Choledocholithiasis

Choledocholithiasis denotes the presence of gallstones within the bile ducts (including the common hepatic duct/common bile duct).

Epidemiology

Choledocholithiasis is relatively common, seen in up to 20% of patients undergoing cholecystectomy for gallstone-related complaints ².

Clinical presentation

Stones within the bile ducts are occasionally asymptomatic and may be found incidentally. However, more frequently they lead to symptomatic presentation with:

• biliary colic

• ascending cholangitis

• obstructive jaundice

• acute pancreatitis

Pathology

Stones within the bile duct most commonly pass from the gallbladder but may form in situ. When recurrent, they tend to be pigment stones, and are thought to be associated with bacterial infection ¹.

Radiographic features

Ultrasound

Although ultrasound is usually the first investigation for biliary disease, it has average sensitivity for the detection of biliary stones within the bile duct.

Ultrasound should be performed both longitudinally and transversely through the duct with particular attention paid to the very distal portion of the common bile duct as it passes through the pancreatic head (best assessed transversely).

Findings include:

• visualization of stone(s)

  • echogenic rounded focus

  • size ranges between 2 to >20 mm

  • shadowing may be more difficult to elicit than with gallstones within the gallbladder

  • ~20% of common bile duct stones will not shadow

  • twinkling artifact may be useful to detect occult stones

• dilated bile duct

  • >6 mm + 1 mm per decade above 60 years of age

  • >10 mm post-cholecystectomy

  • dilated intrahepatic biliary tree

• gallstones should increase suspicion, especially if multiple and small

Recently endoscopic ultrasonography (EUS) has also been used with very high sensitivity and specificity.

CT

Routine contrast-enhanced CT is moderately sensitive to choledocholithiasis with a sensitivity of 65-88% ³, but it requires attention to a number of potentially subtle findings. These include:

• target sign

  • central rounded density: stone

  • 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 150 HU has been reported to improve sensitivity.

Biliary dilatation may also be visible.

CT cholangiography

CT with prior administration of biliary excreted contrast agents is highly sensitive (88-96%) and specific (88-98%) ⁸ for choledocholithiasis. The difficulty is, however, two-fold:

1. contrast agents have relatively high complication rates

2. obstructive cholestasis diminishes excretion, and thus is only viable in patients with largely normal liver function tests

MRCP

Magnetic resonance cholangiopancreatography (MRCP) has largely replaced ERCP as the gold standard for diagnosis of choledocholithiasis, able to achieve similar sensitivity (90-94%) and specificity (95-99%) ^7,8 without ionizing radiation, intravenous contrast, or the complication rate inherent in ERCP.

Filling defects are seen within the biliary tree on thin cross-sectional T2 weighted imaging. Care should be taken not to use thick slabs for the diagnosis as volume averaging may obscure smaller stones.

However, if the diagnosis has already been secured by ultrasound or CT, there is no additional value of MRCP, and the next step is therapeutic ERCP (see below).

Percutaneous or oral cholangiography

Both investigations are no longer used for routine diagnosis having been replaced by ultrasound, CT and MRCP.

Treatment and prognosis

Endoscopic retrograde cholangiopancreatography (ERCP) with sphincterotomy is the treatment of choice for choledocholithiasis, however, is associated with a complication rate of 5.8-24% (10 years follow-up) ¹.

Complications of ERCP and sphincterotomy include:

• acute pancreatitis

• acute cholangitis

• perforation of esophagus, stomach or duodenum due to endoscopy

Failure of endoscopic clearance of bile duct stones may require either intraoperative bile duct exploration, or percutaneous biliary drainage to decompress the biliary system to temporise and allow subsequent definitive management.

Differential diagnosis

There is usually little differential, and differential will depend on the modality. The most frequent entities to consider include:

• malignancies

  • cholangiocarcinoma

  • ampulla of Vater carcinoma: arises from a distal position, at the pancreaticobiliary junction, and has low attenuation

  • pancreatic adenocarcinoma

• other filling defects

  • air bubbles

  • parasites

• mimics

  • partial volume averaging of bowel gas

  • vascular calcification

  • surgical clips

• MRCP specific potential pitfalls ⁶

  • susceptibility artifacts

  • flow voids

  • vascular impressions

  • sphincteric contraction or pseudocalculus sign