Abdominal x-ray - an approach (summary)

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This is a basic article for medical students and other non-radiologists

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

Bowel gas pattern

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
  • large bowel
    • less than 6 cm wide, cecum 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 and are widely-spaced
    • contains feces - 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 cecum and sigmoid colon should measure less than 9 cm.

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

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.

Abdominal organs

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 major muscles
    • symmetrical triangles either side of the lumbar spine
    • narrowest near the diaphragm, widest at the pelvis
  • kidneys
    • sit on the psoas major muscles
    • often just see the rounded lower pole
  • lung bases
    • pulmonary vessels in the bases projected over upper abdomen

Calcification/artifacts

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

Bones and joints

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 visualized on abdominal radiographs. Make sure that you look at the bones to check for other causes of abdominal pain. Evidence of diskitis, bony metastases etc.

Playlist

Example normal cases: playlist

Medical student radiology curriculum