Transverse folds in the proximal ureter: a normal variant in infants.

Infants frequently have a "corkscrew" appearance of the upper segment of the ureter at excretory urography. In most instances, this tortuous appearance is due to thin transverse folds. These folds are full-thickness inward projections of the ureteral wall. They are believed to represent a persistence of normal fetal tortuosities of the ureter.