Книги по МРТ КТ на английском языке / Advanced Imaging of the Abdomen - Jovitas Skucas

the dependent portion; or, in some cysts, a fluid–fluid interface is evident. A gas–fluid level within the cyst implies communication with bile duct or viscus, although occasionally an infected, noncommunicating cyst has a gas– fluid level. Detachment of the inner layer into the cyst lumen results in a soft tissue tumor either floating or in the most dependent portion of the cyst, an appearance termed the water lily sign.

Daughter cysts lead to a cyst-within-a-cyst appearance. At times numerous daughter cysts result in an imaging finding of multiple small cysts in an otherwise solid-appearing tumor, an appearance mimicking a honeycomb.

Computed tomography and US often visualize intrabiliary hydatid material once biliary communication is established. Computed tomography reveals intrabiliary hydatid membrane particles as “sand”; at times the actual communication is identified. In some patients adjacent bile ducts dilate.A fat–fluid level within the cyst is a sign of biliary communication. Occasionally, hydatid material is observed in the gallbladder lumen.

A hydatid cyst sonographic classification is outlined in Table 7.5. This classification differs from the general imaging classification of hydatid cysts outlined above; it divides cystic hydatid disease into a proliferative stage and an involution stage. The US findings of types I through V represent the proliferative stage, and patients should be treated, but types VI and VII are part of disease involution and these patients do not require therapy. The cyst becomes hyper-

echoic as its content changes from a watery consistency to a viscid gel and the germinal layer folds within the viscid gel assume a curvilinear appearance, which no longer moves with a change in patient position.

At times endoscopic retrograde cholangiopancreatography (ERCP) is helpful, although MR cholangiography also defines bile duct involvement. Cyst communication with bile ducts, bile duct obstruction, and debris in the bile ducts can be detected (Fig. 7.9) and, at times, treated by endoscopic sphincterotomy. Extensive publications confirm that ERCP is safe in a setting of hepatic echinococcosis.

Magnetic resonance is useful in cyst characterization and in defining its relationship to the surrounding structures. Magnetic resonance imaging, MRA, and MR cholangiography should detect all hydatid cysts on both T1and T2-weighted images and suggest a biliary communication.

Angiography is rarely performed for suspected hydatid cysts. These are avascular, often multilocular cysts.

Table 7.5. US classification of hydatid cysts

Source: Adapted from Caremani et al. (21).

Figure 7.9. Echinococcal cyst communicating with bile ducts. Contrast partly outlines the cyst (arrow).

One should keep in mind that not all multilocular liver cysts are infectious in origin or even benign. The imaging appearances of an embryonal cell carcinoma or hepatobiliary cystadenoma mimic a hydatid cyst. With multiple hydatid cysts, liver parenchyma becomes sufficiently replaced that differentiation from polycystic disease becomes difficult.

Infection with E. multilocularis results in somewhat different imaging findings. Irregular, necrotic liver lesions often mimic a neoplasm (Fig. 7.10). Focal calcifications develop with both E. multilocularis and E. vogelii infections.

Biopsy/Drainage

Drainage can be both diagnostic and therapeutic. Cysts that are heavily calcified, however, are probably inactive and often are left alone.

Some biopsies are performed unintentionally without suspecting the true diagnosis and others are done on purpose. With suspicion that a lesion may indeed be hydatid in origin, the cytologist should be so informed when submitting aspirated material; in regions of low prevalence the pathologist may not consider this diagnosis. Some investigators believe that dilated pericystic bile ducts are a relative contraindication to nonsurgical treatment because of the danger of complicating biliary obstruction (22).

A number of older publications cautioned against biopsy or drainage of a hydatid cyst, although more recent experience suggests that percutaneous drainage is a relatively safe procedure. Minor allergic reactions, such as urticaria,

are encountered after aspiration in an occasional patient. A rare patient develops a major reaction, including shock, and the interventional radiologist must be prepared to deal with these reactions. Fatal anaphylaxis has been reported with percutaneous therapy. Also, a possibility of seeding exists due to a spill of cyst material, although intraperitoneal leakage of cyst fluid is rare. A superimposed bacterial infection also develops occasionally.

Percutaneous

Percutaneous treatment consists either of several installations of hypertonic saline (with interval aspiration) or placement of a catheter, injection of hypertonic saline, or drainage, followed in 24 hours or later by injection of a scolicidal solution. After therapy the endocyst becomes detached and serial US shows most cysts decreasing in size and the cyst wall becoming irregular and thicker. A second drainage is necessary only if a cyst contains membranes or multiple cysts are present. Both adults and children have been treated with percutaneous drainage.

Albendazole prophylaxis is instituted and catheter drainage generally continued until drainage is <20mL per day. Recommended imaging follow-up varies but US every month for 6 months, a control CT at 6 months, and then US and CT at yearly intervals is reasonable. The abscess cavity typically becomes obliterated within 6 months. Local recurrence is an uncommon occurrence. Another option is to treat by puncture, aspiration, injection, and reaspiration of smaller cysts and catheterization of larger cysts using hypertonic saline and absolute alcohol as cytotoxic and sclerosing agents (23).

Surgical

Surgical pericystectomy is advocated by some surgeons. Laparoscopic surgery with cyst aspiration is also performed. Hepatic resection is necessary only if multiple cysts involve the same lobe or if a cyst has essentially replaced a lobe.

Recurrent hydatid disease develops occasionally, either in the liver or other structure, even in the peritoneal cavity. Postdrainage US establishes a baseline and allows distinction of recurrence from postoperative change.

ADVANCED IMAGING OF THE ABDOMEN

Biliary strictures develop in some patients after surgery. These strictures tend to be long, multiple, and proximal in location.

Tuberculosis

Weight loss is common in patients with hepatic tuberculosis. Not all patients with liver involvement have hepatomegaly.

Tuberculous liver infection usually presents as a diffuse process, at times called miliary; less common is a macronodular tumor, or tuberculoma, mimicking an infiltrating tumor. Computed tomography reveals a hypodense tumor that enhances less than liver parenchyma. An occasional hypodense nodule is surrounded by an enhancing rim.

Ultrasonography reveals mostly welldelineated hypoechoic tumors.

Tuberculomas are mostly hypointense on T1and isointense on T2-weighted MR images, although considerable variation exists, ranging from hypointense to hyperintense on both T1and T2-weighted MRI. They do not enhance post-MR contrast but some exhibit rim enhancement. The MR appearance of hepatic tuberculomas is thus not specific, being influenced by the presence of calcifications, blood, and necrosis. A biopsy is necessary for diagnosis.

Extensive multiorgan tuberculosis is illustrated by a woman with multiple calcified brain nodules and calcified hypodense tumors in the liver and spleen (24); liver tuberculomas were hypointense on T1-weighted spin-echo (SE) images and hypointense but contained a hyperintense region on T2-weighted images.

Percutaneous needle biopsy in these patients should be diagnostic. After successful antibiotic therapy the sonographic appearance should revert to that of a normal liver.

Fungal

Most fungal abscesses occur in a setting of malignancy or immunocompromise. Most of these abscesses are small and tend to be scattered throughout the liver. Each individual abscess often has an imaging appearance similar to that of a pyogenic abscess, including rim enhancement.

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A biopsy, especially if obtained from the periphery of a lesion, may not provide a diagnosis.

Some of these abscesses calcify after therapy.

Candidiasis

Typically CT reveals Candida albicans abscesses as multiple hypodense lesions scattered throughout the liver. The appearance mimics metastases. The spleen is also often involved. A bull’s-eye appearance to the lesion should suggest candidiasis.

The sonographic findings range from an early wheel-like appearance, to a bull’s-eye pattern, to a homogeneously hypoechoic lesion.

Mucormycosis

Mucormycosis is an opportunistic fungal infection developing in patients with an impaired immune system or diabetes.

Mucormycosis in one patient manifested as multiple focal hypodense lesions containing centrally located vessels (25); biopsies revealed hyphae consistent with mucormycosis. Such a hypodense lesion surrounding vessels and without a mass should suggest an angioinvasive organism.

The differential includes other fungal infections, lymphoma, and Mycobacterium tuberculosis or M. avium-intracellulare infections.

Visceral Larval Migrans (Toxocariasis)

Ultrasonography in a patient with persistent eosinophilia and shown to have visceral larval migrans initially revealed a single hypoechoic lesion that progressed to multiple lesions (26); these lesions presumably represented confluent biliary granulomas. Only occasionally are larvae detected on liver biopsy. The diagnosis is confirmed with serologic testing.

world’s population. Both children and adults suffer from this infection. The primary endorgan affected depends on the river fluke involved: Schistosoma japonicum and S. mekongi, primarily Oriental in distribution, affect the liver, S. mansoni involves the liver and rectum, and S. haematobium infestation targets the urinary tract. S. mansoni is found in west central Africa, the Arabic peninsula, some Caribbean Islands, and the Atlantic coast of South America.

Fresh water snails serve as an intermediary host for cercariae. Humans are infected through intact skin, the cercariae migrate from peripheral venules to the lungs and heart, and reach the liver where they mature into adult worms. S. japonicum eggs are carried from mesenteric veins into intrahepatic portal vein terminal branches, where extensive fibrosis and a granulomatous reaction lead to presinusoidal portal hypertension.

Schistosomiasis can be divided into an acute (Katayama syndrome) and a chronic phase. Early diagnosis during the acute phase is based on clinical and laboratory data, with imaging having no direct role. Eventually these patients develop portal hypertension and esophageal varices. They have a normal hepatic venous pressure gradient due to the presinusoidal nature of their portal hypertension. Hemodynamic studies in patients with hepatic schistosomiasis reveal hyperkinetic systemic and splanchnic circulations.

Liver involvement consists of fibrosis and portal hypertension. Some patients progress to cirrhosis and liver failure. In the Middle East, cirrhosis developing in a setting of hepatic schistosomiasis should suggest superimposed hepatitis C virus infection. On the other hand, a Philippines study of prior S. japonicum infection found chronic viral hepatitis to be rare (27).

Patients with chronic liver schistosomiasis are at risk of developing hepatocellular carcinoma.

Schistosomiasis

Clinical

One of the oldest diseases known, even today schistosomiasis infects a large part of the

Imaging

Hepatosplenomegaly and lymphadenopathy are common with acute S. mansoni infection. Left lobe hypertrophy occurs early and is readily detected by US. On a chronic basis the porta hepatis region is usually most extensively

involved, and periportal fibrosis extends intrahepatically for varying lengths. Ultrasonography rather than biopsy is often used in endemic areas to evaluate periportal fibrosis. It reveals widened hyperechoic periportal tracts, a nonspecific finding also seen in some other chronic infections. A relationship exists between the degree of periportal fibrosis as detected by US and the presence of esophageal varices.

Early in the disease MRI shows portal hypertension (Fig. 7.11); then the periportal zones become isodense on T1-weighted images and enhance with contrast. T2-weighted sequences reveal hyperintense periportal regions suggesting inflammation and edema.

Patients with S. japonicum infection develop almost pathognomonic turtleback pericapsular and parenchymal calcifications, best identified with CT; US often shows a patchy network pattern. Calcifications are uncommon with S. mansoni and S. haematobium infection.

Spirochetes are identified in biopsy specimens. Pathologists have described an acquired liver deformity in end-stage tertiary syphilis known as hepar lobatum.

Actinomycosis

Liver infection by an anaerobic gram-positive bacterium of the genus Actinomyces is rare. No predisposing factors are found in most patients.

The diagnosis is confirmed when an Actinomyces species is cultured from pus aspirated from an abscess. Rather than an abscess, some patients have a more solid-appearing tumor, and a neoplasm is suspected. In particular, in a woman with a pelvic tumor and suspected liver metastases, especially if an intrauterine device is in place, biopsy should differentiate between actinomycosis and a neoplasm.

A complication of liver actinomycosis is portal vein thrombosis.

Syphilis

The liver is commonly involved in congenital syphilis. Hepatic failure and extensive liver calcifications develop in some of these neonates.

Secondary syphilis is marked by acute hepatitis and cholestasis. Ultrasonography reveals parenchymal abnormalities due to diffuse inflammation.

Liver involvement in tertiary syphilis is rare. Multiple intrahepatic nodules mimicking metastases are found occasionally. Biopsy reveals granulomas and necrosis.

Botryomycosis

Botryomycosis, also called bacterial pseudomycosis, is a rare, chronic bacterial infection characterized by eosinophilic botryomycotic (bacteria-containing) granules, with grampositive cocci and gram-negative bacilli being most often found. Clinically, the infection tends to mimic actinomycosis or some other fungal infection. Pathogenesis of this condition probably involves a symbiosis between the host and

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bacteria, although the specific pathobiologic interaction is unknown.

Botryomycosis most often involves the skin and is thus familiar to dermatologists. Several patients with liver botryomycosis have been described. Most lesions consist of multiple small liver abscesses containing gram-positive microorganisms. Initial imaging often suggests a neoplasm.

Hepatitis

Imaging has a limited direct role in hepatitis, with laboratory studies and biopsy being bulwarks of diagnosis. Magnetic resonance, however, is of potential value. Among patients with proven chronic hepatitis, histopathology in about two thirds of those with patchy enhancement on early postgadolinium MRI revealed a macrophage infiltrate, hepatocyte necrosis, and steatosis (28). Prominent linear enhancement on delayed postgadolinium MRI is found with fibrosis.

Viral

An unusual cause of acute hepatitis is measles virus infection.

Viral hepatitis is common throughout the world, with the highest prevalence in East Asia. Currently viruses A through G have been identified. At least one other type of enterically transmitted hepatotropic virus probably exists. Hepatotropic viruses A through E induce hepatocellular damage either through a direct cytotoxic effect or through some yet undefined mechanisms. The common end point is hepatocellular necrosis. Co-infection is not uncommon, especially in end-stage disease.

Fat ingestion normally results in gallbladder constriction. In some patients with acute hepatitis, fat results in paradoxical gallbladder dilation, a useful imaging finding. Some patients with acute viral hepatitis present with what clinically appears to be acute cholecystitis. They recover with conservative medical management. Gallbladder US in these patients reveals considerable gallbladder wall thickening, but the gallbladder returns to normal thickness with clinical recovery.

Hepatitis A

Humans appear to be the only host for hepatitis A virus. This infection has decreased in prevalence, especially in East Asia. It is an acute infection and does not lead to a chronic carrier state. Effective immunization exists against hepatitis A virus.

Some patients with hepatitis A virus infection develop acute renal failure and nephrotic syndrome, presumably due to hepatitis A virus– triggered immune-mediated renal injury in genetically susceptible individuals. Acute viral hepatitis A can progressed to autoimmune hepatitis.

Hepatitis B

In many patients hepatitis B virus (HBV) infection is subclinical; others, however, become chronic carriers, serve as a reservoir for further spread, and develop chronic liver disease, including cirrhosis. A direct relationship exists between chronic hepatitis B infection and hepatocellular carcinoma. Thus in South African blacks, those positive for hepatitis B surface antigen had a 23-fold increased risk of developing a hepatocellular carcinoma (29); those positive for hepatitis C serology had a sevenfold increased risk, while those with both hepatitis B and C markers had a relative risk of 82. The study estimates that HBV causes about 43% of hepatocellular carcinomas in South African blacks, hepatitis C 5%, and co-infection with both 20%. Hepatitis B infection probably is a factor in China, while hepatitis C virus plays a similar role in Southern Europe and Japan. Hepatitis B virus is also suspected to have a role in other cancers.

Hepatitis B infection is transmitted vertically from mother to child. Infection in some infants progresses to fibrosis and eventual cirrhosis.

A histologic finding of hepatocyte loss, cholestasis, periportal fibrosis, and inflammation is called fibrosing cholestatic hepatitis. It is a variant of HBV infection, and affected patients have a high rate of liver failure.

Immunization against HBV is available.

Hepatitis C

Hepatitis C virus (HCV) infection is believed to cause at least 90% of previously called non-A,

non-B hepatitis. In the United States approximately 1.4% of the population is infected. Infection is acquired by either blood product transfusions or intravenous drug abuse. It is a common infection in hemophiliacs. In some patients the mode of transmission is not known. Vertical and sexual transmission is uncommon.

Hepatitis during the acute phase is invariably mild and often subclinical, but most infections become chronic. The clinical course of hepatitis C infection is unpredictable.A rough estimate of mean time between initial infection and diagnosis of chronic hepatitis is 10 years, 10 years more for cirrhosis to develop, and another 10 years before hepatocellular carcinoma is discovered, although considerable individual variation exists. Even with advanced disease, half the patients are asymptomatic. Normal biochemical tests do not exclude viral replication in anti- HCV–positive individuals. Different viral genotypes are associated with different severity of liver disease. For instance, HCV type 1b is overrepresented in patients developing cirrhosis and hepatocellular carcinoma and influences the carcinoma risk in cirrhosis.

An association exists between HCV infection and autoimmune diseases. Infection leads to autoimmune hepatitis, membranoproliferative glomerulonephritis, thyroiditis, and such skin disorders as porphyria cutanea tarda and possibly lichen planus.A relationship with Sjögren’s syndrome and possibly even Behçet’s syndrome is suspected. An association with Guillain-Barré syndrome (an acute demyelinating neuropathy believed to have an autoimmune basis) has been suggested. It has been implicated in periarteritis nodosa.

Unlike many other human viruses, hepatitis C virus is an RNA virus and does not appear to be integrated into host cell genome. Carcinogenesis of HCV infection is generally explained by its ability to cause hepatic inflammation, regeneration, fibrosis, and eventual cirrhosis, yet some patients appear to progress from chronic hepatitis directly to carcinoma without developing cirrhosis.

An interesting association appears to exist between HCV serology and primary hepatic lymphoma. Hepatitis C virus is both hepatotropic and lymphotropic and in some patients results in a mixed essential cryoglobulinemia, a lymphoproliferative condition that on occasion

ADVANCED IMAGING OF THE ABDOMEN

evolves into non-Hodgkin’s lymphoma. The virus is detected in some lymphoma tissue. Anti–hepatitis C virus antibodies are detected in almost half of B-cell non-Hodgkin’s lymphoma patients. Likewise, an occasional patient with chronic HCV infection develops reactive lymphoid hyperplasia (pseudolymphoma), with imaging suggesting a focal hepatocellular carcinoma; biopsy should be diagnostic.

Gray-scale US findings do not correlate with liver biopsy findings in patients with chronic HCV infection. Imaging does detect perihepatic lymphadenopathy, however, with number and size related to HCV activity (30). Gray-scale US can document the response to therapy. Lymph nodes appear hyperintense relative to the liver on T2-weighted MRI.

No current immunization is available against this virus. Interferon is the treatment of choice for chronic HCV infection, but relapse rate is high.

Hepatitis D

Humans are probably the only host for hepatitis D virus. Its major focus in the United States is in drug addicts. It progresses to chronic hepatitis and cirrhosis.

Hepatitis E

Hepatitis E has a worldwide distribution and is a cause of considerable morbidity and mortality in the developing world. This virus is spread through contaminated water. Infected individuals develop cholestatic jaundice, generally with few sequelae, although in pregnancy it has led to fulminant hepatic failure.

Hepatitis G

Hepatitis G virus (HGV) is a RNA virus in the family Flaviviridae and is transmitted by blood transfusion. Both acute and chronic infections occur, but its role in hepatitis is uncertain. Parenteral transmission appears common, and IV drug users, hemodialysis patients, and hemophiliacs are prone to this infection, often in association with HBV and HCV infections.

Hepatitis G virus appears to be sensitive to interferon therapy.

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Epstein-Barr Virus

Infectious mononucleosis (Epstein-Barr virus infection) is a rare cause of hepatitis; it has led to fulminant hepatic failure.

Imaging

Hepatitis has no specific imaging findings, with imaging generally performed to exclude other disorders. Necrosis and regeneration on precontrast CT appear as hypodense regions. Periportal edema is seen as periportal hypodense regions on CT and hyperintense regions on T2-weighted MRI. Ultrasonography is usually normal, although at times a heterogeneous hyperechoic appearance is found.

During the initial stage of severe acute hepatitis, a transient decrease in portal blood velocity is followed by a rebound, but in chronic viral hepatitis decreased portal blood velocity correlates with the degree of fibrosis.

Fulminant Hepatic Failure/Necrosis

Clinical

Acute hepatic encephalopathy within 8 weeks of hepatocellular disease in an otherwise healthy patient is considered fulminant hepatic failure. In most patients the etiology is not known, while in others a viral infection or chemical or drug poisoning is the responsible agent. Even exertion-induced heat stroke has led to fulminant liver failure. Coagulopathy is a common feature. These patients have a high mortality rate. An uncommon cause for chronic liver failure is extensive liver involvement by a malignant vascular tumor.

Hypoglycemia is a complication of fulminant hepatic failure; causes appear multifactorial and include associated hyperinsulinemia and possible hypoglycemic agents secreted by the liver.

Therapy focuses on providing temporary liver function until subsequent resumption of regeneration. A number of artificial liver assist devices have been evaluated. Auxiliary liver transplantation, retaining the recipient liver, is one alternative. During immunosuppressive therapy, such an auxiliary liver functions normally while native liver function is almost absent; immunosuppressive therapy is with-

drawn after native liver function improves, and then the graft either atrophies or is removed. Technetium-99m–mebrofenin (2,4,6-trimethyl, 5-bromo iminodiacetic acid) (BrIDA) scintigraphy can distinguish the relative function of both donor and recipient livers.

In some patients liver transplantation is the only viable option. But a word of caution is warranted prior to liver transplantation in a patient with idiopathic fulminant hepatic failure. An occasional patient with massive liver necrosis is found to have diffuse liver carcinoma. Other rare causes of acute hepatic failure are diffuse cholangiocellular carcinoma and infiltration by acute lymphoblastic leukemia.

Imaging

Iodinated contrast agents should be used with caution in these patients to prevent accentuating associated renal failure.

Fulminant liver failure results in heterogeneous CT contrast enhancement. The periportal spaces enlarge, seen as periportal low attenuation regions. This is a nonspecific finding seen also in congestion, bleeding, and tumor infiltration. Serial CT reveals that liver volume changes little in survivors, while it decreases in nonsurvivors. Poorly defined hypodense regions develop in some patients, representing regenerating nodules; they enhance to isoor even hyperdense with contrast. An increase in, or late onset of, ascites is an ominous finding.

Necrotic liver parenchyma is hyperintense on T2-weighted SE images, whereas regeneration appears hypointense. In general, regenerating nodules have an opposite appearance to regions of necrosis.

Blood clearance and receptor indices from Tc-99m-GSA imaging of patients with fulminant hepatic failure and acute hepatitis allow distinction between the two entities (31); also, all fulminant hepatic failure survivors had receptor indices of 0.58 or more, but in five of six patients who later died, the receptor index was 0.58 or less. (The receptor index is the liver radioactivity divided by that of liver plus heart. The blood clearance index is the heart radioactivity at 15 minutes divided by that at 5 minutes after the injection.)

Serial Tc-99m-GSA scintigraphy monitors improvement; it predicts hepatic recovery

earlier than is possible with more conventional biochemical methods and provides information about both hepatic functional reserve and morphologic changes by detecting lobe enlargement or atrophy.

Serial determination of liver and spleen volumes appears related to prognosis. Thus in patients with severe acute hepatitis or with fulminant hepatic failure, a close relationship exists between survival and changing rates of liver and spleen volumes as measured by CT (32); a decrease in liver volume accompanied by a decrease in spleen volume implies a good prognosis; a decrease in liver volume without a decrease in spleen volume implies a bad prognosis.

Drug and Toxin-Related Hepatitis

Numerous antibiotics, other drugs, and chemicals result in cholestasis or, on a more chronic basis, lead to biliary obstruction. Even ecstasy, a synthetic amphetamine, has been implicated. Cholestasis, whether drug-induced or due to some other agent, is discussed later (see Metabolic and Related Disorders). The cholangitislike appearance seen after intrahepatic artery injection of various agents, termed secondary sclerosing cholangitis, is covered in Chapter 8.

Ductular obstruction, also termed cholangiolitis or cholangiopathy, ranges from an acute condition that is reversible when the inciting agent is withdrawn to progressive damage and a picture mimicking biliary cirrhosis.

ADVANCED IMAGING OF THE ABDOMEN

liver and spleen. These granulomas are readily detected by CT and are similar to those seen with tuberculosis.

Autoimmune Hepatitis

Although a primary diagnosis of autoimmune hepatitis is occasionally made, similar to granulomatous hepatitis, patients with autoimmune hepatitis have elevated autoantibodies, hyperglobulinemia, an abnormal serum aminotransferase level, and no other obvious liver disease. Current evidence points to an autoimmune basis as a pathway for a number of other disorders. An overlap of autoimmune hepatitis and primary sclerosing cholangitis exists; its relationship to primary biliary cirrhosis is not clear, although in patients with findings of both autoimmune hepatitis and primary biliary cirrhosis the latter diagnosis generally prevails. Adding confusion, some overlap exists with viral hepatitis and autoimmune cholangitis. It is thus a disease of exclusion.

Autoimmune hepatitis is associated with Felty’s syndrome, Sjögren’s syndrome, measles, interferon therapy, gastric carcinoid, celiac disease, and some drugs. In some patients antibodies against liver cytosol appear to be a specific immunoserologic marker of autoimmune hepatitis.

No specific imaging findings mark autoimmune hepatitis. Any detected abnormalities generally point toward another specific disease.

Granulomatous Hepatitis

Granulomatous hepatitis is not a specific disease but a histologic description. Although tuberculosis and sarcoidosis are commonly associated with liver granulomas, this condition also develops with a number of bacterial,fungal, and parasitic infections and a variety of drugs. An occasional lymphoma results in granulomas. A rare association exists between granulomas and Graves’ hyperthyroidism. Langerhans cell granulomatosis can result in liver nodules. Chronic granulomatosis is a cause of liver failure. A diagnosis is not always clear in a setting of granulomas.

Prior infection by histoplasmosis results in calcified granulomas scattered throughout the

Radiation Hepatitis

Radiation hepatitis manifests clinically as jaundice and hepatomegaly several weeks after radiation therapy. The presumed underlying mechanisms are Kupffer cell and vascular endothelial damage.

Imaging identifies the boundary between normal and irradiated liver to be sharply defined and corresponding to the radiation port, a finding not seen with overlapping ports. Once regeneration starts, the sharp boundary becomes less well defined. Radiation hepatitis is isoto hypodense relative to normal liver on CT (Fig. 7.12). Vessels in the involved region appear normal. Postcontrast, CT appearance is inconsistent and ranges from hypoto hyperdense.

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Figure 7.12. Radiation hepatitis after prior radiation therapy for breast carcinoma. CT outlines a focal, sharply defined anterolateral defect (arrow). (Courtesy of Patrick Fultz, M.D., University of Rochester.)

tis picture predominates. Whether this condition is called hepatitis, cholestasis, or cholestatic hepatitis is a moot point. Other cholestatic conditions, including neonatal hepatitis, are discussed in Chapter 8.

Cholestasis is a manifestation of paraneoplastic syndrome in patients with malignant lymphoproliferative diseases. Extrahepatic Hodgkin’s disease, renal cell carcinoma, and other cancers have been associated with cholestasis.

Acute vanishing bile duct syndrome is usually associated with drug or toxin use and is a rare cause of cholestasis. It develops mostly in adults. Rarely, cholestasis progresses to cirrhosis.

Idiopathic benign recurrent cholestasis is a rare disorder diagnosed mostly by exclusion.

Osteoporosis and osteomalacia develop in patients with chronic liver disease, especially those with chronic cholestasis.

The involved liver parenchyma is mostly hypoechoic on US.

Radiation hepatitis is hypointense on T1and hyperintense on T2-weighted MR images. Anecdotal reports describe iron colloidenhanced MRI showing decreased uptake in acute radiation-induced hepatic injury. Eventually abnormalities either resolve or the involved liver segments atrophy.

Metabolic and Related

Disorders

Cholestasis

An active bile acid transport system by hepatocytes into bile canaliculi is necessary for bile acid flow. Bilirubin, various phospholipids, and other components are secreted by canaliculi, while bile duct epithelial cells secrete a bicar- bonate-rich solution. A breakdown in any step of this complex chain results in cholestasis. Cholestasis, or cholestatic jaundice, is not a separate disease but a manifestation of a number of disorders discussed below.

Drug-induced cholestasis is most often due to impaired hepatocellular bile secretion. With some drugs a cholangiolitis or even a cholangi-

Fatty Liver (Steatosis)

Clinical

Fatty infiltration (steatosis) ranges from diffuse to focal (Table 7.6). Drugs associated with steatosis include tetracycline and tamoxifen (used for adjuvant hormone therapy for breast cancer). Fatty liver develops in a setting of heterozygous hypobetalipoproteinemia, and this entity should be considered as a possible cause

Table 7.6. Conditions associated with fatty liver infiltration

Obesity Hyperlipidemia Starvation Alcohol

Diabetes mellitus Cystic fibrosis

Fatty liver of pregnancy Total parenteral nutrition

Familial heterozygous hypobetalipoproteinemia Drugs

Steroids

Certain hepatotoxins Metabolic liver disorders

Galactosemia Reye’s syndrome

Fructose intolerance Glycogen storage diseases