Choledocholithiasis - MRCP

45 year old female with pain abdomen and jaundice underwent MRI and MRCP revealed calculus in the distal common bile duct obstructing the lumen resulting in mild to moderate upstream dilatation of the intra hepatic biliary radicals.

Discussion:

Choledocholithiasis is relatively common, seen in in 6 - 12% of patients who undergo cholecystectomy. They may present with biliary colic, ascending cholangitis, obstructive jaundice, acute pancreatitis. Stones within the bile duct may form either in situ or pass from the gallbladder, and when recurrent tend to be pigment stones, and are thought to be associated with bacterial infection.
USG: Sensitivity varies from 13 to 55%. Features include dilated duct with stones visualized within. Recently endoscopic ultrasonography (EUS) has also been used with very high sensitivity and specificity.
CT: Moderate sensitivity of 65 - 88% but have to look for very subtle findings. They are

• Target sign - Central rounded density of stone with surrounding lower attenuating bile or mucosa.
• Rim sign: Stone is outlined by thin shell of density.
• Crescent sign: Bile eccentrically outlines luminal stone, creating a low attenuation crescent.
• Calcification of the stone: unfortunately only 20% of stones are of high density

Setting window level to the mean of the bile duct and setting the window width to 150HU has been reported to improve sensitivity.
MRCP: is the gold standard investigations for biliary lithiasis replacing the ERCP. Filling defects are seen within the biliary tree on thin cross-sectional T2 weighted imaging.