CONGENITAL GI
Baby belly
Pyloric Stenosis - congenital hypertrophy of the pyloric smooth muscle, narrowing the stomach’s exit route. Common in males. You can palpate the hypertrophic muscle (feels like an olive-shaped mass). THEY’RE NORMAL AT BIRTH. It takes ~2 weeks time to hypertrophy. When food can’t exit the stomach, peristalsis ramps up (visible abdominal waves to the naked eye), the pressure rises and chyme explodes back up the esophagus (projectile nonbilious vomiting). Treat by cutting out the smooth muscle (pyloromyotomy). Associated with macrolide exposure in utero.
Gastroschisis - Congenital malformation of abdominal wall, exposing the belly’s contents. The abdominal wall is formed when a bunch of folds come together (anterior, posterior and lateral folds), and gastroschisis occurs when the folding goes awry. The bowel is totally exposed (no peritoneal covering), emerging just lateral to the umbilicus. Patients have an elevated alpha fetoprotein (AFP) level. These happen sporadically.
Omphalocele - persistent herniation of bowel into the umbilical cord. This herniation occurs during everyone’s development, since the fetal belly is so small. But it disappears once the bowel undergoes a 90˚ counterclockwise rotation, which pulls the bowel back inside. The hernia is covered by a bubble of peritoneum. Let the O in Omphalocele remind you of the bubble. It’s associated with Edward syndrome, Patau syndrome and Beckwith-Wiedemann syndrome.
Congenital Umbilical Hernia - a baby born with an umbilical hernia. Just like an adult hernia, it’s covered by normal skin and when they bear down the bulge enlarges. It’s associated with Down syndrome and hypothyroidism.
Duodenal Atresia - congenital failure of duodenal canalization (dead end loop of bowel). Associated with Down’s syndrome. The stomach and duodenum balloon up, but remain separated by the pyloric sphincter. This results in the classic “double-bubble” x-ray finding. Since the duodenum is still connected to the stomach, their vomit can contain bile (differentiating it from pyloric stenosis). Polyhydramnios is a problem, since they cannot digest the amniotic fluid.
Jejunal Atresia - congenital blood flow problem with the SMA that leads to a patchy loss of bowel segments. Sometimes the ileum withers away in a unique spiral pattern that’s described as an “apple peel” sign. Look for the “triple-bubble” x-ray finding (stomach, duodenum, jejunum) and a colon without gas.
Meckel Diverticulum - a true diverticulum of the bowel (all 3 layers). Early on in fetal development, the midgut is fed nutrients from the yolk sac -- via a tube called the vitelline duct (it’s VITAL for the midgut during early development). The Vitelline duct appears around week 4, and closes (involutes) around week 7. Persistence of the Vitelline Duct results in a Meckel’s diverticulum. Periumbilical palpation reveals a soft but firm mass (often full of poop). Most cases are asymptomatic. In cases with a completely open duct, babies can pass their meconium out of their belly button. Know the Rules of 2’s. Occurs in 2% of the population, it’s 2 inches long, it occurs within 2 feet of the end of the ileum, and presents during the first 2 years of life (bleeding, intussusception, volvulus or obstruction). Bleeding occurs because the mucosa is heterogeneous, and includes some gastric acid-producing cells. The most common presentation is painless bright red rectal bleeding. It can serve as the trigger point for intussusception.
The 99m-Technetium-pertechnetate scan highlights parietal cells (after enough time, you can see some collection within the bladder too)
MALABSORPTION
Let’s take a step back for a moment. I want you to consider the jobs of the different intestinal organs. The stomach breaks food down. The small intestine absorbs nutrients. The large intestine adjusts fluid and electrolytes. So when considering a case of malabsorption, the problem usually originates in the small intestine.
Fat Malabsorption is pretty complicated. There’s a lot of moving parts involved. You have bile, pancreatic juice, enterocytes and the absorptive lacteals. Therefore, fat malabsorption is either due to a lack of bile (cholestasis or liver disease), a lack of pancreatic juice (pancreatic insufficiency), broken enterocytes (Abetalipoproteinemia) or clogged lacteals (Whipple disease). The most common cause is probably pancreatic insufficiency. Note that if you can’t produce bile, your stools will be pale or clay colored. And if you can’t absorb fat, you can’t absorb fat-soluble vitamins (ADEK). When fat doesn’t get absorbed, it plows through the gut and produces massive, stinky, greasy, floating poops (steatorrhea).
Vitamin A - night blindness, dry eyes, dry skin, Bitot eye spots
Vitamin D - bone loss (osteomalacia, rickets), hypocalcemia
Vitamin E - hemolytic anemia (acanthocytosis), weakness, dorsal column & spinocerebellar demyelination
Vitamin K - bleeding (elevated PT and PTT, normal platelets and bleeding time)
Carb Malabsorption is pretty simple. Lactose is a disaccharide, broken down into a monosaccharide by lactase to be absorbed. You can test carb absorption with D-xylose, a monosaccharide. Patients ingest it and then you test their blood for it. If serum D-xylose is high, they can absorb just fine. THeir complaint is likely due to an enzyme deficiency like Lactose Intolerance. If serum D-xylose is low, suspect villi damage like with Celiac disease.
Protein Malabsorption - is not something you’re expected to know about as a medical student. The only example I know of is Menetrier’s disease, which causes the hypertrophic gastric mucosa to spill proteins. It results in peripheral edema from hypoalbuminemia. Oh, and one other example is protein deficiency in children in the developing world, which causes their abdomen to bulge out as if they were pregnant.
MALABSORPTION DISEASES
Lactose Intolerance is the inability to digest dairy products due to the decreased function of the Lactase enzyme found in the brush border of enterocytes. Lactose is a disaccharide, so it can’t be absorbed as is. Upon drinking milk, patients experience abdominal distension and watery osmotic diarrhea. This is very common, especially in people of color. Some people are born with LI, but most people gradually acquire it as they grow into adulthood. They have normal small intestine biopsies. Sometimes viral gastroenteritis can stun the lactase brush border enzymes, leading to a temporary acquired lactose intolerance.
Celiac Disease is an autoimmune overreaction to certain wheat proteins. Bread contains a molecule called Gluten. Gluten is broken down by your tissue transglutaminase (tTG) enzymes into a nasty molecule called Gliadin. When Gliadin hits the duodenum, white blood cells pick up the Gliadin, and load it onto MHC-2, thinking that it’s a dangerous molecule. They present it to Helper T cells, some of which unfortunately possess a complimentary anti-Gliadin shape. This kickstarts inflammation (type 4 hypersensitivity reaction), which causes abdominal pain. Inflammation eventually destroys the SI villi, resulting in malabsorption. The autoimmune flare up leads to an overproduction of IgA. These IgA antibodies are useful for diagnosing Celiac, specifically the anti-endomysium / tTG / Gliadin antibodies. The less-helpful IgG antibodies should still be tested for because many people have an IgA deficiency. Some of the excess IgA settles into the tips of dermal papillae, which kickstarts a new type 3 hypersensitivity reaction resulting in a vesicular rash on the elbows and knees (Dermatitis Herpetiformis). Celiac Disease causes chronic diarrhea, bloating, steatorrhea and failure to thrive. We believe that helper T cells possess anti-gliadin receptor shapes due to the HLA-DQ2 & 8 genetic trait (eating the cone at a Dairy Queen). CD causes characteristic histological flattening of the villi, hyperplasia of the crypts and intraepithelial lymphocytes. The damage is mostly in the duodenum, since that’s what Gluten reaches first. CD can be controlled with a Gluten-free diet. If their symptoms flare up despite a good diet, you should suspect a carcinoma or T-cell Lymphoma (EATL or Enteropathy Associated T-Lymphoma), although small intestinal cancers are exceedingly rare. Look out for Iron deficiency.
Tropical Sprue is a rare and mysterious disease of the small intestinal villi, which we think is caused by an as of yet unidentified organism. It’s very similar to CD, except (a) it occurs in the tropics, (b) it arises after infectious gastroenteritis, (c) it gets better with antibiotics (Doxycycline) and (d) damage is more prominent in the Ileum and Jejunum. These patients suffer from generalized malabsorption (steatorrhea).
Whipple Disease is an infection that results in thick bulging villi. It begins when the patient gets a Tropheryma whippelii infection, which I guess is asymptomatic on its own, but creates a headache for the macrophages that have to eat them up. Foamy macrophages (with lysosomes full of PAS-positive T. whippelii bacteria) crowd into the the core of the villi (lamina propria) and clog up the lacteal ducts, resulting in fat malabsorption. (Whips are long and slender, which reminds me of the villi, and helps me remember that this is the thick villi disease). The macrophages also settle into joints (arthritis), heart valves, lymph nodes (lymphadenopathy) and CNS.
HERNIAS
A hernia refers to abdominal contents (guts) that protrude outside of the abdomen.
Inguinal hernias protrude into the groin or testicle. They are common in males. There are two varieties: indirect and direct. Both of them cause the same symptoms, but they have a different underlying cause. Namely, the pathway that they traverse into the groin is different. While the indirect hernia slips through the entire inguinal canal, the direct hernia bursts into the middle of the canal.
Femoral hernias protrude into the top of the thigh. They slip underneath the femoral ligament. These are more common in women. Femoral hernias are more likely to develop complications.
Most hernias will pop back into the abdomen if you press on them (this is called "reducing" a hernia). The scary thing about hernias is that they can occaisionally get trapped outside of the abdomen! When a hernia cannot be reduced, we call it incarceration. Sometimes, an incarcerated hernia will lose it's blood supply due to physical compression, and the tissue will become ischemic and die. This is called strangulation. It's a surgical emergency!
