Материал: Advanced Imaging of the Abdomen - Jovitas Skucas

GALLBLADDER AND BILE DUCTS

do not enhance, although some are more prominent postcontrast. They do not communicate with bile ducts.

The larger ones consist of a complex mass ranging from solid to mostly cystic (Fig. 8.22). Calcifications are not common, although an occasional one does contain peripheral calcifications. They tend to be mostly hypodense on postcontrast CT, although solid components enhance with contrast. Some septa also enhance postcontrast.

Ultrasonography reveals these hamartomas to be hypoechoic. Larger ones become inhomogeneous and hyperechoic and contain acoustic shadowing.

Limited MRI of these hamartomas reveals them to be hypointense on T1and hyperintense on T2-weighted MR images (Fig. 8.23). They are even more hyperintense on heavily T2-weighted images and are more apparent and more numerous on T2-weighted MRI and

Figure 8.22. Liver mesenchymal hamartoma in an 8–month- old boy. Computed tomography shows a complex, mostly cystic tumor replacing most of an enlarged liver. Mild contrastenhancement was evident in the solid component. (Courtesy of Luann Teschmacher, M.D., University of Rochester.)

on MRCP than on T1-weighted images. They vary in enhancement postgadolinium, with some enhancing less than does normal liver tissue.

Angiography reveals both hypovascular and hypervascular tumors.

The imaging appearance in young children is similar to that seen with an undifferentiated embryonal cell carcinoma. In fact, some authors believe that a mesenchymal hamartoma represents a benign counterpart of an embryonal cell carcinoma.

Some intrahepatic hamartomas initially contain an enhancing rim, presumably representing compressed adjacent liver parenchyma, and superficially mimic the enhancing rim found with metastases. Hamartoma enhancement, however, does not progress centrally. The imaging differential diagnosis also includes hepatoblastoma and hepatocellular carcinoma. The presence of a cystic component in a liver tumor in children should suggest a hamartoma. Small liver cysts, not communicating with bile ducts and without renal involvement, also favor a diagnosis of hamartomas.

Fine-needle aspiration of these lesions tends to be nondiagnostic, and core biopsies are needed.

ADVANCED IMAGING OF THE ABDOMEN

gallbladder. The pathologic classification of bile duct adenomas is somewhat arbitrary. While most pathologists simply classify them as tubular, papillary, or tubulopapillary, some adenomas appear to originate from peribiliary glands rather than from bile duct epithelium, and consist of a mass of disorganized but mature peribiliary gland acini and tubules, together with variable amounts of stroma, and thus should be classified as peribiliary gland hamartomas.

These tumors occur either singly or are multiple. Some secrete excessive amounts of mucus. They occur in both intraand extrahepatic bile ducts and vary from several millimeters to several centimeters in size. Although a papilloma per se should be benign, histology often reveals cytologic atypia, and differentiation from carcinoma in situ and low-grade carcinoma is not always possible. An association exists between diffuse papillomatosis and cancer.

Most solitary adenomas appear on cholangiography simply as intraluminal polyps (Fig. 8.24). Papillary adenomas, if large enough, result in bile duct dilation due to their intralu-

Other Nonneoplastic Tumors

Although uncommon, cholesterol polyps do develop within bile ducts.

A papilla of Vater lymphangioma is a rare cause of biliary obstruction.

Amputating neuromas develop after cholecystectomy. These are not neoplastic but rather reactive hyperplastic lesions.

Benign Neoplasms

Benign bile duct neoplasms consist roughly of an equal number of adenomas and papillomas, with other types being rare.

Adenoma/Papilloma/Papillomatosis

The terms adenoma and papilloma (and even cholangioma) are used loosely in the literature. Papillomatosis refers to multiple papillomas throughout the bile ducts and often also in the

Figure 8.24. Common bile duct papilloma (arrow). Its imaging appearance is similar to a stone. (Courtesy of Daniel Wolfe, M.D., Williamsport, Pennsylvania.)

GALLBLADDER AND BILE DUCTS

minal mass. Occasionally biliary dilation is secondary to excessive mucus secretion by these tumors, a characteristic but not pathognomonic finding. In papillomatosis the ampulla of Vater is dilated and contains mucin secretions, an appearance mimicking mucin-secreting pancreatic tumors.

Ultrasonography of papillomatosis shows small, multiple, nonshadowing, echogenic tumors adjacent to bile wall. The more proximal bile ducts tend to be dilated due to obstruction. Cholangiography reveals multiple intraluminal tumors.

These tumors enhance homogeneously after MR contrast.

The literature provides little guidance for therapy of extrahepatic papillomatosis. Some patients are managed conservatively with endoscopic follow-up.

Adenomyoma

A bile duct adenomyoma is rare. Imaging often suggests a carcinoma, and histology of a resected specimen is necessary to establish the diagnosis. Complicating this issue is the occasional benign adenomyoma undergoing malignant transformation and the patient presents with metastases.

Malignant Neoplasms

The vast majority of malignant bile duct neoplasms are adenocarcinomas (called cholangiocellular carcinoma and often abbreviated to cholangiocarcinoma) originating from biliary epithelium. Rarely seen are clear cell adenocarcinomas, mucinous adenocarcinomas, adenosquamous carcinomas, anaplastic carcinomas, squamous carcinomas, or undifferentiated carcinomas. Encountered in childhood are embryonal rhabdomyosarcomas (sarcoma botryoides).

Cholangiocellular Carcinoma

Cholangiocellular carcinoma develop throughout the bile ducts. The classification scheme adopted here divides cholangiocarcinomas into three anatomic locations: intrahepatic, hilar, and extrahepatic. These anatomic distributions

reflect their somewhat different clinical presentation, differential diagnosis, and therapy. Perihilar ones are most common; resectability rate increases with a more distal location.

Clinical

A number of extrabiliary conditions are related to bile duct carcinoma (Table 8.6). Common duct stones distal to a cholangiocarcinoma are found in about 20% of patients. Coexisting gallbladder stones are common.

Cholangiocarcinomas tend to grow slowly and the initial clinical presentation with most porta hepatis and extrahepatic cholangiocarcinomas is jaundice due to major bile duct obstruction. An intrahepatic tumor only obstructs part of the bile flow, and thus jaundice is a late finding, after extensive tumor spread.

Most cholangiocarcinomas infiltrate locally and spread to adjacent lymph nodes, although distant metastasis is not uncommon late in the course. As one unusual example, metastatic cholangiocarcinoma to the testicle presented as a painless scrotal tumor (66).

Pathology

Histologically, cholangiocarcinomas range from undifferentiated to well differentiated, with the latter more common. Some are associated with an exuberant fibrotic reaction to the point that malignant cells are scant and the overall appearance mimics a benign stricture. Perineural invasion is common with proximal (towards the

Table 8.6. Conditions associated with cholangiocarcinoma

Sclerosing cholangitis

Clonorchiasis

Inflammatory bowel disease

Long-standing infectious cholangitis

Choledocholithiasis

Hepatolithiasis

Hemochromatosis

Choledochal cyst

Caroli’s disease

Prior thorium dioxide (Thorotrast) use

Certain chemical exposure

Primary biliary cirrhosis (?)

liver) extrahepatic cholangiocarcinomas, but lymph node metastasis is more common with distal ones. Infiltrating tumors tend towards more frequent and extensive periductal spread than polypoid, nodular, or annular ones. Most cholangiocarcinomas are hypovascular.

A useful morphologic differentiation consists of papillary, nodular, and diffuse infiltrating types. A majority of papillary cancers are encountered in the common bile duct. Nevertheless, proximal extrahepatic cholangiocarcinomas tend to be more differentiated than more distal ones (towards the duodenum); the latter, often being moderatelyto poorly-differenti- ated, tend towards an annular or infiltrating appearance.

Whether the rare bile duct carcinoma exhibiting adenosquamous features represents a variant of a hepatic adenosquamous carcinoma or is related to a more typical cholangiocarcinoma is conjecture.

Intrahepatic

Clinical

A peripheral (intrahepatic) cholangiocarcinoma is probably more common than reported. Many are misdiagnosed as a hepatocellular carcinoma or even a benign neoplasm. Also, not all intrahepatic tumors can be clearly categorized into distinct hepatocellular or cholangiocellular origins. Some are even misdiagnosed as metastatic adenocarcinomas. Fine-needle biopsies simply reveal adenocarcinomatous tissue, and a correct diagnosis is made in only about half of these tumors, while in others a metastatic adenocarcinoma is suggested.

Intrahepatic (peripheral) cholangiocarcinomas range from single to multicentric in origin. An occasional one grows intraluminally for varying lengths without major bile duct wall invasion. Also called a malignant papillary neoplasm, an intraductal component may or may not be identified by CT, depending on size (67). Diffuse infiltration predominates in others and can eventually even lead to acute hepatic failure. These intrahepatic tumors tend not to invade portal venous branches, although an occasional one invades the portal vein and leads to portal hypertension (68).

The most common presentation is abdominal pain, weight loss, and malaise. Jaundice is absent

ADVANCED IMAGING OF THE ABDOMEN

unless a tumor invades and destroys sufficient liver parenchyma. An almost constant finding is an elevated serum alkaline phosphatase level. Most of these tumors are rather invasive and often progress rapidly; an exception is with those exhibiting an intraluminal papillary growth pattern and these have a more indolent course.

Imaging

The use of earlier, less precise imaging suggested that with infiltrating tumors imaging could not suggest a specific diagnosis and that imaging findings of most intrahepatic cholangiocarcinomas were similar to those seen with a hepatocellular carcinoma or metastasis. Yet a number of findings, albeit subtle, do suggest a biliary origin. Thus considerably dilated more proximal bile ducts, due to obstruction, are found in about half of patients with an intrahepatic cholangiocarcinoma (69). A patent portal vein branch passing through a tumor is generally considered a sign of a benign lesion; an intrahepatic cholangiocarcinoma, however, often also contains a patent portal vein branch. Also, in distinction to hepatocellular carcinomas, most intrahepatic cholangiocarcinomas develop in a noncirrhotic liver. No capsule is identified. A few of these tumors develop calcifications. A minority grow primarily into the bile duct lumen. These intraluminal (papillary) intrahepatic bile duct carcinomas have rather nonspecific CT findings, but they are also associated with focal proximal intrahepatic bile duct dilation (70) (Fig. 8.25).

Cholangiography reveals obstruction and dilation of more peripheral bile ducts (Fig. 8.26). Only a rare cholangiocarcinoma infiltrates diffusely without occluding bile duct. An occasional tumor manifests with an irregular bile duct lumen, displacement, and multicentric involvement mimicking primary intrahepatic sclerosing cholangitis.

In most patients CT reveals a single, irregular, hypodense, nonencapsulated tumor of varying heterogeneity; contrast enhancement is generally evident, tending to be more pronounced in the tumor periphery, and, in fact, delayed postcontrast CT images are of value in differentiating an intrahepatic cholangiocarcinoma from a hepatocellular carcinoma. Hepatocellular carcinomas tend to have an early

enhancement peak followed by a gradual decrease, with the greatest tumor conspicuity during a delayed phase, several minutes after the start of contrast injection; on the other hand, with most cholangiocarcinomas the

greatest conspicuity occurs during the portal venous phase, and tumor attenuation increases during the delayed phase. Such prolonged contrast retention is probably related to the fibrotic matrix associated with many cholangiocarcino-

Figure 8.27. Intrahepatic cholangiocarcinoma. Contrastenhanced CT identifies a poorly marginated tumor containing regions of necrosis (arrow). Dilated bile ducts are present in the medial segment of the left lobe and the right lobe. (Courtesy of Patrick Fultz, M.D., University of Rochester.)

mas. Exceptions, however, do occur, and a rare cholangiocarcinoma is not definable during any dynamic CT imaging phase (Fig. 8.27).

Ultrasonography reveals either a single nodule having irregular margins or additional satellite nodules. Most tumors are hypoechoic, although some contain hyperechoic regions.

Magnetic resonance imaging identifies intrahepatic cholangiocarcinomas as focal tumors, with some including a wedge-shape defect larger than the tumor itself, presumably secondary to surrounding edema and parenchymal compression, although an occasional infiltrating cholangiocarcinoma is intrinsically wedgeshaped. These tumors are mostly hypointense and occasionally isointense on T1and variable in intensity on T2-weighted images; signal intensity on T2-weighted images depends mostly on the amount of fibrosis, necrosis, and secretions within the tumor. The occasional strongly hyperintense ones contain more secretions and necrosis. Postgadolinium enhancement varies considerably but often is progressive and moderate in extent and the intense immediate enhancement seen with many hepatocellular carcinomas is not evident. Postcontrast, some of these tumors show an enhancing rim, with progressive centrifugal filling of the tumor.

Some of these tumors encase adjacent vessels and result in focal liver atrophy and even a

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central scar. Central regions on T2-weighted images range from hypoto hyperintense, with hypointensity reflecting fibrosis, a common finding with these tumors (69); postcontrast, these central hypointense regions range from homogeneous,to heterogeneous,to no enhancement, with fibrosis enhancing and necrotic regions not enhancing. None of the described findings is pathognomonic, and, with the exception of a dilated duct proximally, colorectal metastases often have a similar appearance.

Adjacent noninvolved liver parenchyma is hyperintense on T1-weighted images; the high signal intensity is not suppressed with fat saturation, and this tissue enhances postcontrast, findings probably related to fibrosis. Preliminary evidence suggests that ferumoxides improves visualization of intrahepatic cholangiocarcinomas (71).

An MRCP outlines bile ducts both proximal and distal to a tumor. Often multiple duct obstructions are detected. An MRCP can establish unresectability by showing extensive tumor spread.

Most of these tumors are hypovascular on angiography. Occasional arterioportal shunting is detected; a large tumor invades adjacent hepatic arteries and portal vein branches and can even invade the inferior vena cava. Hepatic artery invasion influences any planned resection, yet the accuracy of detecting hepatic artery invasion by CT and US is low. Multidetector CT angiography holds promise in detecting vascular invasion, but its specific role is not yet clear.

Occasionally an intrahepatic cholangiocarcinoma contains foci of sarcomatous transformation. One such cholangiocarcinoma containing malignant fibrous histiocytoma-like sarcomatous tissue was hypodense by CT; US showed a well-marginated, heterogeneous hypoechoic tumor, and MRI revealed a hypoto isointense tumor on T1and a heterogeneous appearance on T2-weighted images (72). The cholangiocarcinoma was hypovascular by angiography. Some of these sarcomatous tumors contain internal septa.

Therapy

Of 61 patients with an intrahepatic cholangiocarcinoma seen at the Mayo Clinic over a 31year period, 46% underwent resection for cure