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Part VI ♦ Special Subjects

II. Imaging A. Indications: Determined by patient presentation, but all patients with acute abdomen should have an upright chest x-ray and flat and upright abdominal x-rays or a lateral decubitus view. B. Findings 1. Free air a. Air typically seen under the diaphragm on an upright chest x-ray (see Fig. 18-3). b. Represents a surgical emergency. c. Causes (1) Perforation: Present in 80% of proximal perforations but only 25% of distal perforations. (2) Abdominal manipulation: Less common cause; due to peritoneal dialysis or recent laparoscopic surgery. 2. Pneumatosis intestinalis: Small bubble-like air collections within the intestinal wall; can indicate ischemia or contained perforation. 3. Pneumobilia: Air tracking within the liver; caused by cholangitis, gallstone ileus, or recent endoscopic retrograde cholangiopancreatography (ERCP). 4. Portal venous gas: Seen with necrotic tissue in the drainage bed of the portal system, typically the small intestine, appendix, or colon. 5. Sentinel loop air (in adults): Abnormal; typically due to obstruction.

Gastric fundus air

Dome of liver

Figure 18-3: Free air. The straight arrows at the top left represent the diaphragm. The horizontal arrow at left points to the free air. On the right, the uppermost arrows show the diaphragm, and the curved arrows illustrate the outline of the stomach. The lone central arrow signifies the gastroesophageal junction. (Smith W. Radiology 101, 4th ed. Philadelphia: Lippincott Williams & Wilkins; 2013.)