Aneurysmal Bone Cyst.

This tumour is found at onset in childhood and early adolescence. The sites are the long bones. The lumbar spine may be involved and, in that case, the presentation may be a little late. The commonest site in the spine would be in the neural arch. In the long bones the aneurysmal bone cyst is often metaphyseal and central. It rarely extends to the joint surface being blocked by the epiphyseal plate in the immature skeleton. It is an expanding bone lesion and is associated with thinning and a scalloped appearance of the overlying cortex. The endosteal margin of this tumour is well defined.

Aneurysmal bone cyst is usually not sclerotic, but there may occasionally be slight sclerotic reaction associated with it. The tumour is vascular and shows an increase in the blood pool phase at isotope bone scan. The tumour is benign and is a sponge-like tumour, containing multi nucleate cells.