Abdominal x-ray (summary approach)

Dr Jeremy Jones et al.

Abdominal radiographs can be challenging examinations to look at. It is always best to approach radiographs in a systematic way.

Gas within the bowel forms a natural contrast with surrounding tissues since it has a very low density. Bowel can only be seen if it contains air/gas. If it is completely fluid-filled, bowel will be indistinguishable from its surroundings.

  • stomach
    • left of midline, beneath hemidiaphragm
    • sometimes just a small volume of gas in the fundus
    • do not mistake a rim of gas for pneumoperitoneum
  • small bowel
    • measures less than 3 cm
    • tends to be central
    • only seen if it contains gas
    • mucosal folds (valvulae conniventes) traverse the bowel lumen
  • large bowel
    • measures less than 6 cm (except caecum and sigmoid, up to 9 cm)
    • peripheral
    • ascending and descending colon in fixed positions laterally
    • transverse colon and sigmoid variable position on a mesentery
    • haustral folds do not go all the way across the lumen
    • contains faeces - mottled appearance
3/6/9 rule

In general terms, small bowel should measure less than 3 cm, large bowel less than 6 cm and the caecum and sigmoid colon should measure less than 9 cm.

If the bowel measures greater than this, there is bowel dilatation - think mechanical obstruction.

Abnormal gas pattern

A supine radiograph is not the best test to do to look for free gas (look for an erect chest radiograph). However, with practice it is possible to see free gas within the peritoneal cavity.

Gas outside bowel will make bowel wall much easier to detect because loops with gas on either side of the bowel wall are seen very clearly. See pneumoperitoneum.

The parenchymal organs within the abdomen absorb x-rays as they pass through the patient and therefore alter the appearance of the radiograph. These changes are subtle, but with practice you should be able to make out several organs and muscles.

  • liver
    • right upper quadrant
    • extends to the hemidiaphragm and past the midline
  • spleen
    • left upper quadrant
    • extends to the hemidiaphragm
  • psoas muscle
    • symmetrical triangles either side of the spine
    • narrowest near the diaphragm, widest at the pelvis
  • kidneys
    • sit on the psoas muscles
    • often just see the rounded lower pole
  • lung bases
    • pulmonary vessels in the bases projected over upper abdomen

Look out for abnormal calcification and metal in or on the abdomen. It is worthwhile looking specifically for abnormal density and working out what it represents.

  • lines and tubes
    • NG/NJ tubes
    • femoral line
    • ECG leads
  • surgical
    • vascular clips
    • cholecystectomy clips
    • skin staples
  • clothing/jewellery
    • navel piercing
    • metal from clothing, e.g. metal rings from jogging bottoms
  • calcification
    • vascular, e.g. aorta, phleboliths
    • renal tract, e.g. renal stones

A host of bones and joints can be seen on an abdominal radiograph.

  • spine
    • lower thoracic and lumbar spine should be of similar height
    • intervertebral disc spaces should be similar
    • spinous processes should be visible
  • lower ribs
  • sacrum and pelvis

Sacroiliac joints and hip joints are often visualised on abdominal radiographs. Make sure that you look at the bones to check for other causes of abdominal pain. Evidence of discitis, bony metastases etc.

Example normal cases: playlist


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Article Information

rID: 47278
Section: Approach
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    Figure 1: large bowel
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    Figure 2: large and small bowel
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    Figure 3: liver and spleen
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    Figure 4: kidneys
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    Figure 5: composite
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