CASE REPORT Focal parenchymal sparing in fatty infiltration of the liver BJSher FCRad(D)SA I C Duncan FFRad(D)SA SunninghIlI Medical Institute Sandton, Johannesburg Introduction Fatty infiltration within the liver usually shows a diffuse pattern throughout the organ. However, focal areas of either normal liver tissue sparing or fatty infiltration can occur and can be confused with metastatic disease on sectional imaging, unless one is aware of the typical sites and imaging appearances of these vari- ants. Case report A 40-year-old obese woman pre- sented with intermittent right-sided abdominal pain. Ultrasound exami- nation of the liver showed a solitary well-defined focal echolucent lesion in the region of the caudate lobe just anterior to the common hepatic duct and portal vein, measuring 2 cm in diameter. The rest of the hepatic parenchyma showed increased echogenicity throughout suggesting diffuse fatty infiltration (Fig. I). A computed tomography (CT) scan showed decreased attenuation Fig. 1. Axial abdominal ultrasound showIng diffuse echogenicity of the liver parenchyna with a hypo- echoic 'lesion' near the porta hepatis. throughout most of the parenchyma again suggesting fatty infiltration, but with areas of normal attenuation seen at the liver periphery. Furthermore, in the same area of the caudate lobe a discrete rounded area with the same diameter as that measured on the ear- lier ultrasound examination was noted. This area showed a higher attenuation than the surrounding parenchyma, similar to the areas around the periphery of the liver (Fig. 2). This area showed enhancement during the arterial, portal return and delayed phases of a triphasic contrast- enhanced liver scan compatible with that of normal liver tissue, whereas the rest of the fat-infiltrated parenchyma showed a lesser degree of enhance- ment during all three phases (Figs 3 and 4). On the basis of the ultrasound and CT findings, together with previous 24 SA JOU RNAL OF RADIOLOGY • March 2002 Fig. 2. Non-contrast CT scan of the abdomen show- ing the typical hypodense appearance of a fat-infil- trated liver, with peripheral sparing and the rounded area near the porta hepatis representing focal spar- ing. It is important not to confuse this round area of fatty sparing with a neoplasm. Fig. 3. Post-contrast abdominal CT scan during the portal venous return phase showing that the fat- infiltrated liver enhances less than the area of spar- ing seen in Fig. 2. ultrasound reports which indicated no change in the size or appearance of the focus over a period of several months, it was felt that the focal 'lesion' most probably represented an area of focal fatty sparing. The find- ings were felt to be pathognomonic enough in this particular case so that the added expense of MRI for confir- mation was unwarranted. The spleen was also found to be enlarged (Fig. 4). Discussion The usual causes of fatty infiltra- tion of the liver are alcohol abuse, obe- sity, malnutrition, chemotherapy, hyperalimentation, diabetes, steroid CASE REPORT Fig. 4. Post-contrast CT scan of the abdomen, delayed phase, showing a bulky spleen. This is typ- ically seen in a non-alcoholic fatty liver. administration, Cushing's syndrome and radiation hepatitis. Despite a more typical pattern of diffuse parenchymal infiltration, residual foci of normal unaffected liver parenchyma can be present, usu- ally at the periphery of the liver or abutting the porta hepatis and gall- bladder fossa. These may be mistaken for neoplastic lesions unless one is aware of the patterns of fatty sparing.' Magnetic resonance imaging (MRI) can reliably differentiate nodu- lar fatty infiltration of the liver from metastatic disease, in equivocal cases. Sequences include a combination of in-phase and opposed-phase gradi- ent-echo imaging, fat saturation tech- niques and ferumoxide-enhanced MRIY Splenic enlargement is commonly seen in patients with non-alcoholic fatty liver, and the recognition of this association may halt further attempts at evaluating the cause of the splenic enlargement. 4 References 1. Haaga JR, Lanzieri CF. Computed Tomography and Magnetic Resonance Imaging of the Whole Body. St Louis, Missouri: Mosby-year Book, 1994: 956-959. 2. Kroncke Tl.Multifocal nodular fatty infiltration of the liver mimicking metastatic disease on CT: Imaging findings and diagnosis using MR imaging. Eur Radiol2000; 10: 1095-1100. 3. Hirohashi S. Nondiffuse fatty change of the liver: Discerning pseudotumour on MR images enhanced with ferumoxide: Initial observa- tions. Radiology 2000 November 217: 415-420. 4. Tsushima Y. 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