2 The condition, current treatments and procedure
2.1 Bile duct stones that form from cholesterol or bile pigments can block the bile ducts. Difficult-to-treat bile duct stones are defined by their diameter (above 15 mm), number, unusual shape (such as barrel-shaped), location (intrahepatic or cystic duct), stone impaction, narrowing of the bile duct distal to the stone, or the anatomy of the common bile duct (sigmoid-shaped, short distal length or acute distal angulation of less than 135 degrees).
2.2 Diagnosis and management of bile duct stones is described in NICE's guideline on gallstone disease. Treatments for bile duct stones include bile duct clearance and laparoscopic cholecystectomy. Conventional stone extraction involves endoscopic retrograde cholangiopancreatography (ERCP) and a sphincterotomy, then extracting the stones from the ducts using balloon and basket catheters. For difficult-to-treat bile duct stones, treatment options include temporary stenting to allow biliary drainage if the stones cannot be removed or stone fragmentation (lithotripsy).
2.3 Electrohydraulic lithotripsy (EHL) aims to fragment bile duct stones that cannot be treated using conventional stone removal techniques.
2.4 This procedure is usually done using general anaesthesia and direct visualisation of the stones using an endoscope inserted into the biliary tract. An EHL probe is inserted through the endoscope and the tip of the probe is positioned near the stone. Liquid is then injected around the stone and high-voltage energy from the probe generates shock waves that break the stone into smaller pieces. The procedure is usually done with the endoscope passed orally and through the stomach into the duodenum. However, a percutaneous approach is also possible.
2.5 When the stone fragmentation is complete, the fragments are flushed out or removed by standard techniques (such as a basket or balloon catheter). The endoscope is then removed. This procedure takes longer to complete than a standard ERCP, usually about 60 minutes.