Characterisation of liver masses radiology

Radiology

1. Characterisation of liver masses

2. Detection of liver masses The conspicuity of a liver lesion depends on the attenuation difference between the lesion and the normal liver . On a non enhanced CT-scan (NECT) liver tumors usually are not visible, because the inherent contrast between tumor tissue and the surrounding liver parenchyma is too low . Only a minority of tumors contain calcifications, cystic components, fat or hemorrage and will be detected on a NECT . So i.v. contrast is needed to increase the conspicuity of lesions.

3. Normal parenchyma is supplied for 80% by the portal vein and only for 20% by the hepatic artery. This difference in bloodsupply results in different enhancement patterns between liver tumors and normal liver parenchyma in the various phases of contrast enhancement (figure).

4. Small Hepatocellular carcinoma in cirrhotic liver not visible on NECT (left ), clearly visible in arterial phase (middle ) and not visible in portal venous phase (right)

5. In the  arterial phase   hypervascular tumors will enhance via the hepatic artery, when normal liver parenchyma does not yet enhances, because contrast is not yet in the portal venous system . These hypervascular tumors will be visible as hyperdense lesions in a relatively hypodense liver. However when the surrounding liver parenchyma starts to enhance in the portal venous phase, these hypervascular lesion may become obscured . In the  portal venous phase   hypovascular tumors are detected, when the normal liver parenchyma enhances maximally.

6. In the  equilibrium phase  at about 10 minutes after contrast injection , tumors become visible , that either loose their contrast slower than normal liver, or wash out their contrast faster than normal liver parenchyma . These lesions will become either relatively hyperdense or hypodense to the normal liver.

7. Detection of a lesion depends on difference in attenuation between liver and lesion . LEFT : Arterial phase showing hypervascular FNH MIDDLE : Portal venous phase showing hypovascular metastasis RIGHT : equilibrium phase showing relatively dense cholangiocarcinoma

8. Arterial phase imaging Optimal timing and speed of contrast injection are very important for good arterial phase imaging . Hypervascular tumors will enhance optimally at 35 sec after contrast injection (late arterial phase). On the left a patient who underwent two phases of arterial imaging at 18 and 35 seconds . In the early arterial phase we nicely see the arteries, but we only see some irregular enhancement within the liver . In the late arterial phase we can clearly identify multiple tumor masses. CT of the liver in the early arterial phase (left) and the late arterial pase (right).

9. Portal Venous phase We image the liver when it is loaded with contrast through the portal vein to detect hypovascular tumors (figure ). The best moment to start scanning is at about 75 seconds , so this is a late portal venous phase , because enhancement of the portal vein already starts at 35 sec in the late arterial phase . This late portal venous phase is also called the hepatic phase because there already must be enhancement of the hepatic veins. If you do not seen enhancement of the hepatic veins, you are too early.

10. Hypovascular metastases seen as hypodense lesions in the late portal venous phase . Notice some rim enhancement of the more viable peripheral areas of the metastases.

11. For arterial phase imaging the best results are with an injection rate of 5ml/sec . There are two reasons for this better enhancement: at 5ml/sec there will be more contrast delivered to the liver when you start scanning and this contrast arrives in a higher concentration . Patient with liver cirrhosis and multifocal HCC injected at 2.5ml/sec (left) and at 5ml/sec (right). On the left a patient with cirrhosis examined after contrast injection at 2.5ml/sec and at 5ml/sec. At 5ml/sec there is far better contrast enhancement and better tumor detection.

12. Equilibrium Phase The equilibrium phase is when contrast is moving away from the liver and the liver starts to decrease in density . This phase begins at about 3-4 minutes after contrast injection and imaging is best done at 10 minutes after contrast injection . This phase can be valuable if you're looking for : fast tumor washout in hypervascular tumors like HCC or retention of contrast in the blood pool as in hemangiomas or the retention of contrast in fibrous tissue in capsules (HCC) or scar tissue (FNH, Cholangio ca ).

13. Relative hyperdense lesions in the delayed phase Fibrous tissue that's well organized and dense is very slow to let iodine or gadolineum in. Once contrast gets in however, it is equally slow to get back out in the equilibrium phase. So when the normal liver parenchyma washes out , the fibrous components of a tumor will look brighter than the background liver tissue. Cholangiocarcinoma may have a fibrous stroma and in the delayed phase it may be the only time when you see the tumor (figure).

14. Small cholangiocarcinoma not visible in portal venous phase (left ) but seen as relative hyperdense lesion in the delayed phase (right).

15. Relative hypodense lesions in the delayed phase On the left the importance of the delayed phase in a cirrhotic patient with an HCC is demonstrated. Notice that you do not see the tumor on the nonenhanced scan and also not in the portal venous phase. This is often the case and demonstrates the importance of the arterial phase. HCC in a cirrhotic liver. Notice fast wash out in equilibrium phase compared to surrounding liver parenchyma.

16. Benign lesions typically will not show this kind of wash out. For instance a FNH or adenoma will show fast enhancement in the arterial phase , become isodense in the portal venous phase , but it will stay isodense with liver in the equilibrium phase . Especially in cirrhotic patients you have to rely heavily on this delayed phase to differentiate benign little enhancing lesions from small HCC's.

17. Blood pool and Hemangioma Normally when we look at lesions filling with contrast, the density of these lesions is always compared to the density of the liver parenchyma. In hemangiomas however you should not compare the density of the lesion to the liver, but to the blood pool . This means that the areas of enhancement in a hemangioma should match the attenuation of the appropriate vessels ( bloodpool ) at all times.

18. So in the arterial phase the enhancing parts of the lesion must have almost the same attenuation value as the enhancing aorta , while in the portal venous phase it must match the enhancement of the portal vein . If it does not match the bloodpool in every single phase of contrast enhancement forget the diagnosis of a hemangioma.

19. On the left a characteristic hemangioma. Notice that on the NECT the density of the tumor is the same as the density of the vessels . In the arterial phase it is matching the bloodpool and the attenuation is almost the same as the aorta. In the portal venous phase it matches the density of the portal vein. In the equlibrium phase it has the same enhancement as the vessels . Hemangioma on NECT, late arterial, late portal venous and equilibrium phase. Notice that the attenuation of the hemangioma matches the bloodpool in every single phase (arrows).

20. Characterisation of liver masses From a practical point of view, the approach to characterizing a focal liver lesion seen on CT begins with the determination of its density . If the lesion is of near water density, homogeneous, has sharp margins and shows no enhancement, then it is a cyst.

21. If the lesion does enhance , then the next step is to determine whether the lesion could be a hemangioma , since this is by far the most common liver tumor. The enhancement should be peripheral and nodular, with the same density as the bloodpool in all phases.

22. If it is not a cyst nor a hemangioma, then we further have to study the lesion . Based on the enhancement pattern , we divide masses into : hypervascular and hypovascular lesions . Usually a combination of the enhancement pattern and gross pathologic features, like the presence of fat, blood, calcifications, cystic or fibrotic components, in combination with the clinical history will limit the differential diagnosis (figure).

23. Hypervascular lesions: Arterially enhancing lesions are mostly benign lesions and include primary liver tumors as FNH adenoma small hemangiomas that fill rapidly with contrast . These benign tumors have to be differentiated from the most common hypervascular malignant liver tumor, which is HCC and metastases from hypervascular tumors like melanoma, renal cell carcinoma, breast, sarcoma and neuroendocrine tumors (islet cell tumors, carcinoid, pheochromocytoma ).

24. Hypervascular lesions may look very similar in the arterial phase (figure). Differentiation is done by looking at the enhancement pattern in the other phases and additional gross pathologic features together with clinical findings . Hypervascular metastases will be considered in patients with a known primary tumor. In general HCC is considered when there is a setting of cirrhosis, while FNH is considered in young women hepatic adenoma in patients on oral contraceptives, anabolic steroids or with a history of glycogen storage disease.

25. Four different tumors with enhancement in the late arterial phase. From left to right: HCC in cirrhotic liver; FNH with central scar in adolescent; adenoma in young woman on contraceptives finally a hemangioma with typical enhancement in the other phases (not shown).

26. Hypovascular lesions: Hypovascular liver tumors are more common than hypervascular tumors. Most hypovascular lesions are malignant and metastases are by far the most common. Although primary liver tumors are mostly hypervascular , there are exceptions. 10% of HCC is hypovascular . Cholangioca is hypovascular , but may show delayed enhancement (figure).

27. On the left a hypovascular mass with irregular enhancement in the late arterial and late portal venous phase. This is a sign of malignancy. On the delayed images a relative dense structure is seen centrally , which looses its contrast slower compared to normal liver. This means that this tumor is mainly composed of fibrous tissue. The fibrous tissue has also retracted the liver capsule. These imaging findings are very suggestive of a cholangiocarcinoma .

28. Scar

29. On CT a scar is sometimes visible as a hypodense structure . On MR scar tissue is hypointense on both T1WI and T2WI due to intense fibrotic changes. An example is the central scar of fibrolamellar carcinoma (FLC ) An exception to this rule is the central scar in FNH which is hyperintense on T2WI due to edema . T2WI can be very helpfull if there is a problem in differentiating FNH from FLC. Both on CT and MRI scar tissue will enhance in the delayed phase.

30. On the left a lesion with a typical central scar. It has a hypodense centre on the NECT. In the portal venous phase there is homogeneus enhancement of the lesion except for the scar. Enhancement of the fibrous tissue of the central scar is seen only on the delayed phase images. The combination of homogeneous enhancement and central scar is typical for the diagnosis of FNH.

31. Capsule Liver lesions which may have a capsule are Adenoma, HCC and cystadenoma or cystadenocarcinoma . The most common tumor with a capsule is HCC . The capsule will not enhance in the arterial phase and even in the portal venous phase it will be hypodense , because the fibrous tissue enhances very slowly . A capsule is usually best seen in the delayed phase as a relative hyperdense structure.

32. NECT and Arterial phase image showing hypodense capsule of HCC LEFT: Bright enhancing capsule of HCC in equilibrium phase . RIGHT : Pathologic specimen.

33. Calcifications Central calcifications are seen in: Metastases (especially in colorectal tumors) Fibrolamellar carcinoma (FLC) Cholangiocarcinomas Hemangiomas These calcifications are hyperdense on CT and hypointense on T1 and T2 MR images . NECT of a Fibrolamellar carcinoma with central calcifications

34. Fat Fat within liver tumors is seen in: Adenoma HCC Metastatic liposarcoma Angiomyolipoma Low density area due to fat in Adenoma

35. Hemorrhage Hemorrhage in liver tumors is seen in: Adenoma HCC Hemorrhage within an adenoma. Hemorrhage is most commonly seen in adenomas.

36. Cystic components If a lesion has a near water density in the centre and does not show enhancement in the centre , we usually will call it a cystic lesion . You have to realize, that it still can be a tumor as in cystic metastases or metastases with central necrosis . Secondly you always have to add absces to the differential diagnosis.

37. On the left a patient with hypovascular lesions with a low density , so it may be cystic i.e fluid containing . These lesions are multiple, but not spread out through the liver, so we describe them as clustered or satelite lesions . This is a typical finding which makes the lesions suspective for liver abcesses . This was a case of diverticulitis . The common route is through the portal vein as a result of abdominal infection. The bacteria enter the slow flow portal system, where they layer within the vessel and finally these bacteria 'fall down' into the dependent portion of the right lobe.

38. On the left a typical case of a echinococcus cyst with 'daughter cysts' within the large cyst.

39. If you look at the CT image on the left, the first impression might be that there are only simple cysts within the liver. However, if you look more carefully, you will notice that some of the hypodense lesions show vague rim enhancement . And although you might think that these could be cystic metastases, the US-findings clearly show, that these lesions are hyperechoic solid masses. So you have to be very carefull in calling a lesion cystic, because you might end up missing metastases or looking in the wrong file for a differential diagnosis.

40. Retraction of liver capsule Hepatic and delayed phase in a patient with breast metastases causing retraction of liver capsule. Notice delayed enhancement of the fibrotic tissue (arrows)

41. The most common tumor however to cause retraction is cholangiocarcinoma . The delayed image on the left shows a large cholangiocarcinoma with dense enhancing fibrous tissue and retraction of the liver capsule.

42. Another cause of local retraction is atrophy due to biliary obstruction or chronic portal venous obstruction.

43. Peripheral enhancement and progressive fill in Many will regard 'peripheral enhancement and progressive fill in' as a typical feature of hemangioma, but it is not . Peripheral rim enhancement is a typical feature of malignant lesions and only discontinuous nodular peripheral enhancement that matches bloodpool is a typical feature of hemangioma.

44. LEFT: rim enhancement in metastasis. RIGHT : hemangioma with discontinuous nodular peripheral enhancement

45. Many lesions will show progressive fill in. In hemangiomas this progressive fill in must have the same density as the bloodpool . Many hypovascular metastases will show contrast diffusion into a lesion starting on the outside. Usually the center does not fill in . Cholangiocarcinomas will show progressive fill in because the fibrous centre will enhance slowly. You will see it enhance in the delayed phase . So if you want to make the diagnosis of a hemangioma you have to look at all the other phases to see if the enhancement matches the bloodpool .

46. Progressive fill in in a hemangioma (left ), cholangiocarcinoma (middle ) and metastases (right).

47. Common Liver Tumors

48. Hemangioma Hemangioma is the most common benign liver tumor. The size varies from a few millimeters to more than 10 cm (giant hemangiomas). Calcification is rare and seen in less than 10%, usually in the central scar of giant hemangioma.

49. Flash filling hemangioma in unenhanced, arterial and portal venous phase. Notice it matches the bloodpool . Small hemangiomas may show fast homogeneous enhancement ('flash filling'). Small HCC and hypervascular metastases may mimic small hemangiomas because they all show homogeneous enhancement in the arterial phase . By looking at the other phases to see if the enhancing areas match the bloodpool , it is usually possible to differentiate these lesions.

50. Large hemangiomas can have an atypical appearance . Complete fill in is sometimes prevented by central fibrous scarring . These lesions need to be differentiated from other lesions with a scar like FLC, FNH and Cholangiocarcinoma . Again looking at the bloodpool will help you. On the left two large hemangiomas. Notice that the enhancing parts of the lesion follow the bloodpool in every phase , but centrally there is scar tissue that does not enhance. Giant hemangiomas with scar-tissue. Notice that the enhancement matches the bloodpool in all phases . Central scar is hypodens on NECT and stays hypodens .

51. Peripheral enhancement The enhancement of a hemangioma starts peripheral . It is nodular or globular and discontinuous . Rim enhancement is continuous peripheral enhancement and is never hemangioma . Rim enhancement is a feature of malignant lesions , especially metastases.

52. LEFT: rim enhancement in breast metastasis. RIGHT: nodular discontinuous enhancement in hemangioma.

53. Ultrasound the lesion is hyperechoic to normal liver . If the liver is hyperechoic due to steatosis, the hemangioma can appear hypoechoic (figure ). Another important feature of hemangiomas is the increased sound transmission . This is because the lesion is made of these channels containing blood.

54. LEFT: Classic US appearance of a hemangioma . RIGHT : Also a hemangioma but now in a hyperechoic liver, so the lesion is relatively hypoechoic. Notice increased sound transmission .

55. Differential diagnosis Hemangiomas must be differentiated from other lesions that are hypervascular or lesions that show peripheral enhancement and progressive fill in.

56. Hepatocellular Carcinoma (HCC) HCC may be solitary, multifocal or diffusely infiltrating . In patients with cirrhosis or with hepatitis B/C our major concern is HCC, since 85% of HCC occur in these patients . Larger HCC lesions typically have a mosaic appearance due to hemorrhage and fibrosis.

57. Early appearance of HCC These are small lesions that transiently enhance homogeneously. You will only see them in the arterial phase . Sometimes there is rim enhancement and you might mistake them for a hemangioma . Always look how they present in the other phases and compare with the bloodpool and remember that rim enhancement is never hemangioma.

58. Small HCC seen only in arterial phase in a patient with cirrhosis.

59. Late appearance of HCC HCC is a silent tumor, so if patients do not have cirrhosis or hepatitis C, you will discover them in a late stage . They tend to be very large with a mozaic pattern , a capsule , hemorrhage , necrosis and fat evolution . HCC becomes isodense or hypodense to liver in the portal venous phase due to fast wash-out. On delayed images the capsule and sometimes septa demonstrate prolonged enhancement.

60. Large HCC with mozaik pattern in a non cirrhotic patient.

61. HCC and Portal Vein thrombosis Many patients with cirrhosis have portal venous thrombosis and many patients with HCC have thrombosis . These are two common findings and they can be coincidental . It is very important to make the distinction between just thrombus and tumor thrombus . First, if you have a malignant thrombus in the portal vein, it will always enhance and you'll see it best in arterial phase . Secondly, if you have a malignant thrombus in the portal vein, it will increase the diameter of the vessel . Sometimes a tumor thrombus may present with neovascularity within the thrombus (figure).

62. LEFT: Diffusely enhancing tumor thrombus in HCC with portal vein invasion . RIGHT : Tumor thrombus with vessels within the thrombus.

63. Differential diagnosis Early HCC needs to be differentiated from other hypervascular lesions , that will be hyperdense in the arterial phase.

64. The upper images show a lesion that is isodens to the liver on the NECT . In the arterial phase there is enhancement, but not as dense as the bloodpool . In the portal venous phase the lesion is again isodense to the surrounding liver parenchyma and you can't see it. If you only had the portal venous phase you surely would miss this lesion. The lower images show a lesion that is visible on all images. You see it on the NECT and you could say it is hypodens compared to the liver. However if you look at the bloodpool , you will notice that on all phases it is as dense as the bloodpool . So we have a HCC in the right lobe on the upper images and a hemangioma in the left lobe on the lower images. The key is to look at all the phases.

65. Hypovascular HCC seen in late portal venous phase 10% of HCC are hypodense compared to liver. The imaging findings will be non-specific. The case on the left proved to be HCC.

66. Hepatic Adenoma Hepatocellular adenomas are large, well circumscribed encapsulated tumors. They consist of sheets of hepatocytes without bile ducts or portal areas . 80% of adenomas are solitary and 20% are multiple . Adenomas typically measure 8-15 cm and consist of sheets of well-differentiated hepatocytes . Adenomas are prone to central necrosis and hemorrhage because the vascular supply is limited to the surface of the tumor . In young woman using contraceptives an adenoma is the most frequent hepatic tumor.

67. CT  will show most adenomas as a lesion with homogeneous enhancement in the late arterial phase , that will stay isodense to the liver in later phases . Unfortunately, this homogeneous enhancement in the late arterial phase is not specific to adenomas , since small HCC's and hemangiomas as well as hypervascular metastases and FNH can demonstrate similar enhancement in the arterial phase . Malignant lesions however have a tendency to loose their contrast faster than the surrounding liver, so they may become relatively hypodense in later phases . The finding of hemorrhage as an area of high attenuation can be seen in as many as 40% of adenomas . This is however also a feature of HCC and large hemangiomas.

68. Fat deposition within adenomas is identified on CT in only approximately 7% of patients and is better depicted on MRI . Typically adenomas have well-defined borders and do not have lobulated contours . A low-attenuation pseudocapsule can be seen in as many as 30% of patients . This capsule will only show enhancement on delayed scans . Coarse calcifications are seen in only 5% of patients.

69. On the left an adenoma with fat deposition and a capsule.

70. MRI usually is more sensitive in detecting fat and hemorrhage . Chemical-shift imaging showing loss of signal on out-of-phase images can confirm the presence of fat . HCC is known to contain fat in as many as 40% of lesions, therefore the presence of fat does not help differentiate the lesions.

71. Adenomas may rupture and bleed, causing right upper quadrant pain . The two most common liver lesions causing hepatic hemorrhage are HA and HCC . Although adenomas are benign lesions, they can undergo malignant transformation to hepatocellular carcinoma (HCC ). Although malignant transformation is rare, for this reason, surgical resection is advocated in most patients with presumed adenomas. Adenoma with hemorrhage.

72. Significant overlap is noted between the CT appearances of adenoma , HCC, FNH, and hypervascular metastases , making a definitive diagnosis based on CT imaging criteria alone difficult and often not possible . Clinical correlation in such cases is most helpful . In otherwise healthy young women using oral contraceptives, adenoma is favored . Patients with glycogen storage disease, hemochromatosis, acromegaly, or males on anabolic steroids also are more prone to developing hepatic adenomas. A history of cirrhosis and high AFP levels favor HCC . A history of a primary hypervascular tumor favors metastases. However, if HA or HCC remains in the differential diagnosis, surgery usually is indicated.

73. Adenoma showing capsule in delayed phase

74. Focal Nodular Hyperplasia (FNH) US  will show a FNH as a non specific ill-defined lesion . The central scar may be detected as a hyperechoic area , but often cannot be differentiated . With color doppler sometimes the vessels can be seen within the scar.

75. CT  will show FNH as a vascular tumor, that will be hyperdens in the arterial phase, except for the central scar.

76. On the left a typical FNH with a central scar that is hypodens in the portal venous phase and hyperdens in the equilibrium phase.

77. MRI  will show a hypointense central scar on T1-weighted images. On T2- weighted images the scar appears as hyperintense in 80% of patients, which is very typical . However in 20% of patients the scar is hypointense . Gadolineum enhanced MRI will reveal similar enhancement patterns as on CECT.

78. The diagnosis of FNH is based on the demonstration of a central scar and a homogeneous enhancement . However, a typical central scar may not be visible in as many as 20% of patients (figure). Moreover a central scar may be found in some patients with fibrolamellar hepatocellular carcinoma, hepatic adenoma and intrahepatic cholangiocarcinoma . The key to the diagnosis in the lesion on the left is the fact that it is isoattenuating to normal liver in the portal venous phase and stays that way without a wash out on the delayed phase (not shown ).

79. FNH seen as hypervascular lesion in the late arterial phase and isodense to normal liver in the portal venous phase . No scar was seen.

80. Fibrolamellar carcinoma (FLC) has a dark scar on T2WI and FNH has a brigth scar on T2WI in 80% of the cases . T2WI, T1WI without Gadolineum and a delayed phase after Gadolineum . This means that at times the differential between FNH and FLC will not be possible.

81. Fibrolamellar carcinoma (FLC) FLC is an uncommon malignant hepatocellular tumor, but less aggressive than HCC . FLC characteristically manifests as a 10-20 cm large hepatic mass in adolescents or young adults . FLC characteristically appears as a lobulated heterogeneous mass with a central scar in an otherwise normal liver. Calcifications occur in 30-60% of fibrolamellar tumors.

82. Imaging features of FLC overlap with those of other scar-producing lesions including FNH, HCC, Hemangioma and Cholangiocarcinoma . In contrast to FNH the central scar in FLC will usually be hypointense on T2WI and will less often show delayed enhancement . While FNH is always very homogeneous, FLC is usually heterogeneous following contrast administration.

83. LEFT: FLC in late arterial phase: central calcification and heterogenous enhancement in a lamellar pattern . RIGHT: venous phase with hypodense central scar.

84. On non enhanced images a FLC usually presents as a big mass with central calcifications.

85. Cholangiocarcinoma The diagnosis of a cholangiocarcinoma is often difficult to make for a radiologist and even a pathologist . That is because cholangiocarcinoma has a varied morphology and histology . It can be a constricting or an expanding lesion, because it can have a fibrous or a glandular stroma . It can be located anywhere in the intrahepatic bile ducts or common bile duct.

86. The lesion on the left has the folowing characteristics: The lesion is hypodens in the arterial and portal venous phase with some peripheral enhancement. The lesion is hyperdense in the equilibrium phase indicating dens fibrous tissue. The lesion causes retraction of the liver capsule The finding of an infiltrating mass with capsular retraction and delayed persistent enhancement is very typical for a cholangiocarcinoma .

87. Hepatic Metastases The liver is the most common site of metastases . The most common organs of origin are: colon, stomach, pancreas, breast and lung . Most liver metastases are multiple, involving both lobes in 77% of patients and only in 10% of cases there is a solitary metastasis.

88. Hypovascular metastases  are the most common and occur in GI tract, lung, breast and head/neck tumors . They are detected as hypodense lesions in the late portal venous phase . In this phase the attenuation of the normal liver parenchyma increases , revealing the relatively hypoattenuating metastases, sometimes with peripheral enhancement . The rim enhancement that occurs represents viable tumor peripherally, which appears against a less viable or necrotic center (figure).

89. Hypervascular metastases  are less common and are seen in renal cell carcinoma, insulinomas , carcinoid, sarcomas, melanoma and breast cancer . They are best seen in the late arterial phase at 35 sec after contrast injection.

90. Ultrasound findings At US, metastases may appear cystic,hypoechoic , isoechoic or hyperechoic . Bull's eye or target lesions  is a common presentation of metastases . In these metastases the halo is most probably related to a combination of compressed normal hepatic parenchyma around the mass and a zone of cancer cell proliferation . This pattern suggests aggressive behavior and is seen in bronchogenic, breast and colon carcinoma .

91. However, this pattern is not specific for metastases as it can also be seen in primary malignant liver neoplasms ( eg , HCC) and benign liver neoplasms ( eg , adenoma in glycogen storage disease).

92. Differential diagnosis Hypervascular  metastases have to be differentiated from other hypervascular tumors that can be multifocal like hemangiomas, FNH, adenoma and HCC. Hypovascular  metastases have to be differentiated from focal fatty infiltration, abscesses, atypical hypovascular HCC and cholangiocarcinoma .

93. Focal fatty infiltration. (a) Portal venous phase CT scan shows a hypoattenuating area in segment IV of the liver (arrow) adjacent to the falciform ligament. (b) Portal venous phase CT scan shows an ovoid hypoattenuating area (arrow) at the posterior aspect of segment IV . Note that the lesion appears hypoattenuating , with no mass effect, and contains normal vessels.

94. Focal sparing

95. Metastases in fatty liver Focal fatty sparing in a diffusely fatty liver or foci of focal fatty infiltration can simulate metastases . However on nonenhanced scans these regions of fat variation tend to be nonspherical and geographic , with no mass effect or distortion of the local vessels.

96. On the other hand a fatty liver can also obscure metastases. On a contrast enhanced CT hypovascular lesions can be obscured if the liver itself is lower in density due to fat deposition. On a NECT these lesions usually are better depicted (figure).

97. Steatosis of right liver lobe. No lesions detectable. On US multiple lesions in the same region. If a patient is known to have a fatty liver, it is better to do an MRI or ultrasound for the detection of liver metastases .