Small bowel obstruction (summary)

Last revised by Tom Foster on 14 Sep 2019
This is a basic article for medical students and other non-radiologists

Small bowel obstruction (SBO) accounts for 80% of all mechanical intestinal obstruction; the remaining 20% result from large bowel obstruction. It has a mortality rate of 5.5%.

Reference article

This is a summary article; read more in our article on small bowel obstruction.

  • epidemiology 1
    • 80% of all mechanical bowel obstruction
    • average age: 64 years
    • females comprise 60% of patients
  • presentation
    • abdominal distension, nausea and vomiting
    • the level will determine the acuity of presentation
      • high obstruction presents early, possibly with bilious vomiting
      • lower obstruction presents late and may have feculent vomiting
  • pathophysiology
    • may be complete or incomplete
      • adhesional SBO: almost exclusively from prior surgery
      • herniae (often femoral or inguinal, but incisional occur)
      • foreign bodies or other masses, e.g. gallstones
      • rare: small bowel tumors causing intussusception
  • investigation
    • CT is the most sensitive imaging modality
  • treatment
    • initial treatment is supportive with decompression (NG) and IV fluids
    • in some cases, conservative management fails and surgery is required
  • prognosis
    • depends on the cause and whether complications occur
    • mortality of 5.5% where there are complications:
      • ischemia
      • perforation
  • confirm obstruction
  • demonstrate cause
  • find the transition point
  • identify any complications, e.g. ischemia or perforation

There are a number of ways to investigate small bowel obstruction. A plain radiograph has been the traditional tool for initial assessment and while CT has reduced the use of plain radiographs, they remain a tool used by many.

  • dilated small bowel loops (providing they are filled with gas)
    • if they are fluid-filled, you will not be able to see them
    • small bowel >3 cm in caliber is abnormal (see 3-6-9 rule)
  • small bowel loops
    • tend to be more central than large bowel
    • have valvulae conniventes that traverse the lumen completely
  • the cause may be demonstrated, e.g. gas in the femoral canal
  • dilated loops of small bowel
    • the dilated bowel may be gas- or fluid-filled
  • transition point at the site of obstruction
    • the cause will be at the transition point
    • if no cause is demonstrated, it's likely secondary to adhesions

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Cases and figures

  • Case 1: valvulae conniventes
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  • Case 2: femoral hernia
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  • Case 3: incisional hernia
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  • Case 4: midgut volvulus
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  • Case 5: cecal tumor
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  • Case 6: adhesions
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