History 79-year-old woman with acute severe abdominal pain and new confusion. She is unable to sit or stand. Supine abdominal radiograph.
Abdominal radiographs, released in stages · Click an image to enlarge.
Image B
A further radiograph has been obtained. The examiner releases it during the case.
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 are the pertinent findings on the supine radiograph?
Reveal answer
A Annotated 3 marks Observation
- Both the inner and outer walls of bowel loops are visible (gas on both sides of the wall) (1.5)
- Multiple gas-filled, mildly dilated bowel loops (0.5)
- Search for other supine free-gas signs (0.5 each, max 1): RUQ / perihepatic gas, falciform ligament, football sign, triangular gas between loops (1)
Examiner note The examiner releases image B after Q1 has been answered.
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Q2 [Second image released] What does the second image show, and what is your preferred diagnosis?
Reveal answer
B Annotated 2 marks Interpretation
- Free gas collecting over the liver, under the non-dependent right flank (1)
- Pneumoperitoneum, most likely from a perforated hollow viscus (1)
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Q3 What is the next step?
Reveal answer
2 marks Management/Safety
- Urgent surgical review, resuscitation and the sepsis pathway; stabilise before transfer to CT (1)
- CT abdomen/pelvis with IV contrast once stable, to localise the source (diverticular, peptic, ischaemic, malignant) (1)
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Q4 Why was a LEFT lateral decubitus view chosen, and how should it be performed?
Reveal answer
3 marks Applied sciences
- Right side up: free gas rises over the homogeneous liver, where it cannot be confused with gastric or colonic gas (1)
- Horizontal x-ray beam, so the gas–soft-tissue interface is shown tangentially (1)
- Patient stays in position for about 10 minutes before exposure (Miller & Nelson 1971) (0.5)
- Include the upper (right) flank and lateral liver edge on the film (0.5)
End of the OSCER block (10 marks).
Beyond the exam: teaching extension
Q5–Q9: not part of the 10-mark OSCER block. Untimed, viva-style discussion: mimics and pitfalls, complications, guidelines and report wording.
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Q5 List the supine signs of pneumoperitoneum.
Reveal answer
- Rigler (double-wall) sign (Rigler 1941); usually needs a moderate to large volume of gas
- RUQ / perihepatic gas: the commonest supine sign in Levine et al. 1991; also Morison pouch gas
- Falciform ligament sign, football sign, inverted V (lateral umbilical ligaments), urachus sign, triangular gas between loops, cupola sign
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Q6 What causes a false-positive Rigler sign?
Reveal answer
- Gas-filled loops lying against each other (apparent double wall)
- Fat in the mesentery or bowel wall outlining the serosa
- Confirm with a horizontal-beam view or CT
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Q7 Which patients get a supine-only film, and why does it matter?
Reveal answer
- ICU, frail, obtunded, trauma and post-operative patients
- Supine films often miss free gas; a decubitus view or CT is needed
- Post-operative free gas is expected and usually resolves over days; read new or increasing gas in context
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Q8 This patient's eGFR is 28. Does that change your CT plan?
Reveal answer
- No, in an emergency where CT will change management: the benefit outweighs the small risk; give IV contrast
- Hydrate, avoid repeat contrast doses close together, and document the risk–benefit discussion
- LO 6.1.9–6.1.11 (contrast pharmacology, risks, adverse events); the OSCER reports flag low eGFR and contrast as a weak area
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Q9 Draft the key sentences of your report.
Reveal answer
- 'The supine radiograph shows both sides of the bowel wall (Rigler sign); the left lateral decubitus view confirms free gas over the liver. Pneumoperitoneum, likely a perforated viscus.'
- 'Telephoned to Dr [name], surgery, at [time].'
End of questions. Reveal the diagnosis, key takeaways and syllabus mapping below.
Reveal diagnosis, key takeaways & syllabus mapping
Diagnosis Pneumoperitoneum on supine AXR (Rigler sign) and left lateral decubitus
Key takeaways
- On a supine film, look for gas on both sides of the bowel wall and over the liver.
- If the patient cannot stand: left lateral decubitus, horizontal beam, wait about 10 minutes.
- Confirm a doubtful Rigler sign; loops lying together are the usual mimic.
- Stabilise, call the surgeon, then CT with contrast, even with reduced eGFR.
Syllabus mapping
| OSCER station | Abdominal |
|---|---|
| Learning Outcomes section | §6.6 Abdomen & Pelvis (+ §6.1.9–11 contrast) |
| 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 3 · Interpretation 2 · Management/Safety 2 · Applied sciences 3 (= 10) |
| Learning objectives | Recognise the supine signs of free gas; Justify the left lateral decubitus view; Make a contrast decision in renal impairment |
Mapped to the RANZCR Clinical Radiology Learning Outcomes v1.3 (January 2024), section 6 and Appendix 1.
Further reading
- Rigler LG. Spontaneous pneumoperitoneum: a roentgenologic sign found in the supine position. Radiology. 1941;37(5):604–607. doi:10.1148/37.5.604.
- 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.
- 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.
- 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 Scott1751, CC BY-SA 3.0, via Wikimedia Commons. Changes: resized and re-encoded (WebP/JPEG). Teaching arrows and labels are a separate overlay added by this site. Adapted image shared under the same licence.
- B 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.
Original file titles are listed on the image credits page (they may reveal the diagnosis).