The cystic duct knot sign: case report with description of a new ultrasound sign of gallbladder torsion.

Gallbladder torsion or volvulus is a rare but potentially lethal entity. We report the imaging findings of gallbladder torsion and describe a potentially novel ultrasound sign for the preoperative diagnosis of torsion. An 87-year-old woman presented with a 4-day history of right upper quadrant pain. An initial right upper quadrant ultrasound exam demonstrated cholelithiasis and findings of acute cholecystitis which included gallbladder distension, wall thickening, trace pericholecystic fluid, and a positive sonographic Murphy's sign. Gallbladder torsion was prospectively diagnosed on the subsequent contrast-enhanced CT scan of the abdomen based upon the abnormal transverse orientation of the gallbladder with the neck directed laterally. Ultrasound images were reviewed and a "knot"-like hyperechoic nodular appearance of the torsed cystic duct close to the gallbladder neck was clearly apparent. Prospective identification of the torsed cystic duct may prompt the ultrasound diagnosis of gallbladder torsion.