Common bile duct (CBD) stone disease

What is common bile duct?

The common bile duct (CBD) is the tubethat connects gall bladder to the upper part of the small intestine (the duodenum). The function of CBD is to carry bile from the gallbladder and empty it into the duodenum. CBD is the distal continuation of the common hepatic duct, the tube that carries bile from the liver to the gall bladder.

Gall bladder along with its duct (cystic duct), common hepatic duct, and CBD comprises of the ‘biliary system’.

How can stone come into CBD?

Presence of stones in CBD is known as CBD stones or choledocholithiasis. There are two mechanisms of CBD stones:

• Gallstones can sometimes come out of gall bladder into the CBD, and may get stuck there. About 10%-20% patients have concomitant CBD stones.
• Occasionally stone may form de novo in the CBD. This usually occurs if CBD is narrow due to stricture.

What are the symptoms of CBD stone?

Symptoms of choledocholithiasis include pain in the upper abdomen, jaundice, and occasionally fever. The presence of fever indicates the presence of infection in the bile ducts known as cholangitis, which is life threatening. Rarely the CBD stone may also obstruct the opening of the pancreatic ductbecause these ducts are usually connected.This may cause acute pancreatitis, which is another serious disease manifesting as severe pain, vomiting, fever, and distension.

How are CBD stones diagnosed?

Following tests aid in the diagnosis of CBD stones:

• Ultrasound of the upper abdomen: This is the most commonly used test to diagnose CBD stones. It shows CBD stones as echogenic rounded focus in the CBD. It may occasionally miss CBD stones because of presence of excessive gases in the abdomen; it may nevertheless still show dilated bile ducts, which indirectly indicates presence obstruction of bile duct.
• Liver function tests (LFT): These are set of blood tests used to diagnose diseases of the liver and the biliary system. Usually in presence of CBD stones the bilirubin level, alkaline phosphatase level, and gamma-glutamyltranspeptidase (GGT) levels will be elevated. If CBD stones are complicated by infection (cholangitis), the transaminases will also be elevated. However, LFT alone cannot make the diagnosis of CBD stones, and additional imaging test such as ultrasound will be required to reliably diagnose CBD stones.
• Magnetic resonance cholangio-pancreatography (MRCP): This is an MRI-based tests used for accurate diagnosis of CBD stones. It is noninvasive and does not use ionizing radiation. However, this test cannot be done in patients who are claustrophobic or those who have metallic implants such as joint prostheses or pacemakers.
• Endoscopic ultrasound (EUS): This is also one of the most accurate tests to diagnose CBD stones. It is an endoscopy-based test where a special type of endoscope (echoendoscope) is used that has an ultrasound-probe at its tip. The patient will require conscious sedation for this test.
• Endoscopic retrograde cholangiopancreatography (ERCP): This is another endoscopy-based test, which not only diagnoses CBD stones, but also treats it.
• Computerized tomography (CT) scan: It is more accurate than ultrasound but inferior to MRCP in diagnosing CBD stones. However, recent advances, such as the “helical” CT scan and CT cholangiographyhave increased accuracy in diagnosis of CBD stones.

What is the treatment for CBD stones?

CBD stoneshave to be physically removed and there is no medicine or drugs that can remove or dissolve these stones. The physical removal of CBD stones may be accomplished either by endoscopic method (with or without lithotripsy) or by surgical method (traditional or laparoscopic).

How are CBD stones removed endoscopically?

The most widely used method for treating CBD stones is their endoscopic removal by ‘endoscopic retrograde cholangiopancreatography (ERCP)’. A special type of endoscope known as side-viewing endoscope is introduced through the mouth and its tip is positioned in the first part of small intestine (duodenum) near the opening of CBD. From the tip of endoscope a catheter is introduced into the CBD through which a dye is injected. This dye opacifies the entire CBD as seen by fluoroscopically, and the stone becomes visible as filling defect in the CBD. Subsequently a wire basket is introduced in the CBD which catches the stones and brings it out of CBD into the duodenum from where it can be taken out. To aid the extraction of stone from the CBD a small cut is made at the opening of CBD to enlarge it so that stone can be extracted easily. To completely clear the CBD a special balloon is sweeped in the CBD to remove any stone particles.

What is lithotripsy and how does it help in removing CBD stone?

Lithotripsy physical breaking of stone.The term is derived from the Greek words meaning "breaking (or pulverizing) stones". If the CBD stone is large it cannot be extracted from CBD in one piece and has to be broken into pieces using lithotripsy so that these pieces can be extracted easily by ERCP. There are many types of lithotripsy procedures as given below, and depending on the need and availability any one of them can be used for removal of large stones:

• Endoscopic mechanical lithotripsy
• Endoscopic electrohydraulic lithotripsy
• Endoscopic laser lithotripsy
• Extracorporeal shock-wave lithotripsy

When is surgery needed for CBD stone removal?

When CBD stones cannot be removed endoscopically, they have to be removed surgically. The advantage of surgical treatment is that both CBD stones and gall bladder stones can be taken care of in one stage. Most commonly laparoscopic approach is applied.