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Small Bowel Obstruction

Anatomy of the Digestive Tract & Causes of Obstructions into the Colon

Jul 12, 2009 David Henry

Small bowel obstruction is a serious condition in which a blockage prevents food from passing through the small intestine into the colon.

This is the first article of two on small bowel obstruction. This article describes the anatomy of the digestive tract and the most common causes of small bowel obstruction. The next article describes how to diagnosis and treat this serious condition.

Anatomy of the Digestive Tract

The small intestine (small bowel) consists, in order, of the Duodenum, Jejunum, and Ileum. The order can be remembered using the phrase "Dow Jones Industrial." Food passes from the mouth through the esophagus into the stomach, then through the duodenum, jejunum, and ileum, and finally into the colon (ascending, transverse, descending, and sigmoid) and then the rectum. A blockage of the lumen of the small intestine is called a "small bowel obstruction." Small bowel obstruction is the most common surgical disorder of the small intestine.

Causes of Small Bowel Obstruction

  • Adhesions: cause 75% of small bowel obstructions. Adhesions are bands of fibrous scar tissue that form within the abdomen weeks to months after an abdominal surgery.
  • Hernias: A hernia is an abnormal protrusion of bowel through an opening. If the bowel protrudes, for example, through the inguinal canal into scrotum, the intestinal lumen can be narrowed, preventing the passage of food.
  • Cancers: Primary small bowel cancer is very rare, causing less than 3% of small bowel obstructions. However, other cancers like melanoma can metastasize to the small bowel. If the tumor within the wall of the small bowel grows large enough, it can occlude the lumen and cause an obstruction. In addition to primary small bowel tumors and metastases, a small bowel obstruction can also be caused by direct invasion of a cancer from a nearby location (colon, bladder, etc.)
  • Crohn's disease: Causes strictures, or narrowings, within the small bowel. If severe, these strictures can cause an obstruction.
  • Volvulus: A twisting of the intestine. This can cause a "closed loop obstruction," in which gas or secretions cannot escape the twisted segment either proximally or distally. This can result quickly in strangulation, necrosis (cell death), and perforation of the intestines!
  • Intussusception
  • Intestinal strictures (narrowings) caused by radiation therapy (for cancer)
  • Foreign body: If a child swallows a large marble, for example.
  • Gallstone ileus
  • Hematoma: A collection of blood within the wall of the intestines. If the hematoma expands, it can narrow and block of the lumen (opening) of the intestines, causing a small bowel obstruction.
  • Congenital conditions: Some kids are born with "webs" or other narrowings of the small intestine that can lead to obstruction shortly after birth.

Link to the Diagnosis and Treatment of Small Bowel Obstruction.

Reference

Chapter 27: Small intestine. Brunicardi FC, et al., Eds. Schwartz's Principles of Surgery. McGraw-Hill, 2004. *One of the classic textbooks in general surgery.

The copyright of the article Small Bowel Obstruction in General Medicine is owned by David Henry. Permission to republish Small Bowel Obstruction in print or online must be granted by the author in writing.
Dilated small bowel loops (indicate obstruction), Jeffrey Parks, MD (Medscape) Dilated small bowel loops (indicate obstruction)
   
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