Which radiographic sign is most characteristic of sigmoid volvulus?

• A. Bent inner tube sign
• B. Coffee bean sign
• C. Double bubble sign
• D. Thumbprint sign

Answer: (A)

Twisted sigmoid colon creates a closed-loop large-bowel obstruction, and the most characteristic radiographic feature is the bent inner tube sign. This sign comes from a markedly distended sigmoid loop whose inner mucosal border folds to form a sharp, curved edge that resembles a bent inner tube. The twisting brings the bowel into a single, large loop with this distinctive inner margin, making the image highly suggestive of sigmoid volvulus on plain films or contrast studies.

The coffee bean sign is also a classic clue, reflecting a large, bean-shaped dilation of the sigmoid that points toward the pelvis, but the bent inner tube sign specifically highlights the mucosal folding created by the twist and is more characteristic of the volvulus itself.

Other signs listed are associated with different conditions: the double bubble sign points to early neonatal duodenal atresia, and the thumbprint sign indicates mucosal edema from ischemia or inflammatory colitis, not sigmoid volvulus.