Материал: Advanced Imaging of the Abdomen - Jovitas Skucas

past comparisons involved nonhelical CT; undoubtedly further refinements in multislice technology and user expertise will change these results.

Computer Tomography

Initially the bile ducts are not dilated for several hours or even several days after an acute obstruction. Eventually they dilate, and CT, US, or MR should be able to locate a site of obstruction. With a distal obstruction the extrahepatic ducts dilate first, followed later by intrahepatic ducts.

Normally a fatty meal or IV cholecystokinin produces no visible change in extrahepatic bile

duct caliber; increased bile production and gallbladder contraction are balanced by sphincter of Oddi relaxation. With a distal bile duct obstruction, however, these agents result in an increase in bile duct caliber proximal to the obstruction. This test is most useful with a clinically suspected biliary obstruction but is also helpful with normal or equivocal caliber extrahepatic bile ducts seen with imaging; cholangiography should, of course, detect an obstruction directly.

Ultrasonography

Ultrasonography detects most dilated bile ducts. It provides limited information in

GALLBLADDER AND BILE DUCTS

patients with painless jaundice. It does have a role, however, as a screening test for suspected inflammation or stone disease.

In patients with bile duct strictures or filling defects undergoing intraductal US, bile cytology, and percutaneous transhepatic cholangioscopy, the sensitivity and specificity of intraductal US for diagnosing bile duct cancer were 89% and 50%, respectively (59); the sensitivity of bile cytology (64%) and transhepatic cholangioscopy (93%) increased to 96% and 100%, respectively, if results of intraductal US were included.

Cholangiography

Either percutaneous or endoscopic cholangiography readily evaluate biliary obstructions. With a complete or high-grade obstruction, a percutaneous approach rather than ERCP is preferred because it outlines ducts proximal to an obstruction used by the surgeon for reconstruction. A catheter left in place aids the surgeon in identifying the bile ducts in a surgical field often distorted by tumor or prior surgery.

In general, MR cholangiography is comparable in accuracy to ERC in detecting biliary dilation and suggesting an etiology for a stricture (60). It identifies the site of obstruction and differentiates a stone from neoplasm. It achieves sensitivities and specificities of over 90% in detecting an obstruction. In determining a cause for obstruction, in one strudy, MRCP sensitivity and specificity for choledocholithiasis were 89% and 90%, for malignant obstruction 92% and 88%, for benign stricture 63% and 90%, and for chronic pancreatitis 50% and 99% (61). In general, MRCP should detect duct dilation in all patients with clinical obstructive jaundice and depict correctly the level of obstruction in about 90%; common bile duct obstruction due to stricture and stone can be readily differentiated.

The addition of nonenhanced T1and less heavily T2-weighted images to MRCP images improves the diagnostic accuracy of differentiating benign from malignant biliary strictures (62); gadolinium-enhanced images are useful in select patients. A cholangiocarcinoma tends to be asymmetric, have irregular margins and more often involves a longer bile duct segment than a benign stricture.

Scintigraphy

Although the extrahepatic ducts do not dilate immediately after an obstruction, HIDA scintigraphy is abnormal during this time, and no tracer activity is detected in the small bowel. Nevertheless, in a jaundiced population cholescintigraphy does not reliably differentiate between cholestasis and mechanical obstruction and is generally not employed for this purpose.

Benign Strictures

Clinical

The most common etiology for a benign biliary stricture is prior instrumentation. A stricture can develop shortly after bile duct manipulation or occur months or even years later. Rarely, the appearance mimics a web (Fig. 8.21). The most common clinical presentation is jaundice or, if only some of the intrahepatic ducts are involved, cholangitis.

Once a stricture is identified, the initial task is to exclude an underlying malignancy. A tissue diagnosis should be obtained unless the etiology of a stricture is clear. A biopsy is generally preferred over cytology. Depending on each situation, a biopsy can be obtained as part of ERCP or percutaneously using imaging guidance.

Figure 8.21. Common bile duct web (arrow).The study was performed through a biliary catheter inserted during surgery for gangrenous cholecystitis.

Sphincter of Oddi Stenosis/Dysfunction

Considerable confusion surrounds both the definition and the diagnosis of sphincter of Oddi dysfunction (dyskinesia). The true prevalence of this condition is difficult to gauge; the diagnosis is more often made in Europe than in the United States. Biliary dyskinesia, sphincter dysfunction, and even chronic acalculous cholecystitis are difficult to distinguish on clinical, imaging, and even pathologic grounds. Indeed, whether these are distinct disease entities, different manifestations of a motility disorder, or even exist at all is speculation. Some investigators include under this term all patients with biliary colic or cholestasis who do not have stones or other evidence of an anatomic obstruction proximal to the sphincter of Oddi, while others exclude those with a stricture (stenosis) at the sphincter. In a setting of biliary dilation, delayed biliary emptying of contrast, and no obvious cause of obstruction, some investigators routinely ascribe these findings to papillary stenosis or sphincter of Oddi dysfunction (or spasm), although such an approach undoubtedly includes a number of false positives.

Bile duct contrast retention at the conclusion of ERCP is used by some investigators as a sign of sphincter of Oddi dysfunction, while others rely primarily on biochemical evidence of cholestasis. Another approach is to obtain direct manometric pressure recordings of the sphincter during ERCP. Normal sphincter of Oddi pressure is 5 to 15mm Hg above intraluminal bile or pancreatic duct pressures. Typically, basal pressure is <40mmHg. With sphincter of Oddi stenosis the basal pressure increases. If manometry reveals a basal sphincter pressure >40mmHg, even with no other evidence of stasis, a diagnosis of sphincter of Oddi dysfunction is made. Some employ flow manometry and infuse contrast under constant pressure, such as 30cm of water; papillary stenosis is suggested if the flow rate is <12mL/min and intraluminal pressure is >15 cm of water. Others refine this test using pharmacologic agents to relax the sphincter of Oddi. Nevertheless, a manometric study of amplitude and frequency of sphincter contractions is not always straightforward; some patients have intermittent sphincter spasm,

ADVANCED IMAGING OF THE ABDOMEN

although the basal pressure is still normal. Manometric data may not identify benign papillary stenosis. In such a setting some endoscopists perform an empiric sphincterotomy, but results are mixed.

Papilla of Vater stenosis is often ascribed to damage produced by a prior stone passing through or to instrumentation. In general, a diagnosis of papillary stenosis or dysfunction should not be made lightly, and other conditions should be sought to explain a patient’s symptoms.

Therapy

Endoscopic

One indication for endoscopic sphincterotomy is stenosis of the sphincter of Oddi. Endoscopic manometry is useful to evaluate whether an endoscopic sphincterotomy has been successful. An absent choledochoduodenal pressure gradient indicates a complete sphincterotomy. Unfortunately, a high percentage of these patients restenose.

In general, significant complications occur in 5% to 10% of patients during endoscopic sphincterotomy, with bleeding being most common. Most bleeding stops spontaneously or after coagulation, although an occasional patient requires surgical control. An alternative is angiographic embolization of the bleeding site.

Pancreatitis is a known ERCP complication regardless of whether or not a sphincterotomy is performed. Some patients develop an elevation in pancreatic enzyme values but are clinically asymptomatic.

Most procedure-related perforations are extraperitoneal. Occasionally a perforation manifests only several hours after the procedure. Extraperitoneal gas can be identified either with conventional radiographs or CT. Most of these patients respond to conservative therapy. Sepsis is uncommon and patients are generally treated conservatively.

Experience with long-term stenting of benign bile duct strictures is limited. Nonmetallic stents tend to obstruct and need to be replaced periodically. Metal stents eventually become epithelialized and appear to last longer, but

GALLBLADDER AND BILE DUCTS

some obstruct secondary to mucosal hypertrophy or calculi formation.

Surgical

Surgery for most benign bile duct strictures consists of either stricture repair alone or a choledochojejunostomy. Surgical repair of benign strictures leads to excellent or good results in over 80% of patients; the most common complication of these repairs is subsequent restricture.

The classic repair procedure for major bile duct injuries is a Roux-en-Y hepaticojejunostomy. With such an anastomosis, conventional endoscopy cannot access the anastomotic site, and either a percutaneous transhepatic approach or repeat surgery is necessary in cases of restenosis. At repeat surgery the jejunal limb going to the anastomosis is identified, an enterotomy performed, and endoscopy through the enterotomy used to diagnose and, if necessary, treat a stricture.

A biliary stricture secondary to pancreatitis generally involves a long intrapancreatic segment. An endoscopically placed stent temporarily relieves the obstruction, but these patients then require a surgical bypass. With pancreatitis limited to the head of the pancreas, a pancreaticoduodenectomy may be indicated.

Transhepatic

In some patients both endoscopic and percutaneous transhepatic therapeutic approaches are viable options. Using either technique, an appropriate-sized balloon is inserted to dilate a stricture. Prophylactic IV antibiotic therapy before and during the procedure is commonly employed. Stones encountered proximal to a stricture are either fragmented or extracted during the same procedure. Catheter stenting across the stricture provides ready future access in cases of restenosis, with the length of time a stent is left in place varying considerably among institutions.

Complications can be divided into those associated with the percutaneous procedure per se, including transhepatic access to bile ducts, and those associated with balloon dilation. They consist of septicemia, shock,

significant hemorrhage, pancreatitis, and bile duct perforation.

Successful long-term patency after dilation varies considerably. In general, the restricture rate increases with time.

Phytobezoar

Phytobezoars should not collect in the bile ducts, although an occasional one does develop. Some of these form after a cholecystogastrostomy and vegetable concretions end up obstructing the extrahepatic bile ducts.

Mirizzi Syndrome

Mirizzi syndrome is produced by a gallstone impacting either in the neck of the gallbladder or within the cystic duct and secondarily obstructing the hepatic duct. The initial classification of a gallstone either simply compressing adjacent bile ducts as part of an acute episode or a cholecystocholedochal fistula forming on a chronic basis was subsequently expanded to include (63):

Type I: hepatic duct stenosis due to a stone impacting in the cystic duct or gallbladder neck. This is the most common

Type II: hepatic duct fistula due to a stone impacting in the cystic duct or gallbladder neck

Type III: hepatic duct stenosis due to a stone at the duct confluence

Type IV: hepatic duct stenosis as a complication of cholecystitis and no impacted calculus

A rationale for this classification is that the surgical approach differs in each of these four types. Thus in the presence of a cholecystocholedochal fistula (Mirizzi syndrome type II) the fistula must be repaired at surgery. A gallbladder remnant pedicle graft (choledochoplasty) can be used for repair.

Occasionally obstruction is caused by xanthogranulomatous cholecystitis, with inflammation extending to adjacent structures— whether to label such a presentation as Mirizzi syndrome is a matter of definition.

In most instances cholangiography, regardless of how it is performed, should be diagnos-

tic. Although most patients suspected of having Mirizzi syndrome undergo laparotomy, laparoscopy is also feasible in these patients. Mirizzi syndrome has also been successfully treated by extracorporeal shock-wave lithotripsy.

Extrinsic Obstruction

Vascular

Not all hilar masses represent a neoplasm. In a setting of portal vein thrombosis, large extrahepatic venous collaterals, such as cavernous transformation of the portal vein—also called bile duct varices or portal cavernoma—tend to compress and obstruct adjacent bile ducts to the point of inducing obstructive jaundice. These dilated veins mimic a neoplasm. Prolonged obstruction has led to periportal and perisinusoidal fibrosis and secondary biliary cirrhosis. At times, venous collaterals are mostly in the hepatic and common bile duct wall and result in diffuse wall thickening, mimicking both benign and malignant diseases.

A hepatic artery, gastroduodenal artery, or posterior inferior pancreaticoduodenal artery pseudoaneurysm or a pancreatic pseudocyst can also compress adjacent bile ducts and induce jaundice.Aneurysm embolization or pseudocyst aspiration should relieve obstruction.

Imaging reveals an extrinsic biliary obstruction. Cholangiography shows multiple extrinsic biliary indentations, at times serpiginous, together with proximal bile duct dilation.

Sarcoidosis

A rare cause of obstructive jaundice is hepatobiliary sarcoidosis. Most of these obstructions are secondary to enlarged sarcoidosis-involved hilar lymph nodes compressing adjacent bile ducts. In an occasional patient with sarcoidosis, cholangiography reveals findings similar to those seen with sclerosing cholangitis.

Other Obstructions

While duodenal peri-Vaterian diverticula are common, biliary obstruction by one is rare (these diverticula are discussed in Chapter 3). A

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food bezoar in a duodenal diverticulum or peri-Vaterian diverticulitis can result in biliary obstruction.

Almost any inflammation resulting in perihilar or superior pancreaticoduodenal adenopathy can compress adjacent bile ducts and induce obstructive jaundice. In some parts of the world tuberculous adenitis is a recognized cause. Primary retroperitoneal fibrosis can obstruct the common bile duct.A rare pancreatic hydatid cyst leads to obstructive jaundice.

Nonneoplastic Tumors

Hamartoma (von Meyenburg Complexes)

Mesenchymal and biliary hamartomas, also called von Meyenburg complexes and cholangiofibromatosis, consist of a mixture of hepatocytes, small, dilated bile ducts, and connective tissue, together with varying size cysts. These hamartomas range from solid to largely cystic circumscribed tumors, single to multiple, large or small, intrahepatic or even projecting from the liver surface. Multiple hamartomas are either uniform or random in distribution throughout the liver. A large autopsy study found these complexes in 6% of adults and 1% of children (64). They are more prevalent in polycystic kidney and liver disease.

Larger hamartomas are found mostly in young children. These cystic tumors are only mildly vascular. The a-fetoprotein level is not elevated with these tumors, helping distinguish them from hepatoblastomas.

These hamartomas are considered to be nonneoplastic developmental ductal plate malformations and are not thought to be premalignant, although a rare cholangiocarcinoma does originate in a setting of multiple bile duct hamartomas. A double cancer—a hepatocellular carcinoma and a cholangiocarcinoma—was discovered in a 74-year-old man, with the cholangiocarcinoma arising in hamartomas (65); a histologic progression from hamartomatous to adenomatous and a cholangiocarcinoma was evident.

Some of the larger hamartomas are palpable. Computer tomography reveals small hamartomas as multiple cysts scattered throughout the liver; they tend to be irregular in shape and