History 58-year-old man with sudden severe epigastric pain 4 hours ago, now generalised. Takes regular ibuprofen for back pain. Rigid abdomen; HR 118.
Erect chest radiograph · Click an image to enlarge.
Answer each question aloud before you reveal it. Marks and domains appear only in the revealed answers, as in the exam.
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Q1 What is the pertinent finding?
Reveal answer
A Annotated 2 marks Observation
- Crescent of free gas beneath the right hemidiaphragm, separating the diaphragm from the liver (1.5)
- Check the left side and separate free gas from gastric fundal gas; the diaphragm appears as a thin line with gas on both sides (0.5)
Examiner note Examiners: don't volunteer the diagnosis in an observation answer. Describe it.
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Q2 What is your preferred diagnosis, and what is the most likely cause in this patient?
Reveal answer
2 marks Interpretation
- Pneumoperitoneum (free intraperitoneal gas) (1)
- Perforated peptic (duodenal or gastric) ulcer, given NSAID use and epigastric onset (1)
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Q3 What is your recommended next step?
Reveal answer
3 marks Management/Safety
- Urgent surgical referral with resuscitation (IV access, fluids, analgesia, nil by mouth, antibiotics per the sepsis pathway); stabilise before imaging (1)
- CT abdomen/pelvis with IV contrast (portal venous phase) once stable, to confirm and localise the perforation (1)
- Don't delay theatre for CT if the patient is peritonitic and unstable; check renal function, but don't withhold contrast in an emergency where CT will change management (1)
Examiner note 2026 S1 report: 'Stabilise a sick patient before doing a CT'. The critical patient is your responsibility until handover (LO 6.1.15, 6.1.19).
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Q4 Why is an erect chest radiograph used here, and how should it be performed?
Reveal answer
1 mark Applied sciences
- Free gas rises to the highest point, under the domes; a horizontal beam centred on the diaphragm shows it tangentially (0.5)
- Patient upright (or left lateral decubitus) for about 10 minutes before exposure; with good technique, about 1 mL can be shown (Miller & Nelson 1971) (0.5)
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Q5 The patient has been moved to a ward bed awaiting review, and nobody has looked at the film yet. What do you do?
Reveal answer
2 marks Intrinsic roles
- Phone the treating / surgical team directly now; escalate to the consultant if you cannot reach them (1)
- Closed loop with read-back; record who was told, when, and what, in the report (1)
Examiner note LO 6.1.28–6.1.29.
End of the OSCER block (10 marks).
Beyond the exam: teaching extension
Q6–Q10: not part of the 10-mark OSCER block. Untimed, viva-style discussion: mimics and pitfalls, complications, guidelines and report wording.
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Q6 Second patient: erect AXR. What does it show, and which film is more sensitive?
B Second patient: erect abdominal radiograph (arrow is the original author's) Reveal answer
- A thin crescent of free gas under the right hemidiaphragm (the original author's arrow)
- The erect CXR is more sensitive than the erect AXR: the beam is centred at the diaphragm and meets the domes tangentially
- If the patient cannot sit up: left lateral decubitus with a horizontal beam
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Q7 List the mimics of free subdiaphragmatic gas.
Reveal answer
- Chilaiditi sign: colon between the liver and diaphragm (haustra visible; gas does not move with position)
- Gastric fundus or splenic flexure gas under the left hemidiaphragm
- Subphrenic abscess, basal bulla, subdiaphragmatic fat, curvilinear atelectasis
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Q8 What are the causes of pneumoperitoneum?
Reveal answer
- Perforated hollow viscus: peptic ulcer, diverticulitis, ischaemia, malignancy, closed-loop obstruction, trauma
- Iatrogenic: recent laparotomy or laparoscopy (expected; resolves over days), endoscopy, peritoneal dialysis
- Non-surgical: pneumatosis cystoides intestinalis, barotrauma in ventilated patients tracking from the chest
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Q9 Which CT signs localise the perforation?
Reveal answer
- Extraluminal gas bubbles clustered near the site; a focal wall defect, wall thickening, adjacent fat stranding or fluid
- Upper GI perforation: gas around the liver, falciform ligament and lesser sac
- Colonic perforation: gas in the pelvis or mesocolon; faecal material outside the bowel
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Q10 Draft the key sentences of your report.
Reveal answer
- 'Free gas beneath the right hemidiaphragm, in keeping with pneumoperitoneum; in this setting a perforated viscus is likely.'
- 'Urgent surgical review. Telephoned to Dr [name], general surgery, at [time]; read-back confirmed.'
End of questions. Reveal the diagnosis, key takeaways and syllabus mapping below.
Reveal diagnosis, key takeaways & syllabus mapping
Diagnosis Pneumoperitoneum on erect CXR (perforated peptic ulcer)
Key takeaways
- Look under both hemidiaphragms on every erect film in the acute abdomen.
- Free gas is a critical result: phone it and document it.
- Resuscitate and call the surgeon first; CT localises once the patient is stable.
- Know the mimics: Chilaiditi and gastric fundal gas.
Syllabus mapping
| OSCER station | Abdominal |
|---|---|
| Learning Outcomes section | §6.6 Abdomen & Pelvis (+ §6.1.15, 6.1.19, 6.1.26, 6.1.28–29) |
| Appendix 1 condition | Pneumoperitoneum (Appendix 1 F, Peritoneum / mesentery incl. abdominal wall and cavity, p77) |
| Category | Category 1 |
| Key Condition | Yes |
| Core marks by domain | Observation 2 · Interpretation 2 · Management/Safety 3 · Applied sciences 1 · Intrinsic roles 2 (= 10) |
| Learning objectives | Recognise free subdiaphragmatic gas and its mimics; Put resuscitation and surgical referral before CT; Communicate a critical abdominal result |
Mapped to the RANZCR Clinical Radiology Learning Outcomes v1.3 (January 2024), section 6 and Appendix 1.
Further reading
- Miller RE, Nelson SW. The roentgenologic demonstration of tiny amounts of free intraperitoneal gas: experimental and clinical studies. Am J Roentgenol Radium Ther Nucl Med. 1971;112(3):574–585. PMID 5570369.
- Levine MS, Scheiner JD, Rubesin SE, et al. Diagnosis of pneumoperitoneum on supine abdominal radiographs. AJR Am J Roentgenol. 1991;156(4):731–735. PMID 2003436.
- RANZCR. Clinical Radiology Learning Outcomes, v1.3 (January 2024), §6 and Appendix 1. Sydney: RANZCR.
- RANZCR. Clinical Radiology Phase 2 OSCER Sample Questions, v1.6 (4 May 2026). Sydney: RANZCR. (Format reference only; no RANZCR images reproduced.)
Always check current Australian/local guidelines.
Image credits
- A by Bill Rhodes, CC BY 2.0, via Wikimedia Commons. Changes: resized and re-encoded (WebP/JPEG). Teaching arrows and labels are a separate overlay added by this site.
- B by James Heilman, MD, CC BY-SA 3.0, via Wikimedia Commons. Changes: resized and re-encoded (WebP/JPEG). Adapted image shared under the same licence.
Original file titles are listed on the image credits page (they may reveal the diagnosis).