Материал: Advanced Imaging of the Abdomen - Jovitas Skucas

GALLBLADDER AND BILE DUCTS

conjecture. An interesting observation is that the odds of having primary sclerosing cholangitis is significantly decreased among those who smoke (49).

Pathology

Fibro-obliterative inflammation of both intraand extrahepatic bile ducts is a constant feature of PSC. The presence of liver noncaseating and nonnecrotizing granulomas is generally considered a feature of primary biliary cirrhosis, although similar granulomas are occasionally detected in PSC.

In Japan, eosinophilia is found in a large minority of patients with primary sclerosing cholangitis. Similarly, about a third of patients with PSC are antinuclear antibody positive.

Imaging

Both intraand extrahepatic bile ducts are involved. In a minority of patients only intrahepatic ducts are affected (Fig. 8.17), some of the bile ducts become amputated, and the imaging appearance superficially mimics that seen with primary biliary cirrhosis. A minority of patients develop diverticular-like outpouchings (Fig. 8.18). These intramural diverticula appear as cyst-like structures within the bile wall and, if present, are almost pathognomonic of sclerosing cholangitis.

Classic findings in sclerosing cholangitis consist of multiple strictures varying in length and caliber. A beaded appearance to the bile ducts is not uncommon, with beading ranging from a fine, barely perceptible change in caliber to a coarse, undulating outline. Beading is difficult to evaluate with CT; dilated intrahepatic ducts, regardless of cause, often have an apparent beaded appearance as they course through different axial planes. Extensive hepatic fibrosis and bile duct wall thickening are common. On noncontrast CT fibrosis appears as hypoattenuating regions that become isoattenuating postcontrast. Duct wall thickening ranges from diffuse to focal.

Periportal fibrosis results in hyperechoic portal triads. Bile duct wall thickening appears variable in echogenicity with endoluminal US.

In some studies of PSC patients, MRCP has better defined intrahepatic bile ducts and identified more strictures than ERCP (50). Its noninvasive nature makes it attractive for following established disease and evaluating intrahepatic ducts not visualized by ERCP. Once PSC is well established, MRI identifies intrahepatic bile duct dilation, intrahepatic and extrahepatic bile duct stenosis, occasionally a resultant beaded appearance, and bile duct wall thickening and enhancement (51). A major function of MR is to identify underlying parenchymal damage. Magnetic resonance imaging identifies peripheral wedge-shaped hyperintense regions on T2-weighted images, regions often showing increased arterial-phase enhancement and an occasional reticular pattern (51,52). The significance of the MR parenchymal findings is not clear, and this topic is ripe for further research.

Scintigraphy confirms bile retention within bile ducts. Single photon emission computed tomography (SPECT) images reveal multiple focal regions of tracer retention due to bile stasis. In some patients an otherwise normal gallbladder fails to visualize with radiotracer.

Lymph node enlargement is not uncommon, with both porta hepatis nodes and other intraabdominal sites involved. Periportal edema is also detected.

Biliary abnormalities in most patients gradually progress over years; a more sudden change in a stricture should suggest an underlying cholangiocarcinoma. Eventually, cirrhosis and portal hypertension ensue. The right and left lobe atrophy, the caudate lobe hypertrophies, and the liver develops a prominent lobular appearance,a finding less commonly found with other causes of cirrhosis.

In spite of an occasional optimistic statement that cholangiocarcinomas can be detected in a setting of sclerosing cholangitis, not uncommonly an unsuspected cancer is first discovered by a pathologist after liver transplantation. Distortion by underlying disease makes detection of superimposed tumors difficult. Intraluminal polypoid cancers are least common in these patients; more often, a dominant stricture is found to consist of fibrosis with interspersed cancer cells. Even delayed CT contrast enhancement, a prominent feature with most cholangiocarcinomas, is often missing with these

Figure 8.18. Irregular diverticular-like outpouchings (arrow) are an uncommon but characteristic finding in sclerosing cholangitis.

Endoscopic dilation of major duct stenoses is a temporizing measure in this generally progressive condition. In a minority of patients one extrahepatic bile duct stricture is responsible for most obstructive symptoms. Bile duct stricture dilation, especially surgical repair, should be approached cautiously. An occasional patient develops rapid progression of sclerosing cholangitis postoperatively; whether a fibroproliferative response is induced by duct manipulation is speculative.

A stent through a major stricture provides temporary relief in some, although stent occlusion is a common long-term complication. One variant is to provide short-term stenting; interestingly, these ducts tend to remain patent for months afterward.

Also of interest is that immunosuppression after liver transplantation does not influence inflammatory bowel disease in these patients.

Autoimmune Cholangitis

Autoimmune cholangitis is a newly described entity containing features suggestive of primary biliary cirrhosis and autoimmune hepatitis; a relationship between autoimmune cholangitis and autoimmune hepatitis is not clear. Indeed, whether these should be considered separate entities or whether they simply represent specific liver pathways responding to an insult is unknown (primary biliary cirrhosis and autoimmune hepatitis are discussed in Chapter 7).

Clinically these patients have cholestasis, elevated antinuclear antibody titers, and negative antimitochondrial antibody titers, while histology reveals findings of primary biliary cirrhosis together with inflammation.

An occasional patient with Sjögren’s syndrome has findings consistent with autoimmune cholangitis.

Gallbladder Tumors

Gallbladder polyps range from nonneoplastic to neoplastic, from sessile to pedunculated, from small to large. Most are several millimeters in size and are nonneoplastic. They are rare in children.

Secondary Sclerosing Cholangitis

Secondary sclerosing cholangitis is associated with some infections, including HIV, bile duct ischemia, some pharmacotherapy, hepatic artery chemotherapy, and embolization and

Detection

Computed Tomography

Larger gallbladder polyps are readily identified by CT. Precontrast CT reveals a majority of benign polyp to be isodense to bile and

most malignant polyps to be hyperdense. Both benign and malignant polyps enhance postcontrast and, especially for smaller ones, postcontrast imaging is necessary for their detection.

Ultrasonography

The prevalence of gallbladder polyps in diabetics and matched controls in an epidemiologic study of gallstones was 7%, with a marked male predominance (53); 90% of these polyps were <10mm in diameter. No statistical difference in polyp prevalence was evident between diabetics and nondiabetic controls.

Conventional US readily detects gallbladder polyps. The prevalence of cancer increases directly with polyp size, and polyps >1cm in diameter are at considerable risk for carcinoma. The vast majority of polyps <5mm are cholesterol polyps, but an occasional cancer is <1cm in diameter.

Endoscopic US also detects gallbladder polyps. The endoscopic US contour of a pedunculated gallbladder polyp is helpful in its differentiation; polyps having a granular contour and a foamy or globular echo pattern are mostly nonneoplastic, while a smooth, nodular, and solid appearance suggests a neoplasm.

Magnetic Resonance Imaging

A majority of polyps exhibit varying degrees of postcontrast MR enhancement, thus distinguishing them from gallstones. Cancers tend to have early and prolonged enhancement, but benign tumors vary in their washout patterns.

Nonneoplastic Tumors

Cholesterol Polyp/Cholesterolosis

Cholesterol polyps, or cholesterolosis, are the most common gallbladder polyps. The surgical literature refers to cholesterolosis as a “strawberry gallbladder.” They range from solitary to multiple. Gallstones may or may not be present.

Cholesterolosis is often an incidental diagnosis, usually made by a pathologist. These polyps

ADVANCED IMAGING OF THE ABDOMEN

are not considered premalignant, although an occasional carcinoma is surrounded by glandular dysplasia and cholesterolosis; the carcinoma probably originates first and tumor epithelium then absorbed cholesterol from bile. Cholesterolosis is not part of the spectrum of acute cholecystitis. No association exists with systemic disorders such as atherosclerosis or diabetes.

Even if detected preoperatively, cholesterolosis and adenomyomatosis are not believed to be indications for cholecystectomy.

Smaller cholesterol polyps are not detected with unenhanced CT but become evident postcontrast.

Conventional US shows most larger cholesterol polyps to be pedunculated, have a granular surface, and tend toward a hypoechoic appearance, but smaller ones are mostly hyperechoic. Smaller polyps are nonmobile and adhere to the gallbladder wall, and both large and small are without acoustic shadowing. The smaller ones tend to have a smooth outline; they become irregular with growth. Endoscopic US with its higher resolution is preferred over conventional US when evaluating gallbladder polyps.

Some authors suggest that persistence of gallbladder contrast 24 hours after an oral cholecystogram is indirect evidence of cholesterolosis. No objective data support this statement, and one should not rely on this finding.

Although generally not warranted, US-guided percutaneous transhepatic needle aspiration cytology can diagnose cholesterol polyps.

Adenomyoma/Adenomyomatosis

Adenomyomatosis presents either as a focal gallbladder narrowing or as diverticular-like outpouchings, most often in the gallbladder fundus. These outpouchings, also called cholecystitis glandularis proliferans, are believed to represent both mucosal herniation into muscularis propria and prominent RokitanskyAschoff sinuses. A rare report describes a carcinoma associated with adenomyomatosis, probably being coincidental. Although somewhat controversial, in most patients adenomyomatosis is generally believed not to be associated with symptoms.