RD7.4 | Imaging in Intestinal Obstruction — Summary & Reflection

KEY TAKEAWAYS

Imaging in Intestinal Obstruction — Key Points

• Suspect obstruction clinically (colicky pain, vomiting, distension, absolute constipation); imaging confirms, localises, identifies the cause and detects complications.
• Erect + supine abdominal X-ray is the first investigation — confirms obstruction, suggests the level, shows air-fluid levels, and free subdiaphragmatic gas (perforation); an erect chest X-ray helps detect free air. It CANNOT assess bowel viability.
• Contrast-enhanced CT abdomen/pelvis is the modality of choice to identify the level (transition point), the cause, a closed-loop, and ischaemia (absent bowel-wall enhancement).
• Small-bowel obstruction: central loops, valvulae conniventes crossing the FULL lumen, dilated >3 cm, multiple air-fluid levels, little colonic gas. Commonest cause: adhesions.
• Large-bowel obstruction: peripheral loops, haustra (do NOT cross the full lumen), colon >6 cm, caecum >9 cm. Commonest cause: colorectal carcinoma; sigmoid volvulus = coffee-bean loop.
• Danger signs: free subdiaphragmatic gas (perforation), closed-loop with non-enhancing/thickened bowel + mesenteric oedema + free fluid (strangulation/ischaemia), caecum approaching 9-12 cm with a competent ileocaecal valve (imminent caecal perforation).
• Integrate into management: simple non-ischaemic (adhesional) SBO → conservative 'drip and suck' + monitoring; closed-loop/ischaemia/strangulation/perforation → urgent surgery with resection; LBO → cause-directed (resection, stoma, stent; endoscopic decompression of sigmoid volvulus). Never give barium when perforation is possible.

REFLECT

On your next surgical posting, take the first abdominal film of an obstructed patient and call it yourself before the report arrives: are the loops central or peripheral, do the folds cross the full lumen, and what is the calibre? Then, when the CT is reviewed, find the transition point, name the cause, and — most importantly — decide whether the bowel enhances. Watch how the team uses 'viable and simple' versus 'ischaemic or closed-loop' to choose between a nasogastric tube and a trip to theatre. And keep the caecum in your eye in large-bowel obstruction, because the quiet, distending caecum is the one that perforates. Linking the film, the CT and the surgical decision into a single chain of reasoning is exactly what RD7.4 asks of you.