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bone island

Friday 2 March 2012

solitary enostosis

A solitary fleck of increased density in cancellous bone is not an uncommon incidental finding on radio graphic images.

These foci are found in the intramedullary spongy bone and are composed of compact bone that merges with the surrounding trabecular bone to give a spoke-like pattern at the periphery.

Usually these lesions are only 1 or 2 mm in diameter, but occasionally, they may be as large as 1 cm or even larger.

Occasionally scintigraphy may reveal increased uptake of isotope in these lesions, suggesting active growth.

Scintigram showing increased uptake of 99Tc diphosphonate in the lesion.

The lesions are probably developmental in origin and significant only in differential diagnosis (e.g., of osteoid osteoma when they are small or of sclerosing osteosarcoma if they are large).

Macroscopy

- whitish, circumscribed piece of bone, clearly demarcated from the surrounding cancellous bone.
- peripheral island of dense bone delineated by a fine osteolytic rim.

Microscopy

Microscopic examination of this tissue reveals mature lamellar bone with well-developed haversian and interstitial lamellar systems.

A bone island consists of dense but normal bone distinctly separated from the surrounding cancellous bone spicules.

The spicules merge with the nodule in a radial fashion.

The bone is found to be lamellar when viewed under polarized light.

No endochondral ossification or calcified cartilage is observed.

Dense cortical bone merges imperceptibly with the surrounding cancellous bone.

Differential diagnosis

- osteoid osteoma
- sclerosing osteosarcoma

See also

- bone-forming tumors