A 65-year-old woman presents with colicky central abdominal pain, vomiting, and absolute constipation for 24 hours. She has no prior abdominal surgery but has known right-sided colon cancer diagnosed 3 months ago (not yet treated). AXR shows dilated small bowel loops. CT scan confirms a closed-loop obstruction of the small bowel with venous engorgement. The mechanism distinguishing closed-loop obstruction from simple mechanical obstruction is:

• A Closed-loop obstruction involves a single obstruction point but the bowel proximal to it decompresses via vomiting
• B Closed-loop obstruction involves both afferent and efferent limbs obstructed at a single point, trapping a loop without proximal decompression — causing rapidly progressive ischaemia ✓
• C Closed-loop obstruction occurs only with internal hernias and adhesions, not with extrinsic compression
• D Closed-loop obstruction is distinguished by mesenteric lymphadenopathy on CT

Explanation

A closed-loop obstruction occurs when a segment of bowel is obstructed at two points simultaneously (e.g., a loop twisted on its mesentery, or herniated through a defect with both entry and exit obstructed). Because the loop has no inlet or outlet for decompression, intraluminal pressure rises rapidly leading to venous congestion, mucosal ischaemia, and progression to full-thickness necrosis and perforation much faster than simple mechanical obstruction. CT features include the 'whirl sign' (twisted mesentery), C-shaped or U-shaped dilated bowel loop, and mesenteric vascular engorgement. This is a surgical emergency requiring immediate operative intervention.

Reference: Bailey & Love's Short Practice of Surgery, 27th ed.

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Written and medically reviewed by the StethoPrep medical team.