • May change in size over time, but change usually takes years

Clinical Findings

  • Usually asymptomatic

Imaging Findings

  • Round or ovoid
  • Dense
  • Greater than 2 cm in size (have been reported up to 10 cm in size)
  • Spiculated, feathered or brush-like margin (also called “thorny radiation” “pseudophilia” “cumulus cloud appearance”)
  • Thickening of trabecula
  • No bone destruction
  • No soft tissue mass
  • Radionuclide bone scan usually shows no increased uptake
  • MR: Loss of signal on all sequences, somewhat heterogeneous the larger they become

Differential Diagnosis

  • Osteoblastic metastatic disease
  • Osteosarcoma


  • None required
  • If unsure of nature of lesion, follow-up in 3-6 months


  • None

Giant Bone Island

Giant Bone Island. Frontal and lateral knee radiographs show a large, well-circumscribed, ovoid, sclerotic lesion in the distal femur (white arrow) with its long-axis oriented parallel to the cortex and a spiculated (feathery) margin (yellow arrow).
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Differential Diagnosis in Orthopaedic Oncology. A Greenspan, G Jundt and W Remagen. Lippincott Williams and Wilkins, 2006.