On CT of the abdomen, the 'whirl sign' is identified in the mesentery with twisted mesenteric vessels around an axis. What condition does this sign indicate?

• A Mesenteric adenitis
• B Closed-loop small bowel obstruction with midgut volvulus ✓
• C Ischemic colitis
• D Internal hernia without torsion

Explanation

The whirl sign on CT describes the twisted appearance of mesenteric fat and vessels wrapping around a fixed central axis, resembling a 'whirlpool'. It indicates volvulus or midgut rotation around the superior mesenteric artery axis, typically in closed-loop small bowel obstruction. When combined with a 'beak sign' at the transition point and C-shaped or U-shaped dilated bowel loops, it is diagnostic of small bowel volvulus requiring emergency surgery. The whirl sign can also be seen in cecal volvulus. Mesenteric adenitis and ischemic colitis do not produce a whirl sign.

Reference: Grainger & Allison's Diagnostic Radiology, 7th ed.

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