25. 1 Acute pancreatitis

Вид материала

Документы

Содержание Disease of the biliary tract

Подобный материал:

• Acute biliary pancreatitis. Treatment tactics, 134.96kb.
• The problem of acute pain and its substantial relief is common for every medical field., 344.88kb.

Ultrasonograpy is always the first imaging technique used in a patient with jaundice or cholangitis. Dilatation of the ducts establishes an extrahepatic obstructive cause for the jaundice and may also identify stones in the ducts (Fig. 10) 1233. An expert can identify the site of the obstruction in three-quarters of patients and the cause in one-third. Ultrasound can also be used during surgery to detect bile duct stones.


Contrast radiology

Oral cholecystography

Although this was the standard method of investigating the gallbladder for many years, it is now been superseded by ultrasonography. A biliary contrast medium based on triiodobenzoic acid, which is primarily excreted by the liver, is taken by mouth. It is absorbed into the portal venous system, transported across liver cells into bile, and concentrated in the gallbladder, where it becomes visible on a radiograph (Fig. 11) 1234. Patients are then given a fatty meal: a normal gallbladder contracts. The examination is still useful in patients who present with gallbladder symptoms but in whom no abnormalities are detected on ultrasound examination. It is an essential examination when non-operative removal of gallstones is considered, since a functioning gallbladder is a prerequisite for effective treatment. Failure of the gallbladder to opacify is evidence of gallbladder disease, providing the contrast material has been absorbed and the patient is not jaundiced.


Percutaneous transhepatic cholangiography

A 22-gauge flexible Chiba needle is advanced through the skin and well into the liver under local anaesthesia and antibiotic cover. Blood coagulation must be normal. Contrast medium is gently injected as the needle is slowly withdrawn. The procedure is watched on an image intensifier: when contrast medium enters a bile duct withdrawal is stopped. Contrast medium is then injected to fill the whole biliary tree (Fig. 12) 1235. In skilled hands this can always be achieved if the bile ducts are dilated, and is also possible in about two-thirds of patients in whom the ducts are normal in size. It may be necessary to puncture both the right and the left hepatic systems to outline all the ducts. Bile leakage into the peritoneum, cholangitis, and haemorrhage are the major complications, occuring in about 4 per cent of patients. For this reason it is still best to plan to relieve any obstruction, either surgically or by the percutaneous insertion of a drain or stent, during or fairly soon after the examination. The mortality rate associated with the procedure is about 0.5 per cent.


Endoscopic retrograde cholangiopancreatography

A full description of this technique is given in Section 27.2 166. The ability to outline the biliary tree and the pancreatic duct as well as to inspect the ampulla of Vater has completely revolutionized the management of many benign biliary problems. Not only has diagnosis been improved (Fig. 13) 1236 but therapeutic techniques have been developed which have improved patient care significantly. Endoscopic retrograde cholangiopancreatography (ERCP) requires technical skill and sophisticated imaging, and is not as widely available as the percutaneous approach. The endoscopic route is preferred initially since it does not transgress the peritoneum, but there are occasions when it is essential to outline the bile ducts from above as well as from below.


Computed tomography

Computed tomography (CT) is useful in the diagnosis of biliary tract disease although the evidence is usually indirect. It is easier to identify pathology in the liver, the pancreas, and the gallbladder than the bile duct itself, although the ducts are easily seen when they are dilated (Fig. 14) 1237. CT is probably superior to ultrasonography in identifying the level and the cause of biliary obstruction, but the latter is cheaper, simpler, and safer.


Malignant disease in or around the biliary tree can best be staged by CT; this may also be needed to allow a biopsy to be undertaken. It is not of great value in the management of the common inflammatory conditions, where ultrasound is of greater use. However ultrasound and CT should be regarded as complementary investigations and in difficult cases it is common to use both.


Other imaging techniques

A variety of other imaging techniques may be of value. Intravenous cholangiography, where the bile ducts are outlined directly following intravenous administration of contrast medium, has largely been superseded by ERCP and percutaneous transhepatic cholangiography, which provide better detail.


Isotopic scanning of the gallbladder may be useful in the diagnosis of acute cholecystitis. A technetium-labelled derivative of iminodiacetic acid (HIDA, PIPIDA) is administered intravenously and images are then recorded by a gamma-camera (Fig. 15) 1238. In acute cholecystitis the cystic duct is occluded and so the gallbladder will not opacify; opacification excludes acute cholecystitis. A HIDA scan is particularly useful in the diagnosis of acute acalculous cholecystitis. False positive results may occur in patients with alcoholic liver disease and in those maintained on total parenteral nutrition, in whom the gallbladder is atonic. The isotope may fail to enter the gallbladder despite a patent cystic duct.


Arteriography is essential before any major operation on the biliary system because of the wide variation in biliary arterial anatomy (Fig. 16) 1239. The liver, gallbladder, and pancreas can all be imaged by magnetic resonance (MRI), but the information currently provided is no better than that obtained from CT.


Liver function tests

Biochemical measures of liver function abound. In a surgical context interest has focused on bilirubin, alkaline phosphatase, which is excreted by liver cells, and transferase enzymes, which are predominantly located within liver cells. Changes in these three parameters have traditionally been used to differentiate between intra- and extrahepatic causes of jaundice. A rise in alkaline phosphatase signifies an extrahepatic obstruction while changes in enzyme levels indicate disease within the liver cells themselves. These changes are never totally reliable and they have been superseded by ultrasound and the demonstration of dilatation of the bile ducts. They are, however, useful indicators of disease severity, and their main use is to monitor the effects of treatment. Prothrombin time is also a useful measure of liver function, since it depends on the synthetic functions of the liver. Prolongation of the prothrombin time, which might lead to excessive haemorrhage, must be corrected by the administration of Vitamin K or fresh frozen plasma before embarking on any surgical procedure.


Biliary manometry

Biliary manometry is used to assess the function of the sphincter of Oddi. Pressure traces can be obtained either by placing a special perfusion catheter across the sphincter from below at ERCP or from above during surgical exploration of the common bile duct. The former is used to detect stenosis and dyskinesia of the sphincter of Oddi in patients with persistent pain following a cholecystectomy. Sphincter stenosis is diagnosed by an elevated basal sphincter pressure, and these patients are often cured of their symptoms by an endoscopic sphincterotomy. Other manometric abnormalities have been identified, such as rapid phasic contractions, excessive retrograde contractions, and a paradoxical response to cholecystokinin, but their clinical relevance is not yet clear. Manometry in conjunction with peroperative cholangiography can detect small stones in the bile duct, but the technique is time-consuming and difficult to perform accurately. It is not much used.


DISEASE OF THE BILIARY TRACT

Congenital abnormalities

Biliary atresia (see also Section 36.8 167)

Biliary atresia has an incidence of 1 in 12 000 live births and presents in the first week of life as cholestatic jaundice. Untreated it pursues a relentless course, with progressive liver failure and death before the age of 3 years. The cause of the atresia is unknown, but failure of vacuolation of the solid biliary bud in the early weeks of intrauterine life is one possible explanation. Inflammatory obliteration of previously patent ducts occurring about the time of birth is currently considered to be the cause. Viruses and metabolic disorders are two possible causes of such inflammation.


Classification

Three pathological types of atresia are recognized: Type 1, atresia of the common bile duct; Type 2, atresia of the common hepatic duct; and Type 3, atresia of the right and left hepatic ducts. Types 1 and 2 are relatively easy to correct surgically. In Type 3 disease there is often a conical area of fibrous tissue at the hilum of the liver which contains within it multiple small biliary radicals. The number of these ducts decreases with time and this adds to the urgency of diagnosis.


Diagnosis

Biliary atresia is notoriously difficult to diagnose. Jaundice in the newborn can be caused by hepatocellular disease, intrahepatic bile duct hypoplasia, or a choledochal cyst, as well as biliary atresia. Conventional methods of investigation which are useful in adults are less valuable in infants. For example there is rarely any intrahepatic duct dilatation, so that ultrasound is of limited help. Histological examination of a liver biopsy is the most reliable method of diagnosis, but in clinical practice a range of tests is usually needed.


Treatment

The discovery on microscopy of small biliary radicals in the fibrous tissue at the hilum of the liver has led to the development of portoenterostomy for the treatment of Type 3 biliary atresia. In this procedure all of the fibrous tissue and atretic ducts at the porta hepatis are resected en bloc. An open enterotomy in the antimesenteric border of a jejunal loop is then sutured to the edge of the fibrous tissue in the porta hepatis. Bile drains from the liver into the bowel through the tiny ducts at the liver hilum. This Kasai operation allows long-term survival of nearly half of the patients (Fig. 17) 1240. If atresia involves only the extrahepatic bile ducts, it is possible to anastomose the residual dilated hepatic ducts to a Roux-en-Y loop of small bowel. Unfortunately the results of hepaticojejunostomy are not much better than those of portoenterostomy. Various modifications of the Kasai procedure have been suggested, including bringing up the Roux loop to the skin surface in order to allow easy access to the hepatic anastomosis, but this appears to convey little advantage.


Bacterial cholangitis and portal hypertension are the two common complications of the Kasai operation. Cholangitis requires treatment with systemic antibiotics and the exclusion of a surgically correctable obstruction such as kinking of the Roux loop. Portal hypertension consequent upon hepatic fibrosis is a long-term problem: injection sclerotherapy is the treatment of choice for children who develop varices.


Even though the Kasai operation has markedly improved the management of biliary atresia the results are not completely satisfactory. However, the results of liver transplantation in children have improved so much that it is now the treatment of choice for children with end-stage liver failure (see Section 10.6 74). Since there are few paediatric liver donors it is necessary to reduce the size of an adult liver for transplantation into an infant, but the surgery and the immunosuppression is tolerated without difficulty. Portoenterostomy remains the first treatment for biliary atresia; liver transplantation is available when portoenterostomy is impossible or liver function fails.


Choledochal cyst

Choledochal cyst is an aneurysmal dilatation of the bile duct. It is a rare condition, with an incidence between 1 : 100 000 and 1 : 150 000 live births in the West, although it is probably more common in the East. Females are affected two to four times more often than are males. Most patients present in infancy, although a significant minority are diagnosed as adults.


Aetiology

The aetiology is unknown. Partial biliary obstruction and a weakness of the wall of the bile duct are the two basic defects required for the formation of a cyst: both these abnormalities may be congenital or acquired. Abnormal recanalization of the bile duct, which is complete by the fifth week of intrauterine development, may result in areas of stenosis and dilatation. This theory is supported by the occurrence of choledochal cysts in neonates and by the finding of multiple areas of stenosis and dilatation in some patients with a choledochal cyst. A cyst may also develop following trauma, or from fibrosis and stenosis of the distal common bile duct due to recurrent cholangitis associated with stones in the bile duct. Early changes of this type are sometimes seen at ERCP.


Classification

Cystic dilatation may affect any part of the biliary system: five patterns have been described. Type 1, a cystic or fusiform dilatation of the common bile duct, is the most common (82 per cent). Type 2 (3 per cent) is a supraduodenal diverticulum of the common bile duct, and Type 3 (5 per cent) is a diverticulum of the intraduodenal bile duct, or choledochocoele. Type 4 (9 per cent) consists of multiple cysts: Type 4A cysts affect both the intrahepatic and extrahepatic bile ducts, while Type 4B cysts affect the extrahepatic duct only. Type 5 (1 per cent) describes cysts of the intrahepatic bile ducts. These may be solitary or multiple, and this type includes Caroli's disease (Fig. 18) 1241. They can vary in size from 2 cm in diameter to giant cysts, and the wall is composed of fibrous tissue which may be up to 1 cm thick. The cyst is lined by cuboidal biliary epithelium, which is often ulcerated in adults.


Diagnosis

Choledochal cysts present either as a mass or with biliary obstruction. The classic triad of abdominal pain, jaundice, and a mass occurs in less than one-half of patients. Most adults present with jaundice or cholangitis. Infants also present with jaundice, but may vomit due to duodenal compression and may also have a palpable mass in the abdomen.


Ultrasonography will usually confirm the diagnosis. Cholangiography is absolutely essential to delineate the biliary anatomy accurately and thus determine the best approach to surgical treatment. ERCP is the easiest method of obtaining a cholangiogram (Fig. 19) 1242, but percutaneous and operative cholangiography may also be needed. An arteriogram to delineate the relationship of the cyst to the hepatic artery and the portal vein may be very valuable before embarking on surgical treatment.


Treatment

Once diagnosed the treatment of a choledochal cyst is surgical. Although numerous operations have been described, a Type 1 cyst should ideally be excised completely. The distal bile duct is then anastomosed to the small bowel—usually the jejunum via a Roux-en-Y loop. In infants the structures may be sufficiently mobile to allow use of the duodenum. Anastomoses between the cyst wall and the bowel are usually unsatisfactory in the long term. The cyst wall is often devoid of mucosa and is lined only by granulation tissue, so that a stricture develops. This leads to recurrent cholangitis and the development of stones within the cyst. The high risk of carcinoma developing in a choledochal cyst is also a reason for complete excision. This is usually possible but if it is difficult it is acceptable simply to excise the lining of the cyst and thus protect the portal vein by a partial thickness of the cyst wall. Previous surgery, recurrent cholangitis, and portal hypertension all make treatment difficult.


Type 2 cysts can usually be excised, the defect in the common bile duct being repaired by primary suture over a T-tube brought out through a separate incision in the duct. Small choledochoceles (Type 3) may be treated by endoscopic sphincterotomy. Larger ones require a surgical sphincterotomy using the transduodenal approach. Type 4 cysts are treated by a combination of techniques, depending on the precise anatomy in each individual case. Segmental resection of the liver may be necessary, particularly if there are intrahepatic stones, strictures, or abscesses as well as an extra-hepatic cyst. Hepaticojejunostomy is then necessary to reconstitute biliary drainage.


Complications

Rupture may occur spontaneously in infants, and cholangitis develops in both adults and children. Gallstones can develop within the cyst, more commonly in adults (Fig. 19) 1242. Secondary biliary cirrhosis supervenes in 15 per cent of adults with chronic bile duct obstruction. Carcinoma develops within the cyst in 8 per cent of patients and is a fatal complication. The diagnosis is usually made at operation or at autopsy. Most patients are in their thirties, and 75 per cent of tumours are adenocarcinomas, although squamous carcinoma and cholangiocarcinoma also occur. The mean survival after diagnosis is 8.5 months.


Acquired disease

The most common acquired abnormality of the biliary system is gallstones. In most patients these remain dormant, but they may cause biliary colic simply by mechanical obstruction. More frequently, stones lead to acute or chronic inflammation within the biliary tree and causes symptoms. Inflammation without stones can occur in both the gallbladder and the bile duct, but is unusual, as are infarction of the gallbladder and benign neoplasms of the biliary tract. Damage to the bile duct occurs rarely at the time of cholecystectomy. It may lead to the development of a benign biliary stricture, which is one of the most serious complications of biliary tract surgery. Abnormalities of biliary function probably do occur but at the present time they are poorly understood.


Stones in the gallbladder

Prevalence

Gallstones are very common, with a prevalence at autopsy of 11 to 36 per cent. There are at least 5 million people in the United Kingdom and 25 million people in the United States of America with gallstones. Overall the prevalence has probably increased in Western societies over the last 50 years, and it certainly increases with age, from 4 per cent of people in the third decade to 27 per cent in the seventh. This may be related to changes in the biochemistry of bile with age. Women are three times more likely than men to develop stones, and first-degree relatives of patients with gallstones have a two-fold greater prevalence. There are geographical variations. The prevalence is very high in certain American Indian communities (Pima and Chippewa tribes), in Mexico, Sweden, Czechoslovakia, and Chile, and low in Greece, Japan, India, and China. Certain conditions predispose to the development of gallstones. Obesity is a risk factor for gallstones in women under the age of 50. Pregnancy, but not consumption of the oral contraceptive pill, probably predisposes to the development of gallstones (Fig. 20) 1243. Dietary factors which have been implicated include a high energy intake, increased consumption of unrefined carbohydrate, and diets low in fibre. Crohn's disease, terminal ileal resection, and jejunoileal bypass for obesity are associated with a four-fold increase in prevalence. Biliary infection and parasitic infestation of the biliary tree are important factors in the development of pigment stones in Asia but not in the West. Other diseases associated with the development of gallstones include diabetes mellitus, type IV hyperlipoproteinaemia, cirrhosis of the liver, gastric surgery, and total parenteral nutrition. Patients with haemolytic anaemia due to hereditary spherocytosis, sickle-cell disease, and thalassaemia also show an increased prevalence of pigment stones.


Classification of stones

Cholesterol and bile pigments are the two principal constituents of gallstones. In addition, calcium carbonate, phosphate, and palmitate are present in variable amounts. Pure cholesterol and pure pigment stones do occur, but most stones are mixed (Fig. 21) 1244. Predominantly cholesterol stones account for 75 per cent of all gallstones in the West. They are single or multiple, hard, and usually layered on cross-section (Fig. 22) 1245. Pigment stones are most common in Asia. They are usually black or brown in colour; brown stones crumble when squashed (Fig. 23) 1246. About 10 per cent of stones contain enough calcium to be radio-opaque (Fig. 7) 1230.


Formation of gallstones

Cholesterol stones

Cholesterol is insoluble in water, and is held in solution as micelles of cholesterol, phospholipids, and bile salts. Lecithin forms the major component of phospholipids while the bile salts are glycine or taurine conjugates. The physicochemical state of bile can be determined from a phase diagram (Fig. 24) 1247. The relative proportions of cholesterol, bile salts, and phospholipid are expressed as a percentage of the total lipid content and are plotted on triangular co-ordinates. An increase in the cholesterol concentration or a decrease in the bile salt concentration results in supersaturation of bile with cholesterol, and the formation of a liquid crystalline phase of cholesterol.


The biliary lipid composition of normal bile and gallstone bile is virtually identical, and since at least half of the Western population have supersaturated bile there must be another factor responsible for the formation of stones. Cholesterol will only crystallize from a supersaturated solution if there is a nidus on which the crystals can form. This process is called nucleation, and the time taken for supersaturated bile to form crystals of cholesterol is known as the nucleation time. Normal bile takes 15 days to form crystals, compared with 3 days for bile from patients with cholesterol gallstones. Mucus glycoproteins from the gallbladder wall and bilirubinate have both been proposed as nucleating factors, while a bile protein has been proposed as an inhibitor. The nucleation phenomenon also depends on gallbladder function: the motility of the wall determines the degree of stasis and mixing of the bile within the lumen. One other significant finding is that the size of the bile acid pool is reduced in many patients with gallstones, although the reason for this is unknown.