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Key Clinical Questions

  • image What views are standard to evaluate the acute abdomen?

  • image Which radiograph view is the most sensitive for detecting a small pneumoperitoneum?

  • image What are the conditions simulating air under the diaphragm?

  • image What are the causes of air-fluid levels on an erect abdominal image?

  • image How do you quantify the amount of gas normally seen in the bowel?

  • image What are the radiologic signs of bowel ischemia?

  • image What are the most common abnormalities associated with acute pancreatitis?

Despite the availability of newer imaging modalities to look for intestinal obstruction or perforation, the supine abdominal radiograph (KUB) remains indispensible for evaluating a patient with abdominal pain due to the ease and ready availability for rapidly screening patients with abdominal pain. The standard field of view extends from the lung bases to the pubic symphysis, thereby framing the genitourinary system, imaging kidneys, ureters, and bladder. Additional views include an erect chest radiograph, erect abdominal view, and left lateral decubitus.

Figure 116-1 is a line diagram pointing out the twelfth ribs, lumbar transverse process, kidneys, psoas line, inferior liver edge, terminal ileum, sacroiliac spine, gas in the ileum and jejunum, gas and feces in the transverse colon, haustral folds, and descending colon. A thin layer of adipose tissue should be visible as a lucent line between the transverse abdominal muscle and the peritoneum extending from above the lateral margin of the liver to below the iliac crest and between the dome of the bladder and the pelvic peritoneum.

Figure 116-1

Anatomic line drawing (including right kidney, psoas line, properitoneal fat line, inferior liver edge, terminal ileum, sacroiliac joint; twelfth rib, left psoas, haustral folds, lumbar transfer process, gas and feces in transverse colon, gas in jejunum, descending colon, gas in ileum).

The abdominal radiograph is not symmetric and in fact there is significant variation in a “normal” KUB as seen in Figure 116-2. Systematic review of examinations may be facilitated by use of a checklist (see Table 116-1).

Figure 116-2

Normal supine abdominal radiograph.

TABLE 116-1Checklist for Interpretation

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