Case report: inverted contrast medium--urine level in the bladder on computed tomography.

Fluid-fluid levels within structures are caused by differences between the specific gravity of the fluids. This results in a characteristic appearance on computed tomography (CT), with urine which contains contrast medium and has a high specific gravity layering posteriorly in the dependent portion of the bladder, while lower specific gravity, non-opacified urine is found uppermost. We report a patient in whom the contrast medium-urine level was inverted because of sediment in the dependent part of the bladder.