Pseudoectopic ureter on prone urogram.

An appearance simulating an ectopic insertion of the ureter has often been seen on prone urograms. This is primarily due to the fact that in the prone position contrast medium in the bladder gravitates cephalad into the dependent anterior dome and leaves the trigone area filled with nonopacified urine. The distal ureters appear to extend below the assumed bladder. Jet phenomenon and geometric factors also accentuate the appearance.