USMLE® Step 1 style questions USMLE
A 39-year-old primigravid woman comes to the emergency room in active labor at 34 weeks' gestation. Her prenatal course was notable for elevated β-HCG concentrations noted on triple screen and increased nuchal translucency seen at the 12-week ultrasound. She gives birth to a boy weighing 1870-g. Within two hours, he begins to have bilious vomiting. Temperature is 36.3°C (97.4°F), pulse is 120/min, and respirations are 30/min. Physical examination shows mild abdominal distension. An abdominal X-ray is obtained and is shown below. Which of the following is the most likely diagnosis?
Content Reviewers:Rishi Desai, MD, MPH
Contributors:Tanner Marshall, MS
With intestinal atresia, atresia refers to a passageway that’s closed or gone completely, so intestinal atresia is when a malformation during fetal development results an absent portion of the small or large intestine.
If instead the passageway was just narrowed, then it’s referred to as intestinal stenosis—oftentimes these are both just lumped together as intestinal atresia and stenosis.
The specific type of intestinal atresia is named depending on what section of the intestines is affected.
The underlying cause of duodenal atresia isn’t known, although it’s commonly associated with trisomy 21, also known as Down syndrome, suggesting that it’s likely due to genetic defects affecting normal development.
Although it isn’t known why intestinal atresia develops isn’t known, it is fairly well known how it develops.
Normally, early on in development, the gut’s a hollow tube.
But by around 6 weeks gestation, the epithelium of the duodenum proliferates and it ends up plugging up the lumen making it a completely solid stick of tissue.
After that, the cells in the middle undergo apoptosis, or programmed cell death, and by 9 weeks gestation, the tube’s hollow again, called recanalization.
This entire process is called vacuolation.
In duodenal atresia, this vacuolation process fails, and the duodenum doesn’t recanalize properly, resulting in atresia or stenosis of the duodenum.
Non-duodenal intestinal atresias or stenoses, like those affecting the jejunum or ileum, or even affected the large intestine like the colon, are generally not a result of recanalization, and instead are more likely to result from ischemic injury, meaning lack of bloodflow, to the developing gut.
Now, the jejunum, ileum, and large intestine rely on blood supply from the superior mesenteric artery, while only part of the duodenum does.