Bowel obstruction: Clinical

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Bowel obstruction: Clinical

USMLE® Step 2 questions

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USMLE® Step 2 style questions USMLE

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A 50-year-old woman comes to the emergency department because of colicky abdominal pain for the past hour. She has a medical history of endometriosis and she has had an appendectomy and multiple cesarean sections. Physical examination shows a distended abdomen that is tympanitic to percussion. An abdominal radiograph shows dilated loops of bowel with air-fluid levels. Which of the following is the most likely underlying condition in this patient?     


Bowel obstruction is when the normal flow of contents moving through the intestines is interrupted.

Bowel obstruction can be defined as partial or complete.

Partial obstruction is when gas or liquid stool can pass through the point of narrowing, while complete obstruction is when no substance can pass - and this is defined as obstipation.

The causes of bowel obstruction can be either functional or mechanical causes.

Functional, or adynamic causes disrupt peristalsis, which are the waves that move through the smooth muscles of the bowel walls.

Mechanical causes are actual blockages in the large or small intestines of the bowel, and these mechanical causes are the ones that are usually treated surgically.

Among mechanical causes, one cause of small bowel obstruction in individuals who have previously undergone surgery, are postoperative adhesions.

Adhesions are fibrous bands of scar tissue that causes organs to attach to the surgical site or to other organs, causing the lumen of the bowel to get kinked or pinched tight in certain spots.

Another cause of small intestinal obstructions is hernias - which is when a portion of the bowel protrudes out of the abdominal cavity and can get trapped or tightly pinched at the point where it pokes out.

Large bowel obstructions, on the other hand, are most often due to a volvulus - which is when a loop of intestine twists upon itself, kinking off the lumen.

Sometimes the volvulus can occur around a mass like in colorectal cancer.

Other mechanical causes of both small and large bowel obstruction include inflammatory bowel disease which can cause strictures and adhesions, ingestion of a foreign body which can get lodged along the gastrointestinal tract, and intussusception - which is where a part of the intestine folds into the lumen of an adjacent section of bowel.


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