Question: What is a stent and how is it used to relieve jaundice?

The information provided here should not be treated as a medical opinion and expert advice should be sought.

Answer

What is a stent and why is it used?

Sometimes it is necessary to insert a plastic or metal mesh tube into the bile duct to keep a good flow of bile and relieve the symptoms of jaundice (see note 1) in patients with pancreatic cancer. These tubes are called biliary stents - after Dr Stent who first used these small tubes.

The bile duct will have been blocked by either tumour within the pancreas pressing on the bile duct, which passes through the head of the pancreas, or growth of tumour within the bile duct (especially in bile duct cancer). The stent forces the bile duct to stay open and allows the bile to start flowing again from the liver to the duodenum. A stent can be put in either through the bottom of the bile duct using a technique called an ERCP (endoscopic retrograde cholangio-pancreatography - inserting a flexible telescope into the mouth, through the gullet, stomach and into the duodenum) or through the skin and liver into the top of the bile duct using a technique called a PTC (Percutaneous transhepatic cholangiogram) the choice being determined by a number of factors. Usually the endoscopic technique is tried first. 

Plastic and temporary or metal and permanent

A plastic stent can be referred to as a temporary stent for two reasons. One is that it can be replaced when it becomes blocked. The second is that it is sometimes a temporary measure to relieve jaundice prior to surgery or assessment for surgery. If Whipple's surgery is performed the stent will be removed along with the part of the pancreas and bile duct affected by the cancer and the remaining part of the bile duct will be connected directly to the small bowel without passing through any part of the pancreas. Even if the tumour is not resected the surgeon may perform a "double bypass" (see note 2) which involves bypassing the blocked part of the bile duct into the small bowel and removing the stent.

A metal stent (in the form of a wire mesh) is much wider than a plastic stent and can be referred to as a permanent stent for three reasons. One is that it can't be removed as it has expanded in place and embeds so can't be pulled back out along the bile duct. The second is that it isn't usually used as a temporary measure before surgery. Thirdly as it is wider than a plastic stent it generally lasts longer before it becomes blocked. If it does become blocked it isn't usually removed but a plastic stent, or second metal stent, may be placed inside it.

A plastic stent should normally be used if it is felt that stenting is necessary to relieve symptoms of jaundice but it is intended, or there is a possibility, that surgery will be performed. However a metal stent does not prevent major surgery but the operation is more challenging for the surgeon. This is because, as mentioned above, metal stents are difficult to remove and they are very wide and cause intense surrounding inflammation and fibrosis .

In fact some centres may not routinely insert stents to relieve jaundice before surgery. This is to avoid delays and the slight risk of complications from the stent insertion procedure via ERCP such as infection and inflammation of the surrounding tissue. The decision will probably depend on whether the patient's symptoms are tolerable and not too severe.

A patient must also be fit enough to undergo an ERCP for a stent to be used to relieve jaundice.

Block of stents - urgent action

Plastic stents generally only last about 3-4 months before they get blocked (due to build-up of deposited bilirubin/bile sludge) and need to be replaced. If there is a delay in getting back to the hospital for a replacement there is risk of infection (due to build up of bacteria in the stent). A second plastic stent may occlude faster than the first time.

Metal stents are more expensive (£800-£1000 compared to £20-£80 for plastic stents) but they may last longer before blocking as they are much wider. Randomised trials show an average time of about 5-9 months before blockage in metal stents. They are often preferred in patients when chemotherapy is planned to avoid serious complications due to risk of infection with low white counts. Blockage (and risk of infection) can still occur with metal stents due to tumour growing through the wire mesh or over the ends as they are shorter than plastic stents.

It is important to realise that stents (both plastic and metal) can get blocked so that symptoms of fat malabsorption and jaundice may recur, there may be pain or more importantly symptoms of infection (acute cholangitis - infection of the biliary tree - or septicaemia - infection in the blood) such as fever and rigors may occur. Rigors, a violent attack of shivering often associated with fever, is a classic symptom of blockage (see note 3). The shivering will tend to settle within 20-30 mins, however it will recur if ignored. It is important to seek medical attention as soon as possible if symptoms occur, especially of infection. They can then assess whether a replacement is needed and administer antibiotics if necessary. If the infection is due to cholangitis the stent should always be replaced. Stents may occasionally also dislodge (eg if the tumour has been reduced in size due to treatment) and need to be replaced.

Notes

Both bile acids and pancreatic enzymes are needed to ensure proper digestion of fat. The bile acids are needed to disperse the fat before the pancreatic enzymes break it down. If there are insufficient pancreatic enzymes the stools become pale and greasy (steatorrhoea) as the fat has not been properly digested. If there is a blockage of the bile duct the stools will also become pale due to poor digestion of fat and because it is bile that gives the dark colour to stools. The bile that has been produced in the liver cannot get to the bowel and it goes into the blood and through the kidneys into the urine which becomes dark in colour. Also as it is in the blood the eyes and skin become yellow - yellow jaundice. There is sometimes itching of the skin due to the jaundice.

If surgery is attempted but resection of the tumour is not possible due to findings at operation, a "double bypass" is often performed to prevent future problems. As the tumours become more advanced, they can block both the biliary system (between the liver and the intestine) and the duodenum (first part of the small intestine) resulting in recurrent jaundice or a blocked intestine with vomiting. The preventative surgery involves joining the bile duct (above the blockage) to the small intestine (an hepaticojejunostomy) and the stomach to the small intestine (a gastroenterostomy) thereby giving the liver and stomach an alternative method of emptying even if the tumour expands.

Rigors is a classic symptom of acute cholangitis - When a stent blocks it almost invariably does so with a coagulum containing bile and bacteria - the blockage results in a bacteraemia (bacteria getting into the blood) which causes the patient to have a sudden episode of feeling incredibly cold with uncontrollable shivering (this is a "rigor"). The shivering generates heat which results in the patient developing a fever after about 20 mins when the shivering stops.