Optimal Diagnostic Test for Suspected Bowel Perforation
An erect chest X-ray is the optimal diagnostic test for this patient, as the resonant liver percussion note indicates pneumoperitoneum (free intraperitoneal air), which is best detected on an upright chest radiograph. 1
Clinical Reasoning
Key Physical Finding
- A resonant liver percussion note is pathognomonic for pneumoperitoneum - the free intraperitoneal air displaces the normal liver dullness in the right upper quadrant, creating an abnormal resonant percussion note 1
- This finding, combined with abdominal pain and distension, strongly suggests bowel perforation (most commonly from perforated duodenal ulcer) 1
Why Erect Chest X-ray is Superior
For detecting free air (pneumoperitoneum):
- Erect chest X-ray is more sensitive than abdominal films for detecting small amounts of free intraperitoneal air because air rises to the highest point in the body 2
- Free air appears as a lucent crescent beneath the diaphragm on upright chest radiography 2
- As little as 1-2 mL of free air can be detected on an erect chest X-ray 2
Comparison with other options:
- Supine chest X-ray (Option B) is inappropriate - the patient must be upright for air to collect under the diaphragm 2
- Erect abdominal X-ray (Option C) can show free air but is less sensitive than erect chest X-ray 2, 3
- Supine abdominal X-ray (Option D) has very poor sensitivity for pneumoperitoneum as free air does not collect in a visible location when supine 3
Supporting Evidence
Plain radiography limitations:
- While conventional radiography has limited overall diagnostic value for acute abdominal pain (sensitivity 49% for bowel obstruction), it maintains utility specifically for detecting pneumoperitoneum 4
- Erect abdominal radiographs showed better diagnostic relevance than supine films for bowel obstruction (100% vs 87.2%), but chest X-ray remains superior for free air detection 3
When to Escalate to CT
If chest X-ray is negative but clinical suspicion remains high:
- CT is the most sensitive imaging modality for detecting pneumoperitoneum and can identify the perforation site 2, 5
- CT has 89% sensitivity for urgent abdominal conditions and can detect free air not visible on plain films 5
- CT also provides information about the underlying cause of perforation 2
Common Pitfalls to Avoid
- Do not order supine films when perforation is suspected - they will miss most cases of pneumoperitoneum 3
- Ensure the patient is truly upright for at least 5-10 minutes before obtaining the chest X-ray to allow air to rise 2
- Do not skip imaging based on clinical examination alone - physical findings can be unreliable for confirming perforation 6
Answer: A. Chest X-ray erect (if perforated DU)