What is a Bone Island?

Bone Island is also called enostosis.

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

A hamartoma is a benign  tumor like mass composed of of an overgrowth of mature cells and tissues normally present in the affected part, but with disorganization and often with one element predominating.

 

Other hamartomas in the bone are of following type

Bone-forming

Cartilage-forming

  • Osteochondroma
  • Multiple osteochondroma
  • Epiphyseal osteochondroma
  • Enchondromatosis

Fiber-forming

  • Nonossifying fibroma
  • Fibrous dysplasia

Benign non–matrix-forming

  • Hemangioma of bone
  • Skeletal hemangiomatosis

 Presentation of Bone Island

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

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. However,  some large bone islands have been reported to show increased activity on scintigraphy.

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

Treatment

No treatment is required for bony island. Lesion at the best , needs to be observed.

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