First-line CT for suspected bowel obstruction in a stable adult
In a stable adult (blood pressure and pulse holding up) with suspected bowel obstruction (a blockage of the gut), CT of the abdomen and pelvis is the first-line imaging.
Remember
A stable adult with suspected bowel obstruction needs CT of the abdomen and pelvis first, because it often shows where the blockage is and what is causing it. Suspected perforation (a hole in the bowel wall) is the exception.
Memory aid
Think of the plain film as the headline and CT as the full report.
A plain film only suggests obstruction, while CT often gives much more detail about the level, the cause and the complications.
A bowel obstruction is a problem that inhibits normal movement of gut contents through the bowel. It can lie in the large bowel (the colon and rectum) or in the small bowel.
In a stable adult, the scan to reach for first is CT of the abdomen and pelvis (computed tomography, which uses x-rays to build detailed cross-sectional pictures). That is what first-line means here: the best first test. It often shows where the blockage is and what is causing it, and it looks for complications such as ischaemia (a failing blood supply) and perforation (a hole in the bowel wall). CT often answers where the blockage is, why it is there and how bad the bowel is.
Finding the cause matters, because each cause needs different treatment. In the large bowel, colon cancer is the most common cause. Others include diverticular disease (small pouches in the bowel wall that can become inflamed and scar), volvulus (the colon twisting around its mesentery, the fold of tissue that holds it in place) and inflammatory bowel disease. In the small bowel, adhesions (bands of scar tissue) are the most common cause, and previous abdominal or gynaecological surgery is a risk factor.
The exception is suspected perforation. If it is suspected, for example with peritonitis (inflammation of the abdominal lining), emergency surgery may go ahead without waiting for a CT scan.
Key facts
- Best first test
- CT of the abdomen and pelvis in a stable adult, because it often shows the location and the cause of the blockage.
- What CT adds
- It helps to detect complications such as bowel ischaemia, necrosis (dead bowel) and perforation.
- Exception
- With suspected perforation or peritonitis, emergency surgery may proceed without a CT scan.
- Why it is urgent
- Dehydration, sepsis, bowel ischaemia or necrosis and perforation are risks, so bowel obstruction is a gastrointestinal emergency.
- Plain x-ray
- A plain abdominal x-ray can show dilated loops of bowel but gives little detail about the cause.
- Endoscopy
- In stable patients with a large bowel obstruction it can biopsy a mass causing the obstruction, and can treat a sigmoid volvulus.
Exam traps
- A plain abdominal x-ray is not the best first test for the cause, because it can show dilated loops of colon but gives little detail about soft tissues.
- An erect chest x-ray does not show where the bowel is blocked or why. It looks for free air under the diaphragm, which suggests a perforation, and it is used less often now because it is not reliable.
- Ultrasound is radiation-free and quick, which makes it tempting, but guidelines name CT, not ultrasound, as the best imaging technique for large bowel obstruction.
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