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A 51-year-old man presented to the ED with progressive abdominal pain of one day's duration. He had not eaten all day and had vomited twice. There was no associated diarrhea or melena.

He had a history of alcoholic hepatitis, COPD, and surgical repair of a colonic-bladder fistula 10 years earlier. He had mild constipation and abdominal discomfort for the past few months.

On examination, the patient was in moderate distress due to abdominal pain. Vital signs: blood pressure 130/70 mm Hg; pulse 118 beats/min; respirations 24 breaths/min; temperature 100.8º F (rectal).

His abdomen was distended but soft, with mild diffuse tenderness and no rebound tenderness. His stool was negative for occult blood. He was anicteric.

The initial chest and abdominal radiographs were interpreted as negative (Figure 1A–C). Upon his return from the radiology suite, he vomited dark bilious material that tested positive for blood. A nasogastric tube was inserted. Because of concern that he might have a perforated peptic ulcer, 300 mL of air was insufflated via a nasogastric tube and the upright abdominal radiograph was repeated (Figure 1D). The air noted under the left hemidiaphragm was interpreted as being in the patient’s distended stomach.

Figure 1

A. Erect AP chest radiograph. B. Supine abdomen. C. Upright abdomen. D. Upright abdomen repeated after insufflation of 300 mL air via a nasogastric tube

Two hours later, an abdominal CT was performed that revealed the correct diagnosis.

The diagnosis was evident on the initial radiographs (Figure 1).

  • What do they show?

Detection of free intraperitoneal air (pneumoperitoneum) is one of the principal uses of radiography in patients with abdominal pain. Pneumoperitoneum is nearly always due to perforation of the gastrointestinal tract, and virtually all patients require surgery. In 80–90% of cases, free intraperitoneal air is due to a perforated peptic ulcer. An upright chest radiograph is the preferred imaging test because it readily detects free air under the diaphragm.

Radiography to detect free intraperitoneal air in indicated in patients suspected of having a perforated peptic ulcar. The patient typically presents with an abrupt onset of severe abdominal pain. The abdomen is diffusely tender with rigidity and rebound tenderness. In many patients, there is no history of prior peptic ulcer disease.

In most cases, the clinical and radiographic findings are obvious, and radiography serves to confirm the diagnosis. Diagnostic difficulty arises when the clinical presentation is muted, particularly in elderly or debilitated patients, or when the radiographic findings are subtle ...

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