Fetal Gastrointestinal Tract



hello I'm dr. Barbara Hertzberg from the Department of Radiology at Duke University Medical Center I'm a professor of radiology and an associate professor of obstetrics and gynecology and my talk today is on ultrasound of the fetal gastrointestinal tract you I'm going to be talking about the fetal gastrointestinal tract and we'll start at the level of the esophagus and work our way down the intestinal tract to the level of the colon beginning with the esophagus a common ultrasound diagnosis is Safa joule atresia and this diagnosis is based on visualization of polyhydramnios in conjunction with non visualization or small fetal stomach so in this example here we have polyhydramnios with inadequate inability to visualize the stomach in its expected location in the left upper quadrant on this left parasagittal skin and on the SAC sealskin however gastric visualization does not rule out esophageal atresia in fact most fetuses with esophageal atresia have a tracheal esophageal fistula and fluid traversing this fistula can be sufficient to allow visualization of the stomach so this is a fetus with esophageal atresia and a tracheal esophageal fistula in whom we see a normal-sized stomach many times though in the setting of esophageal atresia and a tracheal esophageal fistula the fluid traversing the fistula is sufficient to allow gastric visualization but the stomach is not normal in size and so this is a fetus with esophageal atresia and a trachea with Sabadell fistula in whom we see a smaller than normal stomach on the Left parasagittal skin and on the axial skin this raises the question of what is too small for the stomach well in actuality usually this is a subjective call in this particular fetus you look at the stomach it's lit like it's just simply too small however if there is any question about it there have been several studies which have investigated the size of the stomach over gestation and resulted in the creation of no more grams of normal stomach size and basically these studies show that stomach size increases with advancing gestation you know one of the more recent studies shows that for example early in second trimester at 13 to 15 weeks the length of the stomach is six millimeters and the AP diameter and width approximately four millimeters aren't average whereas near-term at 37 to 39 weeks the length of the stomach goes up to 30 millimeters and the width and the AP diameter of the stomach have also increased now not so intuitively obvious it is actually possible although rare to have gastric visualization in a fetus with esophageal atresia but no tracheal esophageal fistula and the explanation for this is thought to be that intrinsic gastric secretions are still occurring and cause distension of the stomach allowing its visualization just like gastric visualization does not exclude the possibility of esophageal atresia the opposite is also true that is non visualization of the stomach or a small stomach does not always predict esophageal atresia but rather can see be seen in a variety of other ideologies listed here we'll begin with a logo head Romney Asst in this pregnancy you can see that there is a small stomach and there is severe alla goya hegemonies with only a tiny pocket of fluid our logo Hydra Mateus is actually a very common course for a visualization of a smaller than expected stomach and the reason for this in this situation is that there's very little amniotic fluid to for the fetus to swallow and since gastric visualization depends on swallowed amniotic fluid getting into the stomach the stomach will typically not descend normally non visualization of the stomach can occasionally occur in normal fetuses in which it typically occurs due to the unlucky event of visualizing imaging the region of the stomach during a period of physiologic gastric emptying in in this case the non visualization should be transient gastric emptying is a real phenomenon in the fetus in fact the study has been formed performed which gastric size was measured every minute for a prolonged period of time on a large number of fetuses and this study showed that gastric emptying can be detected by ultrasound as early as 12 weeks of gestation before 24 weeks the changes in gastric size with cycles are smaller in amplitude and the cycle length is quite variable ranging from about 30 to 100 minutes after 24 weeks though the cycles are more predictable and by term cycles stabilized at approximately 80 minutes so it's not surprising then that in this fetus we cannot see the stomach in its expected location in the left upper quadrant at 12:06 p.m. but just 32 minutes later at 12:30 8 p.m. we see a normal appearing stomach and this fetus is normal anything that can impair the swallowing mechanism can also result in a small or non visualized stomach that's because the fetus has to swallow to get the fluid into the stomach to allow its visualization and so central nervous system abnormalities neuromuscular abnormalities and large facial clefts can all be associated with non visualization of the stomach or a smaller than expected stomach as an example this fetus that has a very small stomach had this as a result of this large facial cleft that we see on 3d ultrasound finally the stomach may not be visualized in its expected position in the left upper quadrant because it is not in this position as can be seen with fetuses with diaphragmatic defects and sinus abnormalities so in this fetus the stomach is not seen in the left upper quadrant because it's not in the left upper quadrant rather it is in the chest due to a congenital diaphragmatic hernia a helpful finding to try to distinguish the fetuses with gastric non visualization or a smaller than expected stomach on the basis of esophageal atresia from the very many other ideologies of non visualization and small fetal stomach is to actually visualize a fluid-filled proximal esophageal pouch and what you would be seeing is diagrammed here still on the subject of the fetal stomach ultrasound sometimes detects small conglomerates of material in the stomach these may look like little neoplasms but they will not be neoplasms as they might be if you were looking at an adult patient but rather in the fetus these conglomerates are usually aggregates of swallowed cells that have been stuffed from the fetal skin and as such they are usually a transient phenomenon and they are most commonly seen in normal fetuses so in the patient that we saw on the prior slide for weeks later we see that the stomach looks completely normal with no gastric Sumas present since these gastric pseudo masses are due to cells in swallowed amniotic fluid they are often seen in conjunction with prominent echoes in the amniotic fluid as was the case with this fetus who had a gastric pseudo mass and has lots of echoes within the amniotic fluid in fact echos are so commonly seen in the stomach and in the amniotic fluid with current ultrasound equipment that they're typically considered within the range of normal and rarely are commented on although that is the case I should point out though that they are seen with increased the likelihood in fetuses with certain abnormalities in particular in fetuses with bowel obstructions or eventual abdominal wall defects unlikely due to slowed gastric transit and with slowed transit through the gastrointestinal tract things are more likely to sit in the stomach and conglomerate this is an example of a fetus with the gastroschisis we see there herniated ballots here who also had a gastric pseudo mess the other clinical setting in which gastric pseudo masses are of increased likelihood to be seen is if there is blood in the amniotic cavity and the fetuses swallows intra amniotic blood and this can occur following amniocentesis with bleeding into the amniotic cavity following a placental abruption or in the setting of a sub chorionic hematoma because they are often seen in association with leaking of blood into the amniotic cavity so this fetus with a gastric pseudo mess has it on the basis of a sub chorionic hematoma where we see the elevated amnio chorionic membrane here with that will move a little further down the gastrointestinal tract to the small bowel and the peritoneal cavity we'll start with the duodenum and focus on duodenal atresia and other duodenal obstructions the ultrasound antenatal diagnosis of a duodenal obstruction is based on identification of polyhydramnios in conjunction with the fluid filled double bubble sign so in this fetus we see mild polyhydramnios in association with a double bubble sign here two bubbles within the fetal abdomen one of which is the distended stomach and the other is the duodenal bulb the duodenal bulb should not typically be fluid filled at ultrasound in a normal fetus it is seen typically in the mid abdomen just barely to the right of midline fetus on the right has much more marked polyhydramnios but also has a double bubble sign enlarged stomach enlarged duodenal bulb it's extremely important if you are suspecting a double bubble sign to try to demonstrate the connection between the stomach and the duodenum which makes the sign specific for bowel obstruction so here we have a double bubble sign and on the right now we see the connection between the stomach and the duodenum across the pyloric channel if you see a hugely dilated double bubble sign consider the possibility as we have here of esophageal atresia combined with duodenal atresia the reason this particular combination can give you some of the largest double bubble signs is that you get a blind loop of bowel when you have both esophageal atresia and duodenal atresia but the battle is still secretory so it keeps secreting fluid into this blind loop that keeps getting larger and larger and larger the double bubble sign can be a relatively late finding in gestation that is often it's not seen until the late second trimester or the third trimester but even when the actual full-blown double bubble sign isn't seen in some fetuses early on you can see precursors to it you may see increased amniotic fluid as we see here or a stomach that looks a little bit more prominent than one would expect even though we don't see the double bubble sign in this particular fetus a few weeks later there was a full-blown double bubble sign and here we can see the connection between the stomach and the duodenal bulb in the differential diagnosis for a double bubble sign when you can't see the connection or a wide variety of cysts within the fetal abdomen they include Coley Dhokla cysts a patek cysts are mental sis ovarian cysts duplication cysts cetera in this particular case we have the stomach here and we have an extra bubble here in a really good location for the duodenal bulb except that it did not connect to the stomach and this is a CO Lido closest which oftentimes does occur in the mid abdomen just to the right of midline as is the case in this fetus another phenomenon that can give you apparently an extra bubble with in the fetal abdomen has been termed the pseudo double bubble sign and this occurs because the stomach is curved and so because it's curved in configuration it is possible to get a scan plane that goes through both the fundus of the stomach and the gastric antrum therefore giving you two bubbles in the fetal abdomen here is an example – bubbles within the fetal abdomen but if you scan further in different scan planes you see that these connect up however the connecting up pattern is not that expected of the duodenal bulb connecting to the stomach via the pylorus rather it just looks like the curved stomach which is what this is and if you look back at the original image there is a suggestion that that's what you should be expecting to see because the second bubble is not located in the middle to the right of midline the way the duodenal bulb would be expected to be but rather is located in the left upper abdomen where you would expect the antrum of the stomach small bag beyond the duodenal bulb can be seen if we really try but if you're doing a casual search it's only occasionally seen in normal fetuses if you do look for the stomach especially late in pregnancy it can for the small bowel especially late in pregnancy it can be seen individual segments typically should not exceed seven millimeters in diameter or 15 millimeters in length if the small bowel is normal in calibre and often times the normal small bowel will exhibit active peristalsis on the other hand in the setting of small bowel obstruction oftentimes you'll see multiple interconnecting over distended loops of bowel with the number of loops depending on the level of obstruction and you may or may not see polyhydramnios this fetus has a high jejunal atresia we see a dilated stomach and two additional loops one more loop than you would expect to see with duodenal obstruction the fetus on the right has a lower jejunal obstruction and hence we see multiple loops of dilated small bowel in the setting of small bowel obstruction oftentimes you will see very active peristalsis within the obstructed loops as we see here to journal an ileal atresia are thought to be due to a vascular insult and as such like duodenal atresia which is not due to a vascular insult they occur relatively late in pregnancy typically the ultrasound findings are first identified in the third trimester or late in the second trimester but not all the findings are always seen in a series of 15 fetuses with jejunal or illy Lucretius dilated small bowel loops were seen in third eka genic Bal innate and polyhydramnios only in six and in a large stomach only in five of these fetuses four of the fetuses had ileal atresia and polyhydramnios and enlarged stomach were not seen in any of these four fetuses the polyhydramnios and enlargement of the stomach is more common the higher the level of obstruction a dilated tortuous ureter can sometimes look similar to a dilated bowel loop here is a dilated left ureter and noticed that it creates a sort of hairpin loop configuration compare this to this fetus with a small bowel obstruction in which you see a dilated tortuous loop that also has a hairpin like a configuration so tracing the the pathway of the dilated loops is very important in order to distinguish dilated ureter from dilated bowel likewise a multi cystic dysplastic kidney when very large with very large cysts can on the surface simulate the appearance of a dilated loops of bowel here we see multiple cysts but when one looks a little bit further these this will not connect up the way dilated loops of bowel will and also if you really look at the epicenter of these particular cysts they have a tendency to be paraspinal in location and so getting a coronal image of this fetus you can see that the cysts are localized to the area that you would expect an enlarged kidney to be and and importantly the other kidney looks normal and this is important because a fetus with a multi cystic dysplastic kidney has such a greatly increased incidence of having a contralateral renal abnormality with that I'd like to spend a little bit of time talking about academic now when echogenic bow was first described it was actually thought to represent a normal variant that was typically seen between 16 to 22 weeks and resolved by the late second trimester and here is example of echogenic bowel in a normal fetus things were much simpler than the because we didn't recognize at that point in time that echogenic bow can actually be seen in a lot of other situations one of these situations is you if you look at the colon at term the meconium can be very hyper echoic in the normal fetus typically the contents of the colon the meconium in the colon is most commonly less echogenic than the surrounding bowel contents but in this venous you can see that the contents of the colon are more echo genic than the surrounding contents of the abdomen but this was a fetus near-term and likely is because sometimes the meconium became comes more and more desiccated as term approaches and this was a perfectly normal fetus echogenic bowel can also be seen secondary to swallowed blood blood that's been swallowed from the amniotic fluid it should be transitory if it's due to swallowed blood so here we see a fetus with increased echogenicity in the bowel this was on the basis of a placental abruption here you can see the markedly dilated placenta markedly enlarged placenta in combination with the blood from the abruption as well as increased echoes in the amniotic fluid due to blood cells in the amniotic fluid with time though when the fetus was rescanned the echogenic bow had resolved as it is expected to do in a fetus who has echogenic bow on the basis of swallowed blood likewise this is a fetus with echogenic bowel on the basis of a sub chorionic hematoma presumably with blood cells that got into the amniotic fluid and were swallowed here we see the academic bow and here we see the elevated amnio chorionic membrane due to the sub chorionic hematoma however echogenic bowel also has been described in the setting of multiple abnormalities that are intrinsic to the fetus including fetal aneuploidy cystic fibrosis infections most commonly CMV infections are ugr thalassemia bowel obstructions as well as metabolic defects we'll look at some examples of these echogenic bowel is seen in fetus with aneuploidy and in particular trisomy 21 and here is an example of echogenic Val in a fetus who also had a thickened nuchal fold with the nuchal fold measuring 6 millimeters and we don't know exactly why you see echogenic bowel in fetuses with aneuploidies but it has been postulated that it may be due to decreased bowel motility which then allows for increased water resorption and thickened meconium echogenic bowel can also be seen in 50 fetuses with cystic fibrosis as in this case and is thought in this situation to be due to the abnormally thick and viscous meconium which occurs with cystic fibrosis this is a fetus who has echogenic bow and a pericardial effusion and also has a markedly thickened placenta with subtle cystic spaces throughout the placenta and this fetuses has echogenic thou on the basis of CMV infection and finally this fetus has echogenic bowel and was normal in size at the time this initial ultrasound was performed however subsequently developed severe IUGR and preeclampsia and subsequent to that had a very abnormal umbilical artery Doppler with no diastolic flow seen in fact echogenic valve is a known phenomenon to occur in fetuses who subsequently may develop severe IUGR and so if you see bona fide echogenic bowel in a fetus it's very important to follow growth why would a fetus have normal growth size on initial skin and subsequently develop IUGR and have had echogenic now the etiology of this is not fully known but it has been postulated that it may be due to ischemia secondary to redistribution of the blood away from the bowel in the fetus with growth restriction now increased echogenicity the bow though is a very subjective finding although there have been attempts to quantify it really in in the final when you're finally done with it it's subjective and it varies from observer to observer it also varies with different scan planes and different transducer frequencies behind the transducer frequency used to image the more likely you'll see a kinetic valve as well as with the presence of harmonic imaging and other post-processing sequences as well in fact anything that pretty much increases contrast will tend to make the bow look more at genic here is an example of increased engine is knee in the bow that is dependent on transducer frequency at a frequency of five megahertz as you can see the ballasts quite academic appearing decrease the transducer frequency the imaging frequency to 3.5 megahertz and the bow looks perfectly normal this is important if you're doing into vaginal ultrasound and think you're seeing echogenic bowel because you're using a relatively high frequency imaging to do and a vaginal ultrasound and so if you're attempted to call echogenic bowel at anna vaginal ultrasound you should always look at trans at domina ultrasound should not call echogenic bowel just based on an end of a general ultrasound scan because it's very common for the bowel to look echo genic attend a vaginal ultrasound so because the the observation of bona fide echogenic bowel brings up the scenario of so many possible serious abnormalities with the fetus or the pregnancy we recommend that you only call echogenic bowel if you can see it in different scan planes with different transducer frequencies are at least only with lower transducer frequencies we always take out take off harmonics to be sure the bowel still looks echogenic when harmonics is off and the bowel echogenicity should be at least similar in acquisition to the bones in order to call echogenic bowel now in some fetuses with small bowel obstructions one of the sequela is perforation of the bowel and if the bowel perforates this can lead to meconium peritonitis meconium peritonitis is a sterile chemical peritonitis that occurs or can occur with intrauterine bout perforations of any costs the most characteristic finding of meconium peritonitis is to see calcifications in the peritoneal distribution and these calcifications are due to a peritoneal inflammatory response this response can cause formation of a fibrotic tissue that's prone to calcify and as a result one can get highly echogenic punctate curvilinear or funk or clumped voci that may or may not have shadowing so here are some examples of the calcifications that one can see in the fetal abdomen in the setting of meconium peritonitis here are some very coarse calcifications with posterior shadowing in this fetus though there are multiple calcifications but no posterior shadowing this fetus has scant calcifications no shadowing and this fetus has a very large clumped calcification very coarse very large with shadowing finally this fetus has a figure 8 configuration calcification at the calcifications wrap around the outside of two adjacent abutting loops of bowel calcifications can be seen in another number of other entities in addition to meconium peritonitis for example they can be seen in fetuses with a teratoma or other neoplasm that calcifies in which case they will tend to be pretty localized they can also be seen in anal atresia in which cases the calcifications are not peritoneal and distribution but rather will be intra luminal within the lumen of the colon so here is an example of a fetus with anal atresia and a rectal urinary fistula in which we can see calcifications that are localized to within the loops of colon and it's thought that the calcifications in fetuses with anal atresia are most likely to occur in those with erecto urinary fistula and are likely on the basis of mixing of the meconium with urine now here is a fetus in which there was a big clump of calcifications but also numerous calcifications that seemingly were located all throughout the abdomen and as a result the possibility of meconium peritonitis was considered however later in pregnancy mild ventricular megali developed you can see the atrium of the lateral ventricle is eleven point five millimeters above the 10 millimeter cutoff there were calcifications within the fetal head on postnatal CT scan and postnatal ultrasound showed that the calcifications were actually located within the liver parenchymal EC here as well as within the spleen rather than being in a peritoneal distribution and this fetus proved to have CMV infection so there are though a few clues that can help you distinguish calcifications that are peritoneal and distribution from those that are located within the liver and spleen and one of the clues is to see the calcifications lined up all around the periphery of the liver just outside the liver capsule but not within the parenchymal of the liver as we see here another common pattern for calcifications that are peritoneal and due to meconium peritonitis is to see a curvy linear configuration of the calcifications along the undersurface of the diaphragm this is a fetus who has both the periphery of the liver distribution as well as the diaphragm distribution and this can be best seen in this fetus because of ascites that helps to outline the outline of the liver so here are some calcifications at the periphery of the liver we don't see any calcifications in the liver parenchyma but we do also see calcifications in a curvilinear pattern along the undersurface of the diaphragm if the question of meconium peritonitis is raised in a male fetus always look at the scrotum because the processus vaginalis is paitent during part of fetal development meconium can traverse the processus vaginalis from the abdomen into the scrotum and then the meconium can calcify just like it does in the abdomen here are two fetuses with scrotal calcifications on the basis of meconium peritonitis in this fetus we see a large calcification here as well as a number of smaller calcifications and the fetus on the right has a large calcification here and also has a hydrocele surrounding a portion of the testicle in addition to calcifications additional findings can be seen in meconium peritonitis among them are dilated loops of bowel due to the underlying bowel obstruction ascites polyhydramnios and the meconium pseudocyst the meconium pseudocyst is a phenomenon that a phenomenon that occurs when instead of about perforation healing it stays opening and as a result there can be continued spillage of meconium from within the bow into the abdominal cavity and sometimes fibrous tissue and bow loops can be matted around the perforation site and the the meconium just keeps spilling into that area and assistant cavity filled with meconium just keeps growing and growing and growing and these can become quite large and can take up the majority of the fetal abdomen and actually result in expansion of the fetal abdomen and here we see an example of a very large meconium pseudocyst given the way these form not surprisingly they often will have septation x' within them as well as fluid fluid levels where the meconium is layering out now if one has a fetus with meconium peritonitis and fetal castle and calcifications within the abdomen if you look at the additional findings the number of additional findings that you see in addition to the calcifications can active actually be somewhat predictive of the ultimate prognosis in fact the number of additional findings seen one two or three of the dilated bowel the ascites and the meconium pseudo cysts are strongly correlated with the likelihood that the fetus will need surgery in a recent study when there were no additional findings and only calcifications were seen zero out of 18 needed surgery at one finding and 52% of the fetuses needed surgery two of these findings eighty percent and if all three findings were present all of the fetuses needed postnatal surgery with that will close by moving on and talking about the large bowel the colon and the rectus sigmoid the colon has a large range of diameters in utero like the stomach the colon normally increases in size with advancing gestational age and it can measure quite large 18 millimeters or more in the term fetus it is said that the colon is located around the periphery of the fetal abdomen whereas small bowel loops are located in side the fetal abdomen more in the central portion but in fact the colon has redundancies in turn and turns in the fetus just like it does in the adult and so sometimes one of these loops of colon can traverse right through the middle of the fetal abdomen here are some examples the colon will look like a hypoechoic tubular structure within the abdomen and most fetuses here we see colon in this fetus and notice it just goes right through the center of the abdomen and here's a loop of colon in another normal fetus large bowel obstructions are much more difficult to detect at ultrasound than small bowel obstructions and this is partly because of the wide range of appearance of the normal colon and also because there's no ballot valve dilatation and many fetuses with large bowel obstructions like anal rectal malformations in fact ultrasound is really bad at diagnosing anorectal malformations very insensitive there have been multiple studies that have looked at the frequency of identification of anorectal malformations at antenatal ultrasound and all of them show very poor results antenatal detection rates of 0 to 33 percent in all of the studies in fact even in the recent most largest of these studies there of 69 cases of anorectal malformations only 16 percent were detected with antenatal ultrasound that being said though in some cases you can detect anal rectal malformations at ultrasound and when you can detect them the diagnosis is usually based either on identifying interlocked colonic calcifications in prominent loops of colon as we see here or the ultrasound finding of a dilated loop of bowel in the pelvis and lower abdomen especially when that's you or v-shaped as we see here in this fetus with an anal rectal malformation as part of a complex cloaca l– abnormality and sometimes although some fetuses with anal rectal malformations have no bowel dilatation sometimes the dilatation of the bowel can be striking as we see in this fetus with markedly dilated bowel a large amount of material within the loops of dilated bowel and multiple calcifications within that material in a rectal malformations are seen in conjunction with multiple different abnormalities multiple anomaly syndromes among two of the frequent and well-known associations is the OE is abnormality that stands for omphalocele exstrophy of the bladder imperforate anus and spine defects and another common association that is well known is the factor o abnormalities standing for vertebral abnormalities anal atresia cardiac Edna abnormalities te fistula with esophageal atresia renal abnormalities and limb abnormalities the fetus shown here is bacterial abnormality with dilated loop of colon due to anorectal malformation with calcifications within the colon as well as non visualization of the stomach in its expected location in the left upper quadrant due to esophageal atresia with the trachea esophageal fistula and the fetus also had additional abnormalities as well I will finish by pointing out that the rectal sigmoid in the fetus can be seen and conforms to the expected configuration of the rectal sigmoid you might see in an adult patient that is it comes out of the pelvis and goes kind of in a s-shaped loop towards the left side of the pelvis as we see here and this is important to realize that you can see the rectus sigmoid in normal fetuses because there is a pitfall that has been described whereby in axial scan planes you can see the rectum and potentially mistake it for a priest sacral miss if you don't recognize it as rectum so in this fetus we have an axial scan through the pelvis and instead of just seeing one fluid filled collection in the pelvis that being due to the distended urinary bladder we see a second collection that was thrown on the outside to represent some type of a pre sacral mass when this happens and one should scan through both collections you can confirm that the anterior one is flattered by seeing an empty or or fill or by seeing the umbilical arteries hugging the periphery of the bladder and then scan through the posterior one in a different scan plane get a longitudinal image of it and you can confirm its recto sigmoid by seeing its typical configuration rising out of the pelvis so this concludes our discussion today and I thank you for your attention

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