Unusual patterns of hepatic steatosis caused by the local effect of insulin revealed on chemical shift MR imaging

Diffuse and focal liver fat: advanced imaging techniques and diagnostic insights

The fatty liver disease represents a complex, multifaceted challenge, requiring a multidisciplinary approach for effective management and research. This article uses conventional and advanced imaging techniques to explore the etiology, imaging patterns, and quantification methods of hepatic steatosis. Particular emphasis is placed on the challenges and advancements in the imaging diagnostics of fatty liver disease. Techniques such as ultrasound, CT, MRI, and elastography are indispensable for providing deep insights into the liver's fat content. These modalities not only distinguish between diffuse and focal steatosis but also help identify accompanying conditions, such as inflammation and fibrosis, which are critical for accurate diagnosis and management.

Effects of liraglutide on intrapancreatic fat deposition in patients with type 2 diabetes

BACKGROUND & AIMS

Ectopic fat deposition is associated with worsening of glycemic control. This study was conducted to determine whether liraglutide reduces ectopic fat deposition, especially in pancreas, in patients with type 2 diabetes (T2D).

METHODS

We retrospectively recruited T2D patients who underwent abdominal unenhanced CT scans both before and after administration of liraglutide (N = 13) or glimepiride (N = 29). Using CT values of pancreas (P), liver (L) and spleen (S), we defined the indices of intrapancreatic and liver fat as P-S value and L-S value, respectively. Increase of each value suggests the reduction of each fat deposition.

RESULTS

The values of HbA1c (p = 0.0017) and body weight (p = 0.0081) decreased, and L-S (p = 0.0024) increased significantly after administration of liraglutide compared with those at baseline. Similarly, P-S tended to increase in the liraglutide group (p = 0.0547) and increased significantly in the liraglutide subgroup with fatty pancreas (p = 0.0303), defined as having baseline P-S less than -5. In the glimepiride group, P-S did not increase regardless of baseline P-S. Among patients with fatty pancreas, administration of liraglutide tended to be a significant factor for the change in P-S after adjustment for the change in HbA1c (p = 0.1090) and the change in visceral fat area (p = 0.1030).

CONCLUSIONS

Intrapancreatic fat deposition was decreased after treatment with liraglutide, but not glimepiride, in T2D patients with fatty pancreas. Liraglutide might reduce intrapancreatic fat deposition independently of decreases in HbA1c and visceral fat volume.

De novo non-alcoholic fatty liver disease after pancreatectomy: A systematic review

BACKGROUND

As operative techniques and mortality rates of pancreatectomy have improved, there has been a shift in focus to maintaining and improving the nutritional status of these patients as we continue to learn more about post-operative complications. Although pancreatic endocrine and exocrine insufficiencies are known complications of pancreatectomy, increased longevity of these patients has also led to a higher incidence of de novo fatty liver disease which differs from traditional fatty liver disease given the lack of metabolic syndrome.

AIM

To identify and summarize patterns and risk factors of post-pancreatectomy de novo fatty liver disease to guide future management.

METHODS

We performed a database search on PubMed selecting papers published between 2001 and 2022 in the English language. PubMed was last accessed 1 June 2022.

RESULTS

Various factors influence the development of de novo fatty liver including indication for surgery (benign vs malignant), type of pancreatectomy, amount of pancreas remnant, and peri-operative nutritional status. With an incidence rate up to 75%, de novo non-alcoholic fatty liver disease (NAFLD) can develop within 12 mo after pancreatectomy and various risk factors have been established including pancreatic resection line and remnant pancreas volume, peri-operative malnutrition and weight loss, pancreatic exocrine insufficiency (EPI), malignancy as the indication for surgery, and postmenopausal status.

CONCLUSION

Since majority of risk factors leads to EPI and malnutrition, peri-operative focus on nutrition and enzymes replacement is key in preventing and treating de novo NAFLD after pancreatectomy.

Case report: Peritumoral hepatic steatosis in a patient with a metastatic somatostatin-producing oligosymptomatic neuroendocrine neoplasm

Neuroendocrine neoplasms (NENs) comprise a heterogeneous collection of tumors derived from various neuroendocrine cells and are divided into functioning NEN and non-functioning NEN. Some NENs present with mild symptoms and can secrete somatostatin. These neoplasms are known as somatostatin-producing oligosymptomatic NENs. In this report, we describe a case of metastatic somatostatin-producing oligosymptomatic NEN with peritumoral hepatic steatosis and review the relevant literature. The patient was a 45-year-old woman who presented with mild steatorrhea and melena. A computed tomography scan revealed an enlarged pancreas protruding into the duodenum. Pathology after total pancreatectomy showed a grade 2 pancreatic NEN with positive somatostatin immunostaining. Enlarging masses on the liver were observed after the operation. Ultrasound examination revealed several lesions in the liver, with inner hypoechoic areas that showed rapid enhancement and fast washout on contrast-enhanced ultrasonography and with outer hyperechoic areas with continuous iso-enhancement. Therefore, the inner hypoechoic areas seen on contrast-enhanced ultrasonography were suspected to be true metastases. A biopsy confirmed this suspicion and indicated that the outer areas were peritumoral liver steatosis. This case highlights the importance of the imaging pattern described in this report for accurate diagnosis of metastatic NEN to avoid incorrect estimation of tumor size or a missed diagnosis on biopsy.

Prospective characterization of incident hepatic steatosis in pediatric and adolescent patients after total pancreatectomy with islet autotransplantation

BACKGROUND

Hepatic steatosis has been described as a common finding in adults following total pancreatectomy with islet autotransplantation (TPIAT) but it is unknown if this occurs in children and adolescents.

OBJECTIVES

To define the frequency of post-TPIAT hepatic steatosis in a sample of children and adolescents and to identify clinical predictors of incident steatosis post-TPIAT.

METHODS

In this prospective study, consecutive participants at least 1-month post-TPIAT underwent a liver MRI with proton density fat fraction (PDFF) and blood draw at our pediatric academic medical center between April 2021 and January 2022. Comparison clinical pre-TPIAT liver MRI or ultrasound and insulin use and graft function data were extracted from the medical record. T-tests were used for the comparison of means across continuous variables between participants with and without post-TPIAT steatosis.

RESULTS

A total of 20 participants (mean: 13 ± 4 years; 12 female) were evaluated. Mean liver PDFF at research MRI was 7.4 ± 6.2% (range: 2-25%). Seven participants (35%) had categorical hepatic steatosis (PDFF>5%) post-TPIAT, five of whom had pre-TPIAT steatosis, reflecting a 13% (2/15; 95% CI: 2-40%) incidence of post-TPIAT steatosis. Participant characteristics were not significantly different between subgroups with and without post-TPIAT steatosis. Mean PDFF at research MRI was not different between graft function subgroups (7.5% optimal/good vs. 7.3% marginal/failure; p = .96).

CONCLUSION

Our study shows a moderate prevalence but low incidence of hepatic steatosis in a small sample of children and adolescents post-TPIAT. This study raises questions about a causal relationship between TPIAT and hepatic steatosis.

Atypical Hepatic Steatosis Patterns on MRI After Total Pancreatectomy With Islet Autotransplant

OBJECTIVE. The purpose of this retrospective study was to investigate the prevalence and patterns of hepatic steatosis after total pancreatectomy with islet autotransplant (TPIAT) and to determine if the unique patterns of steatosis seen in this study correlated with islet graft function. MATERIALS AND METHODS. Fifty-two subjects who had undergone MRI after TPIAT were reviewed for the presence of hepatic steatosis. Patterns of steatosis were categorized into three groups: normal (no steatosis), homogeneous, and atypical. Demographics and outcomes were compared between the groups. Islet graft function 1 year after surgery was classified as full graft function, partial graft function, and graft failure. Statistical analysis was performed using ANOVA, Kruskal-Wallis, and Fisher exact tests. RESULTS. Sixty-three percent of patients had steatosis present on MRI after TPIAT (33 subjects of 52 total), and 48% (25/52) exhibited an atypical pattern. Twenty-four percent of the 37 patients who had MRI examinations before TPIAT showed steatosis preoperatively, yet none of these showed an atypical steatosis pattern. Islet graft function was not statistically different between the groups. The only statistically significant variable difference between the groups was body mass index (p = .02). CONCLUSION. Steatosis is a common finding after TPIAT, and atypical steatosis patterns frequently develop after the procedure, implying that the procedure itself is the causal factor. There was no correlation between islet graft function and the presence or pattern of steatosis. An atypical pattern of hepatic steatosis can therefore be considered an incidental finding after TPIAT and does not require additional workup or treatment.

Imaging-based diagnosis of benign lesions and pseudolesions in the cirrhotic liver

Liver cirrhosis is a leading cause of death worldwide, with 1-year mortality rates of up to 57% in decompensated patients. Hepatocellular carcinoma (HCC) is the most common primary tumor in cirrhotic livers and the second leading cause of cancer-related mortality worldwide. Annually, up to 8% of patients with cirrhosis develop HCC. The diagnosis of HCC rarely requires histological confirmation: in fact, according to the most recent guidelines, the imaging features of HCC are almost always sufficient for a certain diagnosis. Thus, the role of the radiologist is pivotal because the accurate detection and characterization of focal liver lesions in patients with cirrhosis are essential in improving clinical outcomes. Despite recent technical innovations in liver imaging, several issues remain for radiologists regarding the differentiation of HCC from other hepatic lesions, particularly benign lesions and pseudolesions. It is important to avoid misdiagnosis of benign liver lesions as HCC (false-positive cases) because this diagnostic misinterpretation may lead to ineligibility of a patient for potentially curative treatments or inappropriate assignment of high priority scores to patients on waiting lists for liver transplantation. This review presents a pocket guide that could be useful for the radiologist in the diagnosis of benign lesions and pseudolesions in cirrhotic livers, highlighting the imaging features that help in making the correct diagnosis of macroregenerative nodules; siderotic nodules; arterioportal shunts; hemangiomas, including fast-filling hemangiomas, hemangiomas with pseudowashout, and sclerosed hemangiomas; confluent fibrosis; pseudomasses in chronic portal vein thrombosis; and focal fatty changes.

Targeted pancreatic beta cell imaging for early diagnosis

Pancreatic beta cells are important in blood glucose level regulation. As type 1 and 2 diabetes are getting prevalent worldwide, we need to explore new methods for early detection of beta cell-related afflictions. Using bioimaging techniques to measure beta cell mass is crucial because a decrease in beta cell density is seen in diseases such as diabetes and thus can be a new way of diagnosis for such diseases. We also need to appraise beta cell purity in transplanted islets for type 1 diabetes patients. Sufficient amount of functional beta cells must also be determined before being transplanted to the patients. In this review, indirect imaging of beta cells will be discussed. This includes membrane protein on pancreatic beta cells whereby specific probes are designed for different imaging modalities mainly magnetic resonance imaging, positron emission tomography and fluorescence imaging. Direct imaging of insulin is also explored though probes synthesized for such function are relatively fewer. The path for successful pancreatic beta cell imaging is fraught with challenges like non-specific binding, lack of beta cell-restricted targets, the requirement of probes to cross multiple lipid layers to bind to intracellular insulin. Hence, there is an urgent need to develop new imaging techniques and innovative probing constructs in the entire imaging chain of bioengineering to provide early detection of beta cell-related pathology.

Focal fat deposition in the liver: diagnostic challenges on imaging

While focal fat deposition in the liver mostly occurs in typical locations related to non-portal venous supply, unusual patterns of focal fat deposition, including multi-nodular, mass-like, and perivascular patterns, mimic malignancies and cause diagnostic challenges. Patients with unusual focal fat deposition often have potential underlying etiologies such as diabetes, alcohol abuse, metabolic disease, or various medications/chemotherapy. Some cases can be explained by non-portal venous supply or ischemia. Chemical-shift MRI or contrast-enhanced ultrasound (CEUS) is useful for non-invasive diagnosis of focal fat deposition. We illustrate a series of US, CT, and MR imaging features of focal fatty deposition in the liver mimicking other conditions and seek possible causes. Understanding of imaging patterns of focal fat deposition and its potential causes can help a non-invasive diagnosis by performing confirmatory imaging tests and prevent unnecessary invasive procedures.

Imaging patterns and focal lesions in fatty liver: a pictorial review

Non-alcoholic fatty liver disease is the most common cause of chronic liver disease and affects nearly one-third of US population. With the increasing trend of obesity in the population, associated fatty change in the liver will be a common feature observed in imaging studies. Fatty liver causes changes in liver parenchyma appearance on imaging modalities including ultrasound, computed tomography (CT), and magnetic resonance imaging (MRI) and may affect the imaging characteristics of focal liver lesions (FLLs). The imaging characteristics of FLLs were classically described in a non-fatty liver. In addition, focal fatty change and focal fat sparing may also simulate FLLs. Knowledge of characteristic patterns of fatty change in the liver (diffuse, geographical, focal, subcapsular, and perivascular) and their impact on the detection and characterization of FLL is therefore important. In general, fatty change may improve detection of FLLs on MRI using fat suppression sequences, but may reduce sensitivity on a single-phase (portal venous) CT and conventional ultrasound. In patients with fatty liver, MRI is generally superior to ultrasound and CT for detection and characterization of FLL. In this pictorial essay, we describe the imaging patterns of fatty change in the liver and its effect on detection and characterization of FLLs on ultrasound, CT, MRI, and PET.

Imaging patterns of fatty liver in pediatric patients

Fatty liver can present as focal, diffuse, heterogeneous, and multinodular forms. Being familiar with various patterns of steatosis can enable correct diagnosis. In patients with equivocal findings on ultrasonography, magnetic resonance imaging can be used as a problem solving tool. New techniques are promising for diagnosis and follow-up. We review imaging patterns of steatosis and new quantitative methods such as proton density fat fraction and magnetic resonance elastography for diagnosis of nonalcoholic fatty liver disease in children.

Liver lipoma: a case report

Liver lipoma is a rare benign mesenchymal tumour without malignant degeneration. Lesions may be asymptomatic, nevertheless they may sometimes cause abdominal pain depending upon the size. Usually liver lipomas are an incidental finding during radiological examinations performed for other reasons, and there is no evidence of familiar genetic cluster or predisposing factors but it seems to have a strong association with impaired lipidic profile. In this report, we describe the case of a 72 year old female with a giant liver lipoma observed during an ultrasound examination. The clinical examination was completed with CT and MRI scans. Features of the lesion such as negative attenuation values on multiphasic CT examination and MRI signal drop-out on T₂ spectral presaturation with inversion recovery sequences, with no enhancement after administration of contrast medium, are suggestive for this kind of benign neoplasm. The purpose of this report is provide an anthological case of liver lipoma, helping to define the diagnostic features with imaging techniques.

The cheating liver: imaging of focal steatosis and fatty sparing

Focal steatosis and fatty sparing are a frequent finding in liver imaging, and can mimic solid lesions. Liver regional variations in the degree of fat accumulation can be related to vascular anomalies, metabolic disorders, use of certain drugs or coexistence of hepatic masses. CT and MRI are the modalities of choice for the noninvasive diagnosis of hepatic steatosis. Knowledge of CT and MRI appearance of focal steatosis and fatty sparing is crucial for an accurate diagnosis, and to rule-out other pathologic processes. This paper will review the CT and MRI techniques for the diagnosis of hepatic steatosis and the CT and MRI features of common and uncommon causes of focal steatosis and fatty sparing.

Insulin Protects Hepatic Lipotoxicity by Regulating ER Stress through the PI3K/Akt/p53 Involved Pathway Independently of Autophagy Inhibition

The detrimental role of hepatic lipotoxicity has been well-implicated in the pathogenesis of NAFLD. Previously, we reported that inhibiting autophagy aggravated saturated fatty acid (SFA)-induced hepatotoxicity. Insulin, a physiological inhibitor of autophagy, is commonly increased within NAFLD mainly caused by insulin resistance. We therefore hypothesized that insulin augments the sensitivity of hepatocyte to SFA-induced lipotoxicity. The present study was conducted via employing human and mouse hepatocytes, which were exposed to SFAs, insulin, or their combination. Unexpectedly, our results indicated that insulin protected hepatocytes against SFA-induced lipotoxicity, based on the LDH, MTT, and nuclear morphological measurements, and the detection from cleaved-Parp-1 and -caspase-3 expressions. We subsequently clarified that insulin led to a rapid and short-period inhibition of autophagy, which was gradually recovered after 1 h incubation in hepatocytes, and such extent of inhibition was insufficient to aggravate SFA-induced lipotoxicity. The mechanistic study revealed that insulin-induced alleviation of ER stress contributed to its hepatoprotective role. Pre-treating hepatocytes with insulin significantly stimulated phosphorylated-Akt and reversed SFA-induced up-regulation of p53. Chemical inhibition of p53 by pifithrin-α robustly prevented palmitate-induced cell death. The PI3K/Akt pathway blockade by its special antagonist abolished the protective role of insulin against SFA-induced lipotoxicity and p53 up-regulation. Furthermore, we observed that insulin promoted intracellular TG deposits in hepatocytes in the present of palmitate. However, blocking TG accumulation via genetically silencing DGAT-2 did not prevent insulin-protected lipotoxicity. Our study demonstrated that insulin strongly protected against SFA-induced lipotoxicity in hepatocytes mechanistically through alleviating ER stress via a PI3K/Akt/p53 involved pathway but independently from autophagy.

Total liver fat quantification using three-dimensional respiratory self-navigated MRI sequence

PURPOSE

MRI can produce quantitative liver fat fraction (FF) maps noninvasively, which can help to improve diagnoses of fatty liver diseases. However, most sequences acquire several two-dimensional (2D) slices during one or more breath-holds, which may be difficult for patients with limited breath-holding capacity. A whole-liver 3D FF map could also be obtained in a single acquisition by applying a reliable breathing-motion correction method. Several correction techniques are available for 3D imaging, but they use external devices, interrupt acquisition, or jeopardize the spatial resolution. To overcome these issues, a proof-of-concept study introducing a self-navigated 3D three-point Dixon sequence is presented here.

METHODS

A respiratory self-gating strategy acquiring a center k-space profile was integrated into a three-point Dixon sequence. We obtained 3D FF maps from a water-fat emulsions phantom and fifteen volunteers. This sequence was compared with multi-2D breath-hold and 3D free-breathing approaches.

RESULTS

Our 3D three-point Dixon self-navigated sequence could correct for respiratory-motion artifacts and provided more precise FF measurements than breath-hold multi-2D and 3D free-breathing techniques.

CONCLUSION

Our 3D respiratory self-gating fat quantification sequence could correct for respiratory motion artifacts and yield more-precise FF measurements. Magn Reson Med 76:1400-1409, 2016. © 2015 International Society for Magnetic Resonance in Medicine.

Mechanisms of liver involvement in systemic disease

The liver may be injured during the course of many systemic diseases. The mechanisms of injury can be broadly divided into four pathways: vascular, toxic, immune, and hormonal. Vascular obstruction may be an early event but is also the late common pathway from all mechanisms. Despite the large number of possible initiating factors, the end results are few, including death of hepatocytes or cholangiocytes, leading to the stereotyped syndromes of acute liver failure, non-cirrhotic portal hypertension, or cirrhosis. This small number of outcomes is a reflection of the few anatomic patterns that can be generated by microvascular obstruction. Vascular obstruction may occur by thrombosis, inflammation, or congestive injury. The innate immunity pathway is activated by endotoxin and other agents, leading to inflammatory infiltration, release of cytokines and reactive oxygen species, and necrosis. The adaptive immune pathway involves the generation of antibodies and antigen-specific cell-mediated attack on hepatic cells. Hormonal effects are principally involved when overnutrition leads to hyperinsulinemia followed by hepatocellular necrosis.

Imaging appearance of severe subcapsular hepatic steatosis: mimicking hepatic embolic infarcts

We report a case of severe subcapsular hepatic steatosis in a middle-aged woman with diabetic nephropathy requiring continuous ambulatory peritoneal dialysis (CAPD). The CT appearances of the liver were initially suspected to be due to embolic infarcts. However, an accurate diagnosis was made only after a history of intraperitoneal insulin administration was elicited, and this was confirmed on MRI with chemical shift gradient-echo pulse sequences. Haemodialysis was recommenced, and follow-up imaging 4 years later showed complete resolution of subcapsular hepatic steatosis.

MR imaging of hypervascular liver masses: a review of current techniques

Major technologic advances in magnetic resonance (MR) imaging, including the advent of novel pulse sequences (eg, diffusion-weighted and steady-state free precession sequences) and the use of hepatocyte-specific contrast agents, have led to better image quality and shorter acquisition times, resulting in dramatic improvements in the noninvasive detection and characterization of hepatic lesions, particularly hypervascular neoplasms. However, as the role of MR imaging in clinical evaluation of the liver continues to evolve, keeping abreast of new developments can be daunting as well as confusing. A systematic approach that makes use of a simple decision algorithm can help differentiate hypervascular hepatic lesions on the basis of their distinguishing MR imaging characteristics and related clinical information.

Sustained reversal of diabetes following islet transplantation to striated musculature in the rat

BACKGROUND

There is an increasing emphasis in the islet transplant community on the development of alternative sites for islet implantation. Striated musculature constitutes a potential alternative, which has been successfully employed in autotransplantation of parathyroid glands for decades. In the present study, a technique for intramuscular islet transplantation was developed and compared with intraportal islet transplantation in a syngeneic rat model.

MATERIALS AND METHODS

Lewis rats were used. Pancreata were digested using Liberase. Islets were either transplanted into m. biceps femoris in a pearls-on-a-string fashion or intraportally, and the ability to reverse diabetes was compared. Eight weeks after transplantation an IVGTT was performed. Real-time quantitative RT-PCR was employed on muscle biopsies to investigate mRNA levels of cytokines in response to the transplant procedure. Explanted livers, muscles, and pancreata were harvested at the end of the experiment for histopathological analyses.

RESULTS

2000 IEQ repeatedly cured diabetic rats at the intraportal site, while 4000 IEQ was required at the intramuscular site. Time to reversal of diabetes, post-transplant weight development, and IVGTT curves did not differ between the groups. Normoglycemia was sustainable to the end of the study (>100 days) for all animals. The transplant procedure upregulated pro-inflammatory cytokines (IL-6 and IL-8) in striated muscle, and peri-islet fibrosis was observed in intramuscular grafts.

CONCLUSIONS

Islet transplantation into striated musculature is feasible; however, in its present form the intramuscular site is less efficient compared with the liver in rats. The intramuscular site allows manipulation of the graft and implantation site prior to transplantation and may therefore have implications for islet transplantation in humans.

Ultrasound changes within the liver after total pancreatectomy and intrahepatic islet cell autotransplantation

OBJECTIVE

Intrahepatic infusion is the most common method of islet autotransplantation. Structural and functional changes within the liver may result from a number of factors, including embolization of the terminal branches of the portal vein, the effects of high insulin concentration on surrounding hepatocytes or responses to the death of admixed exocrine tissue. Awareness of the potential changes in the appearance of the liver on ultrasonography (USS), together with an assessment of liver function, is important in the postoperative surveillance of these patients.

METHODS

We retrospectively reviewed 83 patients who underwent total pancreatectomy between 1993 and 2006. Thirty-three patients had total pancreatectomy alone (control group) and 50 patients underwent total pancreatectomy and islet autotransplantation (islet group). The islets were infused into the left lobe of the liver through the middle colic or recannalated umbilical vein. All patients underwent USS as part of their hepaticojejunostomy surveillance (initially every 6 months and then yearly).

RESULTS

"Echogenic nodularity" of the liver was observed in 25% of the islet group of patients and in none of the control group patients (P=0.03). These USS changes occurred from 6 to 12 months after islet autotransplantation and were not associated with any significant loss of liver function or increase in insulin requirements. The islet group had significantly less insulin requirement compared with the control group (P<0.01).

CONCLUSION

Echogenicity with a nodular appearance is a common ultrasonographic finding in the liver after intrahepatic islet autotransplantation. These changes do not seem to adversely affect liver function or insulin requirement. Appreciating these changes is important to avoid misinterpretation or over-interpretation of postoperative USS images.

Postgastrectomy development or accentuation of focal fatty change in segment IV of the liver: correlation with the presence of aberrant venous branches of the parabiliary venous plexus

BACKGROUND

Focal fatty change in segment IV (S4) of the liver is occasionally a diagnostic dilemma in the postoperative follow-up of gastric cancer patients.

GOAL

To determine whether development of focal fatty change in S4 is related to the presence of aberrant venous branches of the parabiliary venous plexus (PBP).

STUDY

Two hundred seventy-six patients with gastrectomy who had been imaged by thin-slice preoperative computed tomography (CT) and at least one postoperative CT, and had no apparent liver masses were retrospectively analyzed. Preoperative CT were evaluated for the presence of aberrant venous branches of PBP entering S4. Serial postoperative CTs were evaluated for any interval change in the appearance of S4 of the liver.

RESULTS

There were 6 patients out of 276 (2%) in whom focal fatty liver developed or accentuated after the surgery. In 5 out of the 6, preoperative CT demonstrated aberrant branches of PBP; 3 of these were suggested to be aberrant right gastric veins, and the etiologies were not determined in 2. In 1 case, no definite aberrant vessel was seen. Aberrant vessels were found in none of the remaining 270 patients. The incidence of aberrant vessels was significantly higher in patients who developed postoperative radiologic change in S4 than in those who did not (P<0.0001).

CONCLUSIONS

Development or accentuation of focal fatty liver in S4 of the liver was observed in 2% of postgastrectomy patients and was closely related to the presence of aberrant venous branches of PBP.

Role of radiologic modalities in the management of non-alcoholic steatohepatitis

During the last decade, the role of radiologic modalities in management of patients who have fatty liver disease has expanded. Ultrasonography has been used as a noninvasive alternative to biopsy for monitoring patients who have hepatic steatosis, but MRI is more appealing than ultrasonography to denote minor changes in hepatic fat content. Distinguishing patients who have non-alcoholic steatohepatitis from steatosis alone has become of clinical importance; however, the differences are not apparent with any radiologic modalities. Several modalities have been developed to noninvasively and accurately quantify hepatic fat content and diagnose steatohepatitis. In the future, radiologic modalities might be used to monitor the natural history of the disease or evaluate therapeutic interventions in patients who have non-alcoholic fatty liver disease.

Non-invasive quantification of hepatic fat fraction by fast 1.0, 1.5 and 3.0 T MR imaging

INTRODUCTION

Even mild hepatic steatosis in a split liver donor may cause general liver failure and death in the donor. So far, CT density measurements or percutaneous biopsy is used to determine the presence of hepatic steatosis. Magnetic resonance imaging (MRI) may be an elegant method of non-invasive and non-radiation quantification of hepatic fat content.

METHODS

Fast gradient echo (GRE) technique was used to discriminate between fat and water spins. Echo time (TE) was adjusted for field strength dependent in-phase and out-of-phase states at 1.0, 1.5 and 3.0 T. Continuous MR signal transition from 100% water to 100% fat was investigated using a wedge water-oil phantom, which was positioned in such a way, that no spatial resolution occurred, thereby combining water and fat in one slice.

RESULTS

Using the phantom, a significant difference for a 5% difference in fat content was demonstrated in the range from 20 to 80% fat content (p<0.05) for all tested field strengths. In 25 patients MRI data were correlated with the percentage of fat determined by histologic evaluation of a CT-guided liver biopsy. Using the linear correlation calculated from the MRI phantom data at 1.0 T, we determined the liver fat from each patient's MRI measurements. Comparison of these data with the histologic quantified fat fraction of liver tissue showed a strong correlation (r(2)=0.93 for TE 6 ms and r(2)=0.91 for TE 10 ms).

CONCLUSION

The described method can be used to determine the presence of hepatic steatosis of >10% with p<0.05.

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.

Fatty Liver: Imaging Patterns and Pitfalls

Fat accumulation is one of the most common abnormalities of the liver depicted on cross-sectional images. Common patterns include diffuse fat accumulation, diffuse fat accumulation with focal sparing, and focal fat accumulation in an otherwise normal liver. Unusual patterns that may cause diagnostic confusion by mimicking neoplastic, inflammatory, or vascular conditions include multinodular and perivascular accumulation. All of these patterns involve the heterogeneous or nonuniform distribution of fat. To help prevent diagnostic errors and guide appropriate work-up and management, radiologists should be aware of the different patterns of fat accumulation in the liver, especially as they are depicted at ultrasonography, computed tomography, and magnetic resonance imaging. In addition, knowledge of the risk factors and the pathophysiologic, histologic, and epidemiologic features of fat accumulation may be useful for avoiding diagnostic pitfalls and planning an appropriate work-up in difficult cases.

Hepatic subcapsular steatosis in a diabetic CAPD patient receiving intraperitoneal insulin

Hepatic subcapsular steatosis is a rare and specific form of fatty change in the liver. It is a unique finding in diabetic patients receiving continuous ambulatory peritoneal dialysis (CAPD) and intraperitoneal insulin treatment. Intraperitoneal administration of insulin causes a unique pattern of fatty infiltration in the subcapsular location of the liver. Here we report a case of hepatic subcapsular steatosis in a diabetic CAPD patient who received intraperitoneal insulin. A 46-year-old diabetic woman on CAPD presented with general weakness. The patient received a total amount of 110 units of regular insulin via intraperitoneal and subcutaneous injection. Her initial blood chemistry showed increased serum lipid and liver enzyme profiles. Abdominal CT scan images and MRI revealed characteristic findings consistent with hepatic subcapsular steatosis. We assumed that the cause was CAPD and concomitant intraperitoneal insulin treatment; therefore, the patient was switched from CAPD to hemodialysis (HD) and began to receive insulin subcutaneously. Two months after the beginning of HD, the hepatic subcapsular steatosis completely resolved.

Current status of imaging pancreatic islets

The ability to image the pancreatic islet in vivo would enhance our understanding of diabetes and accelerate improvements in islet transplantation. However, the small size of islets and their diffuse distribution (both natively and after transplantation) present formidable challenges for current imaging techniques. This article reviews the relative merits and shortcomings of several imaging modalities in humans and in animal models of diabetes.

Cystic cholangiomas after transplantation of pancreatic islets into the livers of diabetic rats

Islet transplantation is increasingly used as a therapy for human type 1 diabetes mellitus. In our study, we investigated the effect of the transplantation of a low number (n = 350) of pancreatic islets into the right liver part on the neighboring portal bile ducts. Male streptozotocin- diabetic Lewis or autoimmune-diabetic BB/Pfd rats (n = 1065) were subdivided into 11 experimental groups. A few days after low-number islet transplantation, cholangiocytes adjacent to the grafts showed an increase in proliferative activity. During the next 12-24 months, many peri-insular ductules progressed via tumor-like cystic lesions to large cystic cholangiomas, accompanied by a translocation of the insulin receptor into the cytoplasm and an increase in expression of insulin-related signaling proteins (Insulin-receptor-substrate-1, Raf-1, Mek-1). After 24 months, 53% of rats with low-number transplantation exhibited at least one cholangioma >10 mm, significantly outnumbering tumor development in the transplant-free left liver part and in any control group. No cholangiocarcinomas emerged. A graft cell origin of the tumors was excluded by Y chromosome in situ hybridization in cross-gender transplantations. Conclusively, low-number intrahepatic islet transplantation, most likely acting by permanent local hyperinsulinism, leads to prolonged cholangiocellular proliferation in streptozotocin- and in autoimmune-diabetic rats, resulting in the development of benign cystic cholangiomas.

Hepatocellular neoplasms induced by low-number pancreatic islet transplants in autoimmune diabetic BB/Pfd rats

It has been shown that combined high local hyperinsulinism and hyperglycemia after low-number islet transplantation into the livers of streptozotocin-diabetic rats lead to the development of hepatocellular neoplasms but a substantial cocarcinogenic effect of genotoxic streptozotocin could not be ruled out completely. Thus, we herein investigated this model in BB/Pfd rats (n = 805; nine experimental groups), which develop spontaneous autoimmune diabetes similar to human type 1 diabetes. After low-number islet transplantation (n = 450), the liver acini downstream of the islets show insulin-induced alterations: massive glycogen and/or fat accumulation, translocation of the insulin receptor, decrease in glucose-6-phosphatase activity, increase in expression of insulin-like growth factor (IGF)-I, IGF-II/mannose-6-phosphate receptor, insulin receptor substrate-1, Raf-1, and Mek-1, corresponding to clear cell preneoplastic foci of altered hepatocytes known from chemical hepatocarcinogenesis and identical to that in streptozotocin-diabetic Lewis rats. After 6 months, many altered liver acini progressed to other types of preneoplasias often accompanied by an overexpression of the glutathione-S transferase (placental form), IGF-I receptor, and transforming growth factor (TGF)-alpha. After 12 to 15 and 15 to 18 months, 52% and 100% of the animals showed one or multiple hepatocellular adenomas or hepatocellular carcinomas (HCCs), respectively. Conclusively, this study identifies combined hyperinsulinism and hyperglycemia as a carcinogenic mechanism for the development of HCCs in diabetic rats. Hepatocarcinogenesis is independent from additional genotoxic compounds (i.e., streptozotocin), but is primarily triggered by increased intracellular insulin signaling via pathways associated with cell growth and proliferation, such as the Ras-Raf-mitogen-activated protein kinase pathway and the IGF system, and secondarily involves other growth factors, such as TGF-alpha.

Minimal focal steatosis of liver after islet transplantation in humans: a long-term study

Several reports have been published on islet transplantation in humans, but few data are available on the effect of islet infusion on the hepatic structure. Our aim was to evaluate in a longitudinal study the impact on the liver of intrahepatic islet transplantation. Clinical outcome and liver imaging were evaluated in 31 cases of islet-kidney transplantation (follow-up 38 +/- 4 months, range 12-96 months). Patients were divided into three groups: full function (FF, 9 cases: established insulin independence); partial function (PF, 16 cases: transient insulin independence, prolonged C-peptide secretion): no function (NF, 6 cases: exhaustion of C-peptide secretion within the first year). Upper abdomen sonogram was regularly performed during the whole follow-up period. Percutaneous liver biopsy was performed in case of echographic abnormalities. Multiple small areas of focal hyperechogenicity were observed in nine cases after 6-12 months. These findings were observed only in FF (two) and in PF (seven) patients. Fasting C-peptide levels at the time of echography were higher in negative than in positive patients (2.42 +/- 0.16 vs. 1.51 +/- 0.10 ng/ml, p = 0,0001). Liver biopsies showed focal macrovesicular steatosis, surrounded by normal liver parenchyma. Normal liver function was maintained. In conclusion, our results indicate that islet transplantation can lead to structural changes of the liver parenchyma (focal steatosis). It is more often observed in patients with partial function. Sonogram can be considered a specific method to reveal liver changes after islet transplantation.

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.

Disseminated periportal fatty degeneration after allogeneic intraportal islet transplantation in a patient with type 1 diabetes mellitus: a case report

Insulin independence after islet transplantation has been significantly improved by using new steroid-free immunosuppressive protocols and increased islet mass. Only little is known about the influence on the morphology of the liver of intraportally transplanted islets. We describe a case of disseminated periportal fatty degeneration after allogeneic intraportal islet transplantation (ITx). A 35-year-old patient with type-1 diabetes mellitus who was suffering from repeated severe hypoglycemic episodes received two sequential intraportal islet grafts. Liver structure was normal before the first ITx, based upon ultrasound and magnetic resonance imaging (MRI). One week after the first ITx, ultrasound demonstrated normal liver morphology. Four months later, at the second ITx, we detected small, disseminated, and hypodense hepatic lesions (1 to 3 mm) by ultrasound, which were confirmed by MRI and interpreted to be fatty degenerations. Histologically we found focal drop-shaped fatty degenerations with signs of mild periportal chronic inflammation. These liver alterations without clinical symptoms or pathological liver function tests matched the predicted distribution of infused islets. Glucose metabolism markedly improved after the first ITx, namely 58.6% reduction of daily insulin requirements, 1.4% decrease in HbA1c, basal C-peptide of 0.8 to 1.3 ng/dl with no severe hypoglycemia. We interpreted these benign changes in liver morphology as reactions to a local hyperinsulinemia in the neighborhood of the transplanted islets. We hypothesized that a steroid-free immunosuppression with rapamycin and tacrolimus may have contributed to changes in the portal microenvironment.

Technique, complications, and therapeutic efficacy of percutaneous transplantation of human pancreatic islet cells in type 1 diabetes: the role of US

PURPOSE

To retrospectively evaluate the role of ultrasonography (US) with regard to the technique, complications, and therapeutic efficacy of percutaneous intrahepatic transplantation of human pancreatic islet cells with combined US and fluoroscopic guidance.

MATERIALS AND METHODS

The institutional review board approved the study, and informed consent was obtained from all patients. After kidney transplantation, 34 uremic diabetic patients (20 men, 14 women; mean age, 40.9 years; age range, 29-61 years) underwent percutaneous intrahepatic transplantation of islet cells. Portal vein patency and liver echotexture were preliminarily assessed with color Doppler US. US also was used to identify early complications and presence (group A patients) or absence (group B patients) of hepatic parenchymal changes. Differences between the two groups in C peptide serum level and range were analyzed (Mann-Whitney test). Therapeutic efficacy of transplantation was assessed with regard to insulin independence period (rate and duration), exogenous insulin requirement, glycated hemoglobin, and C peptide level. A C peptide level of more than 0.5 ng/mL was considered to indicate well-functioning islet cells.

RESULTS

Fifty-eight procedures were technically successful, with a single puncture used in 51 of 58 patients. Complications occurred in three of 58 patients (hemoperitoneum, hemothorax, and thrombosis in one patient each) and were conservatively treated and resolved. Duration of insulin independence in 12 patients was more than 3 months (mean, 21 months). Well-functioning islet cells at 6 years were found in 19 of 34 patients. Hyperechoic parenchymal changes were evident at US in 12 of 34. No statistically significant difference in C peptide level was found between groups (P > .05), but a wider range of values was recorded in group B.

CONCLUSION

Complication rate of transplantation with US and fluoroscopic guidance was low. Well-functioning islet cells were found in about 50% of patients at 6 years of follow-up. Hepatic implantation of islet cells was evident on US images in more than one-third of patients.

Prevalence of hepatic steatosis after islet transplantation and its relation to graft function

Islet allotransplantation can provide insulin independence in selected individuals with type 1 diabetes. The long-term effects of these transplants on the liver are unknown. Recently, two cases of periportal steatosis after islet transplantation have been described. In this study, we performed ultrasound and magnetic resonance imaging (MRI) in 30 C-peptide-positive islet transplant recipients to detect steatosis and to explore the association of the radiological findings with clinical and metabolic factors. Steatosis was observed on MRI in six (20%) subjects. Histological findings of hepatic steatosis concurred with the imaging findings. Steatosis completely resolved in one subject whose graft failed. More subjects with steatosis required supplementary exogenous insulin than not (67 vs. 21%; P < 0.05). The clinical features of subjects with and without steatosis were otherwise similar, although C-peptide levels were higher in insulin-independent subjects with steatosis (0.98 +/- 0.12 vs. 0.70 +/- 0.18 nmol/l; P = 0.05), despite similar blood glucose levels. Serum triglycerides and the use of exogenous insulin were associated with increased odds of steatosis in a logistic regression model (chi(2) [degrees freedom] = 13.6 [2]); P = 0.001). MRI-detected steatosis is a common finding; the steatosis appears to be due to a paracrine action of insulin secreted from intrahepatic islets. Hepatic steatosis may be associated with insulin resistance or graft dysfunction.

Dual-echo, chemical shift gradient-echo magnetic resonance imaging to quantify hepatic steatosis: Implications for living liver donation

In living liver donation, a fatty liver poses risks for both recipient and donor. Currently, liver biopsy is the standard for assessing the presence and extent of steatosis. The goals of this study were to correlate a steatosis index derived from magnetic resonance imaging (MRI) to the histologic grade on biopsy as well as to determine the topographic distribution of steatosis within the liver. We examined the ability of dual-echo, chemical shift gradient-echo MRI to predict the degree of steatosis on liver biopsy. A total of 22 subjects received both a liver biopsy and detailed MRI evaluation. These individuals included 15 potential living donors and 7 patients with nonalcoholic fatty liver disease. MRI steatosis index was then compared with histologic grade on liver biopsy. The topographic distribution of hepatic steatosis was determined from those subjects in whom MRI detected hepatic steatosis. The steatosis index had a positive correlation with grade of steatosis on liver biopsy (correlation coefficient, 0.84). There was no significant variation in the degree of steatosis among segments. A steatosis index of >0.2 had good positive and negative predictive value for the presence of significant steatosis (>15%) on biopsy. Our quantitative MRI protocol can predict the degree of hepatic steatosis when it is minimal to moderate, and may obviate the need for liver biopsy for the purpose of quantification of steatosis in living donors. Fat saturation added to the MRI protocol may further improve diagnostic accuracy. This technique may be applicable to the larger population with hepatic steatosis.

Magnetic resonance-defined periportal steatosis following intraportal islet transplantation: a functional footprint of islet graft survival?

There is growing interest in more widespread application of isolated islet transplantation for the treatment of type 1 diabetes; however, the sequelae of long-term islet residence within the liver are unknown. We report herein a consequence of intraportal islet transplantation, specifically the development of periportal hepatic steatosis apparently induced by the local secretion of insulin within the liver.