Материал: Advanced Imaging of the Abdomen - Jovitas Skucas

GALLBLADDER AND BILE DUCTS

(73); survival at 3 years of those resected for cure was 60%. Survival of patients undergoing partial liver resection is significantly longer than of patients undergoing only drainage. An occasional patient survives long-term even if a tumor invades adjacent organs.

An orthotopic liver transplantation is performed in an occasional patient with a slow growing tumor, but 3-year disease-free survival after transplantation is only in the teen percents.

Arterial chemotherapy performed through an implanted port system appears to prolong survival of patients with unresectable intrahepatic cholangiocarcinomas (74).

Hilar (Klatskin Tumor)

Clinical

Carcinomas arising at or near the right and left lobe duct bifurcation were described by Klatskin in 1965, and these hilar cholangiocarcinomas often bear his name. Some authors refer to them as central cholangiocarcinomas. Why more cholangiocarcinomas occur at the liver hilum compared to other locations is not known. Most infiltrate diffusely and have a smooth, benign appearance, tend to spread along intrahepatic bile ducts, invade surrounding nerves and blood vessels, and produce multiple obstructions. Obstructed intrahepatic bile ducts dilate. Vascular encasement results in atrophy of involved segments. Distant metastases are uncommon.

Jaundice is the most common presentation. With asymmetrical involvement or only partial intrahepatic duct obstruction, often the only abnormality is an elevated serum alkaline phosphatase level.

Some of these patients develop segmental intrahepatic cholangitis; morbidity and mortality rates for these patients are significantly higher than for those without cholangitis. Preoperative transhepatic drainage of those intrahepatic bile ducts involved with cholangitis results in fewer complications after subsequent hepatic resection.

Imaging

Most Klatskin tumors present with diffuse infiltration and a narrowed bile duct lumen.

Figure 8.28. Hilar cholangiocarcinoma (Klatskin tumor) with complete obstruction. A left duct puncture was performed and thus only the left lobe ducts are opacified.

Lumen involvement is best studied with cholangiography, either percutaneously or using an endoscopic approach. Often the right and left lobe ducts are infiltrated to the point that these ducts no longer communicate with each other (Fig. 8.28). An occasional tumor grows primarily intraductally and presents as a large expansile intraluminal mass. In general, however, although a cholangiogram can readily detect and diagnose these carcinomas, cholangiography cannot evaluate the full extent of tumor invasion.

Calcifications are uncommon in Klatskin tumors.

Unenhanced CT detects half or fewer of these hypovascular tumors. If identified, these hypoto isodense tumors have poorly defined margins. Adjacent liver parenchyma often reveals a mottled appearance due to tumor infiltration. They are readily detected on hepatic artery dominant CT and a majority are identified on portal vein phase images. Most consist of an infiltrating stenosis; an exophytic tumor is less common and an intraluminal polyp is rare (Figs. 8.29 and 8.30).

Similar to other imaging, US reveals dilated intrahepatic bile ducts and normal caliber extrahepatic bile ducts, but the actual porta hepatis tumor typically is not identified; any visualized tumor has variable echogenicity and tends to be poorly marginated. Doppler US can evaluate portal vein involvement.

Magnetic resonance imaging reveals a hypointense tumor on T1and variable intensity (mostly hyperintense) tumor on T2-weighted images, but due to their diffuse infiltration many of these tumors are difficult to detect with MR. A characteristic finding is that they enhance late with gadolinium and delayed images often show a hyperintense tumor not visible previously. Fat-suppression techniques allow easier differentiation from the oftenpresent surrounding fat.

Although ERCP is often performed in these patients, it seldom establishes a diagnosis; full tumor extent and intrahepatic ducts generally cannot be evaluated.

Metastatic disease to the porta hepatis has a similar appearance. A metastasis should be considered if imaging reveals extensive adjacent lymph node involvement. Likewise, on occasion sclerosing cholangitis limited to the porta hepatis mimics a Klatskin tumor. Cavernous transformation of a thrombosed

GALLBLADDER AND BILE DUCTS

portal vein is occasionally also in the differential diagnosis.

Staging

Table 8.7 lists the TNM classification of extrahepatic bile duct tumors. Most imaging modalities tend to understage hilar adenocarcinomas; invasion of adjacent lymph nodes and liver infiltration often occur without significant imaging findings. Computed tomography is inaccurate in establishing resectability in these mostly unresectable tumors. With an extensive tumor, however, imaging studies correctly predict unresectability, and imaging thus is useful when evaluating potential resectability. If

Table 8.7. Tumor, node, metastasis (TNM) staging of extrahepatic bile duct tumors

Source: From the AJCC Cancer Staging Manual, 6th edition (2002), published by Springer-Verlag, New York, NY, used with permission of the American Joint Committee on Cancer (AJCC), Chicago, IL.

needed, intrahepatic spread is best studied with arterial portography. The primary role of angiography is to detect involvement of either the hepatic artery or the portal vein and their branches, although as already mentioned, multidetector CT angiography may supplant this role.

Percutaneous intraductal US can accurately T-stage these cholangiocarcinomas, but this technique is not widely available.

Imaging detects lobar atrophy, level of biliary obstruction, parenchymal invasion, or portal vein invasion. Both CT portography and US understage extrahepatic metastases, which are present at subsequent surgery in almost half of these patients. An MRCP is useful not only to identify an obstruction level but also as an aid in determining the extent of biliary ductal involvement and in planning drainage procedures.

Therapy

Portal vein invasion and obstruction lead to parenchymal atrophy, and imaging detection of atrophy is thus presumptive evidence of such invasion. Hilar cholangiocarcinomas are generally considered unresectable in the presence of metastases, invasion of the right or left hepatic arteries or main portal vein branches, or extensive growth into adjacent liver parenchyma, although portal vein reconstruction is performed in some centers. Portal vein stent insertion is worthwhile in an occasional patient with portal vein invasion to treat portal hypertension with its associated bleeding complications.

If a hilar cholangiocarcinoma is resectable, a surgical intrahepatic anastomosis offers the hope of a cure. At times an extended right hepatectomy is necessary not only for tumor resection but also to resect undrainable segments.

A potential cure is possible with liver transplantation.

A biliary stent is left in place after resection or transplantation, providing access for followup cholangiography and serving as a useful landmark for follow-up imaging.

With an unresectable tumor, either percutaneous or endoscopic biliary stenting provides palliative drainage, relieves pruritus, and

improves quality of life. Percutaneous biliary drainage is technically successful in over 95% of patients. An advantage of percutaneous stenting is that access in then available to the often common associated intrahepatic obstructions. Some develop segmental obstructive cholangitis, which needs to be treated aggressively. Because these are generally slow-growing tumors, catheter drainage rather than stenting is often more appropriate. Also, in distinction to more distal bile duct stenting, endoscopic hilar stenting is more complex.

Controversy exists about whether palliative drainage should be of one or both liver lobes. A retrospective study of malignant hilar obstructions subdivided these patients into three groups (75): group A, one lobe opacified and same lobe drained; group B, both lobes opacified and both lobes drained; and group C, both lobes opacified but only one lobe drained. Among patients with more advanced lesions, median survivals of groups A, B, and C were 145, 225, and 46 days, respectively. The authors concluded that best patient survival is in those undergoing bilateral drainage and the worst survival is in those with both lobes opacified but with drainage of only one.

An extensive tumor can hinder stent insertion. At times endoscopic intraductal radiation therapy sufficiently recanalizes hilar cholangiocarcinoma strictures that a stent can be sequentially introduced. As an example of some of the therapy of unresectable hilar cholangiocarcinomas, five patients underwent percutaneous cholangiography, right and left internal biliary catheter drainage, intraductal brachytherapy using iridium 192 needles and endoprosthesis insertion, followed by external radiotherapy and chemotherapy (76); all patients had initial remission of jaundice, although eventually jaundice recurred in all and led to death, with a mean survival of 7.5 months, versus 1.75 months for 10 other unresectable patients undergoing only percutaneous drainage.

If an extensive tumor prevents stenting, a left lobe anastomoses to the stomach (hepaticogastric anastomosis) provides internal biliary diversion; fluoroscopic and endoscopic guidance are helpful.

The risk of abdominal wall tumor implantation is low after transhepatic biliary drainage in a setting of a hilar cholangiocarcinoma.

ADVANCED IMAGING OF THE ABDOMEN

Extrahepatic

Clinical

At initial presentation not all patients with an extrahepatic cholangiocarcinoma are jaundiced and not all have abnormal liver function tests, although eventually jaundice, pruritus, and weight loss ensue.

Imaging

A typical appearance of an extrahepatic bile duct cholangiocarcinoma consists of a proximally dilated duct ending in an irregular, narrowed segment and a distal normal caliber duct. Most of these cholangiocarcinomas present as a focal stricture or a locally infiltrating tumor (Fig. 8.31). An intraluminal irregular polypoid appearance is less common. The appearance of most of these mucosa-originating cholangiocarcinoma is sufficiently different from the narrowing produced by a metastasis to adjacent lymph nodes to allow differentiation. The smoothly tapered common bile duct narrowing seen with pancreatitis likewise usually can be differentiated from an abrupt cutoff or rat-tail

Figure 8.31. Cholangiocarcinoma obstructing midextrahepatic duct (arrow). The irregular proximal tumor margin argues against a pancreatic head carcinoma.

GALLBLADDER AND BILE DUCTS

appearance characteristic of an infiltrating cholangiocarcinoma.

Endoluminal US of a malignant biliary stricture reveals asymmetrical irregular bile duct wall thickening. While such focal thickening is suggestive of a cholangiocarcinoma, it is not diagnostic.

These tumors are hypoto isointense on T1and isoto mildly hyperintense on T2-weighted images. Postcontrast enhancement tends to be more pronounced during the venous phase.

A midextrahepatic cholangiocarcinoma infiltrating intramurally can spread to the gallbladder and mimic a gallbladder carcinoma. Included in the differential is also metastasis to adjacent pancreaticoduodenal lymph nodes and Mirizzi syndrome.

Staging

Patients with more distal extrahepatic cancer tend to have a better prognosis than those with more proximal ones. Over a 50% 5-year survival can be expected for patients with a resectable lower one-third bile duct tumor, at times even with positive nodes.

The pattern of lymphatic spread does vary by tumor location. Thus proximal extrahepatic cholangiocarcinomas tend to spread to common hepatic artery nodes rather than to the retropancreatic region, midextrahepatic tumors metastasize widely, including to paraaortic nodes, while distal tumors tend to involve nodes around the pancreatic head.

In patients with malignant obstruction, any hypoechoic, rounded lymph nodes or those with a conspicuous margin are generally assumed to be malignant with neural plexus invasion. CT reveals irregular masses extending medially toward the superior mesenteric and celiac arteries (77), findings presumably representing both neural invasion and desmoplastic reaction. Hepatoduodenal ligament invasion is detected by increased fat attenuation between the common bile duct and the proper hepatic artery (77).

Intraductal US has a role in staging not only cholangiocarcinomas but also other malignant biliary obstructions. Intraductal US detects adjacent pancreatic invasion. Aside from the pancreas, intraductal US is limited to hepatoduodenal ligament structures; it visualizes only a limited portal vein segment.

Percutaneous transhepatic cholangioscopy visualizes the duct mucosa and provides access for biopsies. Although biopsies do establish a diagnosis, whether staging is possible from biopsies is debatable; most biopsies are superficial and do not contain muscle or neural bundles.

Therapy

Some studies suggest that radiation therapy prolongs the survival of proximal cancer patients but has less influence on the survival of those with a more distal cancer, yet others have found that tumor location has no impact on survival.

A Whipple procedure is commonly performed for cholangiocarcinomas of the distal common bile duct.

Tumor seeding at a previous drainage site is an uncommon complication.

It is not clear what type of palliation is best with an unresectable tumor; nonoperative palliation appears to offer longer survival than surgical palliation. With stenting, patients with a distal biliary obstruction tend to survive longer and have more effective relief of jaundice than those with a more proximal obstruction. In general, endoscopic rather than percutaneous stenting is preferred for distal biliary strictures.

Intraluminal iridium-192 therapy followed by stenting appears to extend stent patency and increase survival in patients with inoperable cholangiocarcinoma. Intraluminal brachytherapy is performed using either a percutaneous transhepatic or a retrograde ERCP approach. Brachytherapy is often combined with external beam radiation therapy and chemotherapy.

In palliating malignant common bile duct obstruction, transhepatically inserted expandable metal stents appear superior to plastic stents.

Cystic Duct

A diagnosis of cystic duct carcinoma is rarely made. Undoubtedly these tumors are more common than reported, because most are indistinguishable from either a gallbladder carcinoma or carcinoma of adjacent bile ducts. These tumors are not associated with chronic chole-