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
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
Treatment
- None required
- If unsure of nature of lesion, follow-up in 3-6 months
Complications
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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).
For these same photos without the arrows, click here
For more information, click on the link if you see this icon 
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| Differential Diagnosis in Orthopaedic Oncology. A Greenspan, G Jundt and W Remagen. Lippincott Williams and Wilkins, 2006. |
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