Материал: Advanced Imaging of the Abdomen - Jovitas Skucas

cystitis and, in contradistinction to gallbladder carcinomas, are more often found in men.

Papilla of Vater Carcinoma

A carcinoma involving the papilla of Vater can originate from an adjacent duodenal mucosa, a papilla itself, a distal common bile duct, or even be pancreatic in origin. Biopsy simply reveals an adenocarcinoma. Because infiltration of surrounding structures is common, even a resected tumor often does not suggest a specific site of origin. These periampullary carcinomas are discussed in more detail in Chapter 3. Imaging findings range from a duodenal intraluminal irregular polyp, to diffuse infiltration of surrounding structures with little mass effect, to essentially a normal study with the only abnormality being common bile duct dilation (Fig. 8.32).

Magnetic resonance cholangiopancreatography has a limited role in evaluating papilla of Vater cancers; a carcinoma, benign stricture, edema from a recently passed stone, and even an impacted stone are difficult to differentiate.

ADVANCED IMAGING OF THE ABDOMEN

Hepatocellular Carcinoma

Jaundice secondary to a hepatocellular carcinoma generally is a late finding, seen after extensive tumor infiltration throughout the liver.

An occasional hepatocellular carcinoma results in a spill of tumor debris into the bile ducts, growth as a tumor thrombus within the lumen, and, if the right and left lobe duct confluence or even the hepatic duct are involved, subsequent obstruction. Imaging reveals intraductal filling defects and proximal duct dilation.At times the bile ducts are encased by tumor. Cholangiography identifies bile duct obstruction.

A hepatocellular carcinoma is in the differential diagnosis if intrahepatic bile duct obstruction is identified and an adjacent tumor detected by CT. Magnetic resonance imaging likewise can detect an intrabiliary tumor or biliary obstruction by an adjacently located hepatocellular carcinoma.

Lymphoma/Leukemia

Primary bile duct lymphoma is very rare. It manifests as focal or diffuse bile duct wall thick-

GALLBLADDER AND BILE DUCTS

Figure 8.33. Lymphoma obstructing the hepatic duct (arrow) distal to the porta hepatis. A pancreatic head carcinoma can have a similar appearance.

ening without adenopathy; the imaging appearance mimics a cholangiocarcinoma (78). Systemic non-Hodgkin’s lymphomas obstruct bile ducts by extrinsic compression from involved adjacent lymph nodes, most often in the porta hepatis (Fig. 8.33). Only rarely does a lymphoma infiltrate the bile duct wall to the point of obstruction. Thus obstructive jaundice secondary to Hodgkin’s disease is rare. A rare primary hepatic B-cell lymphoma of MALT results in a periportal lymphoid infiltrate and bile duct epithelial involvement to the point of mimicking cholangitis (79).

Anecdotal reports suggest that porta hepatis lymphomas are better defined by MRI than by cholangiography, CT, or US.

Sarcoma

Biliary stromal origin neoplasms are rare. A differentiation between benign tumors and their sarcomatous counterparts is difficult at best, and from an imaging viewpoint an attempt at such distinction generally makes little sense.

The most common biliary stromal tumors are leiomyomatous in origin, with an occasional myoblastoma being reported. Hepatobiliary

sarcomas, with the exception of embryonal rhabdomyosarcoma, are discussed in Chapter 7; most of these sarcomas (and their benign counterparts) are intrahepatic in location, and distinguishing whether they are of liver parenchymal or bile duct origin is not possible.

Embryonal rhabdomyosarcomas originate in bile duct submucosa, occur mostly in extrahepatic bile ducts, and are more common in young children. Histologically, they are similar to rhabdomyosarcomas (sarcoma botryoides tumors) found in the vagina and bladder. They tend to invade locally. These are aggressive tumors, and metastases are not uncommon at first presentation. Imaging reveals an intraluminal, soft tissue density, bulky tumor. Necrosis is evident within larger ones. Ultrasonography of some shows a “Swiss cheese” type of appearance. Cholangiography can be diagnostic if it shows intraluminal grape-like tumor clusters. Imaging findings are not pathognomonic; however, they are suggestive when seen in young children.

Melanoma

Primary bile duct melanoma is sufficiently rare that only a few have been reported. Most patients with metastatic melanoma have been middle-age men presenting with obstructive jaundice. Metastatic melanoma is considerably more common in the gallbladder than bile ducts.

Imaging shows dilated proximal bile ducts (Fig. 8.34). Ultrasonography identifies a hyperechoic tumor, similar to other metastases.

Metastases/Invasion to Bile Ducts

Jaundice is common in a setting of advanced gastric carcinoma. Jaundice is usually secondary to metastasis to hepatoduodenal ligament lymph nodes, with biliary obstruction being at the extrahepatic duct level (Fig. 8.35).

Jaundice in a setting of breast carcinoma is usually secondary to widespread liver metastases. In a minority of patients, similar to those with metastatic colon cancer, jaundice is due to extrahepatic intraductal metastasis or metastasis to adjacent lymph nodes (Fig. 8.36). These latter patients, with limited survival, are amenable to stenting for relief of jaundice.

Figure 8.34. Common bile duct obstruction by metastatic melanoma.

Figure 8.35. Common bile duct obstruction. This patient had colon cancer resected previously, now was believed to have metastases to the pancreaticoduodenal nodes and a bypass catheter was inserted to control jaundice. A cancer in the pancreatic head would have a similar appearance. No follow-up was available. (Courtesy of David Waldman, M.D., University of Rochester.)

Figure 8.36. Long hepatic duct obstruction (arrows) due to an adenocarcinoma, believed to be secondary to colon cancer resected 5 years previously.

Metastasis to the peripapillary region is most often due to pancreaticoduodenal node involvement and secondary obstruction of adjacent bile duct (Fig. 8.37). Rarely metastatic colon carcinoma results in focal intrahepatic bile duct dilation due to intraluminal tumor growth (80); these mimic the appearance of a cholangiocarcinoma.

Therapy of Malignant Obstruction

Preoperative Drainage

Considerable controversy exists whether preoperative percutaneous transhepatic biliary drainage in a clinical setting of obstructive jaundice has a role. Preoperative drainage is more common in Japan than in North America or Europe. On a routine basis, many United States surgeons have abandoned preoperative drainage. In general, preoperative biliary drainage is useful in malnourished patients or in those with suppurative cholangitis. Also, occasionally preoperative drainage aids the surgeon by identifying bile ducts, especially in a setting of extensive fibrosis.

Percutaneous biliary drainage is a technically complex procedure requiring considerable skill and is associated with specific complications. The presence of a catheter presumably promotes infection, but overt cholangitis is uncommon as long as catheter patency is ensured. Other acute complications associated with drainage include hemorrhage and sepsis. Catheter or stent obstruction and dislodgment occur as long-term complications.

Palliation

In a setting of either primary or metastatic bile duct obstruction, palliative biliary drainage, either external or internal, can be established using a surgical, percutaneous, or endoscopic route. The exception is with lymphoma, where radiotherapy has a role. Surgical biliary drainage (choledochojejunostomy) is appropriate if additional surgical procedures, such as a gastric bypass, are also deemed necessary. The choice between percutaneous or endoscopic drainage is somewhat arbitrary and often

revolves around availability and patient referral. In either case, whether to stent a jaundiced patient with an inoperative cancer is individualized. With some cancers, the presence of distal metastases is a limiting factor in patient survival, rather than whether the bile ducts are obstructed or not.

Internal biliary stents provide drainage without an external drainage device. Successful jaundice palliation can be achieved using self-expandable wire mesh stents and plastic stents. Compared to surgical palliation, stenting results in similar morbidity and mortality; however, patients require a shorter hospital stay. Good palliation can be achieved in most patients.

Stent migration occurs with straight stents; migration is not common with wire meshes. Long-term complications of mesh stents include stent occlusion and cholangitis. Most stent occlusions are caused by granulation tissue, bile sludge, and tumor overgrowth rather than by ingrowth. In an uncovered stent an irregular outline develops on the inner surface due to

granulation tissue overgrowth. Overall, selfexpandable endoprostheses have achieved good results and good long-term patency. Patients with a cholangiocarcinoma and gallbladder carcinoma tend to have better results than those with a pancreatic carcinoma or metastatic carcinomas.

After endoscopic plastic biliary stenting, the most common long-term complication is stent clogging. To decrease the risk of obstruction, some endoscopists institute nasobiliary drainage after stent placement.

A transjugular, transvenous approach can be used for biliary catheterization if neither an endoscopic approach nor transhepatic drainage is feasible.

Cystic Neoplasms

Discussed here are hepatobiliary cystadenomas and cystadenocarcinomas, most are biliary in origin. Other cystic, intrahepatic structures are discussed in Chapter 7.

Clinical

Little distinguishes a biliary cystadenoma from a cystadenocarcinoma either clinically or radiologically. Most arise within the liver, with only an occasional one originating from extrahepatic bile ducts. Similar tumors also arise in congenital liver cysts and in the hepatoduodenal ligament.

These rare tumors occur mostly in middleage women. The benign variety is considered premalignant; even if resected, a high recurrence rate is evident.

Histologically, biliary cystadenomas are similar to mucinous cystic tumors found in the pancreas and ovaries. They have a fibrous capsule, internal septations, and varying degrees of nodularity, findings identified with imaging. These tumors contain nonbilious, at times mucinous, fluid. Histologically, most cystadenocarcinomas, especially mucin producing ones, are well differentiated. Pathologic differentiation of benign from malignant is rather subtle and involves gauging the degree of cellular atypia.

ADVANCED IMAGING OF THE ABDOMEN

Some cystadenomas and carcinomas contain mesenchymal stroma. Tumors containing ovarian-type stroma appear to have a better prognosis than those that do not; imaging, however, cannot detect this type of stroma. Some patients also develop a synchronous ovarian cystadenoma or gastric carcinoma, presumably due to a common histogenetic pathway.

An occasional biliary cystadenoma grows large without producing symptoms. An abdominal mass, pain, obstructive jaundice, or even ascites are presenting findings. Some are discovered incidentally. Passage of tumor fragments from a cystadenoma communicating with bile ducts can result in biliary obstruction and obstructive jaundice.

An elevated serum tumor marker CA 19-9 is found with some, especially those containing mesenchymal stroma, but a normal serum level does not exclude a cystadenoma or cystadenocarcinoma. Carcinoembryonic antigen (CEA) and a-fetoprotein levels tend to be normal.

Differential diagnosis includes other cystic liver neoplasms, benign cysts, and, for extrahepatic lesions, pseudocysts and even gastroduodenal duplication cysts. These tumors have been mistaken for and treated as hepatic hydatid cysts.

Imaging

A cystadenoma has imaging findings similar to those of nonneoplastic hepatic cysts. Computed tomography and US show a multicystic tumor containing septations. Their appearance is rather characteristic, with both benign and malignant versions having a similar appearance, although septa without nodularity suggest a benign cystadenoma, and septations with nodularity point to a carcinoma. Computed tomography shows mostly water attenuation fluid within the cyst, although attenuation values differ depending on the amount of cholesterol, blood, and necrotic tissue present. Calcifications within either the septa or the rim are seen on rare occasion. Tumor nodules and septa enhance postcontrast.

Ultrasonography reveals an anechoic tumor, identifying internal septations in some. Hemorrhage leads to a hypoechoic appearance.

GALLBLADDER AND BILE DUCTS

A fluid–fluid level may be present. Tumor nodules are hyperechoic. Transabdominal US differentiates only with difficulty between a solid tumor containing cystic components and a fluid collection. Both tend toward a hypoechoic appearance. Color Doppler US is useful in detecting blood flow within a malignant cystic tumor. Obviously, no flow is seen in benign fluid collections.

These tumors are hypointense on T1and hyperintense on T2-weighted images. Mucin and hemorrhage increase their T1-weighted signal intensity. An occasional tumor is markedly hyperintense on T1and hypointense on T2-weighted MR images, generally due to thick, proteinaceous mucinous fluid. Any septations are readily identified.

Some of these tumors communicate with the bile duct lumen, best identified with cholangiography, and bile cytology is helpful in these tumors.

Occasionally percutaneous transhepatic cholangioscopy provides a biopsy path for these tumors and defines the underlying biliary anatomy.

Mucin-Hypersecreting Tumors

So-called mucinous, ductectatic, or mucinhypersecreting hepatobiliary cystadenomas, cystadenocarcinomas, or cholangiocarcinomas produce massive amounts of mucin within markedly dilated bile ducts. Whether these mucinous tumors are a variant of cystadenomas and cystadenocarcinomas or whether they represent a separate entity is speculation. Complicating the issue is that an occasional biliary cystadenoma secretes excess mucin and mimics an intrahepatic cyst; at times one even contains daughter cysts. The carcinomas invade hepatic parenchyma and vessels. At times widespread metastases are evident.

Their histopathologic features are similar to those of mucin-producing pancreatic duct tumors, and mucous lakes often contain adenocarcinoma cells. A frond-like papillary architecture predominates, often containing elements of

dysplasia, adenoma, and carcinoma in the same tumor.

Excess mucin secretion is a rare cause of markedly dilated bile ducts distal to a tumor. Similar to their pancreatic counterparts, some result in excess mucin draining from the duodenal ampulla; or, excess mucin simply results in obstructive jaundice. An occasional tumor contain calcifications.

A rare peripheral intrahepatic tumor results in duct perforation and spill of mucin and tumor cells—a rare cause of pseudomyxoma peritonei.

Smaller tumors are not detected by imaging, and the only abnormality consists of dilated, mucin-filled ducts. Dilated bile ducts distal to the tumor are readily imaged. Cholangiography shows large intraluminal masses, a result of mucin retention. At times the duct lumen appears narrowed because only a small channel is left for bile and contrast flow. Nevertheless, every effort should be made to detect a tumor.

Mucin has a similar appearance to bile with both CT and MR, except when thick and proteinaceous, when it tends to be hyperintense on T1and hypointense on T2-weighted MR images. Cholangiography identifies mucin as linear or elongated intraductal filling defects. These tumors are hypodense on CT and show little arterial-phase contrast enhancement; peripheral enhancement and internal septations tend to be more evident during equilibrium phase imaging (Fig. 8.38). They are hypointense on T1and hyperintense on T2weighted MRI.

Neuroendocrine

A bile duct granular cell tumor is rare. It is of Schwann cell origin and tends to occur at the juncture of two ducts, such as the hepatic and cystic ducts. It is most common in young women.

Cholangiography reveals a smooth stricture similar to that seen in sclerosing cholangitis. The US appearance can mimic a stone.

Biliary Stones

Clinical

The prevalence of gallstones varies by sex, age, and population makeup. Native Americans have an extremely high prevalence of gallstones, with most stones consisting of cholesterol. Gallstones do occur in the pediatric population.

The prevalence of both gallbladder stones and bile duct stones is greater in pregnant women than in controls. The prevalence of choledocholithiasis in pregnancy is approximately 1 in 1200 deliveries. If needed, surgical exploration is performed, although therapeutic ERC is an alternative.

Fetal cholelithiasis is very rare. Little is known about the sequelae of this poorly understood condition. Ultrasonography identifies multiple, small hyperechoic foci without distal shadowing; these clear shortly after birth.

Gallbladder volume in diabetics is larger than in controls, and they have a severalfold increased prevalence of cholesterol stones. Diabetics with autonomic neuropathy have reduced gallbladder motility, thus promoting stasis and cholesterol crystal formation. Patients with hereditary spherocytosis are at increased risk for gallstones.

Somatostatin inhibits gallbladder emptying. A somatostatinoma or therapy with somatostatin analogues is associated with an increased