History: 1 month old female with in utero hydro and cystic mass on US.
Solution: This patient has complete duplication of the ureter on the right, which is associated with upper pole hydronephrosis from the ectopic ureteral insertion. The lower pole moiety does not show evidence of hydronephrosis and no reflux is seen on the VCUG. However, the VCUG does show what is likely to be an everted ureterocele during voiding. The left side does show hydronephrosis as well, but the underlying etiology is unclear and this resolved over time without intervention. We are all familiar with the Weigert-Meyer rule that says that the upper pole obstructs and the lower pole refluxes, but only one of the two is true in this case. It is a complex decision whether or not to perform surgery on these patients and they often do quite well without surgical intervention. They do often need antibiotic prophylaxis.