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Difficulty: EasyInterpreting Imaging Results

A geriatric care physician evaluates an 82-year-old male resident who abruptly developed generalized, severe abdominal pain and a rigid, board-like abdomen. Vital signs show a heart rate of 112/min, a respiratory rate of 22/min, and a temperature of 38.1°C (100.6°F). An upright chest radiograph is immediately obtained and demonstrates a distinct, thin crescent of radiolucency located directly between the right hemidiaphragm and the superior margin of the liver. Based on this specific radiographic finding, which of the following is the most likely diagnosis?

  1. A
    Uncomplicated acute cholecystitis
  2. B
    Right lower lobe bacterial pneumonia
  3. Gastrointestinal viscus perforationAnswer
  4. D
    Complete small bowel obstruction
  5. E
    Ruptured abdominal aortic aneurysm

Answer

Gastrointestinal viscus perforation
The clinical scenario describes a patient with peritonitis (rigid, board-like abdomen) whose upright chest radiograph shows a radiolucent crescent beneath the right hemidiaphragm. This finding represents free air in the peritoneal cavity (pneumoperitoneum). Gas rises to the highest point in the abdomen when the patient is upright, interposing itself between the liver and the diaphragm. In a patient with an acute abdomen, this strongly points to a perforated hollow viscus, such as a perforated peptic ulcer or diverticulum.

Step-by-Step Solution

1
Analyze the patient's clinical presentation.
The patient has an acute, rigid abdomen with tachycardia and fever, suggesting a severe intra-abdominal catastrophe like peritonitis.
Identifying the acuity and physical exam findings guides the interpretation of the subsequent imaging.
2
Interpret the radiographic findings.
The upright chest radiograph shows a 'crescent of radiolucency' between the right hemidiaphragm and the liver.
This specific description is the classic radiographic appearance of pneumoperitoneum (free intraperitoneal air).
3
Correlate the imaging finding with the differential diagnosis.
Pneumoperitoneum in the setting of an acute, rigid abdomen almost universally points to a perforated hollow viscus.
Air normally contained within the gastrointestinal tract escapes into the peritoneal cavity when a viscus (like an ulcerated stomach or duodenum) perforates.

Key Concept

The presence of a radiolucent crescent under the right hemidiaphragm on an upright chest radiograph signifies pneumoperitoneum, which, in the context of an acute abdomen, most commonly indicates a perforated hollow viscus.
Estimated Time:45s
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Interpreting Imaging Results

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