[Echography for the diagnosis of aneurysmal bone cysts].

Aneurysmal bone cysts are benign tumors which are likely to recur. While growing, they cause severe osteolysis, able to balloon the bone and to thin the cortex. The latter is reduced to a thin bone shell, and sometimes completely interrupted. Tumor mass can spread into the surrounding soft tissues as in other bone tumors, especially malignant ones, which are often misdiagnosed. Whether the cortex is interrupted or only thinned, an acoustic window is obtained which allows an easy study of tumor mass with US. Seven patients were examined, who presented lytic lesions of different bones, produced by aneurysmal cysts. US allowed the expansile lesion to be detected, and its size to be estimated. Moreover, US pattern of the lesion could be determined, which appeared both solid and liquid. A few minutes after beginning the examination, fluid levels could be observed to appear, which are typical of this condition, as both CT and MR imaging demonstrate both in vivo and in vitro. Thus US, thanks to its short execution time, low cost and non-invasiveness, can be considered as the second-step exam, after plain film, in the diagnosis of aneurysmal bone cyst.