What is a Bone Island?

Also called an enostosis.

Bone island, by is a focus of mature cortical bone within the cancellous bone.

Bone island is thought by some to be a tumor-like condition and by others a hamartoma. Most likely, the lesion is congenital or developmental in origin and reflects failure of resorption during endochondral ossification.

Mostly, the bone island is asymptomatic and the lesion is usually an incidental finding.

Pelvis, femur, and other long bones are most common sites though it may be found anywhere in the skeleton. Bone islands usually are 1 mm to 2 cm in diameter. When bone islands are larger than 2 cm, they are classified as giant bone islands.

Imaging

On xray, the typical feature of bone island is homogeneous, sclerotic focus in the cancellous bone with distinctive radiating bony streaks that blend with the trabeculae of the host bone.

On CT scan, a bone island appears as a low-attenuation focus, and on MRI sequences it shows low signal intensity like cortical bone.

A distinguishing feature of bone islands is that they are usually “cold” on skeletal scintigraphy.

Generally speaking, findings on radiographs are considered diagnostic. In cases of large or symptomatic lesions, scintigraphy followed by biopsy may be warranted.

**  Some large bone islands have been reported to show increased activity on scintigraphy.

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