DOI: 10.1148/rg.266065004
Fatty Liver: Imaging Patterns and Pitfalls1
Okka W. Hamer, MD,
Diego A. Aguirre, MD,
Giovanna Casola, MD,
Joel E. Lavine, MD,
Matthias Woenckhaus, MD and
Claude B. Sirlin, MD
1 From the Departments of Diagnostic Radiology (O.W.H.) and Pathology (M.W.), University Hospital of Regensburg, Regensburg, Germany; Department of Radiology, Fundación Santa Fe de Bogotá, University Hospital, Bogotá, Colombia (D.A.A.); and Departments of Radiology (G.C., C.B.S.) and Pediatrics (J.E.L.), UCSD Medical Center San Diego, 200 W Arbor Dr, San Diego, CA 92103. Recipient of a Certificate of Merit award for an education exhibit at the 2004 RSNA Annual Meeting. Received January 20, 2006; revision requested March 6; revision received April 20; accepted May 4. All authors have no financial relationships to disclose.
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Figure 2. Normal appearance of the liver at unenhanced CT. The attenuation of the liver (66 HU) is slightly higher than that of the spleen (56 HU), and intrahepatic vessels (v) appear hypoattenuated in comparison with the liver.
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Figure 3a. Normal appearance of the liver at MR imaging. Axial opposed-phase (a) and axial in-phase (b) T1-weighted GRE images show similar signal intensity of the liver parenchyma.
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Figure 4. Diffuse fat accumulation in the liver at US. The echogenicity of the liver is greater than that of the renal cortex (rc). Intrahepatic vessels are not well depicted. The ultrasound beam is attenuated posteriorly, and the diaphragm is poorly delineated.
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Figure 5. Diffuse fat accumulation in the liver at un-enhanced CT. The attenuation of the liver (15 HU) is markedly lower than that of the spleen (40 HU). Intrahepatic vessels (v) also appear hyperattenuated in comparison with the liver.
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Figure 6a. Diffuse fat accumulation in the liver at MR imaging. Axial T1-weighted GRE images show a marked decrease in the signal intensity of the liver on the opposed-phase image (a), compared with that on the in-phase image (b).
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Figure 6b. Diffuse fat accumulation in the liver at MR imaging. Axial T1-weighted GRE images show a marked decrease in the signal intensity of the liver on the opposed-phase image (a), compared with that on the in-phase image (b).
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Figure 7. Focal fat accumulation in the liver at US. Transverse image shows, adjacent to the left portal vein, a geographically shaped area of high echogenicity that represents accumulation of fat (f) in the falciform ligament, with posterior acoustic attenuation (arrows).
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Figure 8. Focal fat accumulation in the liver at CT. Axial contrast-enhanced image obtained during the portal venous phase shows hypoattenuated regions of focal fat accumulation adjacent to the falciform and venous ligaments and in the porta hepatis, with no evidence of a mass effect.
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Figure 9a. Diffuse fat accumulation with focal sparing at US and CT. Transverse US image (a) and axial un-enhanced CT image (b) obtained at comparable levels show high echogenicity and hypoattenuation, respectively, features indicative of a diffuse accumulation of fat in the liver. Focal sparing (fs) is manifested as a geographically shaped area with relative hypoechogenicity in a and hyperattenuation in b. The focal fatty pseudolesion exerts no mass effect on the adjacent vessel (v in b).
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Figure 9b. Diffuse fat accumulation with focal sparing at US and CT. Transverse US image (a) and axial un-enhanced CT image (b) obtained at comparable levels show high echogenicity and hypoattenuation, respectively, features indicative of a diffuse accumulation of fat in the liver. Focal sparing (fs) is manifested as a geographically shaped area with relative hypoechogenicity in a and hyperattenuation in b. The focal fatty pseudolesion exerts no mass effect on the adjacent vessel (v in b).
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Figure 10a. Multifocal fat accumulation in the liver at CT and MR imaging in a 48-year-old woman with breast cancer. (a) Unenhanced CT image shows multiple hypoattenuated 1-cm nodules (arrows). (b, c) T1-weighted GRE MR images show nodules (arrows) with a signal intensity slightly higher than that of the normal liver parenchyma on the in-phase image (b) but with a signal intensity loss on the opposed-phase image (c). The nodules were mistaken for metastases at CT but were correctly diagnosed as multifocal fat accumulation in the liver on the basis of MR findings.
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Figure 10b. Multifocal fat accumulation in the liver at CT and MR imaging in a 48-year-old woman with breast cancer. (a) Unenhanced CT image shows multiple hypoattenuated 1-cm nodules (arrows). (b, c) T1-weighted GRE MR images show nodules (arrows) with a signal intensity slightly higher than that of the normal liver parenchyma on the in-phase image (b) but with a signal intensity loss on the opposed-phase image (c). The nodules were mistaken for metastases at CT but were correctly diagnosed as multifocal fat accumulation in the liver on the basis of MR findings.
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Figure 10c. Multifocal fat accumulation in the liver at CT and MR imaging in a 48-year-old woman with breast cancer. (a) Unenhanced CT image shows multiple hypoattenuated 1-cm nodules (arrows). (b, c) T1-weighted GRE MR images show nodules (arrows) with a signal intensity slightly higher than that of the normal liver parenchyma on the in-phase image (b) but with a signal intensity loss on the opposed-phase image (c). The nodules were mistaken for metastases at CT but were correctly diagnosed as multifocal fat accumulation in the liver on the basis of MR findings.
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Figure 11a. Confluent foci of fat accumulation in the liver at MR imaging. Axial T1-weighted MR images show a large irregular region with a loss of signal intensity on the opposed-phase image (contour outline in b), compared with the signal intensity on the in-phase image (a). Note the absence of a mass effect.
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Figure 11b. Confluent foci of fat accumulation in the liver at MR imaging. Axial T1-weighted MR images show a large irregular region with a loss of signal intensity on the opposed-phase image (contour outline in b), compared with the signal intensity on the in-phase image (a). Note the absence of a mass effect.
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Figure 12a. Perivenous fat accumulation in the liver at CT and MR imaging. (a, b) Axial unenhanced CT image (a) and axial contrast-enhanced equilibrium phase CT image (b) show halos of hypoattenuation (<40 HU) that closely surround the hepatic veins (arrows) and that are more visible on b than on a. The rest of the liver has normal attenuation (63 HU at unenhanced CT). (c, d) Coronal T1-weighted GRE MR images. Opposed-phase image (c) shows an unequivocal signal intensity loss in the regions that surround the hepatic veins (arrows), which appear slightly hyperintense on the in-phase image (arrows in d). This feature helps confirm the presence of fat accumulation. The signal intensity of the normal liver parenchyma (*) in c differs from that in d because of different window width and level settings.
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Figure 12b. Perivenous fat accumulation in the liver at CT and MR imaging. (a, b) Axial unenhanced CT image (a) and axial contrast-enhanced equilibrium phase CT image (b) show halos of hypoattenuation (<40 HU) that closely surround the hepatic veins (arrows) and that are more visible on b than on a. The rest of the liver has normal attenuation (63 HU at unenhanced CT). (c, d) Coronal T1-weighted GRE MR images. Opposed-phase image (c) shows an unequivocal signal intensity loss in the regions that surround the hepatic veins (arrows), which appear slightly hyperintense on the in-phase image (arrows in d). This feature helps confirm the presence of fat accumulation. The signal intensity of the normal liver parenchyma (*) in c differs from that in d because of different window width and level settings.
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Figure 12c. Perivenous fat accumulation in the liver at CT and MR imaging. (a, b) Axial unenhanced CT image (a) and axial contrast-enhanced equilibrium phase CT image (b) show halos of hypoattenuation (<40 HU) that closely surround the hepatic veins (arrows) and that are more visible on b than on a. The rest of the liver has normal attenuation (63 HU at unenhanced CT). (c, d) Coronal T1-weighted GRE MR images. Opposed-phase image (c) shows an unequivocal signal intensity loss in the regions that surround the hepatic veins (arrows), which appear slightly hyperintense on the in-phase image (arrows in d). This feature helps confirm the presence of fat accumulation. The signal intensity of the normal liver parenchyma (*) in c differs from that in d because of different window width and level settings.
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Figure 12d. Perivenous fat accumulation in the liver at CT and MR imaging. (a, b) Axial unenhanced CT image (a) and axial contrast-enhanced equilibrium phase CT image (b) show halos of hypoattenuation (<40 HU) that closely surround the hepatic veins (arrows) and that are more visible on b than on a. The rest of the liver has normal attenuation (63 HU at unenhanced CT). (c, d) Coronal T1-weighted GRE MR images. Opposed-phase image (c) shows an unequivocal signal intensity loss in the regions that surround the hepatic veins (arrows), which appear slightly hyperintense on the in-phase image (arrows in d). This feature helps confirm the presence of fat accumulation. The signal intensity of the normal liver parenchyma (*) in c differs from that in d because of different window width and level settings.
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Figure 13a. Periportal fat accumulation in a patient with a chronic hepatitis B infection. Axial unenhanced (a) and contrast-enhanced (b) CT images from the late portal venous phase show no morphologic evidence of cirrhosis. Partially confluent halos with hypoattenuation (<40 HU at unenhanced CT) indicative of fat deposition closely surround the portal venous segments (arrows in b), with regions of less marked fat deposition bordering the periportal halos and in the periphery of the liver.
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Figure 13b. Periportal fat accumulation in a patient with a chronic hepatitis B infection. Axial unenhanced (a) and contrast-enhanced (b) CT images from the late portal venous phase show no morphologic evidence of cirrhosis. Partially confluent halos with hypoattenuation (<40 HU at unenhanced CT) indicative of fat deposition closely surround the portal venous segments (arrows in b), with regions of less marked fat deposition bordering the periportal halos and in the periphery of the liver.
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Figure 14a. Differentiation of adenoma from fatty deposition in the liver in a woman with a long history of oral contraceptive use. (a, b) Axial opposed-phase (a) and in-phase (b) T1-weighted GRE images show diffuse fat deposition in the liver, indicated by areas with a signal intensity loss on a in comparison with b. Two round masses in the left lobe of the liver (arrows in a) resemble nodular areas of sparing. (c, d) Three-dimensional T1-weighted GRE images obtained before (c) and during (d) the hepatic arterial phase show enhancement of the masses (arrows in c and d) after the administration of a gadolinium-based contrast agent. The rounded shape of the lesions, as well as their location, which is atypical for regions of fatty liver sparing, are important clues suggestive of tumors. The two masses remained stable in size for several years and most likely are adenomas.
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Figure 14b. Differentiation of adenoma from fatty deposition in the liver in a woman with a long history of oral contraceptive use. (a, b) Axial opposed-phase (a) and in-phase (b) T1-weighted GRE images show diffuse fat deposition in the liver, indicated by areas with a signal intensity loss on a in comparison with b. Two round masses in the left lobe of the liver (arrows in a) resemble nodular areas of sparing. (c, d) Three-dimensional T1-weighted GRE images obtained before (c) and during (d) the hepatic arterial phase show enhancement of the masses (arrows in c and d) after the administration of a gadolinium-based contrast agent. The rounded shape of the lesions, as well as their location, which is atypical for regions of fatty liver sparing, are important clues suggestive of tumors. The two masses remained stable in size for several years and most likely are adenomas.
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Figure 14c. Differentiation of adenoma from fatty deposition in the liver in a woman with a long history of oral contraceptive use. (a, b) Axial opposed-phase (a) and in-phase (b) T1-weighted GRE images show diffuse fat deposition in the liver, indicated by areas with a signal intensity loss on a in comparison with b. Two round masses in the left lobe of the liver (arrows in a) resemble nodular areas of sparing. (c, d) Three-dimensional T1-weighted GRE images obtained before (c) and during (d) the hepatic arterial phase show enhancement of the masses (arrows in c and d) after the administration of a gadolinium-based contrast agent. The rounded shape of the lesions, as well as their location, which is atypical for regions of fatty liver sparing, are important clues suggestive of tumors. The two masses remained stable in size for several years and most likely are adenomas.
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Figure 14d. Differentiation of adenoma from fatty deposition in the liver in a woman with a long history of oral contraceptive use. (a, b) Axial opposed-phase (a) and in-phase (b) T1-weighted GRE images show diffuse fat deposition in the liver, indicated by areas with a signal intensity loss on a in comparison with b. Two round masses in the left lobe of the liver (arrows in a) resemble nodular areas of sparing. (c, d) Three-dimensional T1-weighted GRE images obtained before (c) and during (d) the hepatic arterial phase show enhancement of the masses (arrows in c and d) after the administration of a gadolinium-based contrast agent. The rounded shape of the lesions, as well as their location, which is atypical for regions of fatty liver sparing, are important clues suggestive of tumors. The two masses remained stable in size for several years and most likely are adenomas.
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Figure 15a. Differentiation of hepatocellular carcinoma from fatty deposition in the liver. Axial unenhanced (a) and axial contrast-enhanced (b) CT images obtained during the portal venous phase show a nodular liver contour suggestive of cirrhosis, as well as large gastric varices (arrowheads in b). In b, the right lobe of the liver appears hypoattenuated in comparison with the left lobe, a finding that could be misinterpreted as evidence of regional fatty liver deposition; however, the mass effect with bulging of the anterolateral border of the right liver lobe (arrow), the mosaic enhancement pattern, and the thrombus (t) in the left main portal vein are strongly suggestive of an infiltrative malignancy. This is a case of infiltrative hepatocellular carcinoma.
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Figure 15b. Differentiation of hepatocellular carcinoma from fatty deposition in the liver. Axial unenhanced (a) and axial contrast-enhanced (b) CT images obtained during the portal venous phase show a nodular liver contour suggestive of cirrhosis, as well as large gastric varices (arrowheads in b). In b, the right lobe of the liver appears hypoattenuated in comparison with the left lobe, a finding that could be misinterpreted as evidence of regional fatty liver deposition; however, the mass effect with bulging of the anterolateral border of the right liver lobe (arrow), the mosaic enhancement pattern, and the thrombus (t) in the left main portal vein are strongly suggestive of an infiltrative malignancy. This is a case of infiltrative hepatocellular carcinoma.
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Figure 16a. Differentiation of metastases from fatty liver deposition in a woman undergoing chemotherapy for breast cancer. Axial unenhanced (a, c) and contrast-enhanced (b, d) CT images (c and d at a higher level than a and b) show diffuse fatty deposition in the liver and a geographic pseudolesion at the porta hepatis (arrows in a and b), a finding that represents focal sparing. Multiple round lesions (arrows in c and d), which are more vividly enhanced than the liver parenchyma, represent metastases. If unenhanced CT had not been performed, the region of focal sparing on the contrast-enhanced images may have been mistaken for an enhanced hypervascular tumor.
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Figure 16b. Differentiation of metastases from fatty liver deposition in a woman undergoing chemotherapy for breast cancer. Axial unenhanced (a, c) and contrast-enhanced (b, d) CT images (c and d at a higher level than a and b) show diffuse fatty deposition in the liver and a geographic pseudolesion at the porta hepatis (arrows in a and b), a finding that represents focal sparing. Multiple round lesions (arrows in c and d), which are more vividly enhanced than the liver parenchyma, represent metastases. If unenhanced CT had not been performed, the region of focal sparing on the contrast-enhanced images may have been mistaken for an enhanced hypervascular tumor.
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Figure 16c. Differentiation of metastases from fatty liver deposition in a woman undergoing chemotherapy for breast cancer. Axial unenhanced (a, c) and contrast-enhanced (b, d) CT images (c and d at a higher level than a and b) show diffuse fatty deposition in the liver and a geographic pseudolesion at the porta hepatis (arrows in a and b), a finding that represents focal sparing. Multiple round lesions (arrows in c and d), which are more vividly enhanced than the liver parenchyma, represent metastases. If unenhanced CT had not been performed, the region of focal sparing on the contrast-enhanced images may have been mistaken for an enhanced hypervascular tumor.
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Figure 16d. Differentiation of metastases from fatty liver deposition in a woman undergoing chemotherapy for breast cancer. Axial unenhanced (a, c) and contrast-enhanced (b, d) CT images (c and d at a higher level than a and b) show diffuse fatty deposition in the liver and a geographic pseudolesion at the porta hepatis (arrows in a and b), a finding that represents focal sparing. Multiple round lesions (arrows in c and d), which are more vividly enhanced than the liver parenchyma, represent metastases. If unenhanced CT had not been performed, the region of focal sparing on the contrast-enhanced images may have been mistaken for an enhanced hypervascular tumor.
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Figure 17a. Differentiation of superior vena cava syndrome from fatty liver deposition. Axial contrast-enhanced CT images obtained during the arterial phase at the level of the liver (a) and the upper mediastinum (b) show a hyperattenuated geographic pseudolesion (white arrow in a) in segment IV, at the anterior border of the liver, and obstruction of the superior vena cava by a thoracic mass (arrow in b). With regard to morphologic features, the pseudolesion resembles a focal area of fatty liver deposition or sparing, but its marked enhancement on early phase images helps confirm that the lesion represents a perfusion abnormality—in this case, one associated with superior vena cava syndrome. Note the large systemic collateral veins (arrowheads in a and b) and the collateral draining vessel in segment IV (black arrow in a).
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Figure 17b. Differentiation of superior vena cava syndrome from fatty liver deposition. Axial contrast-enhanced CT images obtained during the arterial phase at the level of the liver (a) and the upper mediastinum (b) show a hyperattenuated geographic pseudolesion (white arrow in a) in segment IV, at the anterior border of the liver, and obstruction of the superior vena cava by a thoracic mass (arrow in b). With regard to morphologic features, the pseudolesion resembles a focal area of fatty liver deposition or sparing, but its marked enhancement on early phase images helps confirm that the lesion represents a perfusion abnormality—in this case, one associated with superior vena cava syndrome. Note the large systemic collateral veins (arrowheads in a and b) and the collateral draining vessel in segment IV (black arrow in a).
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Figure 18. Differentiation of hepatic venous congestion (nutmeg liver) from fatty liver deposition. Axial contrast-enhanced CT image obtained at the level of the liver during the hepatic arterial phase shows irregular areas with low attenuation in the nutmeg pattern, features that could be mistaken for multifocal or geographic fatty liver deposition. However, this pattern was visible only on arterial phase images and early portal venous phase images and not on unenhanced images or images obtained in later phases. A pericardial effusion also was present. Nutmeg liver is a perfusion abnormality that is related to hepatic venous congestion from cardiac disease or other causes.
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Figure 19a. Differentiation of transient hepatic attenuation difference from fatty liver deposition. Axial unenhanced CT image (a) and axial contrast-enhanced late arterial phase (b) and portal venous phase (c) CT images obtained at the same level in the liver. A wedge-shaped peripheral hyperattenuated pseudolesion (white arrows in b) with straight borders appears on the arterial phase image but not in a or c. The wedgelike shape, straight borders, peripheral location, and transient enhancement of the lesion are suggestive of a transient difference in hepatic attenuation rather than a mass or a fat deposition abnormality. Note the arterialized flow in a feeding branch of the portal vein (black arrow in b), a finding that represents an iatrogenic postbiopsy arteriovenous fistula.
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Figure 19b. Differentiation of transient hepatic attenuation difference from fatty liver deposition. Axial unenhanced CT image (a) and axial contrast-enhanced late arterial phase (b) and portal venous phase (c) CT images obtained at the same level in the liver. A wedge-shaped peripheral hyperattenuated pseudolesion (white arrows in b) with straight borders appears on the arterial phase image but not in a or c. The wedgelike shape, straight borders, peripheral location, and transient enhancement of the lesion are suggestive of a transient difference in hepatic attenuation rather than a mass or a fat deposition abnormality. Note the arterialized flow in a feeding branch of the portal vein (black arrow in b), a finding that represents an iatrogenic postbiopsy arteriovenous fistula.
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Figure 19c. Differentiation of transient hepatic attenuation difference from fatty liver deposition. Axial unenhanced CT image (a) and axial contrast-enhanced late arterial phase (b) and portal venous phase (c) CT images obtained at the same level in the liver. A wedge-shaped peripheral hyperattenuated pseudolesion (white arrows in b) with straight borders appears on the arterial phase image but not in a or c. The wedgelike shape, straight borders, peripheral location, and transient enhancement of the lesion are suggestive of a transient difference in hepatic attenuation rather than a mass or a fat deposition abnormality. Note the arterialized flow in a feeding branch of the portal vein (black arrow in b), a finding that represents an iatrogenic postbiopsy arteriovenous fistula.
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Figure 20a. Differentiation of periportal inflammation from fatty liver deposition. Axial contrast-enhanced CT images obtained during the portal venous phase (a) and the equilibrium phase (b). The hypoattenuated halos (arrows) that surround the portal venous tracts in a could be misinterpreted as perivascular fat accumulation, but they retain contrast material and appear hyperattenuated in b. Retention of contrast material on delayed images is suggestive of periportal inflammation with transcapillary leakage of the contrast agent into inflamed periportal tissue; perivascular fat deposition would not be expected to retain contrast material. The attenuation of periportal halos should be measured on unenhanced or delayed phase images, if available, to help differentiate periportal fat deposition from edema or inflammation.
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Figure 20b. Differentiation of periportal inflammation from fatty liver deposition. Axial contrast-enhanced CT images obtained during the portal venous phase (a) and the equilibrium phase (b). The hypoattenuated halos (arrows) that surround the portal venous tracts in a could be misinterpreted as perivascular fat accumulation, but they retain contrast material and appear hyperattenuated in b. Retention of contrast material on delayed images is suggestive of periportal inflammation with transcapillary leakage of the contrast agent into inflamed periportal tissue; perivascular fat deposition would not be expected to retain contrast material. The attenuation of periportal halos should be measured on unenhanced or delayed phase images, if available, to help differentiate periportal fat deposition from edema or inflammation.
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Figure 21a. Differentiation of a fat-containing tumor from fat deposition in the liver. Coronal T1-weighted GRE MR images show a large mass (arrows) with lower signal intensity on the opposed-phase image (a) than on the in-phase image (b), a feature indicative of fat. Vivid arterial enhancement (not shown), the round rather than geographic shape of the lesion, and the mass effect are indicative of a space-occupying lesion rather than fat deposition. The lesion was an exophytic hepatic adenoma.
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Figure 21b. Differentiation of a fat-containing tumor from fat deposition in the liver. Coronal T1-weighted GRE MR images show a large mass (arrows) with lower signal intensity on the opposed-phase image (a) than on the in-phase image (b), a feature indicative of fat. Vivid arterial enhancement (not shown), the round rather than geographic shape of the lesion, and the mass effect are indicative of a space-occupying lesion rather than fat deposition. The lesion was an exophytic hepatic adenoma.
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Figure 22a. Differentiation of metastases from fat deposition in the liver. Axial portal venous phase contrast-enhanced CT images at the level of the right hepatic vein (rhv) (a) and the pancreatic head (b) show innumerable hypoattenuated lesions throughout the liver. Most of the lesions are round or oval, but the largest (m in b) has a geographic configuration. Because of their low attenuation (<40 HU), the lesions might be mistaken for multifocal fat deposition; however, the mass effect of the lesions, which produces bulging of the liver surface (arrow) and compression of the right hepatic vein, as well as the multiplicity of lesions, their predominant round or oval shape, the thrombus (t in b) in the superior mesenteric vein, and numerous heterogeneous lymph nodes (n in b), are suggestive of malignancy. The lesions were identified as hematogenous metastases from pancreatic adenocarcinoma.
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Figure 22b. Differentiation of metastases from fat deposition in the liver. Axial portal venous phase contrast-enhanced CT images at the level of the right hepatic vein (rhv) (a) and the pancreatic head (b) show innumerable hypoattenuated lesions throughout the liver. Most of the lesions are round or oval, but the largest (m in b) has a geographic configuration. Because of their low attenuation (<40 HU), the lesions might be mistaken for multifocal fat deposition; however, the mass effect of the lesions, which produces bulging of the liver surface (arrow) and compression of the right hepatic vein, as well as the multiplicity of lesions, their predominant round or oval shape, the thrombus (t in b) in the superior mesenteric vein, and numerous heterogeneous lymph nodes (n in b), are suggestive of malignancy. The lesions were identified as hematogenous metastases from pancreatic adenocarcinoma.
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Copyright © 2006 by the Radiological Society of North America.
