Fluid levels in aneurysmal bone cysts: a CT feature.

Review of 17 computed tomographic (CT) scans of aneurysmal bone cysts revealed fluid levels in six of the lesions; the fluid shifted after repositioning of two patients. Visibility of fluid levels did not correlate with the type of fluid found within the lesions. Detection of fluid levels depended partly on a period of immobilization before CT and on viewing the images with sufficiently narrow window settings.