Renal duplication with ureterocele (Weigert-Meyer rule)
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The left kidney upper moiety shows moderate hydronephrosis and drains by moderately dilated tortuous ureter that ends in an ectopic location with a ureterocele.
The left kidney lower moiety shows mild hydronephrosis with a mildly dilated ureter draining orthotopically superior to ureter draining upper moiety (Weigert-Meyer rule).
There is a hyperdense calculus in lower moiety of left kidney.
Right kidney is normal. No hydronephrosis or hydroureter noted.
A duplicated collecting system is one of the most common congenital renal tract abnormalities.
Weigert-Meyer rule: With duplex kidney and complete ureteral duplication, upper and lower renal moieties have their own ureters, and each ureter has its own ureteral orifice into the bladder (or elsewhere).
The upper moiety ectopically inserts medial and inferior to the lower pole moiety and frequently ends in a ureterocele.
The lower pole moiety has an orthotopic insertion lateral and superior to the ureter draining upper pole. Classically, reflux occurs up this ureter.