The coffee-bean sign (also known as kidney bean sign and bent inner tube sign 4 ) is a sign on an abdominal plain film of a sigmoid volvulus although some authors have also used the term to refer to closed loop small bowel obstructions.
This thick 'inner wall' represents the double wall thickness of opposed loops of bowel, with thinner outer walls due single thickness.
LINKS:
http://radiopaedia.org/articles/coffee-bean_sign
http://radiopaedia.org/articles/sigmoid-volvulus
------------------------------------------------------------------------------------------------
This patient has undergone an ERCP, on the image you can see air in the common bile duct (ductus choledochus)