Bowel dilatation (summary)

Last revised by Tee Yu Jin on 2 Aug 2023
This is a basic article for medical students and other non-radiologists

Bowel dilatation is a relatively non-specific sign than can be seen on most imaging modalities. In bowel obstruction, dilatation may be demonstrated on a plain radiograph providing the bowel is filled with gas.

Reference article

This is a summary article; we do not have a more in-depth reference article.

  • pathophysiology
  • investigation
    • x-ray can show bowel dilatation when bowel is gas-filled
    • CT is more sensitive
    • US can identify fluid-filled loops of bowel
    • MRI can also identify gas- and fluid-filled loops of bowel

Bowel dilatation can be seen on most modalities to a greater or lesser extent. Normal bowel caliber can be remembered using the 3-6-9 rule:

  • small bowel: <3 cm
  • large bowel: <6 cm
  • cecum/sigmoid: <9 cm

Abdominal radiographs are often performed as an initial imaging test in patients with abdominal pain and distension. Bowel dilatation is only visible when the bowel contains gas. The amount of gas within a loop of bowel may significantly underestimate its caliber.

Bowel dilatation is much more clearly demonstrated on CT. The degree of dilatation can be assessed independent of whether the bowel is filled with fluid or gas. In addition, the bowel wall and other structures can be interrogated.

Bowel dilatation can be seen on ultrasound, but this is usually dependant on the bowel being fluid-filled and there being no gas-filled bowel anteriorly.

Bowel caliber can be assessed on MRI. With fluid-filled loops of bowel, this is most clearly demonstrated on T2 weighted sequences.

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Cases and figures

  • Figure 1: Normal abdominal x-ray
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  • Case 1: Sigmoid volvulus
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  • Case 2: LBO (hernia)
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  • Case 2: LBO (hernia) - CT
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  • Case 3: LBO (sigmoid volvulus)
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