Value of MR imaging in evaluating focal fatty infiltration of the liver: preliminary study.

Focal fatty infiltration of the liver is a well-known entity that occasionally mimics metastatic disease on ultrasonographic (US) and computed tomographic (CT) scans and requires biopsy for diagnosis. To determine if high-field-strength magnetic resonance (MR) imaging might be useful in the differential diagnosis of the lesions, the authors compared US, CT, and MR findings in three patients with biopsy-proved fatty hepatic lesions. Areas of focal fatty infiltration were hyperechoic on US scans and had low attenuation on CT scans. No mass effect of the lesions on vascular structures or liver contours was observed, particularly on contrast material-enhanced CT scans. For all three patients, MR findings suggested the correct diagnosis by demonstrating focal high signal intensity on spin-echo T1- and T2-weighted images. On the basis of these preliminary findings, it appears that focal fatty infiltration of the liver may be differentiated from metastatic disease by means of high-field-strength MR imaging.     

Solitary defect on liver sulfur colloid imaging secondary to focal fatty infiltration

Radionuclide liver-spleen imaging using Tc-99m SC may identify focal defects on routine examinations. Fatty infiltration has generally been described as a diffuse process in the liver that may be manifested on Tc-99m SC liver imaging as a nonhomogeneous pattern of radiopharmaceutical distribution or multiple small defects. This case demonstrates a focal defect on radionuclide imaging, simulating a space-occupying lesion that ultimately proved to be focal fatty infiltration. Although not an uncommon finding on CT, to the authors' knowledge this has not been reported in the nuclear medicine literature to date.     

Multifocal fatty infiltration of the liver: report of six cases

Images of computed tomography (CT), ultrasonography (US), angiography and radionuclide imaging were analyzed in six cases of multifocal fatty infiltration of the liver. Histologic confirmation of fatty infiltration was obtained in one patient by percutaneous biopsy. In the remaining patients, presumptive confirmation of the diagnosis was based on the CT number in one patient and partial or complete resolution of the lesions on repeat CT scans or US in 4 patients. CT and US were performed in all six patients. CT scans demonstrated multiple round areas of low attenuation within both lobes of the liver in all cases. US studies showed hyperechoic foci in three cases and diffuse inhomogeneous hyperechogenicity in three cases. Hepatic arteriograms in five cases and liver scintigrams in four cases showed no evidence of space-occupying lesions. In all cases, the lesions completely or partially resolved in follow-up CT and US, and in four cases the lesions disappeared within two months, so follow-up examinations within about 2 months are necessary to differentiate these from liver neoplasms.     

弥漫型脂肪肝内局灶性病变的CT诊断

目的 研究在弥漫型脂肪肝背景下肝局灶性病变的CT特征,以提高对其诊断的准确率.资料与方法 回顾性分析40例弥漫型脂肪肝合并局灶性病变(35例)或残存肝岛(5例)患者的CT资料,观察脂肪肝对肝局灶性病变CT表现的影响.结果 40例弥漫型脂肪肝中,26例合并多发局灶性肝病变,9例合并单发病变,5例残存肝岛. 35例肝局灶性病变中,转移瘤18例 ,肝细胞癌(HCC)术后复发2例,血管瘤8例,多发囊肿5例,多发腺瘤及单发局灶性结节增生(FNH)各1例.CT平扫肝局灶性病变相对密度随脂肪肝程度而异,边界多不清,增强后强化方式则与无脂肪肝背景的肝内病变相似.结论 弥漫型脂肪肝内局灶性病变,其CT表现与正常背景下有所差异,增强检查尤其是动态增强对病变的诊断与鉴别具有重要意义;对不典型病例,随访对比有助于正确诊断.     

Fat in the liver: diagnosis and characterization

The purpose of this article is to provide an update on imaging techniques useful for detection and characterization of fat in the liver. Imaging findings of liver steatosis, both diffuse steatosis and focal fatty change, as well as focal fatty sparing, are presented. In addition, we will review computed tomography (CT) and magnetic resonance (MR) findings of focal liver lesions with fatty metamorphosis, including hepatocellular carcinoma, hepatocellular adenoma, focal nodular hyperplasia, angiomyolipoma, lipoma, and metastases.     

Focal sparing around the gallbladder in fatty liver: an useful sign in the diagnosis of borderline cases by CT

The role of CT in the diagnosis of fatty liver is well established. CT has been proved to be a useful noninvasive tool for the demonstration of fatty infiltration of the liver. The characteristic finding is a diffuse decrease in the attenuation within the liver compared with that of the spleen. Commonly, fatty infiltration of the liver is generalized and both CT scans and sonograms can easily demonstrate changes related to this condition. Sometimes, fatty infiltration of the liver is focal and occasionally, it is generalized with focal sparing of the normal liver tissue creating some problems in the diagnosis. Recently, some reports have mentioned the appearance of a focal sparing area in the generalized fatty liver. We often found a high attenuation region around the gallbladder bed in the fatty liver patients on CT examination. There appears to be some relationship between the high density around the gallbladder area and the fatty liver. A retrospective study was undertaken to evaluate the relationship. In this paper, we presented the CT scans of 57 fatty liver cases and compared them with the CT scans of 50 normal patients to discuss the possible cause of the phenomenon and its usage in the diagnosis of the fatty liver.     

Focal fatty infiltration of the liver simulating metastatic disease

Two cases are reported in which multiple, well-defined lesions of the liver, as seen on computed tomographic (CT) scans and sonograms, were thought to represent metastatic malignancy. Results from radionuclide scans and biopsies (and surgery in one case) indicated the correct diagnosis was fatty infiltration of the liver. Focal fatty infiltration should be considered in cases of multiple discrete hepatic lesions, especially in patients with a predisposing condition. Radionuclide studies and biopsies may be needed to confirm the diagnosis by CT.     

Focal fatty infiltration of the liver: analysis of prevalence and CT findings in children and young adults

OBJECTIVE: Focal fatty infiltration of the liver, a benign entity that can be confused with a malignant lesion, is well characterized in adults but not in children. The goal of this study was to determine by CT the prevalence and characteristics of focal fatty infiltration in children and young adults. MATERIALS AND METHODS: We retrospectively analyzed 305 consecutive contrast-enhanced abdominal CT examinations of 218 children and young adults with no known liver disease, performed during 2 years at our institution, to identify focal fatty infiltration of the liver. The imaging criterion for focal fatty infiltration of the liver on helical CT was a geometric or ovoid low-attenuation area adjacent to the falciform ligament, gallbladder fossa, or porta hepatis. If a patient's findings met the CT criterion for focal fatty infiltration of the liver, all previous abdominal CT and MR imaging examinations performed for that patient were reviewed to assess the evolution of focal fatty infiltration of the liver. RESULTS: Of 218 children and young adults, 20 (9.2%) met the CT criterion for focal fatty infiltration of the liver. In our population, focal fatty infiltration of the liver was identified only adjacent to the falciform ligament. The prevalence of focal fatty infiltration of the liver increased significantly with advancing age: 0% for ages 1 month-4 years; 7.3% for 5-9 years; 10.2% for 10-14 years, and 25.6% for 15-19 years (p < 0.0001). CONCLUSION: Focal fatty infiltration of the liver was identified in 9.2% of patients in our population, and occurrence of this lesion in children increases significantly with advancing age. However, focal fatty infiltration of the liver is uncommon in infants and young children and should be a diagnosis of exclusion.     

CT studies of the liver in vitro: a report on 82 cases with pathological correlation.

Eighty-two liver specimens were studied by both computed tomography (CT) and pathological examination with serial sectioning. In vitro CT studies showed low density structures within 57 normal livers to be due to portal and hepatic vessels but not to bile ducts. A liver with a minimum of 70% fatty infiltration could be diagnosed correctly on CT. Concerning the presence or absence of circumscribed liver disease, sensitivity was 80% and specificity was 84%. With respect to the total number of space occupying liver lesions (n = 364 in 18 specimens), sensitivity was 72%. The smallest metastases detectable on CT were 0.5 cm in diameter, but CT disclosed focal lesions of this small size in only 15% of the cases. In contrast to previously reported in vivo CT studies, metastases were often found to be of higher density than normal liver tissue in vitro.     

Detection of hepatic metastases by proton spectroscopic imaging. Work in progress

Fourteen patients with hepatic metastases underwent magnetic resonance (MR) imaging using both the conventional spin-echo (SE) technique and the opposed phase of the proton spectroscopic imaging method. The opposed image showed more lesions than the conventional SE image in five patients and provided better contrast between the liver parenchyma and metastases in two patients. Four of these seven patients had associated fatty infiltration of the liver. When compared with the computed tomography (CT) scan, the opposed image either showed more lesions or provided better contrast in six patients, four of whom had fatty infiltration. More significantly, the MR image showed several 1-cm lesions not shown by the CT scan in one patient. Our study discloses the possible explanations for the increased sensitivity of the opposed image in detecting hepatic metastases.     

Hepatic steatosis: combined echography-computerized tomography imaging

The authors report their experience with the combined use of US and CT in the study of diffuse and subtotal fatty infiltration of the liver. An apparent disagreement was initially found between the two examinations in the study of fatty infiltration. Fifty-five patients were studied with US and CT of the upper abdomen, as suggested by clinics. US showed normal liver echogenicity in 30 patients and diffuse increased echogenicity (bright liver) in 25 cases. In 5 patients with bright liver, US demonstrated a solitary hypoechoic area, appearing as a "skip area", in the quadrate lobe. In 2 patients with bright liver, the hypoechoic area was seen in the right lobe and exhibited no typical US features of "skip area". Bright liver was quantified by measuring CT density of both liver and spleen. The relative attenuation values of spleen and liver were compared on plain and enhanced CT scans. In 5 cases with a hypoechoic area in the right lobe, CT findings were suggestive of hemangioma. A good correlation was found between bright liver and CT attenuation values, which decrease with increasing fat content of the liver. Moreover, CT attenuation values confirmed US findings in the study of typical "skip areas", by demonstrating normal density--which suggests that CT can characterize normal tissue in atypical "skip areas".     

CT and MR imaging of fatty tumors of the liver

The presence of fat in hepatic masses narrows the range of differential diagnoses down to hepatic angiomyolipoma, lipoma, adenoma, hepatoma, metastatic fatty tumors of the liver, focal fatty infiltration of the liver, and extrahepatic fatty masses such as intraperitoneal implants from malignant teratomas, and packed omentum. We report six hepatic tumors containing fat (lipoma, hepatocellular carcinoma, and calcified mass with fat-fluid level) with CT and magnetic resonance (MR) imaging. The distribution of fat was diffuse in the lipomas and some hepatocellular carcinomas and localized in other hepatocellular carcinomas and fat-fluid masses. The density ranged from - 100 to 0 HU. High intensity areas on both T1- and T2-weighted MR images corresponded to the hypodense areas on CT.     

Imaging of hepatic steatosis and fatty sparing

Radiology has gained importance in the non-invasive diagnosis of hepatic steatosis. Ultrasonography is usually the first imaging modality for the evaluation of hepatic steatosis. Unenhanced CT with or without dual kVp measurement and MRI with in and out of phase sequence can allow objective evaluation of hepatic steatosis. However, none of the imaging modalities can differentiate non-alcoholic steatohepatitis/fatty liver disease from simple steatosis. Evaluation of hepatic steatosis is important in donor evaluation before orthotopic liver transplantation and hepatic surgery. Recently, one-stop shop evaluation of potential liver donors has become possible by CT and MRI integrating vascular, parenchymal, volume and steatosis evaluation. Moreover hepatic steatosis (diffuse, multinodular, focal, subcortical, perilesional, intralesional, periportal and perivenular), hypersteatosis and sparing (geographic, nodular and perilesional or peritumoral) can cause diagnostic problems as a pseudotumor particularly in the evaluation of oncology patients. Liver MRI is used as a problem-solving tool in these patients. In this review, we discuss the current role of radiology in diagnosing, quantifying hepatic steatosis and solutions for diagnostic problems associated with fatty infiltration and sparing.     

Focal manifestations of diffuse liver disease at MR imaging.

Detection and exclusion of focal liver lesions is especially difficult in patients with diffuse liver disease. Magnetic resonance (MR) imaging may be particularly valuable in these patients. By judicious comparison of appropriate pulse sequences, normal and hypertrophic liver may be distinguished from atrophic, neoplastic, or otherwise abnormal hepatic parenchyma. Chemical shift (lipid-sensitive) techniques allow definitive identification of fatty liver, including focal fatty infiltration or focal sparing. T2-weighted and T2*-weighted images allow identification of iron overload, depicting malignancies as focal masses without iron. Analysis of signal intensity and internal morphology allows confident distinction between regenerative nodules and hepatocellular carcinoma in most instances, and allows diagnosis of early carcinoma within regenerative nodules. MR imaging provides capabilities for noninvasive characterization of liver tissue beyond those available with other noninvasive modalities.     

Imaging features of perivascular fatty infiltration of the liver: initial observations

PURPOSE: To retrospectively identify and describe the imaging features that represent perivascular fatty infiltration of the liver. MATERIALS AND METHODS: The institutional review board approved the study and waived informed consent. The study complied with the Health Insurance Portability and Accountability Act. Ten patients (seven women, three men; mean age, 78 years; range, 31-78 years) with fatty infiltration surrounding hepatic veins and/or portal tracts were retrospectively identified by searching the abdominal imaging teaching file of an academic hospital. The patients' medical records were reviewed by one author. Computed tomographic (CT), magnetic resonance (MR), and ultrasonographic (US) imaging studies were reviewed by three radiologists in consensus. Fatty infiltration of the liver on CT images was defined as absolute attenuation less than 40 HU without mass effect and, if unenhanced images were available, as relative attenuation at least 10 HU less than that of the spleen; on gradient-echo MR images, it was defined as signal loss on opposed-phase images compared with in-phase images; and on US images, it was defined as hyperechogenicity of liver relative to kidney, ultrasound beam attenuation, and poor visualization of intrahepatic structures. Perivascular fatty infiltration of the liver was defined as a clear predisposition to fat accumulation around hepatic veins and/or portal tracts. For multiphase CT images, the contrast-to-noise ratio was calculated for comparison of spared liver with fatty liver in each imaging phase. RESULTS: Fatty infiltration surrounded hepatic veins in three, portal tracts in five, and both hepatic veins and portal tracts in two patients. Six of the 10 patients had alcoholic cirrhosis, two reported regular alcohol consumption (one of whom had acquired immunodeficiency syndrome and hepatitis B), one was positive for human immunodeficiency virus, and one had no risk factors for fatty infiltration of the liver. In three of the 10 patients, fatty infiltration was misdiagnosed as vascular or neoplastic disease on initial CT images but was correctly diagnosed on MR images. CONCLUSION: Perivascular fatty infiltration of the liver has imaging features that allow its recognition.     

Nondiffuse fatty change of the liver: discerning pseudotumor on MR images enhanced with ferumoxides-initial observations

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.     

Imaging the pediatric liver: MRI and CT

The livers of 27 children, 2 weeks to 16 years old, were examined with MRI and CT. Fourteen children had normal livers, 9 had focal liver disease, and 4 had diffuse liver disease. Normal intrahepatic venous anatomy was visualized more frequently with MRI than with CT, regardless of presence of disease, type of disease, or age. Focal hepatic lesions were either iso- or hypointense on relatively T1-weighted images and were hyperintense on T2-weighted images regardless of the pathology. In three cases, lesions seen with MRI were not detected with CT. In two other cases, CT was interpreted as equivocal or abnormal, but the liver was normal on MRI. MRI was superior to CT for evaluation of patency of the intrahepatic portion of the inferior vena cava. Other than in cases of fatty infiltration, CT provided no information additional to MRI. MRI has the potential to replace CT as a technique for imaging the pediatric liver in many cases, especially for infants and young children.     

FDG positron emission tomography in the surveillance of hepatic tumors treated with radiofrequency ablation

PURPOSE: Radiofrequency thermal ablation (RFA) is an emerging technique in the treatment of focal hepatic tumors. Magnetic resonance imaging (MRI) and computed tomography (CT) are currently used to monitor hepatic tumors after RFA for residual disease and recurrence. Fluorodeoxyglucose (FDG) positron emission tomography (PET) is an excellent imaging method for the detection of liver metastases, but it has not been thoroughly evaluated as an alternative to anatomic imaging in the surveillance of liver tumors treated with RFA. The purpose of this investigation was to determine the role of FDG-PET imaging in the surveillance of liver tumors treated with RFA. METHODS: Thirteen patients with histories of malignant tumors of the liver treated with RFA and who had received post-treatment FDG-PET scans were assessed retrospectively. One patient had two post-RFA FDG-PET scans, eight patients had concurrent MRI scans, and six patients had concurrent CT scans. Imaging findings were compared with the results of clinical follow-up. RESULTS: There were either recurrent tumors at the ablation site (8 patients) or new metastases (3 patients) in 11 patients. FDG-PET identified all 11 cases and did not misidentify any cases. Of the seven patients with positive PET findings who received an MRI scan, three were also positive on MRI (42.9%); the other four cases were either negative or equivocal. Of the four patients with positive PET findings who received a CT scan, only two had positive CT scan findings (50%). All recurrences diagnosed by PET were confirmed on clinical follow-up. CONCLUSION: In this preliminary study, FDG-PET was superior to anatomic imaging in the surveillance of patients treated with RFA for malignant hepatic tumors.     

放射性核素显像与常规CT对肝局灶性结节增生的诊断价值

目的分析放射性核素显像和常规CT诊断肝局灶性结节增生（FNH）的各自优势,探讨二者结合对FNH的诊断价值。方法回顾性分析32例（男15例,女17例,年龄22～59岁）FNH患者的病理及影像资料。32例患者均行常规CT（平扫及增强）检查。其中24例行放射性核素显像,在肝胶体显像时加做融合图像采集,经计算机处理后得到SPECT及定位CT的融合图像。对显像发现病灶的患者行肝胆动态显像,包括血流灌注相、早期相及延迟相。检查结果的比较采用四格表∥检验或四格表Fisher确切概率法检验。结果32例患者共切除32个病灶,均为单发。病理均为FNH,其中25个为病理经典型,7个为病理非经典型;大病灶（最大径〉3cm）20个,小病灶（最大径≤3cm）12个。32例患者常规CT检出所有病灶,确诊病理经典型FNH15个,其中大病灶10个,小病灶5个;其余病灶均误诊或诊断不明确。24例患者进行放射性核素显像,结果示大病灶11个,其中病理经典型7个,病理非经典型4个;其余病灶诊断不明确或未检出。常规CT与放射性核素显像对病理经典型病灶确诊率分别为60．0％（15／25）和38．9％（7／18）,病理非经典型为0／7和4／6;大病灶为50．O％（10／20）和73．3％（11／15）,小病灶为41．7％（5／12）和0／9;对FNH的总确诊率为46．9％（15／32）和45．8％（11／24）。24例行放射性核素显像患者同时行常规CT检查,2种方法结合共确诊FNH18个,总确诊率75．0％（18／24）。在病理非经典型、小病灶FNH的诊断方面,常规CT与放射性核素显像比较,差异有统计学意义（P=0．02,0．04）;2种方法结合对FNH的总确诊率与单种方法的确诊率比较,差异均有统计学意义（χ2=4．48和4．27,P均〈0．05）。结论常规CT与放射性核素显像对FNH的诊断各有优势;二者结合可提高对FNH的总确诊率。     

脂肪肝：MRI影像表现及MRI序列选择

目的：选择评估脂肪肝的MRI序列和认识脂肪肝的MRI影像表现以帮助鉴别诊断,方法：18例脂肪肝病人进行了肝脏平扫和增强MRI,采用屏气同,反相位T1加权梯度回波序列,2D FLASH加脂肪抑制T1WI以及HASTE T2WI。结论：18例肝脂肪变中伴有7例肝癌,2例血管瘤,1例囊肿,5例肝硬化;弥漫型脂肪浸润6例,局灶型脂肪浸润12例,脂肪肝影像表现,T1WI同相位表现为稍高或等信号,反相位或加压脂T1WI呈低信号;T2WI呈稍高或等信号,部分脂肪肝伴脂内肿块在反相位或加压脂TWI上可见低信号肿块周边全周或部分环状高信号带,在增强MRI上无明显强化,有时见少量小血管进入其内,结论：同与反相位MRI能较好鉴别诊断脂肪肝,两者互补,缺一不可,可避免脂肪肝的误诊或汤诊。建议对疑有脂肪肝患者行同,反相位T1加权MRI扫描。