Congenital gastrointestinal disorders: Pathology review

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Case Study0:00–0:42

A newborn infant boy named Ahmad gets transferred to the neonatal intensive care unit due to an opening in the abdominal wall.
On examination, there's a sac protruding from the center of the abdomen, with visible bowel loops. Next, a five-week boy named Nathaniel is brought to the clinic with bouts of projectile vomiting after every meal.
On examination, an olive-shaped mass is palpated in the right upper abdominal quadrant. The baby also has sunken eyes and frontal fontanelle, and poor skin tur.
Both children have congenital gastrointestinal disorders. Normally during the 4th week of fetal development, the embryo starts to change from a flat 3-layered disc to something more shaped like a cylinder, a process called embryonic folding.

Gastroschisis0:42–1:48

In the horizontal plane, the two lateral folds eventually come together and close off at the midline, except for at the umbilicus, where the umbilical cord connects the fetus to the placenta.
This folding allows for the formation of the gut within the abdominal cavity. If those lateral folds don't close all the way, an opening is left in the abdominal wall, and that's called gastroschisis, where gastro refers to the gastrointestinal tract, and schisis refers to separation.
For your exams, a good hint is that this opening is almost always to the right of the umbilicus, although it's not really known why.
This defect allows the small bowel and sometimes large bowel loops to protrude out where they are freely exposed to the outside environment.
The result is that these organs become irritated and inflamed. There's a related condition called an halocele, where halo refers to the umbilicus and seal refers to hernia or swelling.

Omphalocele1:48–2:44

Normally, during around the 6th week of development, the liver and the intestines grow really quickly. And because the abdominal cavity is still pretty small, there's limited space, which causes them to herniate through the umbilical ring into the umbilical cord.
At about week 10 though, the abdominal cavity typically has grown enough to allow them to come back from the umbilical cord.
With ymphalocele, abdominal organs fail to return back to the abdominal cavity, and therefore, stay in the umbilical cord all the way through fetal development and even after birth.
Eymphalocele is associated with chromosomal anoploidy syndromes like trisomy 13, also known as Ptau syndrome, and trisomy 21, also known as Down syndrome.

Gastrosch. vs. Omphalo.2:44–4:14

So, both gastroschisis and lymphalocele are abdominal wall defects and involve the abdominal contents herniating out of the abdominal cavity.
They can both be suspected prenatally when alpha fetoprotein or AFP is elevated in the mother's blood. AFP is only produced by the fetus.
It enters the maternal circulation and its levels increase with gestational age or number of fetuses. Remember though, the most common causes of elevated maternal serum AFP levels are dating errors or underestimation of gestational age and multiple gestation.
But still, it can also be due to neural tube defects and abdominal wall defects. These defects can be seen with a prenatal ultrasound.
Ultimately, your test's question will typically center around a newly born infant whose mother received no prenatal care, and will let you choose between gastroschisis and phallocele.
So, you need to know the two key differences. First, in gastroschisis, the abdominal organs protrude through a separate hole on the right side of the umbilicus, while in phallocele, they protrude through the umbilicus itself.
And second, in gastroschisis, the abdominal contents are directly seen, as they are not covered by any peritoneal layer.
Whereas in mphalocele, they are clearly contained in a bubble or peritoneal sac. Now, let's talk about some other types of congenital herniations.

Congen. Diaphrag. Hernia4:14–4:51

First, there's congenital diaphragmatic hernia, where a malformation of the diaphragm leaves a hole that allows the stomach and sometimes the intestines to herniate upwards into the thoracic cavity.
These abdominal organs push against the developing lung, causing pulmonary hypoplasia. They can also push on blood vessels supplying the lungs, causing pulmonary hypertension.
Now, an interesting fact is that the herniation is usually towards the left side, so the left lung is more often affected.
After birth, the infant can develop respiratory problems like tachypnea, breathing difficulties, respiratory failure, and cyanosis.

Congen. Umbilical Hernia4:51–5:30

Next, we have congenital umbilical hernia, which is when the intestines herniate through a weakened umbilical fibromuscular ring.
So the intestines herniate through the umbilicus instead of to the right of it, like in gastroschisis. Another clue is that unlike gastroschisis, the intestines are fully covered by skin.
So, it looks like a protruding bulge from the belly button. Normally, umbilical hernias are self-limiting and disappear within the 1st 2 to 5 years of life.
However, a large hernia can cause bowel strangulation, resulting in ischemia and necrosis. Finally, we have indirect inguinal hernia.

Indirect Inguinal Hernia5:30–7:10

This happens when the deep inguinal ring in the pelvis fails to close and part of the intestine herniates into the inguinal canal.
A high-yield concept here is how to differentiate this condition from direct inguinal hernias, where the intestines herniate directly through a weakened section of the posterior wall of the inguinal canal, often due to weakened muscles or increased intraabdominal pressure.
So first, indirect inguinal hernia can be congenital or acquired, but direct inguinal hernia is only acquired. Next, indirect hernia presents as a bulge lateral to the lower epigastric vessels while direct is medial.
Third, with an indirect herniation, the intestine goes from the deep inguinal ring to the superficial inguinal ring, while a direct herniation only goes through the superficial inguinal ring.
Finally, with indirect herniation, the intestines are covered by three layers the external spermatic fascia, the cremaster muscle, and the internal spermatic fascia.
While in direct herniation, the intestines are only covered with external spermatic fascia. For symptoms, both types cause groin pain, especially when there's increased abdominal pressure, like when you're lifting heavy objects, laughing, or coughing.
In males, the intestine can protrude into the scrotum, causing pain and a sensation of fullness in the testicles. If the bowels become strangulated, there will be a sudden severe pain, along with nausea, vomiting, and sometimes fever.

Esophageal Atresia7:10–8:03

So since we've talked about finding the GI viscera where they don't belong, let's change gears and talk about atresia, or the absence of parts of the GI tract.
So first, there's esophageal atresia, where the esophagus doesn't develop properly and ends in a blind pouch. This is often associated with a defect in the tracheoesophageal septum.
So a problem that often accompanies this condition is tracheoesophageal fistula, where an abnormal connection forms between the esophagus and the trachea.
Since these babies have difficulty swallowing anything, they can present with excessive drooling. When feeding, they'll gag and throw up the food.
The fistula to the trachea also causes problems when feeding, like coughing, choking, and even cyanosis. An important complication is food aspiration, which can lead to pneumonia.

Intestinal Atresia8:03–10:23

Next, we have intestinal atresia. And the two common types are duodenal and jujunoileal atresia.
But it could also happen in the colon or anus. Remember that duodenal atresia is linked with Down syndrome, while Jujuno ileal atresia is linked with cystic fibrosis.
Smoking and premature birth are risk factors for both. Duodenal atresia is caused by a failure to re-canalize.
The primitive gut tube undergoes a solid stage where the proliferating cells fill it up, so it's more like a solid rod. Then it undergoes recanalization where the lumen reforms.
When it fails in the region that gives rise to the Duodenum, we get atresia. Since this region also gives rise to the pancreas and hepatobiliary system, problems like biliary atresia and annular pancreas often accompanies duodenal atresia.
Jujuno ileal atresia, on the other hand, is often due to ischemia, leading to necrosis and reabsorption of sections of the gut tube during development.
Ischemia can be due to malrotation, insusception, or anything else that cuts off the blood supply. Both types of intestinal atresia result in a blind pouch and intestinal obstruction.
There will be dilation proximal to the obstruction, causing abdominal distention, while no air can be found distal to the obstruction.
In duodenal atresia, a high yield sign on radiography is the double bubble sign, where both the duodenum and the nearby stomach become filled with air.
In Jejunal atresia, there's the triple bubble sign, where the jejunum is also dilated. Since the atresia prevents the baby from swallowing anything like amniotic fluid, there will be polyhydramnios before birth, and vomiting and difficulty feeding after birth.
If the obstruction is before the major duodenal papilla, which is where bile and pancreatic juices are emptied into the duodenum, the infant will have non-bilious vomiting.
If the obstruction is distal to the major duodenal papilla, they'll have bilious vomiting. This often occurs just hours after birth.

Hirschsprung Disease10:23–12:05

Finally, failure to pass meconium or the first stool is another sign of intestinal atresia. Let's move on to another congenital condition called Hirsprung disease, also known as congenital a ganglionic megacolon.
A high-yield fact to be aware of is that Hirsprung disease is commonly associated with Down syndrome and with a loss of function mutation in the RET gene.
This disorder occurs when the neural crest cells from the neural tube fail to migrate into the intestinal walls. This failure to migrate happens in the caudal part of the neural tube, and the cells here would normally go to the rectum and distal parts of the colon.
These neural crest cells normally develop into the ganglia, or clusters of nerves of the myenteric or Auerbach's plexus and the submucosal or Meisner's plexus that normally coordinate smooth muscle contraction and relaxation.
Now, babies born with Hirsprung typically fail to pass the meconium, their first stool, a process that normally happens within the 1st 2 days after birth.
The rectum is always affected, and the distal sigmoid colon is frequently affected as well. So feces builds up before the section without ganglion.
This results in serious constipation, distention, and toxic megacolon, which is a risk for rupture. Digital rectal exam will reveal a tight anal sphincter, and it will cause the explosive release of feces.
Diagnosis is made with a rectal suction biopsy of the mucosa and submucosa, which reveals the lack of ganglion cells. Treatment is surgical resection of the a ganglionic section of the intestine.

Pyloric Stenosis12:05–14:23

Next, we have hypertrophic pyloric stenosis, where a baby's pyloric smooth muscle hypertrophies or grows in size, leading to the narrowing of the pyloric sphincter.
For unknown reasons, hypertrophic pyloric stenosis is more common in first-born males. An important risk factor is maternal use of macrolide antibiotics during pregnancy.
A high yield fact is that these babies are usually normal at birth, meaning that stenosis takes time to develop. So symptoms usually present around 2 to 6 weeks of life.
Since food can't pass through the pylorus, it quickly starts to build up to the point where it's expelled through vomiting.
Over time, this gets more intense until it ultimately becomes projectile vomiting. So named because the vomit literally launches out of a child's mouth.
The vomit is also non-bilious, which makes sense since bile is secreted into the duodenum, which happens distal to the pyloric sphincter.
For your exams, it's important to know that this vomiting also leads to hypochloremic, hypokalemic metabolic alkalosis. Loss of stomach juices leads to dehydration, as well as loss of hydrochloric acid, which leads to hypochloremia or low chloride in the blood.
Also, due to having a lowered blood volume from dehydration, the kidneys retain salt and excrete potassium, which results in hypokalemia.
Hypokalemia results in the movement of potassium out of cells and hydrogen ions into cells, as well as secretion of hydrogen ions and reabsorption of bicarbonate ions in the kidneys.
These effects all tend to increase the blood's pH, resulting in metabolic alkalosis. It's also a good idea to remember that on inspection of the abdomen, peristalsis, or intense movement of the stomach against this tight block, is often visible.
And on palpation, the thick and muscular pylorus can also be felt as a tiny olive-shaped mass in the right upper quadrant of the abdomen.

Meckel’s Diverticulum14:23–16:18

At that point, an ultrasound can be used to confirm the disease. Treatment is a pyloromyotomy, where the muscle of the pylorus is surgically cut.
Finally, there's Meckel's diverticulum, which is the most common congenital disorder of the gastrointestinal tract. Normally, after the formation of the umbilical cord, the vitalon or phalomesenteric duct starts to shrink and eventually goes away.
In some cases, the vitalon duct won't regress all the way and will leave behind a tiny remnant that's called a Meckel's diverticulum.
For your exams, know that this is a true diverticulum, meaning that there's outpouching of all three layers of the small bowel wall.
That's in contrast with most diverticula, which are false. In other words, there's outpouching of just the mucosa and submucosa through defects of the muscular layers.
Meckel's diverticulum typically follows the rule of twos, which can help you remember some of the most commonly tested features.
It affects 2% of the population. It's twice as common in males compared to females.
It's 2 inches long, and it's found within 2 ft of the ileocecal valve in the small intestine and may contain two types of ectopic tissue, gastric mucosa, which secretes acid in the intestine, causing it to bleed, and pancreatic tissue, which secretes alkaline pancreatic juices that erode the wall of the intestine.
Most cases are asymptomatic, but if it does present, it's usually by the age of 2. Now, the way it can present involves gastrointestinal bleeding, bowel obstruction, or it can serve as a lead point for volvulus, which is the twisting of the bowel along its mesentery or into susception, where part of the intestine folds into the section next to it, like a telescope.

Review16:18–17:37

A key test for this disorder is the C-technotate scan, also called Mechel scan, which can detect heterotopic gastric mucosa in the intestines.
All right, as a quick recap, congenital gastrointestinal disorders include abdominal wall defects like gastroschisis and omphalocele, which can be detected prenatally or right at birth.
Herniations occur when the intestines move out of the abdominal cavity, like in diaphragmatic, umbilical, and indirect inguinal hernias.
Atresia occurs when a part of the GI tract is absent or ends in a blind pouch. This can be seen in esophageal atresia, which often coexists with tracheoesophageal fistula, and intestinal atresia, like duodenal or ileojujunal atresia.
Next, there's Hirsprung disease, which is when neural crest cells fail to migrate to the rectum and colon, leading to a ganglionic sections of the GI tract.
It manifests as a failure to pass meconium in an infant or severe constipation later on. Hypertrophic pyloric stenosis is due to pyloric smooth muscle hypertrophy and usually presents with projectile vomiting in the first two months of life.

Summary17:37–18:25

Meckel's diverticulum occurs when there's a failure of the vitalin duct to regress completely, leading to a small, true diverticula.
It's asymptomatic in most cases, but can present with bleeding, volvulus, or in susception. OK, but let's not forget about our cases.
Ahmad, the newborn infant, has a sack of abdominal organs protruding inside the umbilical cord, which suggests an omphalocele.
And Nathaniel, the 5 week old boy, has hypertrophic pyloric stenosis, causing projectile vomiting and that olive-shaped mass in his right upper quadrant.
It was confirmed with an abdominal ultrasound.