An unusual case of 'haemorrhagic' bone cyst.

An unusual case of hemorrhagic bone cyst observed over a period of 12 years is presented. The diagnosis was confirmed by surgical exploration and histological examination of the tissue. The lesion continued to expand in spite of repeated surgical mandible. Finally, bone formation obliterated the cavity completely at the age of 19, when the facial deformity was corrected. It is suggested that this hemorrhagic bone cyst is of developmental origin. Since intramedullary haemorrhage and proliferation of giant cells are both responsible for the cavity formation and expansion, it is possible that aberrant formation of giant cells by fusion of endothelial cells of abnormal blood vessels may be an important factor in the pathogenesis of this condition.