Inverted contrast medium-urine layering in the canine urinary bladder on computed tomography.

Contrast medium-urine layering is routinely identified on transverse computed tomography (CT) images in the urinary bladder following intravesicular or intravenous administration of iodinated contrast medium. The contrast opacified urine typically occupies the dependent portion of the urinary bladder whereas the nonopacified urine layers above it. In this retrospective study, three patients with inverted contrast medium layering following intravenous contrast medium administration are described. A review of this phenomenon in humans is presented and an explanation for similar imaging findings in the dog proposed.