Hollow viscus perforation

May be used as an initial screening tool in cases of suspected perforation; however, sensitivity for detecting small volume pneumoperitoneum is limited.

In addition to supine imaging, erect and left lateral decubitus views help increase sensitivity ( Figs. 4.1 and 4.2 ).

Numerous signs of pneumoperitoneum have been described, including:

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  Rigler’s sign: air seen on both sides of the bowel wall.

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  Falciform ligament sign: air outlining the falciform ligament.

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  Football sign: large amount of air confined to the peritoneal cavity.

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  Doge cap sign: air trapped within Morison’s pouch in the right upper quadrant.

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  Cupola sign: air collecting beneath the central tendon of the diaphragm.

Provides dynamic evaluation of the GI tract.

Extraluminal contrast will not follow the luminal contour, does not peristalse, and may collect dependently.

Useful for demonstrating fistulas and communicating collections.

Less commonly performed, but useful as an emergent bedside technique, as well as in pediatric populations.

Peritoneal stripe sign: enhancement of the parietal peritoneum because of a highly reflective interface with an antidependent collection of free air.

Small echogenic gas bubbles associated with comet tail artifact, ring down artifact, or dirty shadowing.

Highest sensitivity for detection of free air, and allows for thorough evaluation of most possible sources.

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  Computed tomography (CT) detects site of perforation in 85% of cases.

If perforation is suspected, always review the full series in lung windows.

Perforation may be seen on CT enterography, which is often obtained in cases of inflammatory bowel disease and includes the use of larger volume negative oral contrast with intravenous contrast.

Although helpful for better tissue characterization and in evaluation of fistula formation, CT is the preferred cross-sectional modality.

Magnetic resonance enterography is useful for following patients with chronic inflammatory bowel disease to reduce radiation exposure.

Any evaluation of suspected hollow viscus perforation should be performed as a single-contrast technique with water-soluble contrast to avoid barium-induced peritonitis.

Scout images should be obtained, to serve as a baseline comparison as well as a check for free air. If possible, upright views are preferred.

Ideally, enough contrast would be administered to distend the lumen in question; however, this is not always possible in an acutely ill patient.

Care should be taken to position the patient so that all mucosal surfaces are evaluated, as small, antidependent disruptions may be missed.

When acquiring initial images, cine mode is helpful to better locate the site of disruption.

If no leak is found, a thin barium solution may be given to improve contrast.

When possible, an ideal examination includes water-soluble oral contrast and intravenous contrast. However, even a noncontrast examination will demonstrate the presence of free air.

CT enterography: the patient should be nothing-by-mouth (NPO) for at least 4 hours before the scan, and instructed to drink 1.5 to 2 liters of neutral or low-density oral contrast over 45 minutes. Single phase supine axial images are obtained 50 seconds after administration of IV contrast (enteric phase) with 2 mm slice thickness and 0.75 mm reconstruction intervals.

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  Some institutions also choose to use antiperistaltic agents, such as glucagon or hyoscine butylbromide.

Emergent appendicitis protocol: although losing favor, rectal contrast may be given in lieu of oral contrast to reduce the time to scan. Up to 1500 mL of contrast is administered under gravity via rectal tube, with scout imaging confirming that it has reached the cecum. Following injection of IV contrast, thin section axial slices are obtained through the abdomen.