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(Radiology. 2000;217:415-420.)
© RSNA, 2000

Gastrointestinal Imaging

Nondiffuse Fatty Change of the Liver: Discerning Pseudotumor on MR Images Enhanced with Ferumoxides-Initial Observations1

Shinji Hirohashi, MD, Kouji Ueda, MD, Hideo Uchida, MD, Wataru Ono, MD, Junko Takahama, MD, Megumi Takewa, MD, Satoru Kitano, MD and Hajime Ohishi, MD

1 From the Departments of Radiology and Oncoradiology, Nara Medical University, 840 Shijo-cho, Kashihara-shi, Nara 634-8522, Japan. Received January 5, 1999; revision requested February 18; final revision received March 7, 2000; accepted March 30. Address correspondence to S.H. (e-mail: hirohashi@my.email.ne.jp).


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
PURPOSE: To clarify the findings of nondiffuse fatty change of the liver on ferumoxides-enhanced magnetic resonance (MR) images.

MATERIALS AND METHODS: Of 202 patients who underwent ferumoxides-enhanced MR imaging, eight who had nondiffuse fatty change of the liver at computed tomography (CT) were examined as study subjects. MR imaging findings before and 1 hour after ferumoxides administration were compared with CT findings.

RESULTS: Focal fatty areas of the liver showing low attenuation on CT images were depicted as areas of relatively high intensity on the ferumoxides-enhanced T1-weighted images in all patients. On enhanced T2-weighted images, focal fatty change showed relatively high intensity in three and isointensity in one of the four patients. Focal spared areas appearing as areas of relatively high attenuation on CT images were depicted as areas of relatively low intensity on the ferumoxides-enhanced T1- and T2-weighted images in all patients.

CONCLUSION: Although prior reports of hepatic MR imaging with ferumoxides indicated that there is accumulation of ferumoxides within focal fatty areas that are no longer seen after the administration of contrast medium, this study revealed that focal fatty change and focal spared areas of fatty liver may be pseudotumors because of the relatively high intensity of fatty areas of the liver. Radiologists can distinguish these conditions from hepatic tumors by using the opposed-phase gradient-echo sequence or the fat-saturation technique.

Index terms: Computed tomography (CT), comparative studies, 761.1211, 761.121411, 761.121412, 761.121414, 761.12143 • Iron, 761.12143 • Liver, CT, 761.1211 • Liver, fatty, 761.50 • Liver, MR, 761.121411, 761.121412, 761.121414, 761.12143 • Magnetic resonance (MR), comparative studies, 761.1211, 761.121411, 761.121412, 761.121414, 761.12143 • Magnetic resonance (MR), contrast media, 761.12143


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
Magnetic resonance (MR) imaging enhanced with superparamagnetic iron oxide particles such as ferumoxides is considered the most useful of the noninvasive diagnostic imaging techniques for hepatic tumors (1–10). Compared with computed tomography (CT) during arterial portography, which is the most useful of the invasive diagnostic techniques for hepatic tumors, MR imaging enhanced with superparamagnetic iron oxide is highly specific, with a low false-positive rate (9,10).

Advances in ultrasonography (US) and CT have shown nondiffuse fatty change of the liver that involves focal fatty deposition (11–16) and focal spared areas (17–22). Nondiffuse fatty change is difficult to diagnose when its extent is small, and it is often overlooked at MR imaging in which the conventional spin-echo sequence is used (23–25).

Superparamagnetic iron oxide is a contrast medium incorporated into the reticuloendothelial system. Its uptake may change with various pathologic conditions such as fatty change of the liver. Since there are Kupffer cells in areas of focal fatty change, a commonly held belief has been that, because of the marked decrease in signal intensity in MR images after ferumoxides accumulation, fatty areas are not visible after administration of contrast medium. One experimental study (26) proved the hypothesis, but another experimental study (27) in animals showed a decreased uptake of superparamagnetic iron oxide in fatty liver. Since fatty liver is not a rare condition, we thought it would be useful to clarify whether there is any difference between fatty and nonfatty areas on ferumoxides-enhanced MR images. The purpose of the present study was to clarify the findings of nondiffuse fatty change of the liver on ferumoxides-enhanced MR images; therefore, we performed ferumoxides-enhanced MR imaging in eight patients with nondiffuse fatty change of the liver to establish the MR findings of areas of fatty change in comparison with areas of nonfatty change.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
 REFERENCES
 
Of 202 patients who underwent ferumoxides-enhanced MR imaging to survey for hepatic tumors at our hospital and affiliated institutions between January and September 1998, eight who had nondiffuse fatty change of the liver diagnosed at CT were examined as study subjects. The eight patients (two men, six women; age range, 51–73 years; mean age, 61 years) were selected by reviewing the dictated reports of the CT studies performed in the 202 patients. The diagnosis of nondiffuse fatty change was confirmed by means of surgery in one patient, histopathologic findings from a percutaneous needle biopsy in another patient, and disappearance of the lesion after discontinuation of tamoxifen citrate in a third patient. In the remaining five patients, the diagnosis was based on characteristic CT findings—lower attenuation than that of the spleen and CT numbers ranging from -40 to 30 HU at nonenhanced CT and lack of displacement of the vessels—and no change in the lesion for more than 6 months after CT was performed.

We used four MR imagers: two 0.5-T (MRT50A/II and MRT50A/Super; Toshiba Medical Systems, Tokyo, Japan), one 1.0-T (Magnetom Impact Expert; Siemens, Erlangen, Germany), and one 1.5-T (Signa; GE Medical Systems, Milwaukee, Wis) machine. In one patient, with one 0.5-T machine we used a spin-echo sequence (500/20 [repetition time msec/echo time msec]) for T1-weighted images and a spin-echo sequence (2,000/80) for T2-weighted images. In two patients, with another 0.5-T machine we used a spin-echo sequence (480/15) for T1-weighted images, a spin-echo sequence (2,000/80) for T2-weighted images, and an out-of-phase gradient-echo sequence (170/22; flip angle, 30°). In three patients, with the 1.0-T machine we used a gradient-echo sequence (180/6.4–7.0; flip angle, 70°–90°) for T1-weighted images, a fast spin-echo sequence (2,000/99 [effective]; echo train length, 11) for T2-weighted images, and an out-of-phase gradient-echo sequence (180/3.5; flip angle, 90°). In two patients, with the 1.5-T machine we used a spin-echo sequence (500/16) and a gradient-echo sequence (80/4.2; flip angle, 60°) for T1-weighted images, a fast spin-echo sequence (3,000/90 [effective]; echo train length, seven) for T2-weighted images, and an out-of-phase gradient-echo sequence (80/2.1; flip angle, 60°).

As the superparamagnetic iron oxide, 10 µmol of ferumoxides (Feridex; Eiken Chemical, Tokyo, Japan) per kilogram of body weight was used. Both transverse MR and CT images were reviewed by the two radiologists (S.H., K.U.) by means of consensus reading. MR imaging findings before and 1 hour after ferumoxides administration were compared with the CT findings.

We placed the patients with nondiffuse fatty liver observed at CT into either a "focal fatty change" group or a "focal fatty sparing" group. For the focal fatty change group, we subsequently recorded the relative signal intensity of the fatty area in comparison with the surrounding nonfatty area on both nonenhanced T1- and T2-weighted images and ferumoxides-enhanced T1- and T2-weighted images. Furthermore, for the focal fatty sparing group, we recorded the signal intensity of the nonfatty area in comparison with the surrounding fatty area on both nonenhanced T1- and T2-weighted images and ferumoxides-enhanced T1- and T2-weighted images.


   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
DISCUSSION
 REFERENCES
 
CT showed focal fatty change in four patients (Table 1) and fatty change with focal spared areas along the porta hepatis and around the tumor in four patients (Table 2). Although all eight patients underwent contrast medium–enhanced MR imaging for the survey of hepatic tumors, hepatic tumors were found in only four patients: one had multiple hemangiomas, two had multiple metastases, and one had one hemangioma and multiple metastases.


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  		TABLE 1. Summary of Patients with Focal Fatty Liver at MR Imaging
 

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  		TABLE 2. Summary of Patients with Focal Spared Areas in Fatty Liver at MR Imaging
 
Focal Fatty Change
In the four patients with fatty change, on T1-weighted images before contrast enhancement, focal fatty areas were depicted as areas of high intensity in all three patients examined by using the spin-echo sequence but as isointense areas in all three patients examined by using the in-phase gradient-echo sequence. On T2-weighted images obtained before contrast enhancement, focal fatty change showed high intensity in two of the four patients but showed isointensity in the other two, which made the diagnosis of focal fatty change difficult. In all three patients examined by using the opposed-phase gradient-echo sequence, areas of low attenuation on CT images were depicted as areas of low intensity, which facilitated the diagnosis of focal fatty change.

On ferumoxides-enhanced T1-weighted images, focal fatty areas of the liver showing low attenuation on CT images were depicted as areas of relatively high intensity in all three patients examined by using the spin-echo sequence (Fig 1) and in two of the three patients examined by using the in-phase gradient-echo sequence. On enhanced T2-weighted images, focal fatty change showed relatively high intensity in three and isointensity in one of the four patients.



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  		Figure 1a. Patient 2. Focal fatty change in a 60-year-old woman. (a) Transverse nonenhanced CT scan shows a round area (arrows) of low attenuation on the medial segment of the left lobe of the liver. (b) Transverse contrast-enhanced CT scan shows normal vasculature (arrowhead) in the area (arrows) of low attenuation without displacement, which suggests focal fatty change. (c) Transverse nonenhanced T1-weighted MR image obtained by using the spin-echo sequence (480/15) on a 0.5-T imager depicts the lesion as an area (arrows) of slightly higher intensity. (d) Transverse contrast-enhanced T1-weighted MR image obtained by using the spin-echo sequence (480/15) on a 0.5-T imager shows the lesion is well delineated as an area (arrows) of relatively high intensity. (e) Transverse opposed-phase MR image obtained by using the gradient-echo sequence (170/22; flip angle, 30°) on a 0.5-T imager demonstrates the lesion as a distinct area (arrows) of low intensity.

 


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  		Figure 1b. Patient 2. Focal fatty change in a 60-year-old woman. (a) Transverse nonenhanced CT scan shows a round area (arrows) of low attenuation on the medial segment of the left lobe of the liver. (b) Transverse contrast-enhanced CT scan shows normal vasculature (arrowhead) in the area (arrows) of low attenuation without displacement, which suggests focal fatty change. (c) Transverse nonenhanced T1-weighted MR image obtained by using the spin-echo sequence (480/15) on a 0.5-T imager depicts the lesion as an area (arrows) of slightly higher intensity. (d) Transverse contrast-enhanced T1-weighted MR image obtained by using the spin-echo sequence (480/15) on a 0.5-T imager shows the lesion is well delineated as an area (arrows) of relatively high intensity. (e) Transverse opposed-phase MR image obtained by using the gradient-echo sequence (170/22; flip angle, 30°) on a 0.5-T imager demonstrates the lesion as a distinct area (arrows) of low intensity.

 


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  		Figure 1c. Patient 2. Focal fatty change in a 60-year-old woman. (a) Transverse nonenhanced CT scan shows a round area (arrows) of low attenuation on the medial segment of the left lobe of the liver. (b) Transverse contrast-enhanced CT scan shows normal vasculature (arrowhead) in the area (arrows) of low attenuation without displacement, which suggests focal fatty change. (c) Transverse nonenhanced T1-weighted MR image obtained by using the spin-echo sequence (480/15) on a 0.5-T imager depicts the lesion as an area (arrows) of slightly higher intensity. (d) Transverse contrast-enhanced T1-weighted MR image obtained by using the spin-echo sequence (480/15) on a 0.5-T imager shows the lesion is well delineated as an area (arrows) of relatively high intensity. (e) Transverse opposed-phase MR image obtained by using the gradient-echo sequence (170/22; flip angle, 30°) on a 0.5-T imager demonstrates the lesion as a distinct area (arrows) of low intensity.

 


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  		Figure 1d. Patient 2. Focal fatty change in a 60-year-old woman. (a) Transverse nonenhanced CT scan shows a round area (arrows) of low attenuation on the medial segment of the left lobe of the liver. (b) Transverse contrast-enhanced CT scan shows normal vasculature (arrowhead) in the area (arrows) of low attenuation without displacement, which suggests focal fatty change. (c) Transverse nonenhanced T1-weighted MR image obtained by using the spin-echo sequence (480/15) on a 0.5-T imager depicts the lesion as an area (arrows) of slightly higher intensity. (d) Transverse contrast-enhanced T1-weighted MR image obtained by using the spin-echo sequence (480/15) on a 0.5-T imager shows the lesion is well delineated as an area (arrows) of relatively high intensity. (e) Transverse opposed-phase MR image obtained by using the gradient-echo sequence (170/22; flip angle, 30°) on a 0.5-T imager demonstrates the lesion as a distinct area (arrows) of low intensity.

 


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  		Figure 1e. Patient 2. Focal fatty change in a 60-year-old woman. (a) Transverse nonenhanced CT scan shows a round area (arrows) of low attenuation on the medial segment of the left lobe of the liver. (b) Transverse contrast-enhanced CT scan shows normal vasculature (arrowhead) in the area (arrows) of low attenuation without displacement, which suggests focal fatty change. (c) Transverse nonenhanced T1-weighted MR image obtained by using the spin-echo sequence (480/15) on a 0.5-T imager depicts the lesion as an area (arrows) of slightly higher intensity. (d) Transverse contrast-enhanced T1-weighted MR image obtained by using the spin-echo sequence (480/15) on a 0.5-T imager shows the lesion is well delineated as an area (arrows) of relatively high intensity. (e) Transverse opposed-phase MR image obtained by using the gradient-echo sequence (170/22; flip angle, 30°) on a 0.5-T imager demonstrates the lesion as a distinct area (arrows) of low intensity.

 
Focal Fatty Sparing
In the four patients with focal spared areas, on T1-weighted images before contrast enhancement, both of the two patients examined by using the spin-echo sequence and both of the two patients examined by using the in-phase gradient-echo sequence showed almost homogeneous signal intensity in the liver, which masked the presence of focal spared areas. On T2-weighted images before contrast enhancement, the liver was depicted as having almost homogeneous signal intensity in only one of the four patients; areas of low intensity were observed in the other three patients, which suggests spared areas of fatty liver. In two of the three patients examined by using the opposed-phase gradient-echo sequence, areas showing low attenuation on CT images were depicted as areas of low intensity, which allowed differentiation between fatty areas of the liver and spared areas.

On ferumoxides-enhanced T1-weighted images, focal spared areas that were depicted as areas of relatively high attenuation on CT images were depicted as areas of relatively low intensity in both of the two patients examined by using the spin-echo sequence and in one of the two patients examined by using the in-phase gradient-echo sequence. On enhanced T2-weighted images, focal spared areas were depicted as areas of relatively low intensity in all four patients examined by means of the spin-echo sequence (Figs 2, 3).



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  		Figure 2a. Patient 5. Focal spared area in the fatty liver along the porta hepatis in a 73-year-old woman. (a) Transverse nonenhanced CT scan of the liver shows low attenuation, except for a trabecular area (arrows) of relatively high attenuation along the porta hepatis. The finding suggests a focal spared area along the porta hepatis in the fatty liver. Before contrast enhancement, the transverse (b) T1-weighted (500/20) and (c) T2-weighted (2,000/80) spin-echo MR images obtained on a 0.5-T imager show almost homogeneous intensity in the liver. After contrast enhancement, the transverse (d) T1-weighted (500/20) and (e) T2-weighted (2,000/80) spin-echo MR images obtained on a 0.5-T imager reveal a focal spared area (arrows) along the porta hepatis as an area of relatively low intensity.

 


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  		Figure 2b. Patient 5. Focal spared area in the fatty liver along the porta hepatis in a 73-year-old woman. (a) Transverse nonenhanced CT scan of the liver shows low attenuation, except for a trabecular area (arrows) of relatively high attenuation along the porta hepatis. The finding suggests a focal spared area along the porta hepatis in the fatty liver. Before contrast enhancement, the transverse (b) T1-weighted (500/20) and (c) T2-weighted (2,000/80) spin-echo MR images obtained on a 0.5-T imager show almost homogeneous intensity in the liver. After contrast enhancement, the transverse (d) T1-weighted (500/20) and (e) T2-weighted (2,000/80) spin-echo MR images obtained on a 0.5-T imager reveal a focal spared area (arrows) along the porta hepatis as an area of relatively low intensity.

 


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  		Figure 2c. Patient 5. Focal spared area in the fatty liver along the porta hepatis in a 73-year-old woman. (a) Transverse nonenhanced CT scan of the liver shows low attenuation, except for a trabecular area (arrows) of relatively high attenuation along the porta hepatis. The finding suggests a focal spared area along the porta hepatis in the fatty liver. Before contrast enhancement, the transverse (b) T1-weighted (500/20) and (c) T2-weighted (2,000/80) spin-echo MR images obtained on a 0.5-T imager show almost homogeneous intensity in the liver. After contrast enhancement, the transverse (d) T1-weighted (500/20) and (e) T2-weighted (2,000/80) spin-echo MR images obtained on a 0.5-T imager reveal a focal spared area (arrows) along the porta hepatis as an area of relatively low intensity.

 


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  		Figure 2d. Patient 5. Focal spared area in the fatty liver along the porta hepatis in a 73-year-old woman. (a) Transverse nonenhanced CT scan of the liver shows low attenuation, except for a trabecular area (arrows) of relatively high attenuation along the porta hepatis. The finding suggests a focal spared area along the porta hepatis in the fatty liver. Before contrast enhancement, the transverse (b) T1-weighted (500/20) and (c) T2-weighted (2,000/80) spin-echo MR images obtained on a 0.5-T imager show almost homogeneous intensity in the liver. After contrast enhancement, the transverse (d) T1-weighted (500/20) and (e) T2-weighted (2,000/80) spin-echo MR images obtained on a 0.5-T imager reveal a focal spared area (arrows) along the porta hepatis as an area of relatively low intensity.

 


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  		Figure 2e. Patient 5. Focal spared area in the fatty liver along the porta hepatis in a 73-year-old woman. (a) Transverse nonenhanced CT scan of the liver shows low attenuation, except for a trabecular area (arrows) of relatively high attenuation along the porta hepatis. The finding suggests a focal spared area along the porta hepatis in the fatty liver. Before contrast enhancement, the transverse (b) T1-weighted (500/20) and (c) T2-weighted (2,000/80) spin-echo MR images obtained on a 0.5-T imager show almost homogeneous intensity in the liver. After contrast enhancement, the transverse (d) T1-weighted (500/20) and (e) T2-weighted (2,000/80) spin-echo MR images obtained on a 0.5-T imager reveal a focal spared area (arrows) along the porta hepatis as an area of relatively low intensity.

 


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  		Figure 3a. Patient 6. Fatty liver in a 57-year-old woman with multiple metastases from colon cancer. (a) Photomicrograph of the histologic specimen shows adenocarcinoma and fatty change of the liver; however, there is a thin spared area between the tumor (T) and the surrounding fatty liver (FL). (Hematoxylin-eosin stain; original magnification, x40.) (b) Transverse nonenhanced opposed-phase MR image obtained by using the gradient-echo sequence (180/3.5; flip angle, 90°) on a 1.0-T imager demonstrates the spared area around the tumor as a rim (arrows) of relatively high intensity compared with the surrounding fatty hepatic tissue. Before contrast enhancement, the spared area is barely discernible on the transverse images obtained by using the (c) in-phase gradient-echo (180/7.0; flip angle, 90°) and (d) T2-weighted fast spin-echo (2,000/99[effective]; echo train length, 11) MR sequences on a 1.0-T imager. After contrast enhancement, the transverse MR images obtained by using (e) in-phase gradient-echo (180/7.0; flip angle, 90°) and (f) T2-weighted fast spin-echo (2,000/99[effective]; echo train length, 11) sequences on a 1.0-T imager reveal a focal spared area around the tumor as a rim (arrows) of relatively low intensity.

 


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  		Figure 3b. Patient 6. Fatty liver in a 57-year-old woman with multiple metastases from colon cancer. (a) Photomicrograph of the histologic specimen shows adenocarcinoma and fatty change of the liver; however, there is a thin spared area between the tumor (T) and the surrounding fatty liver (FL). (Hematoxylin-eosin stain; original magnification, x40.) (b) Transverse nonenhanced opposed-phase MR image obtained by using the gradient-echo sequence (180/3.5; flip angle, 90°) on a 1.0-T imager demonstrates the spared area around the tumor as a rim (arrows) of relatively high intensity compared with the surrounding fatty hepatic tissue. Before contrast enhancement, the spared area is barely discernible on the transverse images obtained by using the (c) in-phase gradient-echo (180/7.0; flip angle, 90°) and (d) T2-weighted fast spin-echo (2,000/99[effective]; echo train length, 11) MR sequences on a 1.0-T imager. After contrast enhancement, the transverse MR images obtained by using (e) in-phase gradient-echo (180/7.0; flip angle, 90°) and (f) T2-weighted fast spin-echo (2,000/99[effective]; echo train length, 11) sequences on a 1.0-T imager reveal a focal spared area around the tumor as a rim (arrows) of relatively low intensity.

 


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  		Figure 3c. Patient 6. Fatty liver in a 57-year-old woman with multiple metastases from colon cancer. (a) Photomicrograph of the histologic specimen shows adenocarcinoma and fatty change of the liver; however, there is a thin spared area between the tumor (T) and the surrounding fatty liver (FL). (Hematoxylin-eosin stain; original magnification, x40.) (b) Transverse nonenhanced opposed-phase MR image obtained by using the gradient-echo sequence (180/3.5; flip angle, 90°) on a 1.0-T imager demonstrates the spared area around the tumor as a rim (arrows) of relatively high intensity compared with the surrounding fatty hepatic tissue. Before contrast enhancement, the spared area is barely discernible on the transverse images obtained by using the (c) in-phase gradient-echo (180/7.0; flip angle, 90°) and (d) T2-weighted fast spin-echo (2,000/99[effective]; echo train length, 11) MR sequences on a 1.0-T imager. After contrast enhancement, the transverse MR images obtained by using (e) in-phase gradient-echo (180/7.0; flip angle, 90°) and (f) T2-weighted fast spin-echo (2,000/99[effective]; echo train length, 11) sequences on a 1.0-T imager reveal a focal spared area around the tumor as a rim (arrows) of relatively low intensity.

 


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  		Figure 3d. Patient 6. Fatty liver in a 57-year-old woman with multiple metastases from colon cancer. (a) Photomicrograph of the histologic specimen shows adenocarcinoma and fatty change of the liver; however, there is a thin spared area between the tumor (T) and the surrounding fatty liver (FL). (Hematoxylin-eosin stain; original magnification, x40.) (b) Transverse nonenhanced opposed-phase MR image obtained by using the gradient-echo sequence (180/3.5; flip angle, 90°) on a 1.0-T imager demonstrates the spared area around the tumor as a rim (arrows) of relatively high intensity compared with the surrounding fatty hepatic tissue. Before contrast enhancement, the spared area is barely discernible on the transverse images obtained by using the (c) in-phase gradient-echo (180/7.0; flip angle, 90°) and (d) T2-weighted fast spin-echo (2,000/99[effective]; echo train length, 11) MR sequences on a 1.0-T imager. After contrast enhancement, the transverse MR images obtained by using (e) in-phase gradient-echo (180/7.0; flip angle, 90°) and (f) T2-weighted fast spin-echo (2,000/99[effective]; echo train length, 11) sequences on a 1.0-T imager reveal a focal spared area around the tumor as a rim (arrows) of relatively low intensity.

 


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  		Figure 3e. Patient 6. Fatty liver in a 57-year-old woman with multiple metastases from colon cancer. (a) Photomicrograph of the histologic specimen shows adenocarcinoma and fatty change of the liver; however, there is a thin spared area between the tumor (T) and the surrounding fatty liver (FL). (Hematoxylin-eosin stain; original magnification, x40.) (b) Transverse nonenhanced opposed-phase MR image obtained by using the gradient-echo sequence (180/3.5; flip angle, 90°) on a 1.0-T imager demonstrates the spared area around the tumor as a rim (arrows) of relatively high intensity compared with the surrounding fatty hepatic tissue. Before contrast enhancement, the spared area is barely discernible on the transverse images obtained by using the (c) in-phase gradient-echo (180/7.0; flip angle, 90°) and (d) T2-weighted fast spin-echo (2,000/99[effective]; echo train length, 11) MR sequences on a 1.0-T imager. After contrast enhancement, the transverse MR images obtained by using (e) in-phase gradient-echo (180/7.0; flip angle, 90°) and (f) T2-weighted fast spin-echo (2,000/99[effective]; echo train length, 11) sequences on a 1.0-T imager reveal a focal spared area around the tumor as a rim (arrows) of relatively low intensity.

 


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  		Figure 3f. Patient 6. Fatty liver in a 57-year-old woman with multiple metastases from colon cancer. (a) Photomicrograph of the histologic specimen shows adenocarcinoma and fatty change of the liver; however, there is a thin spared area between the tumor (T) and the surrounding fatty liver (FL). (Hematoxylin-eosin stain; original magnification, x40.) (b) Transverse nonenhanced opposed-phase MR image obtained by using the gradient-echo sequence (180/3.5; flip angle, 90°) on a 1.0-T imager demonstrates the spared area around the tumor as a rim (arrows) of relatively high intensity compared with the surrounding fatty hepatic tissue. Before contrast enhancement, the spared area is barely discernible on the transverse images obtained by using the (c) in-phase gradient-echo (180/7.0; flip angle, 90°) and (d) T2-weighted fast spin-echo (2,000/99[effective]; echo train length, 11) MR sequences on a 1.0-T imager. After contrast enhancement, the transverse MR images obtained by using (e) in-phase gradient-echo (180/7.0; flip angle, 90°) and (f) T2-weighted fast spin-echo (2,000/99[effective]; echo train length, 11) sequences on a 1.0-T imager reveal a focal spared area around the tumor as a rim (arrows) of relatively low intensity.

 

   DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
REFERENCES
 
In fatty liver, focal fatty change and focal spared areas can be discerned as pseudotumor at US or CT (12–22). However, most cases of focal fatty change can be diagnosed at CT on the basis of the characteristic low attenuation of fat, the absence of the displacement of the vessels, and the morphology of the areas of low attenuation and their changes with time (12–16). On the other hand, there are established criteria for CT diagnosis of focal spared areas; these areas can be diagnosed readily on the basis of findings of fatty change in the surrounding area of the liver and the location and morphology of the focal areas (17–22).

MR imaging signals result from protons of free water and protons of fat; however, the differentiation of proton sources is impossible by using the conventional spin-echo sequence or the fast spin-echo sequence, which makes the diagnosis of fatty liver difficult by means of these methods (23–25). However, patients showing high signal intensity on T1- and T2-weighted images have been reported on (28–33). In this study, high signal intensity was observed on nonenhanced T1-weighted images in three of the four patients with focal fatty liver and on nonenhanced T2-weighted images in two of those four. This may be due to the substantial extent of fatty change. On T2-weighted images, focal spared areas showed relatively low signal intensity in three of the four patients, but the entire liver was depicted as being almost isointense on T1-weighted images, which makes the diagnosis of spared areas difficult.

At ferumoxides-enhanced MR imaging, superparamagnetic iron oxide accumulates in Kupffer cells in the liver and decreases their signal intensity. As a result, if the area has a smaller number of normal Kupffer cells or Kupffer cells with abnormal function, the area will show a higher intensity on ferumoxides-enhanced MR images. In this study, the signal intensity in areas showing findings of fatty liver by means of CT was higher than that in the other areas on enhanced T1-weighted images. Therefore, when diagnosis is made by using only MR imaging, focal fatty change is depicted as areas of focal high intensity, which may lead to misdiagnosis as lesions. On the basis of the decreased uptake of superparamagnetic iron oxide in fatty liver in an experimental study (26), the ferumoxides uptake may decrease only in areas of focal fatty change compared with the surrounding liver. Because the degree of the decrease in signal intensity is relatively slight, areas of focal fatty change still may have been depicted as areas of relatively high intensity.

Focal spared areas in fatty liver were depicted as areas of relatively low intensity on both T1- and T2-weighted images. This finding can be explained by the relatively high uptake of superparamagnetic iron oxide in spared areas compared with the decreased uptake in fatty areas of the liver. Itai et al (34) observed a ringlike area of high attenuation around a tumor developing in fatty liver and speculated that this area is peritumoral sparing of fatty liver. In our study, such an area was depicted as an area of relatively high intensity by means of the opposed-phase method and as an area of relatively low intensity after ferumoxides administration. These findings support the speculation by Itai et al (34). In patient 6, this speculation was confirmed histologically. These spared areas showed relatively low signal intensity after administration of ferumoxides.

Because hepatic tumors without Kupffer cells show high signal intensity on ferumoxides-enhanced MR images, the differentiation between focal spared areas and tumors is not difficult. If examiners know to look for the absence of any difference in signal intensity at MR imaging before contrast enhancement and the presence of a clear difference after enhancement with ferumoxides, spared areas of fatty liver are readily diagnosed.

Results of a recent study (35) showed that some pseudotumors detected at CT during arterial portography are depicted as pseudotumors at ferumoxides-enhanced MR imaging by using the T1-weighted gradient-echo sequence. The researchers did not directly refer to an association with fatty liver but suggested a close association between portal blood flow and fatty change in the formation of pseudotumors.

The diagnosis of fatty liver at MR imaging was reported to be possible by using the Dixon method (36,37), chemical-shift imaging (38–41), a special inversion recovery sequence in which inversion pulses are used to decrease signal in the liver (42), or the technique of suppressing water signal (43). The simplest and most sensitive method is chemical-shift imaging, in which phase differences in the proton resonance frequency between protons of free water and those of fat are detected by changing the echo time in the gradient-echo sequence (38). When the phase of free water is the same as that of fat, it is called "in phase," and when the phase of water is opposite, it is called "opposed phase" or "out of phase." In fatty liver, the differentiation between areas of fatty change and normal areas is often difficult to detect by means of the in-phase method, as with the spin-echo sequence. However, with an opposed-phase method, the signal intensity in fatty change is decreased relative to normal tissue, and the diagnosis becomes clear (38–40); quantification of the fatty change is even possible (39,40).

When ferumoxides-enhanced MR images are interpreted, radiologists should know that focal fatty change and focal spared areas of fatty liver may be pseudotumors because of the relatively high intensity of fatty areas of the liver. Radiologists may distinguish these conditions from hepatic tumors by using the opposed-phase gradient-echo sequence or the fat-saturation technique.


   FOOTNOTES
 
Author contributions: Guarantors of integrity of entire study, S.H., H.U.; study concepts and design, S.H.; definition of intellectual content, S.H.; literature research, S.H.; clinical studies, K.U., W.O., J.T., M.T.; data acquisition, K.U., W.O., J.T., M.T.; data analysis, S.H., S.K.; manuscript preparation, S.H.; manuscript editing, H.U., H.O.; manuscript review, H.O.


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 

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