Objectives: Detection of hepatic steatosis in donors is an important step for selection of a suitable liver allograft in living-donor transplant. This study aimed to investigate the role of hepatic computed tomo-graphy volumetry as a noninvasive method for detection of hepatic steatosis in living liver donors.

Materials and Methods: In a cross-sectional study, individuals who had undergone liver biopsy as a pretransplant checkup before living-donor liver transplant were included. The segmental liver volumes were measured by computed tomography scan with intravenous contrast enhancement.

Results: Our study included 179 individuals. Mean total volume of the liver was 1705.2 ± 256.5 cm³ in those with steatohepatitis and 1419.4 ± 241.2 cm³ in those without steatohepatitis (P < .001). Higher total volume of the liver (odds ratio of 1.005; 95% confidence interval, 1.001-1.010; P = .012) and total liver volume-to-standard liver volume ratio (odds ratio of 1.090; 95% confidence interval, 1.021-1.163; P = .009) were independent predictors of steatohepatitis. A cutoff value of 1531 cm³ for total liver volume was a predictor of presence of steatohepatitis in liver biopsies of donors (sensitivity = 83%; specificity = 71%; area under the curve = 0.809; P < .001).

Conclusions: Computed tomography volumetry may be considered as an auxiliary noninvasive method for estimation of hepatic steatosis/steatohepatitis and may be used as a guide to select donor candidates for liver biopsy.

Key words : Donor selection, Liver biopsy, Living-donor liver transplant, Nonalcoholic fatty liver disease

Introduction

Liver transplant is the best treatment modality for end-stage liver disease. Livers recovered from deceased donors are the main source of organs for liver transplant.¹ However, living-donor liver transplant (LDLT) is rapidly growing because of the increasing number of patients on wait lists and organ shortages. Living-donor liver transplant is now the preferred method of liver transplant in pediatric patients.²

Selection of a medically suitable donor is a major step in LDLT. Therefore, a complete and thorough evaluation of potential candidates should be performed prior to LDLT. Evaluation of a liver allograft, including liver imaging and biopsy, is an important step in pretransplant work-up.^3,4

Although minimal hepatic steatosis may be present in considerable numbers of liver biopsies before LDLT, excessive steatosis may threaten graft survival.⁵ Although it is still a controversial issue, substantial evidence has shown that donor hepatic steatosis may increase complications after liver transplant, leading to prolonged intensive care unit and hospital stay, primary graft dysfunction, and nonfunctioning grafts.⁶ Most transplant surgeons discard organs if the total amount of hepatic steatosis exceeds 60%.⁷ Therefore, liver biopsy of donor candidates is generally performed before LDLT for detection of hepatic steatosis and other hepatic pathologies. However, liver biopsy is an invasive method with high overall cost, which can result in morbidity and major and minor complications. Com-plications may occur during or after liver biopsy based on methods used for liver biopsy (ultrasonographic-guided or blind liver biopsy).⁸ Although the incidence of major complications has been reported to be less than 1%, these complications may lead to significant morbidly and mortality.⁹ This risk is substantial when the procedure is performed for evaluation of a donor candidate who is otherwise normal.

Previous studies have investigated whether correlations exist between body mass index (BMI), alanine aminotransferase levels, and waist-to-hip ratio and degree of hepatic steatosis in LDLT.^10,11 Computed tomography (CT) volumetry of the liver is a noninvasive modality for measurement of liver volume.¹² The estimation of total and segmental liver volume is crucial for determination of posttransplant outcomes of living donors and recipients of LDLT.¹³ In this study, we aimed to investigate the association between different indices of liver volumes in CT volumetry and steatosis/steatohepatitis in living liver donor candidates.

Materials and Methods

Study participants
A retrospective study was conducted between August 2013 and August 2015 at Shiraz Organ Transplant Center, Namazi Hospital, Shiraz, Iran. Study participants were healthy liver donors who had undergone liver biopsy for evaluation of liver histology as a routine pretransplant check-up before related LDLT. All study participants were first- or second-degree relatives (father, mother, brother, sister, uncle, aunt) of pediatric patients on a liver transplant wait list due to liver cirrhosis or other indications at our transplant center. Using a data-gathering form, we recorded age, sex, liver function tests, weight, height, lipid profile, and fasting plasma glucose level. Individuals with a history of liver cirrhosis or underlying liver disease who were not proper for liver donation were excluded. All donor candidates underwent ultrasonographic-guided liver biopsy using standard Tru-Cut needles. Hematoxylin and eosin staining method was used for staining of tissue slides. An expert pathologist reviewed liver biopsy specimens, checking for presence and degree of hepatic steatosis and steatohepatitis. Presence of intracytoplasmic fat droplets displacing the nucleus to the cell periphery was defined as hepatic steatosis. Presence of steatosis plus ballooning and/or lobular inflammation as markers of hepatocyte injury was defined as steatohepatitis.

Individuals were divided into those without hepatic macrovesicular steatosis (grade 0), individuals with ≤ 5% hepatic macrovesicular steatosis (grade 1), and those with > 5% macrovesicular hepatic steatosis (grade 2). All donor candidates underwent spiral abdominal CT scan with intravenous contrast enhancement, with results reviewed by an expert radiologist who was blinded to results of pathologic specimens. The total volume of liver and volumes of left lobe and left lateral segment were recorded.

Two indices were used to investigate the association of hepatic CT volumetry with steatosis/steatohepatitis: total liver volume/weight (cm³/kg) and total liver volume/standard liver volume. Standard liver volumes were calculated for each patient using the Vauthey formula: liver volume (mL) = 18.51 × body weight (kg) +191.8.14 These measures were com-pared between those with and without hepatic steatosis/steatohepatitis.

Ethics and consent
The study protocol was approved by the institutional review board of Shiraz University of Medical Sciences (Shiraz, Iran). The study was performed in accordance with the Helsinki Declaration as revised in Seoul 2008. The study was explained to participants, and written informed consent was obtained.

Statistical analyses
Comparisons of continuous variables were per-formed with t tests, and categorical variables were compared with chi-square tests. Nonparametric Mann-Whitney test was used when appropriate. Data are presented as means and standard deviation for numeric variables and percents and counts for categorical variables. Logistic regression analysis was used to test the influence of different risk factors on liver steatosis and steatohepatitis of donors. A one-way analysis of variance (ANOVA) and post hoc Tukey test were used to compare the differences among those with normal liver biopsy, those with only steatosis, and those with steatohepatitis. The optimal cutoffs of liver volumes, calculated based on findings from donor CT scans in association with hepatic steatosis and steatohepatitis in liver biopsies, were analyzed with receiver operating characteristics (ROC) curve using area under the curve. P < .05 was considered statistically significant. Statistical analysis was performed with SPSS version 20.0 (SPSS Inc.; Chicago, IL, USA).

Results

Our study included 179 individuals. Of these, 65 individuals (36.31%) had different degrees of biopsy-proven steatosis and 16 individuals (8.9%) had steatohepatitis in liver biopsy. Baseline characteristics of study participants are outlined in Table 1. In univariate analysis, weight, serum triglyceride, cholesterol, alanine aminotransferase, alkaline phosphatase, and fasting plasma glucose were associated with hepatic steatosis (P < .05) (Table 1). Mean total volume of the liver was 1530.1 ± 273.3 cm³ in those with hepatic steatosis and 1395.4 ± 231.4 cm3 in those without hepatic steatosis (P = .003). Mean volume of left lateral segment of the liver was 221.9 ± 69.9 cm³ in individuals with hepatic steatosis and 196.3 ± 64.7 cm³ in individuals without hepatic steatosis (P = .039). Mean standard liver volume was 1509.97 ± 182.2 cm3 in individuals with hepatic steatosis and 1367.38 ± 172.2 cm³ in individuals without hepatic steatosis (P < .001) (Table 1). In logistic regression analysis, total liver volume, volume of left lateral segment of the liver, and standard liver volume were not predictors of hepatic steatosis (P > .05) (Table 1).

Sixteen individuals had steatohepatitis in their liver biopsies. In univariate analysis, higher weight, serum triglyceride level, and alanine amino-transferase level were associated with steatohepatitis (P < .05) (Table 2). Mean total volume of the liver was 1705.2 ± 256.5 cm³ in those with steatohepatitis and 1419.4 ± 241.2 cm3 in those without steatohepatitis (P < .001). In logistic regression analysis, higher total liver volume was an independent predictor of steatohepatitis (odds ratio [OR] of 1.005; 95% confidence interval [95% CI], 1.001-1.010; P = .012) (Table 3). Mean total liver volume-to-standard liver volume ratio was 1.12 ± 0.19 in those with steatohepatitis and 1.01 ± 0.13 in those without steatohepatitis (P = .015). In a regression model, ratio of total liver volume to standard liver volume was an independent predictor of steatohepatitis in living donors (OR of 1.090; 95% CI, 1.021-1.163, P = .009) (Table 4).

A cutoff value of 1531 cm³ for total liver volume was a predictor of presence of steatohepatitis in liver biopsies of donors (sensitivity = 83%; specificity = 71%; area under the curve = 0.809; P < .001). The ROC curve showing optimal cutoffs of total liver volume and left lateral segment volume in CT scan to predict hepatic steatohepatitis in liver biopsies is outlined in Figure 1. Different cutoff points of total liver volume, left lateral segment volume in CT scan, and total liver volume-to-standard liver volume ration for prediction of steatohepatitis are summarized in Table 5.

Study participants were divided into 3 groups: individuals with normal liver biopsy, individuals with only steatosis in liver biopsies, and individuals with steatohepatitis in liver biopsies. When we compared total liver volume in these 3 groups, we observed statistically significant differences in total volume of livers between groups using one-way ANOVA (F[2,129] = 9.013; P < .001). A Tukey post hoc test revealed that total liver volume was significantly higher in individuals with steatohepatitis than in those with normal liver biopsies (1705.2 ± 256.5 cm³ vs 1395.4 ± 231.4 cm³) and those with steatosis (1705.2 ± 256.5 cm³ vs 1473.4 ± 256.88). We observed no statistically significant differences in total liver volume between individuals with normal liver biopsies and individuals with hepatic steatosis (P = .234).

Study participants were further divided into those without steatosis, individuals with ≤ 5% steatosis, and those with > 5% steatosis. Using one-way ANOVA, we observed a statistically significant difference in total liver volume between these 3 groups (F[2,129] = 5.881; P = .004). On post hoc Tukey test, total liver volume was significantly higher in individuals with > 5% steatosis than in those with normal liver biopsies (1607.1 ± 283.6 cm³ vs 1395.4 ± 231.4 cm³).

Discussion

This study showed usefulness of CT volumetry as a noninvasive tool for prediction of hepatic steatosis/steatohepatitis in donor candidates for LDLT. Mean total volume of the liver was significantly higher in individuals with steatohepatitis in liver biopsy than in those with normal liver biopsy and those with only steatosis. Total volume of the liver was also significantly higher in individuals with > 5% hepatic steatosis than in those with normal biopsies. In regression analysis, higher total liver volume was an independent predictor of steatohepatitis, but not steatosis, in liver biopsies. We also suggested a cutoff value of 1531 cm³ for total volume of the liver for presence of steatohepatitis in liver biopsies. For better estimation, we investigated associations of the ratio of measured total liver volume per standard liver volume calculated by Vauthey formula (total liver volume/standard liver volume) and hepatic steatosis/steatohepatitis. Total liver volume-to-standard liver volume ratio was also an independent predictor of steatohepatitis in liver allografts.

Hepatic steatosis is an emerging problem worldwide, with rapidly increasing incidence and prevalence.¹⁵ A recent meta-analysis estimated that the global prevalence of nonalcoholic fatty liver disease was 25.4%, with the highest prevalence in the Middle East and South America.¹⁶ Although most patients with nonalcoholic fatty liver disease have obesity or other components of metabolic syndrome,¹⁷ this disease may also occur among lean individuals.¹⁸ Hence, hepatic steatosis might be detected in otherwise healthy candidates for liver donation.

Although it is still a controversial issue, detection of steatosis/steatohepatitis in liver allografts before liver transplant is crucial since their presence may have a negative impact on allograft survival. Previous studies have suggested that graft macrovesicular steatosis was associated with more severe ischemic-reperfusion injury following transplant.¹⁹ Others have reported higher primary graft dysfunction and lower overall survival in transplant patients who received steatotic livers.²⁰ Baccarani and associates reported that having > 25% steatosis in liver allografts was a risk factor for biliary complications after liver transplant.²¹ It has also been reported that hepatic steatosis is associated with intrahepatic cholestasis and transient hyperbilirubinemia after LDLT.²² A systematic review reported adverse graft function in moderate to severely steatotic liver allografts.²³

Liver biopsy is currently the criterion standard method for detection of various degrees of hepatic steatosis. Liver biopsy can be performed percu-taneously, transvenously, or surgically using a laparoscopic approach.²⁴ However, it is rather an invasive method that might impose significant morbidity and even mortality. Intraperitoneal or intrahepatic hemorrhage, perforation of gallbladder or colon, and pneumothorax are major complications reported after liver biopsy.²⁵ Therefore, some inves-tigators have tried to find alternative, noninvasive modalities to detect steatosis in donor candidates. Rinella and associates, in their study of the role of BMI for prediction of hepatic steatosis in LDLT, suggested that only patients with high BMI should undergo liver biopsy.¹⁰ Hwang and associates used triple echo magnetic resonance imaging and magnetic resonance spectroscopy for assessment of hepatic steatosis before LDLT.²⁶ Transient elastography (fibro scan) has been also recently used for detection of hepatic steatosis in liver donors before LDLT.^27,28 The results of these studies are controversial, and the optimal noninvasive modality for measurement of hepatic steatosis remains to be clarified. Furthermore, some of these modalities are expensive and not widely available.

A CT scan is an alternative noninvasive imaging modality that has increasingly been used before LDLT for detection of probable pathologies in donor candidates. Several imaging parameters and liver indices in CT scans have been previously investigated for preoperative assessment of hepatic steatosis in LDLT. These include CT density difference between liver and spleen, liver-to-spleen attenuation ratio, and blood-free hepatic parenchymal attenuation.²⁹ However, the association between total and segmental liver volumes in CT volumetry and the degree of donor steatosis/steatohepatitis in LDLT has not been previously investigated.

Our study demonstrated an association between liver volumes measured by CT scan and hepatic steatosis/steatohepatitis. We calculated the ratio of total liver volume to standard liver volume as a better estimation of liver volume. In regression analysis, this ratio was also independently associated with presence of steatohepatitis in liver allografts. Our study population was larger compared with populations in other reports on noninvasive evalu-ations of hepatic steatosis in liver donors. We also suggested a cutoff point for total volume of the liver and the ratio of total liver volume to standard liver volume for detection of steatohepatitis in liver allografts, based on good sensitivity and specificity on ROC curve analysis. Because most LDLT procedures are performed in pediatric patients, liver donors are usually healthy young parents of children on liver transplant wait lists. Therefore, many of our donors had lean body mass without obesity and other components of metabolic syndrome and with only mild steatosis and steatohepatitis. Based on the findings of this study, CT volumetry could potentially be an important tool in detection of even mild degrees of hepatic steatosis among living liver donors.

This study has some limitations. This is a retrospective study, and the results are subject to confounding factors. Computed tomography volu-metry could be time consuming and costly. The volume measurements are operator dependent, and there could be significant intraobserver or inter-observer variabilities in measurements of liver volumes. In addition, there are factors that could potentially affect accuracy of the measurements, such as phase of the contrast administration, method of liver segmentation (manual or automatic), and image section thickness of the raw CT data.¹² Overall, methods of density quantification on CT were shown to have a high accuracy to detect donor livers with significant hepatic steatosis.³⁰ However, these methods were limited when used to evaluate lesser degrees of hepatic steatosis, which is a necessary evaluation for proper donor liver assessment.³¹ Volumetric liver measurements could potentially be considered as a valuable noninvasive, alternative method in early detection of milder degrees of hepatic steatosis in healthy adult liver donors.

Conclusions

We found CT volumetry of the liver to be a safe and noninvasive method that might be considered for detection of hepatic steatosis/steatohepatitis in healthy liver donor candidates before LDLT. This method could be used to guide donor candidate selection for liver biopsy, especially in cases without other significant risk factors for severe hepatic steatosis.

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