Hi, and thanks for your question. As you state, this answer is now
substitute for formal medical advice. That in mind, I'll address each
point in turn. References can be found at the end.
1. What does it mean if someone's kidney is a "double collector"? (How
does this differ from a normal kidney?)
"Double collector" is a somewhat colloquial term, uncommonly used
term, referring to a condition where one has two ureters from one or
each kidney to the bladder. Other terms used include "duplicated
collection system," "duplicated ureter," "bifid ureter."
It's commonly associated with ureteroceles (a dilation of the ureter
closest to the bladder). The Explore Diseases website discusses this
A more in depth journal article published in the Brazil Journal of
Pediatrics discusses this disorder, as well as its surgical treatment.
de Jesus LE, Judice MM, Mello EG. J Pediatr (Rio J). 2003
Mar-Apr;79(2):173-80. [Ureteral duplications and ureteroceles -
surgical treatment] [Article in Portuguese]
While original article is in Portuguese, the full text English version
can be found here:
The PDF (English) version is here:
The following journal article contains an MRI image of a left-sided
duplicated ureter (see Figure 6 on Page 3):
2. What percent of the population is "double collector"?
The following reference answers this question:
Schlussel RN, Retik AB. Anomalies of the ureter. In: Walsh PC, Retik
AB, Vaughan ED, Wein AJ, eds. Campbell?s Urology, 7th ed.
Philadelphia: WB Saunders Company; 1998: 1814?1858.
This source is cited in the journal article below, giving
"Like ureteral injuries, ureteral duplication is uncommon, occurring
in 0.68% to 0.8% of the population."
Pearlstein DP. Brandt M. Introcaso JH. Shah M. Martin T. Sulkowski RJ.
Penetrating trauma causing partial disruption of a duplicated ureter:
case report. Journal of Trauma-Injury Infection & Critical Care.
50(4):755-8, 2001 Apr.
The above article also discusses how ureteral duplication occurs:
"Ureteral duplication is genetically determined and is most often
unilateral. Anatomically, this condition usually presents as double
ureters with their bladder orifices inverted in relation to the
collecting systems they drain. This phenomenon has been termed the
Weigert-Meyer law. It is manifested by the orifice of the lower pole
occupying the usual, lateral position, whereas the orifice of the
upper pole ureter can be found anywhere along an ectopic pathway
extending caudal and medial, all the way to the prostate."
3. What kinds of problems can having a "double collector" kidney cause?
The primary potential problems caused by duplicated ureters are
Intractable urinary infections. Another problem can be
vesico-ureteral reflux, where variable amounts of urine flow backwards
from the bladder back to the ureter. Partial ureteral duplication can
result in ureteroureteric reflux, where urine flows into the partially
duplicated ureter, but hits a blind end and must flow backwards
(retrograde), causing delayed urine drainage. Reference  below
discusses this condition:
"Partial ureteric duplication may cause delayed drainage of urine from
the upper tracts because of ureteroureteric "see-saw" reflux. This can
be eliminated by the procedure of ureteropyelostomy, in which the
partially duplicated ureter is converted into a bifid renal pelvis.
This operation leaves a short anastomotic suture line and has a low
complication rate. We report seven patients who have undergone
ureteropyelostomy for symptomatic ureteroureteric reflux. All remain
symptom-free after follow-up for a minimum of 1 year."
As mentioned, one of the duplicated ureters can be "blind," meaning it
doesn't travel all the way to the bladder. Rarely, stones can lodge
in this blind ureter. Reference  discusses such a case:
Another description of obstructed duplicated collecting systems can be
found here, from the Yonsei Medical Journal:
Ureteroceles (dilations of a ureter) have been associated with
duplicated ureters, which can result in urinary tract infections.
Reference  discusses the treatment of two girls who had this
combination of conditions. References [21,30] also discuss treatment
of this condition.
From Reference :
"Herein we report two cases of complete ureteric duplication
associated with ureterocele. A 4-month-old girl with non-visualizing
left kidney was hospitalized with complaints of cloudy urine and
fever. An antegrade left pyelogram revealed a completely duplicated
collecting system; a duplex tortuous ureter, and round radiolucent
filling defect in the bladder. Under the diagnosis of completely
duplicated ureter associated with the upper pole ureterocele,
ureterocystoneostomy was performed. A circumferential incision was
made around the base of the ureterocele and the Politano-Leadbetter
technique was employed. Her postoperative course was uneventful.
However, an excretory urogram showed a mild hydronephrotic upper pole.
A 1-year and 4-month-old girl with the history of repeated urinary
tract infections and fever attacks was admitted. The excretory urogram
showed a left hydronephrotic lower pole with a "drooping flower" and
no opacification of the upper pole. A radiolucent filling defect was
seen in the bladder. A left antegrade pyelogram demonstrated the
massively dilated upper pole with a hydroureter terminating in the
ureterocele. Left heminephrectomy with partial ureterectomy was
performed and left hydronephrosis and hydroureter with an atrophic
kidney were seen. The postoperative course was uneventful."
Cancer in the duplicated ureter is rare, but has been described.
References [13, 23, 25] discuss such cases.
The duplicated ureter can also insert in the wrong place. Such
ectopic ureters have been described inserting in to the vagina, the
vas deferens, See References [5, 27] for example.
4. Is there anything specific that someone with this condition can do
to minimize problems?
The primary problems that might be amenable to lifestyle-type changes
would be the formation of stones and urinary tract infections.
According to Reference , as cited in Reference , "[k]idney
stones affect up to 5% of the population, with a lifetime risk of
passing a kidney stone of about 8-10%."
Reference  goes on to say
" improved standards of living and is strongly associated with race or
ethnicity and region of residence. A seasonal variation is also seen,
with high urinary calcium oxalate saturation in men during summer and
in women during early winter. Stones form twice as often in men as
women. The peak age in men is 30 years; women have a bimodal age
distribution, with peaks at 35 and 55 years. Once a kidney stone
forms, the probability that a second stone will form within five to
seven years is approximately 50%Calcium oxalate (alone or in
combination) is the most common type of urinary stone Low urine volume
is the most common abnormality and the single most important factor to
correct so as to avoid recurrences Risk of a recurrent stone is about
From the Summary Points of Reference , to minimize the formation
of renal calcium oxalate stones, one should strive for a diet low in
salt (<50 mmol/day) and low in animal proteins (<52 grams/day). The
article also states that diets low in calcium are not encouraged,
since they can result in increased urinary oxalate excretion (making
stones worse) and a negative calcium balance (bad for the bones).
A family history of kidney stones increases one's risk by a factor of
3. Other risk factors include insulin resistant states (e.g. Type II
Diabetes), hypertension, primary hyperparathyroidism, gout, chronic
metabolic acidosis, and surgical menopause.
Reference  is, unfortunately, not available for free online, but
might be worth obtaining from your local library (or purchasing
online) if you are interested in a more in depth discussion of kidney
stones. The article includes multiple summary boxes that put together
the multiple risk factors for various types of stones. You might also
request a reprint from Dr. Parmar at this address:
In patients who are particularly symptomatic, surgery may be an option
to correct the anatomic duplication of the ureter.
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? ? ?
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I hope this information was helpful. Please feel free to request clarification.