Bilateral duplex collecting systems

Case contributed by Dr Derek Smith


Investigation for right iliac fossa pain. No relevant previous imaging studies. Normal renal function.

Patient Data

Age: 65 years
Gender: Male

Incidental bilateral duplex collecting systems.

The left lower pole renal pelvis is mildly dilated (unchanged from prior studies). The left sided pelvises fuse to form a single ureter at the PUJ.

The right sided abnormality is more subtle (and missed on initial reading). The lower pole pelvis does not fuse with the upper pole, with a thin tube coming close to the main ureter at the level of the aortic bifurcation. The ureters run adjacent to each other, but are still discrete, into the bladder. No ureterocele, single ureteric orifice suspected but no delayed/urographic phase.

Remaining structures unremarkable; sigmoid diverticulosis.

Annotated image

Axial and coronal planes showing the fusion of the left renal pelvises into a single ureter (red arrows) and separate right sided upper (yellow arrows) and lower (blue arrows) moiety ureters.

Case Discussion

Duplex renal collecting systems are a common normal variant (approximately 1% of normal population), but is increased in patients investigated for urinary tract issues. There is a variety of degrees of abnormalities - see main article.

In some circumstances (but not this patient) the Weigert-Meyer rule can be followed with:

  • upper pole hydronephrosis and ectopic insertion into the bladder with ureterocele
  • anatomically normal lower pole ureter but predisposed to reflux

Bilateral duplex systems (disappointingly not referred to as "duplex duplex"!) are not uncommon, but are usually associated with other renal tract abnormalities. If you see an abnormality on one side, don't forget to examine the other.

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Case information

rID: 60831
Published: 4th Jun 2018
Last edited: 14th Aug 2019
System: Urogenital
Inclusion in quiz mode: Included