Bile duct

The common bile duct (ductus choledochus) is a tube-like anatomic structure, about 10-13 cm in length, in the human gastrointestinal tract. It's formed by the union of the common hepatic duct and the cystic duct (from the gallbladder). It is later joined by the pancreatic duct to form the ampulla of Vater. This is the narrowest point of the duct, where it narrows to an average of 6 mm in diameter. There, the two ducts are surrounded by the muscular sphincter of Oddi.
When the sphincter of Oddi is closed, newly synthesized bile from the liver is forced into storage in the gall bladder. When open, the stored and concentrated bile exits into the duodenum. This conduction of bile is the main function of the common bile duct. When a person is not eating, about 25% of the bile produced by the liver passes straight into the bile duct with the rest being redirected into the gall bladder. The hormone cholecystokinin, when stimulated by a fatty meal, promotes bile secretion by increased production of hepatic bile, contraction of the gall bladder, and relaxation of the Sphincter of Oddi. Although the Sphincter of Oddi surrounds both ducts, it also contains a separate sphincter for each of the two ducts that pass through it.
Several problems can arise within the common bile duct. If clogged by a gallstone, a condition called choledocholithiasis can result. In this clogged state, the duct is especially vulnerable to an infection called ascending cholangitis. Both of these can be life threatening conditions if not treated promptly and should be treated as medical emergencies. Either the infection may spread (with the possibility of sepsis) or bilirubin may build up in the liver. A lengthy blockage can cause chronic liver disease or biliary cirrhosis. Very rare deformities of the common bile duct are cystic dilations (4 cm), choledochoceles (cystic dilation of the ampula of Vater (3–8 cm), and biliary atresia.
There are several other conditions that can result in a blockage of the duct, although gallstones are by far the most common case. These include cysts, enlargement of the lymph nodes in the porta hepatis, inflammation of the duct itself, narrowing from scarring (sclerosing cholangitis), tumors of the bile duct or pancreas, other tumors (particularly liver tumors) that have spread through the biliary tree and liver flukes. An infection can also cause a blockage, particularly if the patient is immunocompromised. This is a common complication in patients with AIDS.
As a result, even when an issue is traced to the bile duct, a differential diagnosis can be difficult and often requires a team of different specialists to come to a definitive diagnosis. This could include a surgeon, radiologist, endoscopist, and oncologist.
About 65% of bile duct tumors occur at the point where the hepatic ducts join, the hilum, and are often called hilar tumors or Klatskin tumors. The remainder start further down the duct and are referred to as distal bile duct tumors. About 95% of all bile duct tumors are adenocarcinomas which develop from the mucous membranes that line the inside of the duct. Most of the rest are sarcomas, lymphomas, or small-cell carcinomas. However, not all tumors of the bile duct are malignant - some are benign adenomas.
The bile duct can be damaged during medical procedures. One of the common complications of a cholecystectomy is accidentally severing the bile duct instead of the cystic duct. In addition, both a cholecystectomy or an ERCP can damage the duct, causing it to leak. In addition, after a cholecystectomy, the seal on the now removed cystic duct can also leak. If the damage is noticed during surgery, the surgeon can usually repair the damage, although it will require an open procedure and will prolong the period under anesthesia, the recovery time, and the possibility of infection and further complications. However, if the leak is only discovered after the incisions are closed, a shunt usually has to be inserted to drain the bile until such time as the area heals well enough to allow a second procedure to repair the damage. In either case, most of the bile duct is removed and a graft is attached to both ends of the remaining duct.
When diagnosing issues with the bile duct, the patient's medical history should be reviewed for a history of gallstones, chronic pancreatitis or pancreatic cancer, any recent injury to the abdomen, any recent surgery in the area of the biliary ducts and any recent biliary cancer.
Typical symptoms of bile duct issues include abdominal pain on the upper right side, darkened urine, fever, itching, jaundice, nausea, vomiting, and pale-colored stool (from the lack of bile). A physician or nurse will usually start with tests for bilirubin, alkaline phosphatase, and liver enzymes, all of which will typically be elevated. Radiological investigation usually starts with an ultrasound (which will find gallstones if they exist). After that, the physician will proceed with a CT Scan, an Endoscopic retrograde cholangiopancreatography (ERCP), a Percutaneous transhepatic cholangiogram, and/or an MRI.
A blocked bile duct can affect the results of a number of tests, such as those for amylase, a gallbladder radionuclide scan, lipase, prothrombin time, and bilirubin in the urine.
Treatment focuses on removal of the blockage. For example, during an ERCP, the gallstones can be removed from the duct using the same endoscope used for the examination. However, in many cases, surgery may be required. Antibiotics are usually administered to deal with both the infection caused by the blockage and any infection that may result from surgery. In these cases, the outcomes for the patient are generally positive. If the blockage is due to cancer, the duct may be dilated to make it wider, or a shunt may be inserted to bypass the blockage. However, if the blockage is caused by cancer, the prognosis for the patient is usually very poor.
A rare complication of common bile duct blockage is Vitamin K deficiency as although the patient may still be getting dietary Vitamin K, without bile, the body cannot process the vitamin. Another rare symptom of bile duct blockage is Kayser-Fleischer rings.
==On the show==
*During the differential diagnosis of newborn Kayla, Chase thought that her hepatic ducts were dilated while her bile duct was normal. He thought it might be a congenital condition, Caroli's syndrome.
*During the differential of sleepy Hannah, House ordered an endoscopic examination of her bile duct to look for what might be damaging her liver.
*House suspected Hank Hardwick might have had sclerosing cholangitis and ordered an endoscopy of the bile duct. Instead, the team found the strongyloides parasite.
*After looking at Alice Hartman's X-rays, House noted that her bile duct was dilated and, despite the fact she was only about five years old, thought the duct was blocked by a gallstone. Although his team disagreed with him, an ultrasound confirmed House's diagnosis.
*A biopsy showed Abigail Ralphean had severe inflammation of the bile duct. As a result, Cuddy ordered an ERCP to look for cancer.
Common bile duct at Wikipedia
Category:Anatomy
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