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Recognizing Bowel Obstruction and Ileus


In Chapter 12, Chapter 13 , we discussed how to recognize the normal intestinal gas pattern on conventional radiographs and computed tomography (CT). In this chapter, you will learn how to recognize and categorize the four most common abnormal bowel gas patterns and their causes. These abnormal patterns of bowel gas will appear the same whether imaged initially by conventional radiography or by CT scanning. CT is superior in revealing the location, degree, and cause of an obstruction and in demonstrating any signs of reduced bowel viability.

Case Quiz 14 Question

This is a supine view of the abdomen in a 57-year-old who has been having crampy abdominal pain for several hours. What diagnosis does this appearance suggest? See the correct answer at the end of this chapter.

  • Abnormalities of bowel function are suggested by the history and clinical findings.

  • The key questions in assessing bowel obstruction on imaging studies are:

    • Are there dilated loops of small and/or large bowel?

    • On CT, is there a transition point?

    • On plain films, is there air in the rectum or sigmoid?

Abnormal Gas Patterns

  • Abnormal intestinal gas patterns can be divided into two main categories, each of which can be subdivided into two subcategories ( Box 14.1 ).

    BOX 14.1
    Abnormal Bowel Gas Patterns

    Functional Ileus

    • Localized ileus (sentinel loops)

    • Generalized adynamic ileus

    Mechanical Obstruction

    • Small bowel obstruction (SBO)

    • Large bowel obstruction (LBO)

  • Functional ileus is one main category in which it is presumed that one or more loops of bowel lose their ability to propagate the peristaltic waves of the bowel , usually because of some local irritation or inflammation , leading to impaired propulsion of bowel contents proximal to the affected loop(s).

  • There are two kinds of functional ileus.

    • Localized ileus affects only one or two loops , usually of small bowel (also called sentinel loops ).

    • Generalized adynamic ileus affects many loops of large and small bowel , and frequently the stomach as well.

  • Mechanical obstruction is the other main category of abnormal bowel gas pattern. With mechanical obstruction, a physical, organic, obstructing lesion prevents the passage of intestinal content past the point of either the small or large bowel blockage.

  • There are two kinds of mechanical obstruction.

    • Small bowel obstruction (SBO)

    • Large bowel obstruction (LBO)

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