An abdominal x-ray (AXR) is not as useful as a chest-x-ray. Most of the structures are soft tissues, and thus not seen well on abdominal x-ray, and lots of organs overlie other organs, so it’s not always easy to tell which bit is which. As a result, they are not often particularly useful.
Despite this, because they are easily available, a lot of patients end up having AXRs when they present with acute abdominal pain. It is also worth noting that an AXR will expose a patient to up to 35x more radiation than a CXR (because there’s a lot more ‘stuff’ to fire the x-rays through – and a lot less air!).
Before requesting any investigation you should be able to justify how the results will change your management plan. If it won’t change the management, then there’s no need to do it!
In one study (Stower et al – Evaluation of the plain abdominal X-ray in the acute abdomen. J R Soc Med1985 ) the results of abdominal x-rays only changed the management plan in 4% of patients!
If you suspect any of the following, then abdominal x-ray may help confirm your diagnosis:
- Toxic megacolon
- Renal colic
- KUB – Kidenys-Ureters-Bladder – is a specified type of abdominal x-ray to look at the urinary system. About 90% of renal stone are visible on an AXR (radioopaque).
- Perforation (of the bowel) – although an erect CXR is likely to be more useful
- Ingestion of foreign body
Not indicated for
- Gallstones (only about 10-20% of gallstones are visible on an AXR)
- Constipation – faecal impaction is often visible on an AXR, but the diagnosis of constipation should be made clinically
- Everything else!
Use a system to make sure you don’t miss anything. Most solid objects (opacities) will be clearly visible. Check the size of the small and large bowel loops.
Small bowel obstruction
- In a normal small bowel, the diameter of the bowel is <3cm. On most modern x-ray viewing software at hospital you can measure this with a tool from the toolbar.
- If there is obstruction, then the bowel loops become distended and will be >3cm diameter.
- The valvulae conniventes are the mucosal folds of the small bowel. They can be used to differentiate the small bowel from the large bowel. The valvulae conniventes traverse the entire width of the small bowel, but the equivalent haustra in the large bowel are not the entire width of the large bowel.
Large Bowel Obstruction
- Normal large bowel is <6cm diameter. Dilated loops are >6cm.
- Again, look for the haustra to confirm whether small or large bowel.
- Toxic megacolon is a complication of Inflammatory Bowel Disease (usually Ulcerative Colitis, but occasionally seen in Crohn’s), and of bowel infections, e.g. clostridium difficile.
- It is diagnosed when there is a suspicious clinical history (e.g. known IBD, signs of bowel obstruction, fever, abdo pain, shock, signs of sepsis)
- On the AXR you will see huge dilated loops of large bowel.
- It is often fatal if untreated. It can resolve within the first 24 hours with decompression, but many patients will require a colectomy.