Abdominal X-ray - Abnormal bowel gas pattern
Small bowel obstruction/ileus

Key points

  • Dilated small bowel >3cm is considered abnormal
  • Small bowel obstruction and ileus can have similar appearances

If a patient presents with clinical features of obstruction then radiological assessment can be very helpful in determining the level of obstruction, and occasionally the cause.

There are features visible on a plain abdominal X-ray that may help locate the level of obstruction. These are partly determined by a knowledge of small and large bowel anatomy. See the page on normal Bowel Gas Pattern.

Dilatation >3cm of the small bowel is considered abnormal, however the longer the segment of bowel that is dilated, the more likely bowel dilatation represents a genuine obstruction.

Small bowel obstruction - features

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Small bowel obstruction - features

  • Centrally located multiple dilated loops of gas filled bowel (arrowheads)
  • Valvulae conniventes (arrow) are visible - confirming this is small bowel
  • Evidence of previous surgery - note the anastomosis site (red ring) - this suggests adhesions is the likely cause of obstruction (confirmed at surgery)

Small bowel obstruction - causes

The most common causes of obstruction are adhesions secondary to intra-abdominal surgery, hernias, tumours and Crohn's disease. Regardless of whether there is evidence of these causes on an abdominal radiograph, a full surgical history should be taken and examination of the hernial orifices should be performed.

Ileus

Ileus is a term used for aperistaltic bowel not caused by a mechanical obstruction. This phenomenon is common after abdominal surgery. The radiological features can be similar to those of obstruction.

Post operative ileus

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Post operative ileus

  • Appearances are similar to those of mechanical obstruction
  • There are multiple loops of gas filled bowel projected centrally over the abdomen
  • This patient had prolonged non-colicky abdominal pain following a Caesarian section - recovery was spontaneous

Sentinel loop

Intra-abdominal inflammation, such as with pancreatitis, can lead to a localized ileus. This may appear as a single loop of dilated bowel known as a 'sentinel loop.'

Sentinel loop

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Sentinel loop

  • A localized loop of small bowel is dilated in this patient with acute pancreatitis
  • This appearance is not diagnostic of intra-abdominal inflammation, but rather an occasional associated feature