Unexpected hydronephrosis following the Weigert-Meyer law

A 43-year-old female patient presented several times to the Emergency Department complaining of an increasing left-flank mass with associated pain. No significant alterations were found on the complete blood count.

A contrast-enhanced CT in portal phase was performed showing a duplicated collecting system in the left kidney (Fig. 1b) with an upper-pole grade IV hydronephrosis and megaureter (Fig. 1a). Note the ectopic inferomedially insertion of the megaureter ending up as an ureterocele (Fig. 2, arrow)

The lower pole of the kidney is relatively spared depicting only mild hydronephrosis (Fig. 1a) probably because of vesicoureteral reflux through a normally inserted ureter (Fig. 3b)

The diagnosis of duplicated renal collecting system in adulthood is rare, as most of these anomalies are detected in childhood [1]. When complete polar ureteral duplication occurs, both the upper and lower moiety ureters drain separately into the bladder, each one having its own orifice.

The Weigert-Meyer law [2] predicts the anatomy of the duplex collecting system as follows:

1. The upper moiety ureter presents an ectopic insertion (inferomedially) being prone to obstruction, often due to an ureterocele.

2. The lower moiety ureter presents an orthotopic insertion but is prone to vesicoureteral reflux.

In the case of our patient, all conditions were met, with CT showing an enlarged left kidney with a grade IV hydronephrosis of the upper pole secondary to the presence of an obstructing ureterocele. Meanwhile, the inferior collecting system is mildly dilated (grade II hydronephrosis) probably due to vesicoureteral reflux.

Althought uncommon, exceptions to this rule have been described in the literature. Stephen’s ectopic pathway [3] describes a superomedially ectopic insertion of the upper moiety ureter (instead of inferiomedially) breaking the Weigert-Meyer law.

Writen informed patient consent for publication has been obtained.