History 82-year-old man from residential aged care with 4 days of increasing abdominal distension and no bowel motion or flatus. Long-standing constipation.
Abdominal radiographs: frontal and left lateral decubitus (horizontal beam) · 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 are your observations?
Reveal answer
A Annotated 3 marks Observation
- Massively dilated ahaustral loop of large bowel forming an inverted U ('coffee bean') rising out of the pelvis (1)
- Apex extends into the right upper abdomen; the limbs converge towards the left lower quadrant / pelvis (1)
- Dilated proximal colon with haustra (0.5)
- Gas-free rectum (0.5)
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Q2 What is your preferred diagnosis? Give two differential diagnoses.
Reveal answer
2 marks Interpretation
- Preferred: sigmoid volvulus (1)
- Differentials (0.5 each, max 1): caecal volvulus; acute colonic pseudo-obstruction (Ogilvie syndrome); distal large bowel obstruction from carcinoma (1)
Examiner note Caecal volvulus: a single dilated loop, apex usually towards the left upper quadrant, dilated small bowel, collapsed distal colon.
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Q3 What do you recommend next?
Reveal answer
3 marks Management/Safety
- CT abdomen/pelvis with IV contrast to confirm (whirl sign, bird's beak) and look for ischaemia or perforation (1)
- No peritonitis, ischaemia or perforation: endoscopic decompression (flexible sigmoidoscopy) ± rectal tube (1)
- Emergency surgery for peritonitis, perforation, ischaemia or failed decompression; recurrence is common, so discuss definitive sigmoid resection in fit patients (WSES 2023) (1)
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Q4 Which anatomical and clinical factors predispose to this condition?
Reveal answer
2 marks Applied sciences
- A long, redundant sigmoid colon on a narrow mesenteric base (1)
- Chronic constipation, older age, institutional care, neuropsychiatric illness and its medications; also high-fibre-diet regions, Chagas disease, pregnancy (1)
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 Which plain-film and CT signs are described?
Reveal answer
- Plain film: coffee bean; northern exposure sign (apex above the transverse colon); liver and left flank overlap signs; inferior convergence
- CT: whirl sign of the twisted mesentery, bird's beak at the transition points, X-marks-the-spot (crossing limbs), split-wall sign (Levsky 2010)
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Q6 Compare caecal and sigmoid volvulus.
Reveal answer
- Sigmoid: older, often institutionalised; ahaustral loop from the pelvis; endoscopic decompression first
- Caecal: younger to middle-aged, mobile caecum; haustrated loop, often in the left upper quadrant; small bowel dilated
- Caecal volvulus is not treated endoscopically: it needs surgery (right hemicolectomy)
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Q7 What are the complications?
Reveal answer
- Venous then arterial compromise: ischaemia, gangrene, perforation, faecal peritonitis
- Recurrence after non-operative decompression is high (Raveenthiran 2010; WSES 2023)
- Aspiration from vomiting; electrolyte disturbance
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Q8 Why add a decubitus film or CT rather than more plain films?
Reveal answer
- A horizontal beam (decubitus) shows fluid levels and free gas when the patient cannot stand
- CT confirms the diagnosis and, crucially, shows ischaemia and perforation, which decide endoscopy vs surgery
- A water-soluble contrast enema (bird's beak) is now rarely needed
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Q9 Draft the key sentences of your report.
Reveal answer
- 'Massively dilated ahaustral inverted-U loop arising from the pelvis with a gas-free rectum, consistent with sigmoid volvulus.'
- 'Recommend urgent surgical review and CT with IV contrast to assess bowel viability before endoscopic decompression.'
End of questions. Reveal the diagnosis, key takeaways and syllabus mapping below.
Reveal diagnosis, key takeaways & syllabus mapping
Diagnosis Sigmoid volvulus
Key takeaways
- A coffee-bean loop from the pelvis with a gas-free rectum is sigmoid volvulus until proven otherwise.
- CT decides management by looking for ischaemia and perforation.
- Decompress endoscopically if viable; recurrence is common, so plan definitive treatment.
- Caecal volvulus is a surgical, not endoscopic, problem.
Syllabus mapping
| OSCER station | Abdominal |
|---|---|
| Learning Outcomes section | §6.6 Abdomen & Pelvis |
| Appendix 1 condition | Volvulus including caecal and sigmoid (Appendix 1 F, Large intestine, p73); Large bowel obstruction (p73) |
| Category | Category 1 |
| Key Condition | Yes |
| Core marks by domain | Observation 3 · Interpretation 2 · Management/Safety 3 · Applied sciences 2 (= 10) |
| Learning objectives | Recognise sigmoid volvulus on AXR; Use CT to assess viability; Know the endoscopic vs surgical pathway and how caecal volvulus differs |
Mapped to the RANZCR Clinical Radiology Learning Outcomes v1.3 (January 2024), section 6 and Appendix 1.
Further reading
- Raveenthiran V, Madiba TE, Atamanalp SS, De U. Volvulus of the sigmoid colon. Colorectal Dis. 2010;12(7 Online):e1–e17. PMID 20236153.
- Tian BWCA, Vigutto G, Tan E, et al. WSES consensus guidelines on sigmoid volvulus management. World J Emerg Surg. 2023;18(1):34. PMID 37189134.
- Levsky JM, Den EI, DuBrow RA, et al. CT findings of sigmoid volvulus. AJR Am J Roentgenol. 2010;194(1):136–143. PMID 20028915.
- 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 Hellerhoff, 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 Hellerhoff, 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).