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USMLE® Step 1 questions

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A 5-year-old girl is brought to the pediatrician for evaluation of abdominal pain and bloody stools. The symptoms began three-weeks ago. The abdominal pain is intermittent and usually self-resolves within an hour. Past medical history is noncontributory. She has been meeting all developmental milestones. Physical examination reveals a nontender and nondistended abdomen with normal bowel sounds. Laboratory testing reveals the following:
 Laboratory value  Result 
 Hemoglobin  15.2 g/dL 
 Platelet count  260,000/mm3 
 Prothrombin time  14 seconds 
 Partial thromboplastin time  32 seconds 
A radiolabeled technetium-99 scan is performed and reveals increased uptake in a structure located in the right lower abdominal quadrant. The walls of this structure will most likely consist of which of the following? 

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Abdominal pain

intussusception p. 394

Henoch-Schönlein purpura p. 322

intussusception p. 394

Intussusception p. 394

Meckel diverticulum as cause p. 393

Pediatric patients

intussusception in p. 394


Intussusception is a condition that occurs when a part of the intestine folds into another section of intestines, resulting in obstruction.

This is commonly referred to as telescoping, because it’s similar to how one part of a collapsible telescope retracts into another part.

Intussusception is the most common cause of intestinal obstruction in infants and young children, with about two-thirds of them happening among infants under one year of age, though adults can occasionally have intussusception too.

Now, intussusception usually happens in the ileocecal region of the intestines, which is where the ileum of the small intestine and cecum of the large intestine meet, and almost all intussusceptions happen when the ileum folds, or telescopes, into the cecum.

In adults, telescoping is usually caused by an abnormal growth in the intestine, like a polyp or a tumor, which serves as a lead point or leading edge.

What happens is that the normal wave-like contractions of the intestine, called peristalsis, grab this leading edge and pull it into the part of the bowel ahead of it.

In babies the leading edge is most often caused by lymphoid hyperplasia, or the enlargement of lymphoid tissue.

There are a ton of tiny lymph nodes sprinkled throughout the intestines called Peyer’s patches, and they’re particularly common in the ileum.

When a child gets some sort of viral infection in the gastrointestinal tract, usually caused by rotavirus or norovirus, the Peyer’s patches enlarge to help fight off the infection, and sometimes become a lead point that drags the ileum into the cecum, causing intussusception.

Intussusception can also be caused by a Meckel’s diverticulum, which is an abnormal outpouching of gastrointestinal tissue, that sticks out of the ileum and into the peritoneal cavity.


  1. "Robbins Basic Pathology" Elsevier (2017)
  2. "Harrison's Principles of Internal Medicine, Twentieth Edition (Vol.1 & Vol.2)" McGraw-Hill Education / Medical (2018)
  3. "Pathophysiology of Disease: An Introduction to Clinical Medicine 8E" McGraw-Hill Education / Medical (2018)
  4. "CURRENT Medical Diagnosis and Treatment 2020" McGraw-Hill Education / Medical (2019)
  5. "Intestinal Intussusception" Clinics in Colon and Rectal Surgery (2008)
  6. "Intestinal Intussusception: Etiology, Diagnosis, and Treatment" Clinics in Colon and Rectal Surgery (2016)
  7. "Ultrasonographic findings of small bowel intussusception, focusing on differentiation from ileocolic intussusception" The British Journal of Radiology (2007)

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