Perforated Peptic Ulcer Imaging
A 38-year-old man has four hours of sudden severe abdominal pain after months of frequent NSAID use for joint pain. He is able to stand. Temperature is 37.8 °C and white cell count 13 × 10⁹/L. The abdomen shows generalized tenderness, board-like guarding and absent bowel sounds. Which of the following is the most appropriate initial imaging?
- A.Abdominal ultrasound scan
- B.Erect chest radiographCorrect
- C.Supine abdominal radiograph
- D.Contrast enhanced abdominal CT
Explanation
Abrupt severe abdominal pain, chronic NSAID use and generalized peritonism with absent bowel sounds indicate a perforated viscus, most often a perforated peptic ulcer. The diagnostic target is pneumoperitoneum, gas that has escaped from the perforated lumen into the peritoneal cavity. An erect chest radiograph is the correct first imaging study because when the patient is upright, free gas rises to the highest point in the abdomen and collects under the domes of the diaphragm, appearing as a thin crescent of lucency between the diaphragm and the liver or gastric fundus. The patient must sit or stand for at least 10 to 15 minutes beforehand for even small volumes of gas to accumulate. The test is fast, cheap and available everywhere, delivers a tiny radiation dose, and a positive result is sufficient to take the patient to theatre without further imaging. It is important to remember that an erect chest radiograph detects free gas in only about 70 to 80 percent of perforations, so a negative film does not exclude the diagnosis. CT is the most sensitive test and detects tiny volumes of gas, but it is slower, costlier and higher in radiation dose, so it is reserved for a negative or equivocal radiograph with persisting suspicion. A supine film is insensitive because gas does not collect in one recognisable place, and ultrasound is unreliable for free gas.
Why each option
- A.
- Ultrasound is unreliable for detecting free intraperitoneal gas and is not used for this indication.
- B.
- Correct. An erect chest radiograph rapidly demonstrates free subdiaphragmatic gas and, if positive, is enough to proceed to surgery.
- C.
- A supine film is much less sensitive because free gas does not collect at a single identifiable point when the patient lies flat.
- D.
- CT is the most sensitive test for pneumoperitoneum but is second line, used when the erect film is negative and suspicion remains.
Reference: WSES Guidelines for the Management of Perforated Peptic Ulcer, World J Emerg Surg 2020
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