Congenital anomalies of the urinary tract
Males and females share almost the same urinary organs but differ in the genital
organs, so we have the same kidneys, same ureters and same bladders.
The upper urinary tract is the kidneys and ureters, the lower urinary tract is the
bladder and urethra.
The kidneys produce urine, and this is taken to the bladder through 3 mechanisms:
1) Peristalsis in the ureters: the most important.
2) Pressure difference: the pressure in the kidneys and ureters is higher than the
bladder.
3) Gravity: the least important.
Then urine is stored in the bladder until you want to urinate, so there will be (1)
bladder contraction and (2) outflow relaxation of the sphincter in the urethra, and
urine goes though the urethra outside the body.
Embryology of the urinary tract
In the following box you will find what the doctor said regarding embryology. If you
are ok with it then skip page 2, but if you want more accurate information, skip the
box and go to page 2 !
The cloaca will divide in to anterior and posterior divisions.
The anterior division forms the genitourinary tract, while the posterior forms
the gastrointestinal tract.
The anterior division is divided into ureteric bud and vesical bud
The ureteric bud will go into the urogenital sinus. It will form the ureter and
base of the bladder. It will meet with the kidney which develops from the
metanephros.
So the embryonic origin of the kidney is different from the origin of the ureter,
so the pathologies that affect the kidney differ from those affecting the ureter.
Some pathologies affect both of them where they meet.
- Now the kidneys develop from the pronephros, the mesonephros and lastly
the metanephros. They develop in the retroperitoneum at the pelvic girdle and
then ascend and rotate so that the hilum faces medially.
Of course while they ascend they pull the ureters with them.
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The following is mainly from Before We Are Born, 7th
Edition, I will try to be as simple and concise as
possible:
Three kidneys develop during intrauterine life,
cranially to caudally:
1) Pronephros: completely degenerate.
2) Mesonephros: what remains from this one is
the mesonephric tubules and mesonephric
ducts which give other structures later on.
3) Metanephros: they will develop into the
permanent kidneys from two parts
a. Ureteric bud : a budding from the
mesonephric duct. It’s the primordium
of the ureter, renal pelvis, major and
minor calyces, and collecting tubules.
b. Blastema: the primordium of nephrons.
The kidneys ascend from their pelvic origin to the
abdominal retroperitoneum and reach their
permanent normal position by the 9th week. As they
ascend they rotate so that the hilum faces
anteromedially.
The urogenital sinus is the ventral part of the
cloaca. It has three parts: cranial (vesical),
middle and phallic.
The whole bladder develops from the cranial
EXCEPT the trigone, which develops from the
mesonephric ducts.
(So the mesonephric ducts give rise to two
things, ureteric bud and trigone of bladder).
The urethra is derived from the middle and
phallic parts of the urogenital sinus (many
details in this regard, look for them if
interested!)
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Now back to the original lecture!
Congenital anomalies of the kidneys
1) Agenesis
Which means that one or two kidneys may not develop.
Bilateral agenesis is inconsistent with life. Why?
Because in the fetal life we need our kidneys to produce urine, then we swallow our
urine for normal lung development. The surfactant, which is very important to lung
development and function, contains some proteins that are found in urine. So the
baby dies of respiratory, not renal, failure.
Unilateral agenesis
-Incidence: 1 in 1500
- Males are more affected
- In half of patients, the ureter is also affected. It can be absent or atretic (from
atresia)
- The suprarenal gland won’t be affected, it has a different origin.
“When planning a nephrectomy the surgeon should consider the possibility that the
other kidney is congenitally absent” – Bailey and Love’s
2) Supernumery kidney
It means having 3rd or 4th kidney!
Very rare, 1 in a million.
3) Anomalies of ascent
What’s the normal position of the kidney?
At the level of T12-L3 for the left one, and
slightly lower in the right side.
So the kidneys may stop at a level lower than
the normal level (pelvic kidney) or may go higher
up than the normal level.
Right: CT scan showing right ectopic thoracic
kidney.
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Incidence: 1 in 1100
Males are more affected
Whenever we see a case like this, we should inform the parents that this patient will
be more prone for urine stasis, either due to pelviureteric junction obstruction
(stenosis) or vesicoureteric reflux, so the patient will be more prone to infections and
stones.
Remember that we have 3 normal anatomical constrictions in the ureter:
1) The pelviureteric junction (PUJ).
2) Where the ureters cross the common iliac bifurcation
3) The vesicoureteric junction (VUJ - the narrowest)
4) Anomalies of fusion
Normally, kidneys are separated at either side of the body. Sometimes, we have both
kidneys fused at one side. The fusion occurs either from the upper poles, lower poles
or side by side.
The most common is the horseshoe kidney; the
kidneys are united at the bottom.
It’s very common in males, 1 in 400.
More incidence of stones and infections.
Some people claim that they have increased risk
of renal tumors. The most common cancer of the
kidney is adenocarcinoma (renal cell carcinoma RCC)
What to do? Nothing !
5) Cystic degeneration
Instead of having paranchyma, some of the nephrons produce urine that accumulates
and forms cysts. It can be congenital or acquired.
*The congenital is two types:
1) Autosomal recessive polycystic kidney disease (infantile):
This one has very early presentation.
Usually they have diffuse hepatic fibrosis
90% die in utero, rarely they survive the 1st year of age.
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2) Autosomal dominant polycystic kidney disease (adult)
Later presentation (during adult life)
Main symptoms: loin pain and hematuria
Associated with other anomalies: hepatic and pancreatic cysts, berry
aneurysms, colonic diverticula, RCC
* The acquired can be single or multiple:
1) Multiple cysts: the whole kidney is transformed into many cysts (multicystic
dysplastic kidney). The kidney is non-functional. To remove the kidney or not is
a controversy. The doctor personally leaves it in the body because it won’t
cause any problem and with time it will “autonephrectomize” itself.
If it causes problems like pain or hypertension you have to take it out.
2) Simple cyst (can also be multiple simple cysts!): very common, in about 50% of
the general population.
6) Antenatal hydronephrosis (ANH)
It is the most common anomaly of the urinary tract that we see and diagnose.
Hydronephrosis : accumulation of fluid in the pelvicalyceal system.
The kidney is composed of 2 parts: cortex and
medulla. Normally the medulla is empty, but if
urine accumulates there we can see it as a dilated
black structure on ultrasound.
Mostly we diagnose it antenatally.
What’s the most common cause of accumulation of urine in the kidney antenatally or
in the newborn?
Answer: Physiological or transient hydronephrosis, which means that there’s no good
peristalsis to push urine down to the bladder. It may improve after 6 weeks, 2 months
or 6 months.
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Now when it comes to pathology, it can be anywhere along the urinary tract.
Causes of AHN:
1) Obstruction of the PUJ or VUJ.
2) Vesicoureteric reflux due to a wide VUJ.
3) Posterior urethral valve
**The most common of these pathologies is the PUJ obstruction.**
PUJ obstruction occurs more in males, and more on the left side
20% can be bilateral
Presentation can be at any time.
Pathophysiology: aperistaltic segment > collapse > overcome by overperistalsis and
pain or hydronephrosis [this is what the doctor said!]
Diagnosis mainly depends on ultrasound. We will see the medulla enlarged with fluid
and compressing the cortex.
To see the site of obstruction we can give contrast and do IVP (intravenous
pyelography). Usually we don’t do it in patients below 2 years of age because the
kidney may be not there (agenesis) so we get the false impression that we have
obstruction.
The best method is nuclear scan (DMSA –dimermercaptosuccinic acid). Normally both
kidneys should take the contrast equally and excrete it to the bladder. When a kidney
is obstructed, it won’t drain into the bladder.
We usually give the patient a diuretic (Lasix) to force diuresis, so if the scan still shows
impaired drainage then there’s obstruction but if there’s some duresis it means it
may improve in the future.
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<<in nuclear scan, what’s right is right and what’s left is left, unlike other radiological
images>>
Treatment:
Mild obstruction: conservative, we just wait and see.
Severe obstruction: We have to cut the narrow area and re-anastomose in a wide
area that is dependent, no need to know more than this.
**Vesicouretric reflux**
Same incidence in boys and girls but more presentations in girls because they have
more incidence of infection.
When a boy is affected, he has a worse grade.
Pathology of reflux:
The ureter comes from behind the bladder and enters the muscular wall of the
bladder (VUJ) and this intramural segment should have a certain length. If it’s short it
will become a valve, so the closure pressure is less than usual and the fluid will reflux
to the kidneys.
Grading of reflux
Grade I : lower ureter.
Grades II and III: almost equivalent with some dilation and tortiousity.
Grades IV and V: the whole tract is like a bag of urine
Secondary reflux:
The VUJ is normal but there’s increased volume or pressure inside the bladder. The
bladder is not like a balloon, it won’t rupture. So the contents have to find a way out:
either through the urethra (urge incontinence) or through the ureter (secondary
reflux).
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Presentation:
Patients with reflux can present at anytime but the most common presentations are
ANH, failure to thrive, or UTI, and rarely renal failure if the problem is bilateral (or a
unilateral problem if the patient also has a single kidney!)
The main diagnostic tool for patients with reflux is Voiding
Cystouretherogram (VCUG). We put a catheter inside the
bladder, give contrast and see where does it go. If it goes to
the ureter this is reflux and we can grade it, if it goes to the
urethra this is normal.
Now we have new modalities like using the ultrasound
renogram.
The worst thing that could happen is intrarenal reflux. Instead of fluid going from
proximal tubule> Henle’s loop> distal tubule> etc..it will go the other way round, so
there’s abnormal kidney function and the patient proceeds into renal failure.
Kidney scars can be either a result of inflammatory process or an injury healing
fibrosis inside the kidney. The best diagnostic test to see it is the DMSA. (I think the
doctor talked about scarring here because reflux can cause scarring)
How to treat reflux?
Either I make the intramural segment longer (re-implantation), or make the orifice
narrower (bulking agent for the ureter).
**Posterior urethral valve (PUV)**
The rarest but most serious pathology. This is a male disease, and it’s equivalent of a
female hymen.
The urethra is normally divided into anterior (distal) and posterior (proximal) parts by
the external urethral sphincter. If we have a valve in this area, it will lead to
incomplete bladder emptying, retention and poor stream. With time, more urine is
formed so it will backflow to the kidneys (reflux) or impede renal emptying because
there’s no more peristalsis and no more pressure difference.
The doctor talked about a baby born in Jordan weighing 4.5 Kgs and was big and
puffy, the doctors told the parents that he will lose the fluids in the coming weeks.
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After 26 days the baby presented with renal failure (creatinine level was 2000 μmol/L)
and the actual problem was posterior urethral valve.
Morale of the story: If you don’t know it, you won’t think of it.
So to diagnose posterior urethral valve we can also use VCUG and we will see a filling
defect and dilated posterior urethral valve with reflux.
Antenatal ultrasound can also suggest the diagnosis of PUV. If you see a
hydronephrosis with full bladder, then retake the picture after 20-30 minutes (to
allow the bladder to empty) and still there’s full bladder then it may be PUV.
Urethrocele:
instead of opening just with the bladder, the urethra also opens to a sac. It’s more
common in females. The treatment is to puncture this sac.
Hypospadias
The penis is composed of three “cylinders”, 2
corpora cavernosa and 1 corpus spongiosum.
The cavernosa are responsible for erection while
the spongiosum has the penile urethra.
If the urethra is short, the opening won’t be on
the tip of the glans, it can be anywhere on the
ventral aspect of penis. At the same time there
will be a hooded foreskin, so the foreskin is only
covering the dorsal aspect of the penis (normally
it should cover all the way around).
Hypospadias are associated with penile chordae,
which is a downward curvature of the penis on
erection.
In the case of hypospadias, it’s better not to circumcise the baby because when you
want to repair it, you can use part of the foreskin as a flap.
Difference between flap and graft:
Flap = skin with its blood supply
Graft = skin only
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Ambiguous genitalia
If you are not sure about the sex of the baby, don’t tell the parents that it’s a boy or a
girl!
Remember: don’t circumcise and always rule out congenital adrenal hyperplasia
(CAH).
We have many types of CAH depending on the deficient enzyme.
The most common is 21-hydroxylase deficiency, we call them “Salt losers” (because
aldosterone won’t be formed). They usually die of hyperkalemia (cardiac arrest).
Epispadia is when the meatus is on the dorsal aspect of penis.
Bladder Exstrophy is when the bladder and urethra open into the anterior abdominal
wall.
Note: Exstrophy is usually associated with epispadias
The End
I know the lecture is deficient of pictures but I think it’s better to search for it yourself
to see things clearly, and after all, it’s just a lecture about congenital anomalies :P
Stay hungry. Stay foolish.
By: Khaled Shunnar
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