Optimal Diagnostic Test for Abdominal Pain with Resonant Liver Percussion
The optimal diagnostic test is an erect chest X-ray (Option A), as a resonant liver percussion note indicates free air under the diaphragm from bowel perforation, which is best detected on an upright chest radiograph. 1
Clinical Reasoning
Understanding the Key Physical Finding
- A resonant liver percussion note (instead of the normal dullness) is a critical physical examination finding that indicates pneumoperitoneum (free intraperitoneal air) 2
- This finding, combined with abdominal pain and distension, strongly suggests bowel perforation as the underlying pathology 3
- The presence of free air displaces the normal liver dullness, creating an abnormal resonant percussion note over the right upper quadrant 2
Why Erect Chest X-ray is Superior
An erect chest X-ray is the most sensitive plain radiographic technique for detecting free intraperitoneal air:
- Erect chest radiography can detect as little as 1-2 mL of free air under the diaphragm, appearing as a crescent of lucency between the diaphragm and liver 1
- This view is significantly more sensitive than abdominal radiographs for detecting pneumoperitoneum 3
- The erect chest film combined with supine abdominal view diagnosed normality or abnormality in 98% of patients with abdominal pain 1
Why Other Options Are Less Appropriate
- Supine chest X-ray (Option B): Free air rises to the highest point in the body; a supine position does not allow air to collect under the diaphragm where it is most easily visualized 1
- Erect abdominal X-ray (Option C): While this can show free air, it is less sensitive than erect chest X-ray and provides less diagnostic information 1
- Supine abdominal X-ray (Option D): This is the least sensitive view for detecting free air, as air does not collect in an easily visible location when the patient is supine 1
Important Clinical Context
When CT is Ultimately Needed
- While erect chest X-ray is the optimal initial test for confirming free air, CT is the most sensitive technique for depicting free intraperitoneal air and is valuable for determining the cause of perforation 3
- CT should be considered after plain radiography if the diagnosis remains unclear or surgical planning is needed 3
- However, in the acute setting with classic physical findings suggesting perforation, the erect chest X-ray provides rapid, cost-effective confirmation 1
Common Pitfalls to Avoid
- Ordering only abdominal films: The erect abdominal view can be eliminated from routine series without significant loss of diagnostic information, but the erect chest view remains essential 1
- Relying on supine films alone: Studies demonstrate that elimination of the erect abdominal view is acceptable, but the erect chest study must be retained for optimal diagnostic accuracy 1
- Delaying imaging: In a patient with suspected perforation based on physical examination, prompt imaging is critical for surgical decision-making 3
The Role of Plain Radiography vs. Advanced Imaging
- While some evidence suggests limited utility of plain abdominal radiography in general acute abdominal pain 4, the specific clinical scenario of suspected perforation (resonant liver percussion) is an exception where plain radiography remains highly valuable 3, 1
- The erect chest X-ray provides rapid, radiation-efficient confirmation of free air before proceeding to CT for surgical planning 1