Exercise: Focal Liver Diseases

EXERCISE 11-2. FOCAL LIVER DISEASES

11-5. What is the most likely diagnosis in Case 11-5 (Figure 11-23)?

A.         Pyogenic liver abscess

B.         Echinococcal disease

C.         Candidiasis

D.         Amoebic abscess

11-6. What is the most likely diagnosis in Case 11-6 (Figure 11-24)?

A.   Hemangioma

B.   Metastatic disease

C.   Angiosarcoma

D.   Focal nodular hyperplasia

11-7. What is the most likely diagnosis in Case 11-7 (Figure 11-25)?

A.         Hemangioma

B.         Hepatocellular carcinoma

C.         Metastatic disease

D.         Liver cell adenoma

11-8. What is the most likely diagnosis in Case 11-8 (Figure 11-26)?

A.   Metastatic disease

B.   Hepatocellular carcinoma

C.   Liver cell adenoma

D.   Abscess

Radiologic Findings

11-5. In this case, CT shows a large, fluid attenuation mass in the posterior dome of the liver with rim enhance-ment and irregular margins (arrow). In this patient from the United States with fever, the most likely diag-nosis is pyogenic abscess. If this patient were from an-other country or had an appropriate travel history, then amoebic or echinococcal abscess could also be considered (A is the correct answer to Question 11-5).

11-6. In this case, CT shows a focal lesion in the central liver that demonstrates peripheral, nodular, discon-tinuous enhancement (arrow). Delayed imaging (not shown) would demonstrate centripetal accumulation (“fill in”) of contrast. These features are characteristic of cavernous hemangioma (A is the correct answer to Question 11-6).

11-7. In this case, there is a focal lesion occupying the left lobe of the liver (M), and there is a focal enhancing mass in the pancreatic tail (T), representing a pancre-atic neoplasm metastatic to the liver (C is the correct answer to Question 11-7).

11-8. In this case, CT shows a hypervascular mass (arrow) on arterial phase CT (Figure 11-26 A). This demonstrates typical washout on portal venous phase imaging (Figure 11-26 B) with an enhancing “pseudocapsule” (arrows) of compressed adjacent hepatic tissue. Both are typical features of HCC (B is the correct answer to Question 11-8).

Discussion

Recognition of the focal or diffuse nature of liver disease is helpful for sorting out the possible causes. The two can over-lap, especially because one may lead to another: for example, cirrhosis can cause hepatocellular carcinoma.

Pyogenic liver abscesses are relatively common focal in-flammatory lesions of the liver most commonly caused by bacteria. These lesions have high morbidity and mortality, if undiscovered. They are multiple in many cases, involving both hepatic lobes. These abscesses create a severe leukocytosis and can lead to sepsis. Pyogenic abscesses occur when collections of leukocytes undergo necrosis and become walled off. The imaging studies, although not definitive, have helpful find-ings. On US, these lesions often are well demarcated, may be multiloculated, and have fluid centers and irregular walls. Gas within an abscess creates an echogenic structure with “dirty” shadowing. On CT, the abscess appears as a low-density le-sion. Intra-abscess gas occurs in approximately 50% of ab-scesses (Figure 11-27), and enhancement of the border of the lesion after intravenous contrast infusion also occurs in ap-proximately 50% of abscesses. Low-density edema may sur-round the abscess (Figure 11-23). Rapid enhancement of the edge of an abscess after bolus injection of contrast material may be helpful. On technetium-99m sulfur colloid scans, the abscess appears as a defect within the liver. MR imaging demonstrates signs of an irregular, fluid-containing lesion, that is, low signal intensity on T1-weighted examinations and high signal intensity on T2-weighted examinations. Edema may be visible surrounding the lesion on T2-weighted images. Pus demonstrates restricted diffusion on MR.

Echinococcal disease is a parasitic infestation that involves multiple organs, most commonly the liver. It is endemic in sev-eral regions around the world. The most common form is due to Echinococcus granulosus, which, after being ingested by hu-mans, is carried into the gut, transmitted to the portal circulation, and eventually deposited in the liver, where it develops into large, occasionally multiloculated, cysts, which may calcify. On US, these lesions appear as well-defined cysts with regular bor-ders, which may contain swirling debris and multiple septae. Smaller, “daughter” cysts often surround them. Small calcifica-tions are present. CT shows similar morphologic findings, as well as enhancement of the wall after intravenous contrast ma-terial infusion. Calcifications are crescentic, corresponding to the membranes. MR imaging shows a cystic mass with a rimlike periphery of low signal intensity on both T1- and T2-weighted images and with a central matrix of high signal intensity.

Candidiasis is a fungal disease. It affects the liver primarily in renal transplant patients and patients who are immuno-compromised by malignancy or chemotherapy for the malig-nancy. The organism forms multiple microabscesses, whichcreate the characteristic appearance on imaging studies. US shows several patterns, the most common being multiple small hypoechoic structures containing a hyperechoic central spot, the “bull’s-eye” lesion. Other patterns may occur. CT shows similar multiple small abscesses (Figure 11-28), in-cluding the bull’s-eye lesion.

Amebic abscesses are caused by a parasite, Entamoeba his-tolytica, and the liver is the most commonly involved organ. The leukocytosis is much less severe than with a pyogenic ab-scess. Unlike pyogenic abscesses, which require drainage, ame-bic abscesses can often be cured by medical treatment. Like echinococcal abscesses, amebic abscesses start when organ-isms reach the liver through the portal circulation from thebowel. The abscesses may rupture into the peritoneal cavity or even into the thorax. Imaging studies, including NM, US, and CT, are usually nonspecific and demonstrate focal defects within the liver (Figure 11-29). The lesions can resemble echinococcal abscesses. One helpful finding is intraperitoneal or intrathoracic fluid, if rupture has occurred.

Hemangioma is the most common benign tumor of the liver and is second only to metastases as the most common tumor overall within the liver. Hemangiomas are often pe-ripherally located in the liver, less than 2 cm in diameter, and not associated with abnormalities in liver function tests. They are most commonly single. On US, they are usually homoge-neous and hyperechoic (Figure 11-30 A), but an important variant is the isoechoic mass with hyperechoic periphery. They are often peripheral, with posterior acoustic enhance-ment. Some large lesions have central scars. CT shows homo-geneous, low-attenuation lesions, which enhance after intravenous contrast material administration, have discon-tinuous peripheral nodular enhancement (called “puddling” of contrast material), and accumulate contrast material cen-tripetally over a period of several minutes (Figure 11-24). This finding is most useful when the patient has no known primary tumor; otherwise, this pattern is more likely due to a metastasis. Technetium-99m labeled red blood cell scans are diagnostic for hemangioma when early vascular-phase images show decreased activity and delayed blood-pool scans demon-strate increased activity at the lesion site (Figure 11-30 B). MR imaging demonstrates lesions with low signal intensity on T1-weighted scans, which is typical for most lesions. However, T2-weighted MR imaging demonstrates high signal intensity similar to that of fluid, which is considered diagnos-tic of hemangioma or cyst. Intravenous Gd “puddles” in cav-ernous hemangioma and gradually migrates centripetally toward the center of the lesion (Figure 11-31), analogous to the distribution of iodinated contrast material in cavernous hemangioma on CT, and likewise is considered diagnostic of cavernous hemangioma. This puddling in cavernous heman-gioma is different from the more curvilinear or heteroge-neous distribution of contrast accumulation seen in malignant tumor. Angiography can be very helpful, as it shows punctuate collections of contrast material shortly after injection, analogous to the puddling seen in CT or MR imag-ing (Figure 11-32 A). These collections become denser, usu-ally within a minute, because contrast puddles in the vascular spaces of the tumor (Figure 11-32 B). On all modalities with intravenous contrast, hemangiomas usually enhance early and retain contrast.

Although typically diffuse, steatosis of the liver can pres-ent as focal deposits of fat. Furthermore, sometimes steatosis can present as the reverse, namely, residual focal islands of hepatic tissue unaffected by fatty deposition. Both of these conditions can be confusing because they may resemble focal solid masses including tumor on CT or US. MR imag-ing is the most accurate means to identify sites of focal fat or focal fatty sparing. In particular, a pulse sequence called “out-of-phase” T1-weighted imaging, which emphasizes the presence of fat intermixed with any host water-containing tissue, is very sensitive in the detection of the presence or ab-sence of fat within focal fat or focal fatty sparing, respec-tively. Wherever fat is intermixed with water-containing parenchyma, there is loss of signal intensity on out-of-phase images. Therefore, focal fatty infiltration appears as sites of relative signal loss, whereas focal fatty sparing appears as sites of relative signal gain (Figure 11-33). This imaging technique is the most sensitive and specific cross-sectional modality for characterizing focal fatty distribution, a very common condition.

The liver is a common and important site for metastatic disease. As many as 25% to 50% of cancer patients have liver metastases at autopsy. Most tumors metastasize to the liver, and metastasis to the liver strongly affects the stage of the tumor and prognosis of the patient. Most metastases are multiple, diffusely distributed, variable in size, and solid. They may be necrotic and appear more cystic. Liver metastases may be present even when both general and specific serum markers for tumor, such as liver function tests and carcinoembryonic antigen, are normal. Metas-tases may be poorly vascularized or highly vascular, a dif-ference that affects their appearance after intravenous contrast administration. Metastases from renal cell carci-noma, thyroid carcinoma, carcinoids, and neuroendocrine tumors are classically hypervascular. Mucin-producing carcinomas, such as breast and colon carcinoma, fre-quently produce calcification, which can be detected with imaging studies. Metastases are almost always evaluated with cross-sectional imaging studies. However, more re-cently, PET has been used to detect certain malignancies, including liver metastases. Because the liver physiologically takes up the radiopharmaceutical used in PET, metastatic lesions can be obscured. Although US can evaluate for liver metastases when used by skilled operators, it is limited by relative insensitivity to subtle lesions, especially against the background of preexisting liver disease. On US, metastasesare usually hypoechoic, poorly defined, and hypovascular, and they may have a peripheral halo (Figure 11-34). Some types, such as breast cancer, may be diffusely distributed in minute form. In most institutions, CT is used to survey and monitor patients for liver metastases, because CT can de-tect metastases and is probably the most useful technique for evaluating extrahepatic disease. On CT, metastases are usually multifocal, of low attenuation, and often better shown after administration of intravenous contrast mate-rial when compared to preinfusion scans (Figure 11-35). Again, some forms present as diffuse inhomogeneity. Be-cause of its sensitivity and potential for characterizing some lesions specifically, MR imaging may become the pre ferred technique for detecting and characterizing liver metastases. Lesions have low signal intensity on T1-weighted images and higher signal intensity (but never as high as in cavernous hemangioma) on T2-weighted studies (Figure 11-36). Certain lesions, such as melanoma, carci-noid, and endocrine tumors of the pancreas, have very high signal with strongly T2-weighted scans. Hepatocyte-specific contrast agents, such as gadoxetate disodium, are also being used to detect metastases. Because metastatic le-sions do not have normal hepatocytic function, they do not retain the contrast, making them conspicuous as areas of relatively decreased enhancement compared to the normal surrounding liver.

Angiosarcoma is a rare, highly vascular tumor of the liver. It is seen in patients who have had an occupational ex-posure to certain chemicals, particularly polyvinyl chloride or thorotrast. If lesions rupture, they may produce serious hemorrhagic sequelae. On US, angiosarcoma is usually hy-poechoic. Sometimes the attendant fibrosis so obscures the tumor that it is impossible to identify. On CT, the lesions have low attenuation, may enhance markedly, and, if arising in the presence of thorotrast, can displace and distort the thorotrast collections.

Focal nodular hyperplasia (FNH) and liver cell adenoma are easily confused. Both are histologically benign liver disorders that produce single or multiple lesions. Both processes can occur in young adults. On imaging studies, they can resemble primary or metastatic liver tumors. How-ever, some important differences pertain. FNH is probably a hamartoma of the liver, that is, a localized overgrowth of mature cells that are identical to the types constituting the liver and contain fibrous tissue, blood vessels, bile ducts, and occasional well-differentiated hepatocytes. Adenoma is a true benign tumor composed of one tissue element of the liver, the hepatocyte. FNH often contains a central fibrotic scar. Adenoma is associated with the use of oral contracep-tives, whereas FNH probably is not. Adenoma, unlike FNH, tends to undergo hemorrhage, and thus to present as acute abdominal pain. US is nonspecific in studying FNH. Ade-noma is usually hyperechoic but heterogeneous. On CT, FNH is transiently but markedly and uniformly hypervas-cular, and the central scar may be seen (Figure 11-37). Adenoma usually shows low density, may demonstrate hemor-rhage as high-density collections on preinfusion scans, and enhances variably. On Tc-sulfur colloid NM scans, FNH can show increased, decreased, or normal activity compared to that of liver. Adenoma usually shows no increased uptake in NM studies, but this varies. FNH has low signal intensity on T1-weighted MR imaging and slightly high signal intensity on T2-weighted images. As on CT, it shows uniformly early enhancement and the central scar (Figure 11-38). If the central scar is present, it may exhibit high signal intensity on T2-weighted images. Adenoma, like many lesions, has a nonspecific appearance of low signal intensity on T1-weighted examinations and slightly high signal intensity on T2-weighted examinations. Hemorrhage is recognizable as high signal intensity on T1-weighted images. Angiographi-cally, FNH is hypervascular with radiating branches that produce a “spoke-wheel” appearance. Adenoma has a vari-able angiographic appearance but is generally less vascular than FNH.

Hepatocellular carcinoma (HCC), or hepatoma, is a primary malignancy of the liver. It is found in older cirrhotic patients in the United States and in younger patients in areas of the Far East and Africa, where it is endemic. Chronic hepatitis B and C infection and exposure to aflatoxin predispose to for-mation of hepatocellular carcinoma. On imaging studies, hepatocellular carcinoma appears as (1) a single predomi-nant lesion (most common form), (2) a predominant lesion with multiple, smaller, surrounding daughter lesions, or (3) diffuse tumor. Portal vein invasion by the tumor in any form is relatively common and can aid in distinguishing hepato-cellular carcinoma from other lesions. On US, hepatocellular carcinoma is most commonly a discrete lesion with in-creased, similar, or decreased echogenicity in comparison to that of liver. On CT, lesions are most commonly of low den-sity and may enhance if fast scans in the arterial phase are performed after contrast material administration (Figure 11-39). Portal venous thrombosis can be seen, and preexist-ing cirrhosis or thorotrast can be demonstrated. MR imag-ing findings are similar to those of CT, but as with CT, the lesion is inhomogeneous.