Weigert-Meyer Rule of Duplicated Moiety
The Weigert-Meyer rule states that in duplicated collecting systems, the upper pole ureter inserts ectopically and inferomedially into the bladder (or below it), while the lower pole ureter inserts normally and superolaterally, with the upper pole moiety typically associated with obstruction and the lower pole with vesicoureteral reflux 1.
Anatomic Relationship in Duplicated Systems
The rule describes a predictable embryological pattern:
- Upper pole moiety: The ureter drains inferomedially and ectopically, most commonly inserting into the bladder trigone below the normal position or even into the urethra, vagina, or other pelvic structures 1
- Lower pole moiety: The ureter drains superolaterally and inserts at the normal anatomic position in the bladder trigone 1
- This crossing pattern occurs because during embryonic development, the ureteric buds that form later (upper pole) are carried more caudally as the urogenital sinus develops 1
Clinical Implications
The anatomic positioning directly predicts the pathology encountered:
- Upper pole obstruction: The ectopic insertion of the upper pole ureter frequently results in ureterocele formation or obstruction, leading to hydronephrosis of the upper pole moiety 1
- Lower pole reflux: The lateral and superior insertion of the lower pole ureter creates an inadequate intramural tunnel length, predisposing to vesicoureteral reflux 1
Important Caveats
Exceptions to the Weigert-Meyer rule exist but are extremely rare 1. One documented case reported a lower pole ectopic ureter with massive dilation and an involuted lower pole renal moiety, violating the traditional rule 1. When encountering anatomic findings that don't follow the expected pattern, consider:
- Complete imaging with ultrasound and voiding cystourethrogram to map the actual drainage pattern 1
- Nuclear medicine studies (MAG3 or DMSA scan) to assess differential function of each moiety 1
- Cystoscopy to directly visualize ureteral orifice positions when imaging is inconclusive 1
This rule applies specifically to renal duplications, not gastrointestinal duplications, which follow entirely different embryological principles related to notochord development and gut anlage endoderm herniation 2, 3.