Not always is the quick answer. Bowel obstructions or bowel blockages do not always show up on X-rays of the abdomen. When we say bowel, we mean the small intestine or colon. Patients with a bowel obstruction will often have pain, nausea, vomiting and present to the emergency room.
Will abdominal X-rays show us a bowel blockage?
Abdominal X-rays are frequently done as an initial test to evaluate for suspected bowel obstruction. Abdominal X-rays are not very good at detecting bowel obstruction in every patient who has one. CT is a much better test for that.
What does bowel blockage look like on X-ray?
The bowel shows up as dark when it’s filled with gas. It is often not filled with gas but fluid. In these cases it shows up as white on an X-ray. Everything around the bowel in the abdomen is also white. The bowel blends in with everything else in the abdomen when it is not gas filled.
The problem is that the bowel is not seen on an X-ray when it is filled with fluid. A lot of times, bowel can be obstructed and filled with fluid. Therefore, a bowel obstruction will not be seen despite one being present.
Additionally, there are various grades of obstruction. One that is completely blocked may be seen whereas one where the bowel is partially blocked may not be seen or look like normal bowel. This is even if we do see the gas filled bowel.
Abdominal X-rays are therefore not the best test for bowel blockage. When we do see it, it classically looks like dilated loops with air-fluid levels with transition to non dilated bowel at the site of blockage. This appearance is more commonly seen on CT.
What is a non specific bowel gas pattern?
More commonly, we see what’s called a non specific bowel gas pattern. This means that the radiologist interpreting the scan thinks the bowel does not look quite right, but is not sure it’s abnormal. A normal patient who swallowed a lot of gas, or drank a soft drink may have a lot of gas in their bowel. Similarly, a patient who has an early blockage may look the same.
What if the abdominal X-ray doesn’t show the blockage?
Clinical doctors who order abdominal X-rays are aware of the limitations. They know that their clinical impression carries a lot of weight. They know that an abdominal X-ray may not identify an obstruction or even over diagnose one. Often they will order a CT to clarify the findings on X-ray. They may order a CT when they have a strong suspicion for bowel obstruction and the X-ray is inconclusive.
An abdominal X-ray therefore is a good start. Sometimes it shows us a classic bowel obstruction and that helps. Other times, it’s inconclusive or normal looking. In these cases further testing will be required. Bowel obstruction is a serious condition and needs immediate treatment. The clinical presentation of the patient and the doctors impression is important to lead to the correct diagnosis.