Duplex kidneys are categorized under congenital abnormalities of the kidney and the urinary tract (CAKUT). They are the developmental malformations that happen during embryogenesis as a result of mutations in the developmental genes. The blood supply is shared by the bifurcation of the artery and vein coming from the heart. They can be unilateral (in only one kidney) or bilateral (occurring in both kidneys). They usually remain asymptomatic in the absence of associated complications. Complications mainly occur as a result of urinary obstruction.
What Are Duplex Kidneys?
Duplex kidneys are also known as multiplex kidneys, duplicated ureters, or duplicated urinary systems. It is a congenital anomaly formed due to the incomplete fusion of the upper and lower poles of the kidney, thereby creating two separate ureters in the kidney. These formed ureters can drain separately into the bladder, or they unite together and drain as one into the bladder.
How Are Duplex Kidneys Formed?
The development of ureters begins in the fourth week of intrauterine life. The mesonephric duct gives rise to the ureteral bud. Usually, the ureteric bud, after forming the ureters, will be absorbed by the bladder trigone. In the case of duplex kidneys, two ureteric buds arise from the mesonephric duct. The caudal ureter and the cephalic ureter. The cephalic ureter drains the upper pole of the kidney, with the caudal ureter draining the lower pole of the kidney. Both the ureters can open up separately into the bladder, or they unite along their path and drain into the bladder.
What Is the Etiology of Duplex Kidneys?
As it is a developmental abnormality, the etiology is reported to be due to the aberrant gene expression of the genes involved in the embryonic development of the urinary system. The genes involved in the pathogenesis of duplex kidneys include,
ROBO2 Gene - Roundabout guidance receptor 2.
Slit2 - Slit guidance ligand 2.
FOXC1- Forkhead box C1.
SOX11 - SRY-Box transcription factor 11. etc.
How Are Duplex Kidneys Classified?
Duplex kidneys are classified into five types, it includes:
Incomplete Duplication - It is characterized by the duplicated ureters from the poles of the kidney sharing the same ureteral orifice of the bladder.
Inverted Y-Shaped Duplication - This is a condition in which the normal kidney is drained by two ureteral orifices. It is reported to be the rarest form of duplex kidneys.
H-Shaped Ureter - It is characterized by the duplicated ureters from the kidney sharing the two separate ureteral orifices of the bladder.
Blind Ending Ureters - This is a condition in which the duplicated ureter fails to connect to the bladder or the kidney.
V-Shaped Ureters - This is a condition in which the duplicated ureters from the kidney join the bladder wall giving a V-shape.
What Is the Epidemiology of Duplex Kidneys?
It is one of the common developmental malformations of the urinary system, with an overall incidence of 0.8 %. In 20 % of cases, it is seen affecting both the kidneys. It is more commonly reported in females than males.
What Are the Symptoms of Duplex Kidneys?
Duplex kidneys are usually asymptomatic, but in some cases, they produce symptoms because of their structural complexity. Symptoms include,
Flank Pain - It may be caused as a result of cysts formed in the non-functional ureters producing pressure in the adjacent structures, thereby causing pain.
Recurrent Urinary Tract Infections - It may occur as a result of urine stasis in the urinary tract.
Urine Incontinence - This is the loss of bladder control, so the urine is passed without control.
Urine Obstruction - Any obstruction along the path of drainage of the urine.
Hematuria - Blood in the urine.
What Are the Complications of Duplex Kidneys?
The complications include:
It is a condition that occurs when the ends of the ureters that are draining into the bladder do not develop properly. These ends may swell like a balloon, thereby preventing the flow of urine from the ureter to the bladder. So the urine gets stagnant within the ureteral tube and the kidneys. Due to the presence of duplex kidneys, ureteroceles can develop.
2) Vesicoureteral Reflux:
It is characterized by the backward flow of urine from the bladder to the ureter or even up to the kidneys. It may occur as a result of the improper connection between the ureter and the urinary bladder in duplex kidneys.
It is a condition in which there is swelling of one or both kidneys that occurs due to the improper drainage of urine. It may happen as a result of blockage or obstruction in the urinary tract. In duplex kidneys, due to improper connection between the bladder and the ureters, hydronephrosis occurs.
4) Ectopic Ureter:
It is a condition in which the ureters do not connect to the bladder or connect in the wrong place. Leading to blockage or leakage of the urine into other parts of the body. This, in turn, results in further complications.
How Are Duplex Kidneys Diagnosed?
1) Antenatal Diagnosis: The antenatal diagnosis is quite difficult, but with careful observation in the ultrasound examination, the duplex kidneys can be identified with the findings such as hydronephrosis, larger kidneys than usual, and the presence of two collecting systems. All these findings will give a clue to the existence of duplex kidneys.
2) Postnatal Diagnosis: As it is asymptomatic in most cases, it is an accidental finding when doing routine scans or scans for other causes. The methods in diagnosis include,
All these imaging modalities would help to visualize the presence of duplex kidneys and the complications associated with it, such as hydronephrosis, ureterocele, ectopic ureter, etc.
How Are Duplex Kidneys Managed?
Duplex kidneys that are asymptomatic do not need any treatment. In symptomatic cases, the problem has to be addressed with any one of the following treatment measures.
In this procedure, part of the affected kidney, along with the duplicated ureter, is removed to relieve the symptoms.
This procedure is done in cases where one side of the kidney is functioning properly. The affected side is causing continuous problems such as repeated urinary tract infections and deteriorating kidney function. In such a case, the affected side is removed entirely to prevent the risk of developing further complications.
3. Ureteral Reimplantation:
In this procedure, the duplicated ureter, which is not draining properly into the bladder, is surgically corrected by cutting and rejoining it in the proper place to facilitate urine drainage into the bladder.
It is done to correct the ectopic ureter, where it is surgically linked to the normal ureters to allow proper drainage of urine from the kidneys to the bladder.
5. Treating the Complications:
The complications associated with the condition should be managed, such as treating urinary tract infections with prompt antibiotics. Other conditions probably resolve on their own once the primary problem is addressed.
Duplex kidneys are a common congenital anomaly of the kidney. The aberrant expression of the genes involved in the embryogenesis of the urinary system is the etiology of duplex kidneys. Most of the time, it remains asymptomatic; when it causes symptoms, it should be treated to prevent further complications.