Mistakes to Avoid in the 2nd and 3rd Trimesters: Fetal Anatomy and Measurement - SD

Introduction

Hello, my name is Dr. Mary Freddy's. I'm the assistant director of ultrasound at Brigham and Women's Hospital in Boston, Massachusetts. And I'm gonna be speaking today on mistakes to avoid in the second and third trimester, particularly looking at fetal anatomy and measurements.

Measurements of the Fetus

We're gonna begin by looking at measurements of the fetus. And it's important when you are measuring a fetus in the second and third trimester to know the rules. And there are rules to follow for measurements of the head, measurements of the abdomen and measurements of the femur. Once you know the rules, you have to follow the rules.

Remember that in the previable fetus, so 20, 22, 23 weeks, a small error in measurements is likely not to be clinically significant. When we get to the fetuses who are at the extremes of measurements, those fetuses that measure less than the 10th percentile, when we're concerned about IUGR or fetuses that are over the 90th percentile and we're worried about macrosomia, that's where the errors are gonna become more clinically important.

Make sure as always with ultrasound that the image is optimized. Use the correct plane and the correct endpoints for measuring.

Biparietal Diameter (BPD)

First discussing the BPD, make sure that the head is symmetric on your image. And what I mean by that is making sure that the third ventricle and the thalami are right in the middle of the image. And you can typically see the falx going down the middle of the head. The calvarium should be smooth and symmetric. The posterior fossa and orbits should not be on the image. The cursors are placed outer to inner or leading edge to leading edge.

Occipitofrontal Diameter (OFD)

When looking at the OFD, it should be the largest possible measurement along the base of the skull with the cavum septum pellucidum identified anteriorly on the image. The calvarium, again should be smooth and symmetric. No posterior fossa on the image, no orbits on the image. The cursors in this instance go middle to middle.

And let's look at some pictures. So for this patient we can see the BPD is measured here from leading edge to leading edge. And the thalami are in the middle, but here is a little bit of posterior fossa on the image and the calvarium is not intact around the side here. And this gives us an OFD that's a little bit too small. When the head, or the probe is angled just a little bit, we get a more oval appearance to the head. The thalami is still in the middle. The falx right down the center leading edge to leading edge, middle to middle. And the OFD has increased significantly.

Abdominal Diameter

Measuring the abdominal diameter. This should be performed at the level of the liver. The liver is the largest intraabdominal organ in the fetus and it gives us the best representation of the fetal weight. The image is taken at the level of the stomach bubble and the intrahepatic umbilical vein. And these measurements go skin edge to skin edge.

When errors get made with abdominal measurements, it's often because you can't see the skin edge. There's a placenta in the way. Oligohydramnios is preventing you from seeing the true edge of the skin. Or there are fetal parts, there's an elbow, there's a knee, something's in the way or sometimes what happens is because of compression from the ultrasound probe, the abdomen itself is compressed and it becomes too oblique. When the measurements are too big, it's typically because the measurement has been taken in an oblique plane rather than a true axial plane. If the fetus is prone, that often leads to measurements that are too big. What happens in the prone fetus is that the spine obscures the landmarks and you're typically not at the correct level.

When the abdominal measurements are too small, that's usually because the entire abdominal wall is not included. Either the rib is mistaken for the skin and the cursor is placed on the rib or the imager doesn't realize that there's more dependent fat on the fetal downside. When anybody lies on their side, the fat or the subcutaneous tissue heads down towards the ground. And so the leading edge or the anterior surface is gonna be thinner and the downside is gonna be thicker. So don't forget to look for more subcutaneous fat on the dependent side of the fetus when you're struggling to get an accurate abdominal measurement because sometimes it can be quite difficult in a late term fetus.

Remember that a round image is best. It's important to always keep the abdominal diameter measurements within 10 millimeters of each other and this will give you a pretty good estimate even if you can't see the other internal landmarks.

So let's look at a few examples. In this instance, we have a prone fetus. The fetal spine is at the top of the image, and that's a pretty good cursor, but this one is a little bit more difficult to say where the true edge of the fetus is. Same thing over here. I'm not exactly sure where the edge is because there's an arm in the way that's blocking the edge of the subcutaneous tissue. And this cursor down here, Lord knows where it's supposed to be because the spine has completely shadowed out this side of the fetus and you just can't be accurate.

Here's a better image of the same fetus. And all that's happened is that the probe has been moved just a little bit immediately on the mom's anterior abdominal wall. And now we can see the skin surface to fluid, skin surface very clearly. And we can see that our measurements are very close to each other. So I know that I have a true circular diameter.

Femur Length

When measuring the femur, it's important to keep the long axis of the bone or the ossified portion of the bone parallel to the transducer. And remember that we're only measuring the diaphysis and the metaphysis. We are not including the epiphysis on the femur measurement. The measurement should happen at the junction of the cartilage and the bone, not at the longest bright white spot in the distal femur that is termed the distal femoral metaphysis, which is not a true anatomic structure.

Here's an example of a fetal measurement that should not be performed. This image is set with a depth of approximately 20 centimeters, but only five or six centimeters would be necessary to have an accurate look at this femur. And you can't see the distal landmark and the proximal landmarks clearly enough to know that your measurements are accurate.

Case Example: 41-Week Pregnant Patient

So here's a real case that came into our department about a month ago, and this is a patient who's 41 weeks pregnant. And these are the measurements that were submitted.

So looking first at the abdominal diameter, we see we've got the stomach here, we've got the intrahepatic umbilical vein, but there's also a kidney on this image. You can see the subcutaneous fat and the leading edge and the cursor is here anteriorly and the cursor here posteriorly, those look pretty good, but this is the diameter that's throwing us off. You really can't see where the edge is posteriorly behind the spine. And again, the anterior mark is somewhere in this black, not an accurate location. And notice these measurements are 113 millimeters to 138 millimeters. This is way over the 10 millimeter cutoff and tells me that this is a very oblique measurement and probably not accurate.

Looking at the femur length, we don't have the sharp crisp ends at each side. That would help us know that it's an accurate measurement. And this is the distal end. And here's the distal femoral metaphysis heading down. And a better spot to put, or more accurate spot to put the cursor would be right here. And this end, again, you don't have the sharp end and it's difficult to know where exactly on this curve is the correct spot for the femur.

Here's the BPD measurements that were submitted or the head measurements. So we have leading edge to leading edge here, the falx and the thalami and the third ventricle are seen right in the middle. So that's a pretty good BPD measurement. But notice how round this head is and how short the OFD is. And there's a little bit of posterior fossa on here and the plane of the center of the head would be in this direction, not across here. So for many reasons this OFD is suspect.

So the imager actually went on to take this OFD and this is a little bit better. We can see that it's along the plane of the falx. It's more elongated. We got the measurement up to 124. It's a little bit unclear whether this is the true anterior skull margin, but the rest of these measurements are certainly very accurate. But instead of using either one of these, these were averaged to have a measurement in the middle of 115, which is not the best way to do it. If you have a measurement that's technically poor, that measurement should not be included as an average, that measurement should be discarded and stick with the better measurement.

So here's the second set of measurements that I performed going back in the room. And again, we have a very similar OFD of 95. We've got the falx running right down the center of the head and a more accurate OFD again coming up with 116, which happens to be the average of both of these, but a more accurate measurement and more reliable.

Looking at the femur in this fetus, here's the proximal end of the femur and you can see the end of the ossified portion of the bone. And here's the cartilaginous epiphysis and the ilium. And this is starting to look like a neonatal hip ultrasound. You can see the image that shows that this hip is normally located in the glenoid. The measurement should be marked right at this end. And then at the far end of the femur, here's that distal femoral metaphysis and the epiphysis with a little bit of ossification in the center. And this is where the cursor belongs at this end of the femur. And this gives us a more accurate femur measurement when these landmarks are used of 74 millimeters.

Once again, here's the incorrect abdominal diameter and here's another attempt at a better abdominal diameter. Here we see stomach, intrahepatic umbilical vein. There's no longer a kidney on the image and we can see sharp echogenic skin to amniotic fluid margin here. Skin margin here, skin margin and skin margin.

So when we take these measurements that were performed on September 24th, these are the initial measurements at 40 weeks and the fetal weight came out nine pounds, 10 ounces or almost 4,400 grams in the 96th percentile. And at our institution, patients whose weights are above 5,000 grams are sent directly to cesarean section for macrosomia and fetuses whose weights are at 4,500 grams will go directly to C-section if they're gestational diabetics. So this patient is flirting with the possibility of a primary cesarean section without even a trial of labor. Because of the size of this fetus with the more accurate measurements, we see that the weight is actually, or possibly eight pounds and five ounces, which is in the 74th percentile, not the 96 percentile.

Okay, what's the answer? Nine pounds and 10 ounces or eight pounds and five ounces. The patient delivered on October 3rd, which was nine days later. And we do understand that fetuses gain approximately a half a pound a week so that the true weight of this fetus approximately nine days later was eight pounds and 11 ounces. A little bit more than a half a pound larger than we had estimated with the accurate measurements. Reminding us all that the correct measurement technique is critical.

Fetal Anatomy: Head

Moving into the second portion of the talk discussing fetal anatomy, we're gonna start with looking at mistakes to avoid when imaging the fetal head.

One thing that it's important to avoid is describing normal anatomic variants as pathology. And here I'm showing you an example of the cavum vergae. The cavum vergae is a posterior extension of the cavum septum pellucidum. It's seen in the midline between the lateral ventricles and it can be seen here underneath the corpus callosum on the sagittal view. When the cavum vergae extends posteriorly, it's termed the cavum velum interpositum. And here we see it earlier on in the midline at 19 weeks. And on the sagittal image at the posterior aspect of the corpus callosum, a little tiny cavum velum interpositum, a normal variant does not need to be even included in the ultrasound report.

Remember that everything cystic in the brain is not a normal variant. In this case, we have an irregular fluid collection that's right in the midline but has a curved shape to it and possibly some extensions out of this shape. And don't forget to turn on the color doppler in this instance because we see that this is a vein of Galen aneurysm.

Another cystic thing in the brain is this round structure here it is not in the midline, it's off center on one side it's posteriorly and related to the tentorium seen underneath the temporo-occipital lobe region here. And this is an arachnoid cyst.

It's important when looking at the fetal head to spend some time looking at the lateral ventricles and not to overcall ventricular enlargement. The plane of imaging to measure a lateral ventricle must be level. Any off axis measurement will increase the size of the ventricle. It's important to put the calipers exactly where the edge of the lateral ventricle is just on the inside of the ventricular lining. And be careful not to measure the medial surface of the brain rather than the medial wall of the ventricle. And remember, we can assume that the ventricles are symmetric unless you visualize asymmetry. Always use the smallest technically accurate measurement. Any measurement that you take of the lateral ventricle that is artificially increased is due to measuring this ventricle obliquely so that the true measurement, the smallest measurement you get is the true measurement. It's impossible to measure a dilated ventricle as smaller than it truly is, but it is possible to take a normal size ventricle and make it larger.

The other thing that you can look at that might help you is the presence of a dangling choroid. The choroid should typically completely fill the lateral ventricle if there is more than three millimeters of space between the medial wall of the ventricle and the choroid plexus. This suggests ventricular enlargement and this is particularly useful early in pregnancy, but should be monitored rather than diagnosed as abnormal.

Here's an example of how to correctly measure the lateral ventricles. This is the down ventricle and we see a choroid here and then the calipers sit in the atrium of the lateral ventricle along the medial edge here and the lateral edge here. An example of the dangling choroid where the choroid is separated from the medial wall of the lateral ventricle. And we can measure this distance from here to here. And if you see as much as three millimeters, it suggests that there is underlying ventricular enlargement. And again, this is useful early in gestation where the 10 millimeter cutoff might be a little bit too big.

Why does it matter? Here's an example of a fetus where we were measuring both right and lateral ventricles and clearly there's hydrocephalus. There's no question that these ventricles are dilated, but if you notice on this up ventricle, the measurement is 33 millimeters, but here's the falx and the presence of the falx and the back third of the head tells me that we're oblique through the head. The falx should be running right down the middle. So we have artificially increased the size of this lateral ventricle. Here's the same fetus in the down ventricle and we have also artificially increased the size of the ventricle to 36 millimeters because we've crossed the midline. And this is at least part of the third ventricle and possibly part of the up ventricle that's being measured as well.

More accurate measurements for this fetus. The falx is right down in the midline and we're back in the atrium and we have a measurement of 24 millimeters. And on the downside again, here's the dangling choroid, the medial aspect of the ventricle and the lateral aspect of the ventricle 25 millimeters.

Why is this important? This fetus is being monitored for progression of the hydrocephalus because of the presence of a lumbosacral meningocele seen here on the sagittal view and seen on the clip in the transverse view with the open posterior elements. And the patient's obstetrician is using the size of the ventricle to determine whether this fetus is stable or whether there needs to be an intervention because of progressive ventricular enlargement.

A few words about choroid plexus cysts. These occur in less than 1% of fetuses and are associated with trisomy 18, but as we know, choroid plexus cysts are often a transient normal finding. And when we see a choroid plexus cyst, it probably is more often normal statistically than associated with trisomy 18. Choroid plexus cysts are discrete, round cystic structures. They should measure over two millimeters and they should be completely within the choroid. In addition, you ought to be able to turn on a choroid plexus cyst and see it in every plane of imaging. When cysts are over called mistakenly, it's typically because it's not a true cyst. The lesion is not round in three planes and it more likely is something that we call a spongy choroid.

So here are two different patients with choroid plexus cysts. This is much earlier in gestation and there's the round black discrete structure completely within the echogenic choroid plexus cyst in this fetus with trisomy 18. Here's a different fetus. The choroid plexus cyst is much larger indeed, it almost replaces the entire choroid and this fetus had normal chromosomes. Compare those discrete black circles to these two fetuses who have a more smudgy, irregular ill-defined sort of blackness throughout the choroid plexus, but no discrete, well-defined sphere on either one. And these have been termed the spongy choroid, but a spongy choroid is a normal choroid. It does not need to be put into the report. And this head and this head are both normal.

Dandy Walker variants occur when there's absence or hypoplasia of the cerebellar vermis remember that vermian development is incomplete until at least 18 weeks. And when mistakes are made with the diagnosis of Dandy Walker variant, it's often because the fetus is too young, the cerebellar vermis has not completely formed. And what needs to be done is a follow-up exam in two to three weeks and give that vermis a chance to show up. Another reason why Dandy Walker variant can be over called is if the images are too oblique or obtained in a semi coronal plane. If the posterior fossa is imaged in a coronal plane, you can take a picture underneath the vermis and make a suggestion of a Dandy Walker variant.

So if there's a question of a Dandy Walker variant, it's important to confirm that you're in an axial plane and then to go on a search for the fourth ventricle and the vermis. Here's an example of a patient who was felt to have a Dandy Walker variant. Here's the posterior fossa here and the cerebellar hemisphere here, and then the fourth ventricle, which appears to open posteriorly into the cisterna magna. But if you notice the calvarium in this instance is incomplete. It stops right about here and we don't pick it up till the other side. And that's our clue that this image was taken in a coronal fashion. And if the probe was tipped so that the calvarium is intact along the back of the posterior fossa, we see as we do on this image here, that there is indeed a vermis and a distinct fourth ventricle just in a different spot than was being imaged on the first image.

Here's an example of a patient with a true Dandy Walker variant. The fourth ventricle here is wide open into the cisterna magna and the cerebellar hemispheres are flattened and distorted, particularly on the superior aspect of this patient with the true Dandy Walker variant, mega cisterna magna is often over called as pathology. When the cisterna magna appears prominent, it's important to look at the underlying anatomy of the posterior fossa and identify a well-formed cerebellar vermis and fourth ventricle. Again, remember, these need to be imaged in the axial plane. There are normal septi that run through the back of the cisterna magna and those can be identified and should not be mistaken for a cyst. And again, when the cisterna magna appears large, do a careful search of the brain for other malformations. If it's an isolated finding, the likelihood that there will be a good outcome in the fetus.

Here's a mega cisterna magna here, a large amount of fluid in the posterior fossa, cisterna magna region. Notice the little crossing septations here and here the measurement is 11 millimeters, but we have a well-formed cerebellum and a midline vermis.

Fetal Face

Moving on to mistakes that can occur in the face. Remember that when you're imaging the face, we need two different images. I need an image of the nose and lips looking at the superficial soft tissue of the lips and outlines of the nostrils. And don't forget to image the orbits. There has to be two orbits in every fetus to call the face a normal face.

Here's a really cute picture of a fetus. The parents were delighted. I show it multiple times, doesn't it look great? You can see the eyes and the cheek and it's an adorable picture. Is it normal? You can't call the face normal because you do not see the soft tissues of the nose and lips. Here's the image of the nose and lips. You can see the lower lip here and the upper lip and there's a cleft indeed coming from the right nostril down into the upper portion of the mouth. So make sure that to call a face normal, that soft tissue plane of the upper lip is seen in completion.

Here's another patient who was brought to my attention because of the possibility of a cleft lip. And here's the upper lip right here. The rest of the face would be here and there is a cleft or a vague cleft right in the midline sort of obliquely there. But if we scan a little bit more posteriorly, we can see that actually the lip is completely intact when I have the nose on the image. And this is just a prominent philtrum or that cleft in the soft tissue in the upper lip and it can be confirmed if possible with 3D imaging. There's an image of the fetal face and we can see that the upper lip is completely intact.

What do I mean by orbits? I wanna see two bony orbits here and here. They should be symmetrical in the head. It's not enough to just see the top orbit. Both of them need to be identified. Here's an image of the orbit in a patient. This is why we're looking at the orbits because in this instance the two orbits and the nose, there's a big soft tissue mass here protruding from the anterior aspect of the nose between the two orbits. And here it is seen on the more sagittal plane and you can see that the tissue here is identical in echo texture to the tissue of the brain. And this is an encephalocele glioma.

Another structure that can be identified on fetal ultrasound in the region of the orbits is this structure right here, a little round cystic spherical shaped structure with through transmission possibly identified right in the region of the orbits. And on this axial image of the lower portion of the orbits here and here we can see the little tiny black circle. And this is a dacryocele. This is a blocked lacrimal duct and the tears back up into a little bubble of fluid. It has no clinical consequence and will disappear after the baby is born. Should not be considered to be pathology.

Here's another patient again looking for the orbits. This is the axial view of the head and this is the region of the orbits, but we do not have the well-defined bony structure of the orbits on either side and the nose is very flattened. And on this profile view of the fetus, you can see the chin and the lips and notice that the nose is completely absent in this fetus. And here's the 3D image. You can see a prominent forehead and just collapsed soft tissue areas where the orbits should be and no visible nose. And indeed this child was delivered at term with no nose and no orbits.

Fetal Kidneys

A few words about mistakes that can occur in the kidneys. The kidneys in particular can be very challenging on the 18 week survey. And a typical mistake that happens is that the adrenal glands are identified and labeled as kidneys rather than the kidneys themselves. And your clue that you could be looking at the adrenal glands as if the stomach is on the image because the stomach is typically higher than the level of the kidneys. Another clue. Adrenal glands are very prominent and very hypoechoic and they're easy to see. The kidneys are isoechoic, they're very difficult to see. They can be quite subtle at 18 weeks if you're lucky, they'll be a midline black slit or a little bit of fluid in the renal pelvis that will help you confirm that you're looking at kidneys.

So here's an example of a patient shown to show you at 18 weeks. This is reported as kidneys, but we're at the level of the stomach. And here's the hypoechoic area on the left hypoechoic area on the right. These are the adrenal glands and this image taken much lower down with no stomach on the images. The kidneys, here's a kidney here and a kidney here. And indeed they're very subtle, they're hard to see at 18 weeks. There's a clip going from the pelvis up through the abdomen starting at the bottom down by the bladder. And again the kidneys here and the adrenal above.

There's a patient who was seen at 18 and a half weeks with normal kidneys reported and this is the image that came out labeled kidneys. And here's the stomach here and we can see a probable kidney on the right here, but there's nothing convincing on the left. There's a little hypoechoic structure here, but this is too high to be in the region where a left kidney should be because we have the stomach right there. And indeed when this patient returned at 30 weeks, again, here's the right kidney aorta, IVC stomach bubble and a little hypoechoic area here, but no definite kidney seen in the left renal fossa, sagittal images of each kidney were performed. Here's the right kidney, 32 millimeters right where it belongs under the diaphragm, but on the left kidney we see the lying down adrenal sign where the adrenal is elongated and stretched along the spine because there is no kidney in the left renal fossa.

Okay, so there's no kidney in the left renal fossa, we don't stop there, we need to go looking for it because sometimes it's not missing, it's just in a different spot. And down in the pelvis we can see posterior to the bladder. Here's the left kidney and this fetus has a left pelvic kidney which was missed at the 18 week scan.

Fetal Heart

A few comments about mistakes to avoid in imaging the heart. One of the pitfalls that commonly occurs on the four chamber view is the possibility of looking at a ventricular septal defect. Remember that the top of the ventricular septum is very, very thin and you can get dropout which is artifactual in that spot. So if there's a question of a VSD, you wanna make sure that you change your angle and come in from the side and from the rather than from the apex to see the top of the septum. Also remember that for ventricular septal defect evaluation color is imperative.

So what do I mean by dropout? On this image of the four chamber we can see the interventricular septum here and it gets very, very thin. And there's a suggestion that there's a big hole here between the right ventricle and the left ventricle. Could this be a VSD? When we turn the image just a little bit, slide the probe a little bit more medially so that you're coming in perpendicular to the interventricular septum. You can see that that septum is intact all the way up to the root of the aorta. Let me just say this is right atrium and right ventricle and there's an echogenic stripe running through the right atrium. But if we change the angle here that echogenic stripe is gone and what we're imaging here is maybe the coronary sinus.

Another image of the heart. We see what looks like a beautiful four chamber view. But remember when you're looking at a four chamber, a static image is not enough. It looks like we have a beautiful interventricular septum here, but on the clip I think you can appreciate that the interventricular septum stops and there is a VSD running right over the top of the septum.

Another what looks like a beautiful four chamber view. We can see the tricuspid valve and the mitral valve. But if you look here on the very top of the apex, it looks like there's a black structure here on the end. And this is where color is helpful because with color imaging we can see that there's a small ventricular septal defect in a membranous portion of the septum in a very unusual location. But the color makes it very easy to see that ventricular septal defect yet again.

Another four chamber view looks beautiful, interventricular septum here, good motion of the valves. The color image though again shows us the ventricular septal defect. And once we know it's there we can angle the probe to see the VSD right here.

When looking at the heart, remember that a pericardial effusion is normal if there's pericardial fluid is normal. If there's less than two millimeters, it's not defined as a pericardial effusion until it's larger than two millimeters. And be careful not to mistake the hypoechoic myocardium as pericardial fluid.

So what do I mean by that? Here's the possible pericardial effusion seen here, but this is actually just the edge of the myocardium. You can see some echogenic inner edge and then the hypoechoic myocardium here. When in doubt I try to identify whether this possible fluid goes past the level of the valves. If it crosses the level of the valves, it's much more likely to be fluid as seen in this patient where we see the myocardium here and the pericardial fluid going all the way around the level of the mitral valve.

When imaging the heart, remember that a four chamber view only is not enough to report a normal heart. It's important that the aorta and pulmonary artery or the left and right ventricular outflow tracts are included in your exam and technique is extremely important. With these outflow tracts, the aorta must be imaged in the axial plane. You must identify that the interventricular septum is contiguous with the wall of the aorta and there must be a right ventricle on the image.

Here's a patient where we see a normal four chamber view and a normal four chamber is not enough because when we move to the outflow tract view of the left ventricle, we can see that the left ventricular outflow tract, which comes out here, is actually arising from both ventricles. There's a VSD and an overriding aorta. And this instance of tetralogy of Fallot again seen here would've been missed if we stopped on the four chamber view alone.

One thing I do wanna clarify is that the plane of imaging for the aorta is key on this image which is taken coronal. And I know it's coronal or in the sagittal plane because I can see the diaphragm here and the liver and I can see the lungs and I can see the ribs. So I've got a sagittal image. This is the lower portion of the heart or the inferior aspect of the heart. This is the anterior wall of the heart along the sternum. And so that makes this the superior wall of the aorta or the anterior wall of the aorta and the posterior wall of the aorta. And then this is the entire left ventricle. The issue is that the superior and inferior walls of the aorta are normal even when there's an overriding aorta, it's the medial wall of the aorta that we care about. And you can't see the medial wall of the aorta when you take an image in this plane. So the medial wall of the aorta is in here somewhere.

So the better technique for taking an image of the aorta is to stick on the four chamber view, stay with the axial plane and follow the interventricular septum up. So you see that medial wall of the ascending aorta and you can know that you do that if you keep the right ventricle and the left ventricle on the image at the same time. So you follow the ascending aorta out. And this tells you right this continuity between the interventricular septum and the medial wall of the aorta excludes with confidence an overriding aorta and a tetralogy of Fallot.

Here's another patient we see a four chamber view looks beautiful, but when we look at the image of the aorta, we can see now when we follow with both right and left ventricles on the image to see the ascending aorta, that there's an overriding aorta here and a ventricular septal defect. And we're then able to identify the overriding aorta in the tetralogy of Fallot.

Pseudoascites

Last case that I'm gonna show is an example of pseudoascites. Pseudoascites is or ascites is mistakenly identified when the hypoechoic rim along the abdominal wall is mistakenly thought to represent ascites. If that is the only place where you see the ascites, you should think to yourself maybe it's not real. Start looking other places particularly easy to see ascites in the fetal pelvis down by the bladder.

So here's an example of pseudoascites. We have a transverse view of the abdomen here and there's this hypoechoic rim seen along the edge of the anterior abdominal wall. But notice that this is the musculature that extends from the edge of the rib and is not intraperitoneal. And when we go down to the pelvis, we can see that there's absolutely no fluid down near the bladder or around the kidneys, and there was no ascites in this fetus.

Conclusion

That brings me to the end of my slides and I thank you so much for your attention.