What does a finding of abdominal free air indicate in the workup of necrotizing enterocolitis (NEC)?

Updated: Dec 27, 2017
  • Author: Shelley C Springer, JD, MD, MSc, MBA, FAAP; Chief Editor: Muhammad Aslam, MD  more...
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Abdominal free air is ominous and usually requires emergency surgical intervention. The presence of abdominal free air can be difficult to discern on a flat radiograph, which is why decubitus radiographs are recommended at every evaluation. A subtle, oblong lucency over the liver and abdominal contents is characteristic of intraperitoneal air on a flat plate. It represents the air bubble that has risen to the most anterior aspect of the abdomen in a baby lying in a supine position. The free air can be difficult to differentiate from intraluminal air.

For this reason, left-side down (left lateral) decubitus radiography is essential and allows the detection of intraperitoneal air, which rises above the liver shadow (right-side up) and can be visualized more easily than it can be on other views. Obtain this view with every AP examination until progressive disease is no longer a concern.

Although free air typically indicates intestinal perforation, other causes include dissecting mediastinal air from barotrauma in a ventilated neonate, gastric perforation (most commonly due to a nasogastric tube), and Hirschsprung disease. Free air is seen in only 50-63% of infants who have intestinal perforation identified at surgery.

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