Suppose one day you have an ultrasound and the doctor tells you that your left kidney is duplicated. What does that mean? It means that you have two kidneys and two ureters on your left side. Would you be happy? If the duplicated kidney is not fluid-free and the duplicated ureter is fine, you can be happy.
Why? Because duplicate kidneys are not simply multiple kidneys!
Above: The left kidney is a duplicate kidney duplicate ureteral malformation. As you can see, the left duplicate kidney, just the left kidney is slightly larger than the normal kidney, not the left side has two separate kidneys! It just has two collecting systems that collect the urine produced by the upper and lower part of the kidney respectively. So I would say that the expression duplicated kidney is inaccurate, and a more accurate expression would be duplicated collecting system. But the duplicated kidney has become a generic term, so I will continue to use the terms “duplicated kidney”, “upper kidney” (referring to the upper part of the duplicated kidney) and “lower kidney” (referring to the lower part of the duplicated kidney). (the upper part of the duplicated kidney) and “lower kidney” (the lower part of the duplicated kidney), just so you understand.
How is the duplicated kidney formed?
Let’s go back to the embryonic period and look at the normal development process.
Above: In the fifth week of embryonic life, the ureteral bud from the middle renal duct grows into the primordium of the posterior kidney
Above: Kidney development during embryonic period. The ureteral bud enters the posterior renal primordium and gradually forms the collecting system
Above is the normal ureteral development and below is how the duplicated collecting system is formed.
Above: If a ureteral bud originates from the mesonephric duct, but this ureteral bud bifurcates before reaching the posterior renal primordium and then enters the posterior renal primordium separately, a double collecting system is formed in which two ureters merge into one and enter the bladder. This is called incomplete ureteral duplication.
There is another situation, see above: two ureteral buds arise from the middle renal duct and each grows into the posterior renal primordium. Two ureters and two collecting systems are formed on one side. This forms a duplicated kidney and a duplicated ureter. This is called complete ureteral duplication. Looking at the diagram above, from A to B to C, we note a detail that after a series of changes, eventually the lowermost opening of the upper ureter tends to be lower and more medial than the lowermost opening of the lower ureter. This is the Weigert-Meyer law. This dictates that it is always the ureter of the upper kidney that has an ectopic opening, not the lower ureter.
Well, now you can easily understand that duplicated kidney malformations can take the following forms (see the figure below).
Above: In addition to the difference between duplicated kidney, complete or incomplete ureteral duplication, you should also pay attention to the difference in ureteral openings, especially the presence of ureteral cysts and ectopic ureteral openings. As we can see from the picture above, the manifestations of duplicated kidney duplicated ureteral malformation are still very diverse.
Some will never have symptoms for the rest of their lives, such as those in which both ureters enter the bladder, or those in which both duplicated ureters enter the bladder as one, and will only be detected by chance during an examination. Others are less fortunate and may have ectopic openings in the ureter (see ectopic openings in the previous issue) or cysts at the end of the ureter that protrude into the bladder or even into the urethra, and will likely have symptoms. Other problems such as obstruction at the pelvic ureteral junction, vesicoureteral reflux, obstruction at the ureteral bladder junction, and urinary tract infections can likewise occur in duplicated kidneys and duplicated ureters, ultimately adding to the diversity of clinical presentations. Two more points should be added here: duplicated kidneys and duplicated ureters can occur on both sides at the same time, and the type of presentation can be the same or completely different on both sides. If three ureteral buds grow on the middle nephron during embryonic period or if the ureteral buds develop an extra fork, there can even be triple kidneys and ureters.
Above: IVP of several duplicated kidneys with duplicated ureters, you can visualize the diverse manifestations
I would love to make the problem simpler, but I don’t dare to leave it out, but what doctors are dealing with is actually so complicated. Thankfully, advances in medical imaging have facilitated further clarification of its manifestations. Ultrasound, IVP, CT, MRI, ECT (nuclear scan), cystography, vaginography, and cystoscopy, to name a few, all have some diagnostic value. How to choose?
For incidental findings on ultrasound, no further testing is needed if there are no complications. Ultrasound is the first choice for prenatal examination and follow-up. IVP is inexpensive and can show images of the functional part and has some value. CT has the advantage of showing both function and morphology and is more accurate and can be used as a second choice. MRI has the advantage over CT for showing the non-functional and fluid-filled part. The biggest advantage is that it is not radioactive and can be used for prenatal examination. A nuclear scan can show renal function more accurately. Cystography can show reflux. Vaginography is indicated for girls who wet their pants. Cystoscopy visualizes the ureteral opening in the bladder and intubation angiography can show ureteral travel if necessary.
The examination must answer four questions
1. Is there a duplicated malformation?
2. What is the path and opening of the duplicated ureter?
3. the function of the contralateral kidney and the upper and lower kidney on the affected side?
4. other conditions, including: is there a ureteral cyst? Is there any reflux of the vesicoureter? Therefore, the examination of each person should be selected individually according to the need, and it is not necessary to examine all of them.
The specific form of presentation varies and so does the treatment. The variety of forms also determines the variety of treatment. Those with no symptoms or complications do not need treatment, and those with symptoms or complications only need surgery. The surgical modalities are so diverse that I didn’t want to talk about them because they will vary from case to case. But as an in-depth science, it is better to talk about it, as different methods respond to different situations.
Above: Repeat ureteral cyst with cystoscopic window, most of them will be decompressed very effectively, but some of them may have vesicoureteral reflux and eventually require ureteral reimplantation
Above: Upper kidney and its ureter resection for hydronephrosis or ectopic opening of the upper kidney and its ureter
Above: Pyelopelvic anastomosis, for upper kidney worth preserving
Upper picture: uretero-ureteric anastomosis for upper kidney and ureter worth preserving
Upper two pictures: Repeat ureteral reimplantation for those with vesicoureteral reflux
Upper picture: lower kidney and ureter resection for hydronephrosis and poor function of the lower kidney
Upper picture: repeated ureter combined with ureteral cyst (the cyst can be inside or outside the bladder), which is a more complicated situation and relatively troublesome to deal with, likely requiring cystectomy and repeated ureteral reimplantation.
The fact that there are many methods only shows that the problem is complex or that each method has limitations. Trust your doctor to choose an appropriate option. When I see some patients who have consulted seven or eight doctors on the Internet for the same problem and still haven’t figured it out, I always want to ask, “You don’t want to learn and then operate the surgery yourself,” and I always want to advise, “You have to trust a doctor.