Материал: 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.

LIVER

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

LIVER

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,