Aneurysmal bone cysts of soft tissue represent true neoplasms: a report of two cases.

A neurysmal bone cyst was first described by Jaffe and Lichtenstein in 1942. It is considered a benign, locally aggressive lesion with a potential for local recurrence, and it typically appears in the metaphysis of the long bones and in the vertebral column. Mostly, children and young adults are affected. No sex predilection has been observed. Radiographically, aneurysmal bone cyst is seen as a lytic lesion, usually eccentrically located and expansile but with well-defined margins. Histologically, there are blood-filled cysts separated by fibrous septa, with fibroblasts as well as osteoclast-type giant cells and reactive woven bone. Historically, aneurysmal bone cyst was believed to occur exclusively in bone. In 1972, Salm and Sissons noted soft-tissue lesions resembling aneurysmal bone cysts, and this was probably the first description of this entity. For many years, aneurysmal bone cyst was thought to be a lesion, reactive in nature, caused by a circulatory abnormality leading to an increased venous pressure and resulting in dilation of the vascular network. In recent years, strong evidence has supported the neoplastic nature of aneurysmal bone cyst. In 1999, Panoutsakopoulos et al. demonstrated chromosomal