Anomalies of the Fetal Genitourinary Tract - SD

Introduction

My name is Dr. Carol Benson.
I'm from Brigham and Women's Hospital
and Harvard Medical School in Boston, Massachusetts.
Today my lecture topic is entitled Fetal Anomalies
of the Genital Urinary Tract.

Assessment of the Kidneys

The kidneys should be assessed on every second
and third trimester ultrasound.
First they should be looked for to make sure
that they're present. In their absence there could be
renal agenesis.
Second, we wanna look at their location
to make sure they're in the appropriate location
to exclude ectopia or other forms of displaced kidneys.
We then look at the size and echogenicity of the kidneys
and that is to exclude dysplasia
or autosomal recessive polycystic kidney disease.
And then lastly, we look at the collecting system
of the kidneys to exclude hydronephrosis.

Normal Appearance of the Kidneys

The kidneys are located in the renal fossa on either
side of the spine.
Here you can see the spine on this transverse view of the
fetus and you can see a kidney on one side
of the spine in the renal fossa and the other kidney.
On the contralateral side,
the kidneys are typically hypoechoic compared
to the surrounding bowel in front of them
and they often have an echogenic capsule.
Sometimes the echoes in the middle
of the kidney are brighter than the rest of the kidney.
That's the renal sinus or a collecting system.
On longitudinal view, the kidney is reniform shape.
It has hypoechoic areas in the cortex
and more increased echogenicity
in the central part of the kidney.
The renal sinus echoes.
Here's a fetus who has a little bit
of fluid in the collecting system of each of the kidneys.
Again, this is a transverse view of the fetal abdomen.
You can see the spine posteriorly casting a shadow,
and on either side of the spine we can see a kidney.
And within each of these kidneys we
see a little bit of fluid.
This is fluid in the collecting system
and in this case this is the normal amount of fluid
that you might see in the renal collecting system.
We can also confirm presence of the kidney
by using color doppler and looking for the arteries
and veins that come from the kidney to the aorta
and the inferior vena cava.
Here you can see a view of the abdominal aorta
and you can see that one renal artery is leaving the aorta extending towards one kidney
and on the other side, just opposite
that artery is an artery to the contralateral kidney.
Likewise in this case up here you can see the vessels,
the aorta traveling through the abdomen
and you can see the renal arteries on either side.

Amniotic Fluid and Fetal Renal Function

Now, amniotic fluid volume is important
for the fetal development
and so it's important to assess the volume of amniotic fluid
around the fetus throughout gestation.
The volume depends on homeostasis between the renal function
of the fetus and the fetus's swallowing
and gastrointestinal resorption.
So here is just a couple slides showing a fetus
drinking the fluid in the amniotic fluid.
And here's a fetus replenishing the fluid
by urinating into the amniotic cavity
and that's the balance that allows for a normal amount
of amniotic fluid.
In the absence of renal function,
the fetus will not replenish the amniotic fluid
and prolonged severe oligohydramnios will develop.
Presence of prolonged oligohydramnios.
The fetus will not develop appropriately.
The fetus will develop pulmonary hypoplasia
because it will be compressed by the uterine muscle
because of the absence of the buffer of the amniotic fluid.
In addition, the face will be compressed
so the face will be abnormal
and you'll get limb positional anomalies from the
severe oligohydramnios.

Bilateral Renal Agenesis

Bilateral renal agenesis is a case
where there is no renal function.
Severe oligohydramnios develops and on ultrasound will look
and look and look and be unable to identify any kidneys
or a urinary bladder, and that's
because they're absent in these cases.
A clue to the absence of the kidneys is
that the adrenals are located in a longitudinal
orientation parallel to the spine.
And fortunately for fetuses
who do have bilateral renal agenesis,
this anomaly is incompatible with life.
Here is a fetus who developed without kidneys.
There's bilateral renal agenesis.
You can see immediately that there is no amniotic fluid
around this fetus on either of the views.
You can also see on the longitudinal view of the fetus
that when we look in the posterior aspect of the abdomen,
we see that the adrenal glands both are located parallel
to the spine and that there's absence of the kidneys
and no urinary bladder could be found in the pelvis.

Unilateral Renal Agenesis

Now unilateral renal agenesis is a much less severe anomaly.
This is completely compatible with a normal life.
While the fetus only develops one kidney,
that kidney does compensatory enlarge
and develops more tubules than a single kidney would have
and thus the renal function is normal.
On ultrasound, we'll have an empty renal fossa.
The adrenal gland on the side
of the absent kidney will be oriented in a longitudinal
direction parallel to the spine
and we can measure the contralateral kidney
and see that it is large for gestational age.
So here's a case of unilateral renal agenesis.
You can see on our transverse view of the back
of the fetus we have the spine and its posterior shadowing
and adjacent to that,
on the left side we see a normal kidney,
but in the right renal fossa we could not identify a kidney.
On the longitudinal view of the aorta,
we see only a single vessel coming from the aorta at the
level of the renal arteries
and no renal artery on the other side
because of agenesis of that kidney.
Looking carefully at the region of the absent kidney.
In another case we can see
that the left kidney was absent in this case
and we can see that the adrenal gland is located parallel
to the spine oriented in a longitudinal direction.
Likewise, on this fetus, when we interrogated the aorta,
we saw only a single renal artery that
feeds the right kidney
because again, in this case the left kidney was absent.

Renal Ectopia

Now the kidney can be located somewhere
besides in the renal fossa.
This is termed renal ectopia
and the most common location
for an ectopic kidney is in the pelvis.
So if you don't see a kidney up in the renal fossa, do look
around throughout the abdomen
to see if you can find the kidney somewhere else.
If the kidney is not in the pelvis it could be crossed
and fused to the other side.
That's called crossed fused ectopia
and sometimes the kidneys are fused across the midline in
the lower abdomen and form a horseshoe kidney.
So this fetus has a pelvic kidney.
You can see looking at the right renal fossa,
we have a normal kidney oriented in the proper location
located in the correct place.
But when we looked in the left renal fossa in the fetus,
we couldn't find it. When we looked more carefully down in
the lower abdomen, we found the left kidney located in the
left pelvis adjacent to the urinary bladder.
This is another fetus with a pelvic kidney.
You can see that we looked down in the pelvis
and next to the bladder we identified this kidney
and we also confirmed that this was a kidney
by looking at the descending aorta
and seeing an aberrant vessel feeding this
what we thought was a pelvic kidney
and proved to be a pelvic kidney,
this is the renal artery coming off the lower aorta
and feeding the pelvic kidney.
This fetus has a cross fused ectopic kidney.
I do have a clip to show you how it works,
but first I wanna get you oriented.
This is a transverse view of the fetal abdomen.
The spine is located here with shadowing
and you can see one kidney in the renal fossa.
There was no kidney in the other renal fossa,
but when we looked at the lower pole of the kidney
properly located, we saw more
renal tissue extending across the midline in front
of the aorta and the inferior vena cava.
So here you can see on the clip as we slide up
and down that there's two kidneys fused together,
one in the appropriate location
and then one crossing into the midline fused
with the lower pole of this kidney.
This fetus has a horseshoe kidney.
You can see when we scan the lower abdomen
of the fetus we're quite low as we're at the level
of the urinary bladder
and we saw reniform tissue in a U-shaped
crossing over in front of the aorta
and the inferior vena cava.
This kidney was completely fused located
in the lower abdomen.
You can see on the clip the reniform tissue
crossing in front of the aorta and the inferior vena cava.

Hydronephrosis

Now we often see fluid in the renal collecting system
and so it's important to evaluate this
to see if the fetus in fact has hydronephrosis.
We diagnose hydronephrosis when we see dilated calyces
as well as a dilated renal pelvis
or if the dilated renal pelvis measures seven millimeters
or more at 16 to 20 weeks or 10 millimeters or more
after 20 weeks.
Sometimes though we see fluid in the kidney that is not
as large as I listed up here.
And for those cases, rather than discount them
and call them normal, we call those possible hydronephrosis
and that's when the dilated renal pelvis measures four
to six millimeters from 16 to 20 weeks
or five to nine millimeters after 20 weeks.
It's important to identify these fetuses
because about 10% of them will have significant problems
after birth from mild either reflux or obstruction.
So here's a fetus at 18 weeks gestation.
You can see that there's fluid in both
of the renal pelvises in each
of the kidneys on either side of the spine.
And when we measure the anterior posterior dimension
of the renal pelvis, we see
that it's six millimeters on each side
so this would be classified as possible
hydronephrosis for this fetus.
This fetus is 32 weeks gestation.
You can see again that posterior view of the back
of the fetus with the spine here
and the shadowing behind it.
And we can see that one kidney has a dilated is dilated
to almost nine millimeters.
The other kidney is dilated to 10 millimeters.
So this is a case of hydronephrosis
that should be followed after birth.
The pediatrician should be alerted to this anomaly.
This fetus has fairly severe hydronephrosis.
You can see that they're markedly dilated
calyces throughout the kidney.
So this is marked ectasia
and the definitive diagnosis of hydronephrosis
typically should be followed at when it's
first diagnosed in utero
because during gestation it might resolve
but it also might progress to become more severe.
So we do tend to follow these
to see whether they do resolve,
stay the same or become worse.
It's important to follow these not necessarily
through gestation
but at least one time
to see whether there is any progression.
So here's a fetus
who demonstrated progressive hydronephrosis
at 18 weeks gestation.
Actually the kidneys were normal.
You can see a transverse view of the fetal abdomen.
In this case the spine is down on the image
and on either side the kidneys showed no dilated
pelvises on either side.
But here the fetus now is at 34 weeks gestation
and you can see that one kidney has a dilated renal pelvis
of nine millimeters.
The other kidney though has a markedly dilated renal pelvis
at 16 millimeters as well as ectasia.
So this had progressed from no hydronephrosis
to fairly severe hydronephrosis in the intervening 16 weeks.

Causes of Hydronephrosis

Now hydronephrosis can be caused from a number
of different reasons.
It can be result from obstruction at the ureteropelvic
junction and this is something
that's seen more commonly in males than female fetuses
with a ratio of about five to one.
You can also have obstruction at the level
of the distal ureter
and this is something we see with primary megaureter.
Vesicoureteral reflux causes dilated kidney and ureter
and so we get, we will diagnose that as hydronephrosis.
In addition, bladder outlet obstruction
with either posterior urethral valves
or prune belly syndrome causes hydronephrosis.
Notice that these syndromes
or problems related to drainage
of urine from the kidneys
to the bladder are all more common in males than in females.
And in particular the last two diagnoses,
posterior urethral valves
and prune belly syndrome are seen exclusively
in male fetuses.

Ureteropelvic Junction Obstruction

Ureteropelvic junction obstruction is the most common cause
of neonatal hydronephrosis.
It's a functional obstruction that is, there's not a web
or anything across the ureter, it's just more of a kink
that's partial and
therefore does allow some urine to pass through.
About 30% of fetuses have this in both kidneys
and fortunately because the obstruction is functional,
it rarely develops into a dysplastic kidney.
So here's a fetus with bilateral ureteropelvic
junction obstruction.
You can see on a transverse view
of the fetal abdomen there's fluid in both renal pelvises.
It measures 10 millimeters on one side
and nine millimeters on the other.
And a longitudinal view of the kidney shows
that we have dilated calyces as well.
This fetus has fairly severe bilateral ureteropelvic
junction obstruction.
You can see that there's a marked amount of fluid in each
of the renal pelvises
and the measurements as listed here show
that the right renal pelvis measured 16 millimeters
and the left 23 millimeters.
But you'll also notice that the amniotic fluid
around this fetus is normal and that's
because the renal function is normal
and the fetus is able to make urine
and the bladder is able to empty it
and replenish the amniotic fluid.

Vesicoureteral Reflux and Primary Megaureter

Now vesicoureteral reflux occurs when there's abnormal
insertion of the ureter into the urinary bladder.
The reflux allows urine
to climb back up from the bladder into the ureter
and even into the kidney.
And so an ultrasound we'll see hydronephrosis
and hydroureter.
The differential diagnosis of the findings of hydronephrosis
and hydroureter includes primary megaureter.
What's the difference? Well,
there is no difference in ultrasound findings
with primary megaureter when compared
to vesicoureteral reflux, but,
the pathology is very different
with primary megaureter you have an aperistaltic segment
of the distal ureter that does not allow the urine
to drain properly from the kidney into the bladder.
So here's a fetus who has hydronephrosis and hydroureter.
On one side you can see on a view of the kidneys
with on either side of the spine
that there's mild pelvic dilatation on one side
and greater dilatation on the other
where the renal pelvis measures 12.5 millimeters.
On the side of the larger dilatation we were able
to identify a dilated tortuous ureter extending from the
dilated kidney which is here to the bladder.
And so this was hydronephrosis and hydroureter
and there's no way in utero to know whether this is reflux
or primary megaureter.

Renal Duplication

Renal duplication is when the kidney develops
with two regions of the collecting system
and two ureters that travel down to the bladder.
This is more common in females than it is in males.
While this can be a normal finding
and renal function can be normal,
it also can cause problems.
Sometimes the upper pole ureter will become obstructed
and it's not uncommon
to have reflux into the lower pole ureter.
So we identify this in utero,
particularly when there's hydronephrosis in
the affected kidney.
On ultrasound, a duplicated kidney will have an elongated kidney
that measures longer than it should for gestational age
and we may see fluid in the collecting system
that is not the same throughout the kidney.
We'll have differential hydronephrosis
with more fluid in the upper pole than the lower pole.
We also may be able
to identify an ectopic ureter in the bladder if the upper
pole ureter inserts abnormally.
So here is a diagram of
what renal duplication looks like in the fetus
when there is no obstruction you can see
that the duplicated kidney is longer than the contralateral
kidney and that there are two ureters
and typically the upper pole ureter will travel lower into
the bladder and insert than the lower pole ureter.
Now if both insertions work properly,
you'll have no obstruction and no reflux
and here is a fetus where there's renal duplication.
That was not a problem for the fetus.
You can see that the normal left kidney is much smaller than
the enlarged right kidney which had two small areas
of fluid, normal amount of fluid in the region of both parts
of the collecting system.
When the upper pole ureter is obstructed,
you'll get dilated ureter
and dilated kidney in the upper pole of it.
This is another diagram showing this in a fetus.
You can see that the lower pole ureter is normal
and inserts appropriately,
but the upper pole ureter inserts in an aberrant location such
that it doesn't drain into the bladder properly.
And so you have dilatation of that ureter as well
as dilatation inside the kidney.
And here is a fetus with a renal duplication
and asymmetric dilatation of the collecting system.
You can see that the normal kidney is being measured
and it measures 4.1 centimeters.
Compare that to the contralateral duplicated kidney which
measures 5.2 centimeters.
So we already have a clue that this kidney is different
and when we look closely at the collecting system on the
right side we can see fluid in the lower pole collecting
system separate from the fluid in the upper pole which is
more dilated than the lower pole.
Looking even more carefully, we were able
to identify the dilated ureter
that drains the fluid from this collecting system down into
the bladder but in an obstructed location.
So there's backup of urine in the ureter
and in the upper pole of the kidney.
Here's another fetus with renal duplication.
You can see an enlarged kidney with duplication
of the collecting systems
and dilatation only of the upper pole calyx and pelvis
and proximal portion of the upper pole ureter.
When we got down to the bladder we were able
to identify what's called a ureterocele.
This is where that ureter is obstructed
because it's not draining properly,
it is obstructed at this point back with a backup
of urine into the ureter and into the upper pole.

Renal Dysplasia

Now renal dysplasias occur when there's obstruction
of the kidney that leads to damage to the renal parenchyma
and there are two types of renal dysplasia.
The first type occurs when the obstruction
to the kidney occurs after 10 weeks gestation
or when the obstruction to the kidneys is incomplete
and this leads to a dysplastic kidney
that may have a thin echogenic renal cortex and may
or may not have hydronephrosis.
This is very different than the multicystic dysplastic
kidneys that develop when there is early obstruction
to the kidney that's complete.
So if the obstruction to the kidney is incomplete,
you may have a thin echogenic kidney
and if obstruction is complete
and early in gestation it'll be a
multicystic dysplastic kidney.
This fetus has renal dysplasia
and hydronephrosis due to bladder outlet obstruction.
You can see that both kidneys are markedly dilated
with severe hydronephrosis
and you can see that the cortex
around the kidney is very thin and very echogenic
and this is a clue that these kidneys can
no longer function.
On the clip you get a better idea of how thin
and echogenic the cortex is for each of these kidneys.
While I mentioned earlier
that ureteropelvic junction obstruction does not typically
lead to renal dysplasia in a few cases it does
and here's one such case.
This is an 18 week fetus who had a normal kidney on one side
and a dilated kidney on the other.
This kidney had a dilated renal pelvis as well
as dilated calyces.
So the diagnosis of ureteropelvic junction obstruction was
made when this fetus came back.
However, the right kidney was no longer hydronephrotic
and no longer normal in size
but had shrunk in size so
that there was very thin residual cortex
and still dilatation of the central collecting system.
As you can see, compare it was much smaller than the normal
left kidney that was not obstructed.

Multicystic Dysplastic Kidney

When a multicystic dysplastic kidney develops instead
of seeing a kidney in the renal fossa you see a large
multicystic mass.
Typically this is a unilateral process
but when it's bilateral it is unfortunately incompatible
with life because the fetus develops in the absence
of renal function and thus cannot replenish the amniotic
fluid so it's surrounded by severe oligohydramnios.
Here's an example of a multicystic dysplastic kidney.
You can see on the transverse view
of the fetal abdomen you have a normal kidney on one side
of the spine and on the contralateral side you see a large
multicystic mass replacing the normal kidney.
This mass contains multiple cysts
that do not communicate with each other.
On the longitudinal view you can see that multicystic mass,
you can see how it's much bigger than a normal kidney would
be and has very little residual parenchyma.
Now here's a fetus who developed a multicystic dysplastic
kidney from her ureteropelvic junction obstruction.
You can see that at 18 weeks gestation there was a dilated
renal pelvis to 6.6 millimeters
and there were dilated calyces.
So this was a hydronephrotic kidney
when the patient returned for a 36 week follow up,
the kidney was no longer hydronephrotic
but had been replaced with multiple cysts
and almost complete destruction of the renal parenchyma.

Polycystic Kidney Diseases

Autosomal Recessive Polycystic Kidney Disease

Autosomal recessive polycystic kidney disease is a disease
that affects the kidneys such
that there is severe renal failure
and these fetuses may develop a hepatic fibrosis.
The severity of the disease in utero and shortly
after birth depends on the degree of renal involvement.
What we see on ultrasound is
that we see enlarged echogenic kidneys
because these kidneys are typically non-functional,
there will be severe oligohydramnios
and we are often unable to identify any bladder
because then there's no urine to fill it.
Here's the typical appearance, this is a longitudinal view
of the fetal abdomen.
You can see that there is no amniotic fluid
around this fetus
and on either side of the spine we see markedly enlarged
echogenic kidneys.
Now they do retain their reniform shape
but they're much more echogenic than you would expect to see
and much larger than you would expect to find.
This fetus also has autosomal recessive
polycystic kidney disease.
In this case you can see some
of the tiny cysts in the kidneys.
You can see how big each kidney is.
You can see that this kidney on this side of the spine
extends about halfway across the abdomen.
The kidney on the other side extends almost from the back
of the abdomen to the front of the abdomen.
Notice there are lots
of little cysts throughout these kidneys.
This fetus also had a cyst in the liver.
This is not an uncommon finding in these fetuses.
They can have hepatic cyst, splenic cyst,
even pancreatic cysts.

Meckel-Gruber Syndrome

Now Meckel-Gruber syndrome does have polycystic kidneys
but also has some other anomalies that allow us to detect
that this is a syndrome and not just polycystic kidneys.
These fetuses often have encephalocele,
they have polydactyly, they often have cardiac anomalies
and as with polycystic kidney disease they often
have liver cysts.
They may also often have a cleft palate.
So here is a fetus with Meckel-Gruber.
You can see in the view of the abdomen
that the almost entire abdomen is filled with
very large echogenic kidneys with cysts.
So these are the polycystic kidneys.
When we look at the clip
through the hand we can see there's polydactyly
with an extra digit on one side.
Here's the thumb, here are the forefingers,
here's the extra digit
and when we looked in the head we saw an encephalocele
with protrusion of intracranial contents
outside of the cranium.
Here's another case of Meckel-Gruber.
You can see the kidneys here are mildly enlarged
and quite echogenic.
You can see that the hand has six digits instead of five
and the foot does as well.
So there's polydactyly involving both the hands and the feet.

Autosomal Dominant Polycystic Kidney Disease

Now autosomal dominant polycystic kidney disease typically
does not present until someone is an adult.
But occasionally we will see indications
that a fetus has autosomal dominant
polycystic kidney disease.
We may see a few cysts.
With adults the findings are hypertension
and renal failure and multiple cysts.
So some of those findings we might see in utero.
We might see enlarged kidneys, we might see a few cysts,
but typically these fetuses still have normal renal function
so we'll have normal amniotic fluid
and the urinary bladder will be present.
So here's a fetus with autosomal dominant
polycystic kidney disease.
You can see in scanning through the fetal abdomen,
the kidneys are extremely echogenic, they're not enlarged
and they do retain their reniform shape.
On longitudinal view you can see the echogenic kidneys
but normal reniform shape on each side.
There also is normal amniotic fluid around this fetus.

Differential Diagnosis of Echogenic Kidneys

When we see echogenic kidneys we don't always know the cause
but we do need to consider the differential diagnosis
which I've listed here.
And the differential diagnosis includes obstructive
dysplasia as I showed you
with the obstructed hydronephrotic kidneys from
posterior urethral valves.
Sometimes multicystic dysplastic kidneys look like
echogenic kidneys.
We also can have echogenic kidneys from genetically
inherited renal disease, either autosomal dominant
or autosomal recessive polycystic kidney disease.
Echogenic kidneys can be seen
with some genetic syndromes such as Perlman
or Beckwith-Wiedemann or Meckel-Gruber.
As we've discussed.
Other causes include nephroblastoma, renal vein thrombosis,
some toxic injuries, some infections such
as cytomegalovirus, ischemia and aneuploidy.
So here's a fetus
who had an unusual appearing right kidney can see the right
kidney and we saw some echogenic areas within the central
part of the kidney as well
as increased echogenicity of the cortex.
When we interrogated with the doppler, we discovered
that this fetus had renal vein thrombosis
that had tracked from the kidney into
the inferior vena cava.

Renal Cysts and Masses

Renal cysts are uncommon in the fetus but not unheard of.
They can be an isolated finding
or an early sign of dysplasia.
So here is a fetus
who has a renal cyst in the upper pole of the left kidney.
Here's the kidney, here's the small cyst next to the,
in the upper pole of the kidney.
You know it's the left kidney
because it's posterior to the stomach.
And here we see on the clip that it is an isolated cyst
and the rest of the parenchyma appears normal.
Here's another fetus
with a large renal cyst extending off the lower
pole of the right kidney.
Here's the kidney, here's the cyst here is the kidney here a
longitudinally with the cyst extending off the lower pole?
The most common mass to find in the kidney
of a fetus is a mesoblastic nephroma.
This is a hematoma, it's not a malignancy.
It's more common in male than female fetuses
and it appears as you expect it would
as a mass in the renal fossa taking up
some or all of the kidney.
Here's a case where the mass completely replaced the kidney.
This is a transverse view of the fetal abdomen.
The spine is over here
and you can see a well encapsulated solid mass
in the position of the normally placed kidney.
This was a mesoblastic nephroma
because it does retain its renal capsule.
Surgical excision is fairly simple.
Here's another mesoblastic nephroma.
You can see on a longitudinal view
of the kidney there's an echogenic mass occupying most
of the upper and mid pole of the kidney with a little bit
of residual normal renal tissue.
Here again, you can see a little bit
of residual normal renal tissue.
The rest of the kidney is replaced by the solid mass.
Here it is on fetal MRI.
You can see the large mass occupying most of the left kidney
with a little bit of residual renal tissue inferiorly
and here it is a pathology large mass,
little bit of normal tissue.

Evaluation of the Urinary Bladder

Now as part of the evaluation
of the fetal genital urinary system, it's important
to look at the urinary bladder first
to make sure that it's present.
Absence of the urinary bladder would suggest absent renal
functions such as bilateral renal agenesis,
bilateral multicystic dysplastic kidneys
or autosomal recessive polycystic kidney disease.
We also wanna look at its size
because marked enlargement should raise concern
for posterior urethral valves or prune belly syndrome.
Normally we'll be able to see the urinary bladder in the
pelvis by the time the fetus reaches the age
of about 13 weeks gestation.
We certainly should see it on all our second
and third trimester ultrasounds.

Posterior Urethral Valves

When the bladder's enlarged,
we could have posterior urethral valves.
This is an anomaly exclusively found in male fetuses
and it is the second most common cause
of hydronephrosis after ureteropelvic
junction obstruction,
posterior urethral valves prevent the flow
of urine from the bladder to the amniotic space
and thus the urine backs up into the kidneys
through the ureters.
So the typical ultrasound findings are oligohydramnios
because the fetus is unable to urinate dilated bladder
and posterior urethra and a dilated ureters
and a dilated kidneys.
Now sometimes the urine leaks from the kidney into the
peritoneal cavity and then you'll have urine ascites.
This is the typical appearance of posterior urethral valves.
You can see a markedly dilated bladder in the lower abdomen
of the fetus and a protruding protrusion from the lower
bladder which represents the posterior urethra.
If you look closely you'll see small,
a small echogenic kidney here.
This is a dysplastic kidney.
This obstruction has led to dysplasia of both kidneys.
There's also oligohydramnios around the fetus.
This is a different fetus with similar findings.
You can see the markedly dilated bladder filling
the lower abdomen.
You can see the dilated posterior urethra
and here we can see the dysplastic kidneys.
In this case they have dilatation.
There is urine within the kidneys so you see hydronephrosis,
but you see the thin echogenic cortex around both
of these dysplastic kidneys.
There are interventions that can be done
with posterior urethral valves that can sometimes lead
to salvage of the kidneys.
We can do this by draining the urine from the bladder
and sometimes by putting shunts in the bladder
to allow continuous drainage
of urine from the bladder into the amniotic space.
So here you can see we're initially putting a needle into
the fetal bladder because we're going
to drain the urine from this dilated bladder.
Now sometimes posterior urethral valves will present
late in gestation.
Here is such a case at 20 weeks gestation there was normal
amniotic fluid, normal sized urinary bladder
and the kidneys had no hydronephrosis.
But this fetus returned 10 weeks later at 30 weeks gestation
and now had a dilated urinary bladder oligohydramnios
and hydronephrosis in both of the kidneys.
Now with late presentation,
the prognosis is much better.
There is a chance that we can preserve the renal function in
these kidneys by relieving the obstruction in the bladder
or by delivering the fetus
and having surgical removal of the obstruction.
So in this case
what we did is we drained the urine from the bladder
to help drain the kidneys and see whether it would recur
or whether we could at least decompress the kidney
to buy the fetus a few more weeks in utero.

Prune Belly Syndrome

Prune belly syndrome is another cause of dilated bladder
and urinary obstruction.
This occurs in male fetuses
and leads to absence of the abdominal musculature
and very abnormal smooth muscle.
Throughout on ultrasound we'll see dilated bladder just like
posterior urethral valves,
we'll see hydronephrosis hydroureter.
We might even see a dilated urethra in the penis.
The difference though between prune belly syndrome
and posterior urethral valves is
that the amniotic fluid volume can be normal.
And that's because although these fetuses have
obstruction, the obstruction
to the bladder outlet is not complete
and so the amniotic fluid can be replenished.
So here's a fetus with prune belly syndrome.
You can see the kidneys are markedly dilated.
They both have mildly echogenic cortex can see the bladder
is very large with a very large dilated posterior urethra
but there was still amniotic fluid around this fetus.
This is a view of the penis of the fetus.
Notice that there is urine filling the penile urethra
as we can see it here.
As with the posterior urethral valves, we do want to confirm
that the renal function is preserved in these fetuses.
So we pass a needle into the urinary bladder
and drain the fluid to assess the electrolytes.
Here you can see after drainage
that the penile urethra has collapsed.
It still has fluid in it, it
but nowhere near as much as prior to our drainage.

Bladder Exstrophy

Now bladder exstrophy is an unusual anomaly
where there is an opening in the lower part of the abdomen
and the bladder is exposed to the amniotic cavity.
It may be everted or exteriorized.
This kind anomaly is associated
with other genital urinary anomalies.
On ultrasound, we will have normal kidneys,
normal amniotic fluid,
but we may not be able to see the bladder
because there it may be so everted
and exteriorized that no fluid will collect into it.
And instead we may see a small mass protruding from the
anterior abdominal wall.
So here is a fetus who has bladder exstrophy.
There's normal amniotic fluid. The kidneys appeared normal.
In fact the cord insertion appears normal.
But just below the cord insertion we see a bulge
of soft tissue from the anterior part of the abdomen.
And this is the everted bladder protruding from an opening in
the anterior abdominal wall.
Here is another one with the same diagnosis.
You can see in the lower abdomen
of the fetus a soft tissue protrusion from a defect
in the abdominal wall.
And here you can see that fetus at birth with extrusion
of the bladder through that defect.

Ovarian Cysts

Now as part of the genital urinary tract,
we do look at the other structures related to the system
and one of these is that we may see abnormalities
of the female fetus.
When there are ovarian cysts.
Ovarian cysts appear
as cysts in the lower pelvis of the fetus.
They're typically simple,
but occasionally they'll be complex if there's torsion
or hemorrhage to that cyst.
The finding is usually a unilateral cyst adjacent
to the urinary bladder.
In this case it was on the right side, we saw a cyst next
to the urinary bladder.
Here you can see the clip showing the cyst located adjacent
to the urinary bladder.
It's important when you do see a cyst in the fetus
to look at the genitalia
to see whether it's a female or male fetus.
And then to determine whether the cyst involves the kidneys
or some other structures.
Here's another ovarian cyst you can see next
to the bladder is a nice round simple cyst.
And here with inversion mode on a 3D ultrasound,
you can see the cyst here next to the urinary bladder.
If the ovarian cyst develops torsion
or hemorrhage, you'll see echoes inside the cyst.
Here is one such case where we saw a small ovarian cyst
and on follow-up scan we now saw layering echoes
inside the cyst likely due to hemorrhage.

External Genitalia

We also look at the external genitalia on the female fetus.
We should be able to identify the labia
and on the male fetus we identify the scrotum and the penis.
While there are a few anomalies
that affect the external genitalia, those
that do may be a clue to other anomalies within the fetus.
Here are two normal fetuses. On this side.
We have a normal female fetus in the third trimester
where we see the labia and the clitoris.
And on this side you can see a normal male fetus
where we see the penis.
And here with 3D we can see the outline of a female fetus
where we see the labia sitting in parallel here
and the male fetus with the penis pointing forward
in the region of the genitalia.
It's not uncommon in the male fetus to see a little bit
of fluid in the scrotum surrounding the testicles.
As we see here, these small hydroceles are normal,
but large hydroceles may be seen
with abnormalities including hydrops.
So here you see a little bit of fluid in either side
surrounding these scrotal contents.
Now ambiguous genitalia is an abnormal finding.
It's associated with a variety of syndromes as well as
with bladder exstrophy.
It also may be seen with unusual karyotypes.
So it is very important for these patients to be counseled
and given the opportunity
to determine the karyotype of the fetus.
So here we see a fetus with ambiguous genitalia.
This one did prove to be a male fetus
and the fetus had exstrophy.
Notice you'll see what looks like splaying of the scrotum
or enlarged labia.
And we see a small structure protruding between the two.
This is either a small penis with hypoplasia
or it could be an enlarged clitoris.
You can't tell from these pictures
and that's why it is important to get the karyotype.
And here's another case of ambiguous genitalia.
This was also a male fetus at 23 weeks.
You can see that the scrotum is splayed to either side
and the penis points downward instead of in its usual
location above the fused scrotum.
Here on the other 3D picture,
again you can see the splayed scrotum
with the penis in an inferior location pointing downward.

Conclusion

So I've given you a run through the important structures
to be evaluated in the genital urinary system
and a clue as to what abnormalities you might be able
to find and detect when you do your second
and third trimester ultrasounds.
Thank you.