ross-sectional imaging findings of

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1 bdominal Imaging asaran et al. Imaging of Fat-ontaining Liver Lesions eyla asaran 1 Musturay Karcaaltincaba 1 Deniz kata 1 Nevzat Karabulut 2 Devrim kinci 1 Mustafa Ozmen 1 Okan khan 1 asaran, Karcaaltincaba M, Deniz, et al. Received June 7, 2004; accepted after revision September 22, Department of Radiology, Hacettepe University School of Medicine, Sihhiye, nkara 06100, Turkey. ddress correspondence to M. Karcaaltincaba (musturayk@yahoo.com). 2 Department of Radiology, Pamukkale University Hospital, Denizli, Turkey. JR 2005;184: X/05/ merican Roentgen Ray Society Pictorial Essay Fat-ontaining Lesions of the Liver: ross-sectional Imaging Findings with Emphasis on OJEIVE. The purpose of this pictorial essay is to identify different types of liver lesions that contain fat. ross-sectional imaging findings of fat- or lipid-containing lesions can help in characterizing focal liver lesions. We searched our archive retrospectively and reviewed the literature for fat-containing liver lesions and identified 16 different types. ONLUSION. These lesions can contain macroscopic fat (i.e., angiomyolipoma, lipoma, liposarcoma, hydatid cyst, lipopeliosis, adrenal rest tumor, pseudolipoma, hepatic teratoma, pericaval fat, extramedullary hematopoiesis, and metastases) or intracellular lipid (i.e., focal steatosis, adenoma, focal nodular hyperplasia, regenerative nodules, and hepatocellular carcinoma).,, and sonographic findings of these lesions can help in characterization by allowing specific diagnosis or narrowing the differential diagnosis of liver lesions. ross-sectional imaging findings of fat- or lipid-containing lesions can help in characterizing focal liver lesions. We searched our archive retrospectively and reviewed the literature for fat-containing liver lesions and identified 16 different types. Liver lesions can contain macroscopic fat or intracellular lipid (Table 1). Macroscopic fatcontaining liver lesions include angiomyolipoma, lipoma, liposarcoma, hydatid cyst, lipopeliosis, adrenal rest tumor of the liver, pseudolipoma of a Glisson capsule, hepatic teratoma, fat adjacent to intrahepatic inferior vena cava (pericaval fat), extramedullary hematopoiesis, and metastases. Macroscopic fat-containing lesions can be easily characterized on and by negative Hounsfield values and hyperintensity on T1- and T2-weighted images and signal loss on fat-saturated MR images, respectively. Fat droplets can be seen in hydatid cysts. Intracellular lipid-containing lesions include focal hepatic steatosis, hepatic adenoma, focal nodular hyperplasia (FNH), regenerative nodules, and hepatocellular carcinoma (H). Intracellular lipid-containing lesions can be characterized objectively by chemical shift techniques (in- and out-of-phase T1-weighted gradient-echo images) and dynamic gadolinium-enhanced studies. Sonography is currently the first screening method for focal hepatic lesions, but sonographic findings of many hepatic nodules are nonspecific. Fat generally produces high echogenicity when present in nodular lesions on hepatic sonographic screening. However, hyperechogenicity is also characteristic of some non fat-containing lesions such as cavernous hemangioma. ecause hyperechoic liver nodules cannot be characterized on sonography, subsequent examination using, conventional, or even fine-needle aspiration cytology is necessary in symptomatic or oncology patients. The characteristics of some nodules with fatty components can also be nonspecific, because of the lack of sufficient lipid pixels. hemical shift gradient-echo imaging is a readily available technique that can help to determine with certainty whether a given hyperechoic nodule contains fat [1]. JR:184, pril

2 asaran et al. Intracellular Lipid-ontaining Liver Lesions Focal Hepatic Steatosis Fatty change in the liver can result from excessive triglyceride deposition, and it may be uniform, patchy, or focal. Focal hepatic steatosis may mimic the appearance of hyperechogenic mass lesions such as hemangioma, angiolipoma, lipoma, or metastasis on sonography. Recognition of diffuse hepatic steatosis on requires liver attenuation to be 8 10 H lower than that of the spleen on unenhanced images. Focal hepatic steatosis of the liver may present as focal lesions [2]; is common in the medial segment of the left lobe of the liver, adjacent to the falciform ligament, central tip of segment IV, and, less commonly, along the gallbladder; and can be multifocal. Sometimes varying degrees of hepatic steatosis of the liver can occur, and focal hypodense areas (more fatty) can be present in diffusely steatotic liver on (Fig. 1). is particularly effective in evaluating focal hepatic steatosis. Out-of-phase T1- weighted gradient-echo imaging is a highly accurate technique to distinguish focal hepatic steatosis from neoplastic masses. Focal hepatic steatosis is isointense or hyperintense to liver on in-phase images and loses signal homogeneously on out-of-phase images, which is highly diagnostic for focal steatosis (Fig. 2). The morphology of focal hepatic steatosis most often permits distinction from fat within tumors, such as H, adenoma, angiomyolipoma, or lipoma. Focal hepatic steatosis usually has angular, wedge-shaped margins that are usually relatively well defined and appear isointense to liver on gadolinium-enhanced T1-weighted MR images [3]. Diagnosis is also suggested by lack of mass effect on vessels or the biliary system. t times, blood vessels traversing the focal steatotic areas are identified. H The histologic pattern, the degree of tumor differentiation, the amount of fibrosis, the presence of internal necrosis or hemorrhage, and the intracellular content of glycogen, fat, or metal ions greatly affect the radiologic appearance of the H. These factors affect Fig year-old woman with breast cancer., xial image shows diffuse fatty infiltration of liver and hypodense lesion (arrow) suspicious for metastasis in segment IV. and, xial in-phase () and out-of-phase () images show greater signal drop of lesion in (arrow, ), consistent with hypersteatosis (more fatty) compared with diffusely fatty infiltrated liver JR:184, pril 2005

3 Imaging of Fat-ontaining Liver Lesions particularly the appearance, which may range from hypointense to iso- or hyperintense on T1-weighted images and from hypointense to hyperintense on T2-weighted images [4]. H occasionally contains fat (Fig. 3). H with fatty metamorphosis was found in up to 17% of the lesions. Some investigators have suggested that fatty metamorphosis is the principal cause of hyperintensity on T1-weighted images of some Hs and that this finding can help in establishing the diagnosis [4, 5], but other causes of hyperintensity on T1-weighted images with conventional spin-echo sequences can be present such as Fig year-old woman who had prior ovarian cancer surgery and multiple liver lesions., Sonogram shows multiple hyperechogenic lesions.. and, xial T1-weighted in-phase () and out-of-phase () images show multiple lesions with signal drop on opposed-phase images consistent with focal fatty infiltrations. MR images were obtained on 0.5-T system with TEs of 14 and 6 for inand out-of-phase images, respectively. content of glycogen, subacute hemorrhage, clear cell formation, and excessive copper accumulation [5]. In characterizing H for fat content, chemical shift imaging has been reported to be very useful in the detection of lipomatous nodules in cirrhotic liver [3]. However, benign regenerative nodules can also contain fat. FNH FNH is a well-circumscribed mass, lacking a true capsule, and is characterized by a central scar. The typical appearance is usually isointense or nearly isointense on both T1- weighted and T2-weighted images. The central scar appears hypointense on T1-weighted images and hyperintense on T2-weighted images. The lesion shows intense enhancement, with the central scar being unenhanced in the arterial phase of gadolinium-enhanced dynamic. In the portal phase, the lesion undergoes rapid washout of contrast material, becoming isointense to liver. The central scar may show delayed enhancement [4]. In a recent study, the authors reported markedly heterogeneous FNH due to extensive intralesional fat [6]. Previously, investigators reported intratumoral JR:184, pril

4 asaran et al. Fig year-old man with cirrhosis. and, xial in-phase () and out-of-phase () MR images show signal drop of lesion (arrow) in segment V. and D, rterial () and delayed (D) phase axial gadolinium-enhanced MR images show hypervascularity and contrast washout of hepatocellular carcinoma (arrow), respectively. D Fig year-old woman with hepatic adenoma. and, xial T1-weighted in-phase () and out-of-phase () images show signal drop of peripheral lesion (arrow, )., MR image shows enhancing lesion (arrow) in arterial phase, consistent with adenoma JR:184, pril 2005

5 Imaging of Fat-ontaining Liver Lesions Fig year-old woman with tuberous sclerosis. xial image shows fat-containing liver lesion (arrow) consistent with hepatic angiomyolipoma. Note bilateral multiple renal angiomyolipomas. fat depicted on MR images of FNH, and they considered it as an exaggerated expression of this patient s native hepatic disease characterized by fatty liver [7]. Hepatocellular denoma Hepatocellular adenoma is an uncommon primary benign tumor. Oral contraceptives and androgen steroid therapy have been identified as definitive causes. denoma presents as a solitary lesion in most cases and is typically a well-circumscribed tumor. Histologically, adenoma is composed of cords of hepatocytes, which contain increased amounts of glycogen and sometimes fat. The content of glycogen and fat is the main element responsible for the hyperintensity of adenoma on T1- weighted images. Nevertheless, areas of internal subacute hemorrhage are markedly hyperintense on T1-weighted images. hemical shift imaging (Fig. 4) can confirm fat content by showing a decrease in tumor signal intensity on opposed-phase images [4]. On dynamic contrast-enhanced, the lesion shows early enhancement during the arterial phase, with rapid washout accounting for its typical hypervascular nature [8]. Macroscopic Fat-ontaining Liver Lesions ngiomyolipoma Hepatic angiomyolipoma is a rare tumor, which may occur as a solitary mass or as an associated finding with tuberous sclerosis [9]. ngiomyolipoma is a benign mesenchymal tumor, with a mixture of mature fat, smooth muscle, and thick-walled blood vessels. It occurs frequently in the kidney but rarely in liver (Fig. 5). Patients usually have no symptoms, and most of these tumors are found incidentally on routine sonographic studies. The accuracy of preoperative diagnosis is very low as a result of variable imaging appearances due to the varying content of the three components and the rarity of the lesion. The fat component of angiomyolipoma varies between 10% and 90% [9]. In one study, angiomyolipoma (11/12 lesions) appeared as a hypodense lesion on unenhanced scans and markedly enhanced on the arterial phase with central Fig year-old man with an incidentally found echogenic liver lesion. xial image shows pure fat-containing lesion consistent with lipoma (arrow). Note peripheral location of lesion. JR:184, pril

6 asaran et al. Fig year-old woman with acute leukemia. xial image shows fat-containing lesion (arrows) in right lobe extending to caudate lobe that was not present on 1 year ago. ttenuation measurement of lesion revealed 32 H. iopsy of lesion revealed hepatic necrosis with fatty replacement consistent with lipopeliosis. vascular opacification in eight lesions [9]. On the portal venous phase, eight lesions remained enhancing with central vessels seen in six lesions. We suggest that presence of central vessels within the lesions may be a characteristic feature of angiomyolipoma. The feeding blood vessels can be seen in other hypervascular lesions such as H and FNH, but the vessels in those cases usually are located in the periphery of the lesions. is also an important diagnostic technique that allows fat suppression and multiphase dynamic contrast-enhanced scanning. The lesions have various signal intensities from slight to strong hyperintensity on fast spin-echo T2-weighted images because of the different proportion of smooth muscle and vessels. Dynamic contrast-enhanced imaging on is similar to that of with the central vessels seen in the lesions [9, 10]. Metastatic Liver Disease Metastatic liver disease is one of the most common problems in oncology patients. Liver metastases generally represent the histotype of the primary neoplasm. Fat-containing primary tumors such as teratoma, liposarcoma, Wilms tumor, and renal cell carcinoma that are high in signal intensity on T1-weighted images can metastasize to the liver [3, 4]. Lipoma and Liposarcoma Hepatic lipomas are rarer than angiomyolipomas and can occur sporadically. They are homogeneous and circumscribed and show fat attenuation on and do not enhance after IV administration of contrast Fig year-old woman with liver hydatid disease. xial image shows two liver hydatid cysts. Note hypodense fat droplets ( 25 H) within medially located cyst (arrow) JR:184, pril 2005

7 Imaging of Fat-ontaining Liver Lesions Fig year-old woman with prior hydatid cyst surgery. xial image shows fat-containing lesion (arrow) consistent with omentopexy area due to prior surgery for hydatid cyst. material [2, 11] (Fig. 6). On, lipomas can be multiple and appear as fatty tumors that are hyperintense on T1-weighted images and hypointense on fat-suppressed T2- weighted images [3]. Liposarcoma is a rare mesenchymal malignant tumor, which usually originates in the retroperitoneum and the extremities. Primary liver liposarcoma is extremely rare, and what is believed to be the first reported case was published in Sonography of liver liposarcoma showed a poorly defined, lobulated, infiltrating echogenic tumor with shadowing and heterogeneity secondary to areas of hemorrhage and necrosis. low-attenuation mass of fat density was confirmed on [12]. Lipopeliosis Peliosis hepatis is characterized by dilated, blood-filled sinusoids. However, lipopeliosis is described as another distinct peliosis-like lesion that occurs in a transplanted steatotic liver after centrilobular hepatocyte injury and necrosis [13, 14]. Lipopeliosis is an unusual liver lesion in which sinusoids become engorged by fat globules. lthough lipopeliosis is seen in the setting of necrosis of fatty hepatocytes in the transplanted liver, any fatty condition of the liver with a superimposed ischemic injury may result in a similar lesion [13, 14]. To our knowledge, findings of lipopeliosis are first described in our patient (Fig. 7). Hepatic Hydatid yst The liver is the organ most commonly affected by hydatid cysts. Mendez Montero et al. [15] reported fat fluid levels inside hydatid cysts in two patients in the form of either fat fluid levels or fat droplets (Fig. 8). They identified a large perforation in the cyst wall communicating with a main biliary radicle on both sonography and in two of the cysts, Fig year-old man with abdominal pain who underwent examination., xial image shows fatty lesion (arrow) adjacent to intrahepatic inferior vena cava., Sagittal reformatted image shows protrusion of apical portion of pericaval fat into inferior vena cava lumen (arrow). JR:184, pril

8 asaran et al. TLE 1 Fat-ontaining Lesions of Liver Lesions Preferred Diagnostic Imaging Method for Fat ontent Intracellular Focal hepatic steatosis Hepatocellular carcinoma Hepatic adenoma Focal nodular hyperplasia (rare) Regenerative nodules Macroscopic ngiomyolipoma, Lipoma, Liposarcoma Hydatid cyst (in the form of droplets) Lipopeliosis drenal rest tumor of liver, Pseudolipoma of Glisson capsule Hepatic teratoma, Pericaval fat Metastases Focal hepatic extramedullary hematopoiesis and they suggested that fat droplets inside the hydatid cysts are derived from the lipid elements in bile [15]. lso, omentopexy changes seen after hydatid cyst surgery can mimic fatty liver lesions (Fig. 9). Focal Fat djacent to the Intrahepatic Inferior Vena ava Focal fat can be seen adjacent to the intrahepatic inferior vena cava on (Fig. 10). This lesion can be a normal variant, which is more frequently seen in patients with chronic liver disease and can mimic a fat-containing liver lesion [16]. Miscellaneous lso, adrenal rest tumor of the liver, pseudolipoma of a Glisson capsule, and hepatic teratoma can contain fat. Recently, focal intrahepatic extramedullary hematopoiesis has been reported to contain fat [17]. onclusion Fat can be present in a variety of benign and malignant liver lesions. The presence of fat can allow specific diagnosis or narrow the differential diagnosis of liver lesions. Preferred imaging methods for the diagnosis of fat content are shown in Table 1. References 1. Martin J, Puig J, Falco J, et al. Hyperechoic liver nodules: characterization with proton fat water chemical shift MR imaging. Radiology 1998;207: Fultz PJ, Hampton WR, Skucas J, Sickel JZ. Differential diagnosis of fat-containing lesions with abdominal and pelvic. Radiology 1993;13: Semelka R, raga L, rmao D, et al. Disease of the hepatic parenchyma. In: Semelka R, ed. bdominal-pelvic. New York, NY: Wiley-Liss Press, 2002:60, 106, 249, artolozzi, ioni D, Donati F, Lencioni R. Focal liver lesions: MR imaging pathologic correlation. Eur Radiol 2001;11: Martin J, Sentis M, Puig J, et al. omparison of inphase and opposed-phased GRE and conventional SE MR pulse sequences in T1-weighted imaging of liver lesions. J omput ssist Tomogr 1996;20: Stanley G, Jeffrey R Jr, Feliz. findings and histopathology of intratumoral steatosis in focal nodular hyperplasia: case report and review of the literature. J omput ssist Tomogr 2003;27: Mitchell DG, Palazzo J, Hann HW, Rifkin MD, urk DL, Rubin R. Hepatocellular tumors with high signal on T1-weighted MR images: chemical shift MR imaging and histologic correlation. J omput ssist Tomogr 1991;15: hung KY, Mayo-Smith WW, Saini S, et al. Hepatocellular adenoma: MR imaging features with pathologic correlation. JR 1995;165: Hooper LD, Mergo PJ, Ros PR. Multiple hepatorenal angiomyolipomas: diagnosis with fat suppression, gadolinium-enhanced. bdom Imaging 1994;19: Yan F, Zeng M, Zhou K, et al. Hepatic angiomyolipoma: various appearances on two-phase contrast scanning of spiral. Eur J Radiol 2002;41: Horton KM, luemke D, Hruban RH, Soyer P, Fishman EK. and MR imaging of benign hepatic and biliary tumors. RadioGraphics 1999;19: Khan, Sherlock DJ, Wilson G, utterworth D. Sonographic appearance of primary liver liposarcoma. J lin Ultrasound 2001;29: Ferrel L, ass N, Roberts J, scher N. Lipopeliosis: fat induced sinusoidal dilatation in transplanted liver mimicking peliosis hepatis. J lin Pathol 1992;45: ha I, Nathan, Ferrel L. Lipopeliosis: an immunohistochemical and clinicopathologic study of five cases. m J Surg Pathol 1994;18: Mendez Montero JV, rrazola Garcia J, Lopez Lafuente J, ntela Lopez J, Mendez Fernandez R, Saiz yala. Fat-fluid level in hepatic hydatid cyst: a new sign of rupture into the biliary tree? JR 1996;167: Gibo M, Murata S, Kuroki S. Pericaval fat collection mimicking an intracaval lesion on in patients with chronic liver disease. bdom Imaging 2001;26: Gupta P, Naran, uh YH, hung JS. Focal intrahepatic extramedullary hematopoiesis presenting as fatty lesions. JR 2004;182: JR:184, pril 2005