Prediction of major complications after ... - Wiley Online Library

Original article

Prediction of major complications after hepatectomy using liver stiffness values determined by magnetic resonance elastography N. Sato1 , A. Kenjo1 , T. Kimura1 , R. Okada1 , T. Ishigame1 , Y. Kofunato1 , T. Shimura1 , K. Abe2 , H. Ohira2 and S. Marubashi1 Departments of 1 Hepato-Biliary-Pancreatic and Transplant Surgery, and 2 Gastroenterology, Fukushima Medical University, Fukushima, Japan Correspondence to: Dr S. Marubashi, Department of Hepato-Biliary-Pancreatic and Transplant Surgery, Fukushima Medical University, Hikarigaoka-1, Fukushima-shi, Fukushima, 960-1295, Japan (e-mail: [email protected])

Background: Liver fibrosis is a risk factor for hepatectomy but cannot be determined accurately before

hepatectomy because diagnostic procedures are too invasive. Magnetic resonance elastography (MRE) can determine liver stiffness (LS), a surrogate marker for assessing liver fibrosis, non-invasively. The aim of this study was to investigate whether the LS value determined by MRE is predictive of major complications after hepatectomy. Methods: This prospective study enrolled consecutive patients who underwent hepatic resection between April 2013 and August 2016. LS values were measured by imaging shear waves by MRE in the liver before hepatectomy. The primary endpoint was major complications, defined as Clavien–Dindo grade IIIa or above. Logistic regression analysis identified independent predictive factors, from which a logistic model to estimate the probability of major complications was constructed. Results: A total of 96 patients were included in the study. Major complications were observed in 15 patients (16 per cent). Multivariable logistic analysis confirmed that higher LS value (P = 0⋅021) and serum albumin level (P = 0⋅009) were independent predictive factors for major complications after hepatectomy. Receiver operating characteristic (ROC) analysis showed that the best LS cut-off value was 4⋅3 kPa for detecting major complications, comparable to liver fibrosis grade F4, with a sensitivity of 80 per cent and specificity of 82 per cent. A logistic model using the LS value and serum albumin level to estimate the probability of major complications was constructed; the area under the ROC curve for predicting major complications was 0⋅84. Conclusion: The LS value determined by MRE in patients undergoing hepatectomy was an independent predictive factor for major complications. Paper accepted 4 January 2018 Published online in Wiley Online Library (www.bjs.co.uk). DOI: 10.1002/bjs.10831

Introduction

Liver resection is the optimal therapeutic option for patients with a malignant hepatic tumour. With advances in surgical techniques and anaesthetic care in the field of liver surgery, extended hepatic resections can be performed even in patients with impaired hepatic function, including those with advanced liver fibrosis1 . Liver fibrosis is recognized as a well known risk factor for morbidity and mortality after hepatectomy. The progression to advanced liver fibrosis or cirrhosis is associated with an increased risk of hepatic dysfunction and portal hypertension, and hence postoperative morbidity remains higher in patients © 2018 BJS Society Ltd Published by John Wiley & Sons Ltd

with advanced liver fibrosis or cirrhosis2,3 . Therefore, the indication for hepatectomy in patients with lower liver function capacity should be determined carefully, and preoperative assessment of liver fibrosis is indispensable for performing a safe hepatic resection. Until now, liver biopsy has been widely accepted as the reference standard for evaluation of hepatic fibrosis. However, liver biopsy is rarely performed to evaluate preoperative liver function because of its invasive nature, sampling error, and intraobserver and interobserver variability in histological interpretation4 . Encouraged by the need for non-invasive surrogates, progress over the past decade has been made in developing BJS

N. Sato, A. Kenjo, T. Kimura, R. Okada, T. Ishigame, Y. Kofunato et al.

techniques for the assessment of liver fibrosis. It has been demonstrated that liver stiffness (LS) measured by elastography using ultrasound imaging or MRI can be used to assess the stage of fibrosis5 . Two meta-analyses6,7 of the diagnostic performance of magnetic resonance elastography (MRE) reported that the area under the receiver operating characteristic (ROC) curve (AUROC) was greater than 0⋅90 for a broad spectrum of patients. Of note, previous studies have shown that the LS value detected by transient elastography8,9 or acoustic radiation force impulse elastography10 was a predictor of complications after liver surgery, but no study has shown the LS value by MRE to be a predictor of outcome after hepatectomy. The present prospective cohort study was conducted to investigate whether the LS value measured by MRE could predict postoperative major complications after hepatectomy.

Methods

This prospective single-centre cohort study was conducted between April 2013 and August 2016. The study protocol was approved by the institution’s ethics committee in accordance with the Declaration of Helsinki (approval number 2163). Written informed consent was obtained from every patient. The study was not sponsored by any MRE manufacturer. All patients scheduled to undergo hepatectomy for any liver disease or liver donation were eligible for the study. Patients who underwent hepatectomy with resection of other organs or the biliary tract, those requiring reconstruction of hepatic veins and those receiving dialysis were excluded. Preoperative LS measurement by MRE was performed within the 2 months before hepatectomy. Demographics, co-morbidities, laboratory data (including liver function test results, physiological function test results, and typical serum biological markers for liver fibrosis) and radiological data (including abdominal CT, MRI and measurement of the LS value), tumour pathology and perioperative data were collected for all patients. The indocyanine green retention rate at 15 min (ICG-R15) was measured after injection of an intravenous bolus of 0⋅25 mg/kg indocyanine green. The Child–Pugh score11 and the liver damage score were calculated according to their respective formulas. The degree of liver damage was classified as grade A, B or C based on the highest grade containing at least two findings such as ascites, serum bilirubin, serum albumin, ICG-R15 and prothrombin activity12 . © 2018 BJS Society Ltd Published by John Wiley & Sons Ltd

All liver specimens were analysed after liver resection by pathologists who were blinded to the LS values determined by MRE and any clinical data. Liver fibrosis in the specimen was graded by the pathologists as F0–F4 according to the METAVIR scoring system13 : F0, no fibrosis; F1, portal fibrosis; F2, periportal fibrosis; F3, septal fibrosis; and F4, cirrhosis.

Magnetic resonance elastography measurement MRE was performed on a 1⋅5-T clinical MR scanner (Optima™ MR450w; GE Healthcare, Waukesha, Milwaukee, USA) with Geometry Embracing Method coils14 . In brief, a passive pneumatic driver 10 cm in diameter was placed against the right chest wall overlying the liver with its centre at the level of the xiphoid process and attached to an acoustic waveform generator. Continuous acoustic vibration at 60 Hz was transmitted from an active driver to produce propagating shear waves in the liver. The propagating shear waves were imaged by using a modified phase-contrast gradient echo sequence to image axial wave images (TR/TE = 50/21⋅7, 256 × 64 matrix, 10-mm slice thickness, 60-Hz magnetization encoding gradient). One slice was obtained that included the level of the hepatic hilum under 14 s of breath-holding. The wave images were automatically processed using an inversion algorithm to yield quantitative images of tissue shear stiffness maps in units of kilopascals. The crosshatch marks represent the 95 per cent confidence threshold mask, and indicate areas unsuitable for stiffness measurement.

Analysis of liver stiffness value LS was measured by one experienced radiological technologist. The technologist placed free-hand regions of interest (ROIs) that were as large as possible on the stiffness map, mainly in the right hepatic lobe, while avoiding apparent pathologies, large vessels, areas with inadequate wave propagation (hot spot or dark spot artefacts) and crosshatch marks15,16 . ROIs were obtained for each patient and the mean value was recorded.

Technique of hepatectomy and perioperative management Operability and surgical procedure were determined with reference to liver function and radiological resectability using 2013 clinical practice guidelines for hepatocellular carcinoma from the Japan Society of Hepatology17 , without LS value by MRE. Laparoscopic hepatectomy was www.bjs.co.uk

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Risk of complications after hepatectomy determined by magnetic resonance elastography

Table 1

Baseline characteristics of the study population Major complication

Patient characteristics Age (years)* Male sex Background liver disease Hepatitis B Hepatitis C Alcoholic liver disease Non-alcoholic fatty liver disease Primary biliary cirrhosis Normal liver Child–Pugh grade B Liver damage score B Serum albumin (g/dl)* Serum total bilirubin (mg/dl)* Prothrombin time (%)* Platelet count (× 103 /μl)* Serum creatinine (mg/dl)* ICG-R15 (%)* LS value (kPa)* Serum hyaluronic acid (ng/ml)* Clinical and pathological diagnosis Hepatocellular carcinoma Intrahepatic cholangiocarcinoma Metastatic liver cancer Benign disease LDLT donor Surgical outcome Duration of surgery (min)* Blood loss (ml)* Intraoperative transfusion

All patients (n = 96)

Yes (n = 15)

No (n = 81)

P†

69⋅5 (62–77) 69 (72)

74 (65–77) 11 (73)

69 (61–76) 58 (72)

0⋅330‡ 0⋅582

9 (9) 24 (25) 5 (5) 6 (6) 1 (1) 51 (53) 6 (6) 12 (13) 4⋅0 (3⋅7–4⋅2) 0⋅8 (0⋅6–1⋅0) 91⋅9 (85⋅2–102⋅7) 151 (126–204) 0⋅77 (0⋅68–0⋅91) 9 (6–14) 2⋅8 (2⋅3–4⋅5) 91⋅9 (45⋅9–174⋅7)

2 (13) 8 (53) 2 (13) 0 (0) 0 (0) 3 (20) 1 (7) 4 (27) 3⋅7 (3⋅1–3⋅9) 0⋅9 (0⋅7–1⋅0) 87⋅3 (75⋅8–96⋅7) 111 (88–150) 0⋅75 (0⋅63–0⋅95) 11 (7–16) 5⋅0 (4⋅3–5⋅8) 96⋅9 (50⋅8–144⋅1)

7 (9) 16 (20) 3 (4) 6 (7) 1 (1) 48 (59) 5 (6) 8 (10) 4⋅0 (3⋅8–4⋅3) 0⋅8 (0⋅6–1⋅0) 95⋅4 (85⋅4–103⋅9) 158 (131–208) 0⋅78 (0⋅69–0⋅91) 9 (6–14) 2⋅5 (2⋅2–3⋅8) 89⋅5 (41⋅0–184⋅0)

0⋅427 0⋅010 0⋅173 – – 0⋅005 0⋅650 0⋅090 < 0⋅001‡ 0⋅100‡ 0⋅204‡ 0⋅030‡ 0⋅721‡ 0⋅148‡ < 0⋅001‡ 0⋅741‡

57 (59) 11 (11) 18 (19) 4 (4) 6 (6)

13 (87) 1 (7) 0 (0) 1 (7) 0 (0)

44 (54) 10 (12) 18 (22) 3 (4) 6 (7)

0⋅016 0⋅457 – – –

259 (221–346) 310 (105–650) 11 (11)

295 (229–436) 650 (480–1800) 5 (33)

258 (221–327) 280 (100–530) 6 (7)

0⋅289‡ < 0⋅001‡ 0⋅013

Values in parentheses are percentages unless indicated otherwise; *values are median (i.q.r.). ICG-R15, indocyanine green retention rate at 15 min; LS, liver stiffness; LDLT, living donor liver transplantation. †Fisher’s exact test, except ‡Mann–Whitney U test.

performed for partial resection or left lateral segmentectomy. Perioperative management was according to the clinical pathway in the department. Intraoperative infusion volume was minimized if cardiocirculatory dynamics were stable to keep central venous pressure low and avoid bleeding from the hepatic vein during hepatic dissection. Intraoperative ultrasonography was carried out routinely to determine an adequate surgical margin of at least 1 cm from the tumour and to ensure no other lesion was present. Parenchymal transection was performed by ultrasonically activated scalpel, cavitron ultrasonic surgical aspirator (CUSA™; Valleylab, Boulder, Colorado, USA) and a soft coagulation system, if needed, under intermittent pedicle clamping (15 min occlusion and 5 min reperfusion). For laparoscopic hepatectomy, a combination of biclamp, CUSA™ and a soft coagulation system was used. Major hepatectomy was defined as removal of two or more sectors of the liver. One or two intra-abdominal © 2018 BJS Society Ltd Published by John Wiley & Sons Ltd

drainage tubes were placed around the liver transection and removed 2–3 days after surgery in the absence of any sign of infection. Prophylactic administration of cefmetazole was started 30 min before surgery and continued until postoperative day 2.

Definition of outcomes The primary outcome was major complications after hepatectomy, and secondary outcomes were overall mortality and morbidity. Complications were categorized from grade I to grade V according to the modified Clavien–Dindo classification18 . In this study, a major complication was defined as grade IIIa or above.

Statistical analysis Descriptive statistics were produced for the demographic, clinical and laboratory characteristics of the study subjects. www.bjs.co.uk

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Table 2

Postoperative complications according to the Clavien–Dindo classification No. of patients

Details of complications

Minor complications Grade I Grade II

1 13

Wound infection n = 1 Intra-abdominal collection requiring antibiotics n = 5 Ascites n = 1 Atrial fibrillation n = 2 Syndrome of inappropriate antidiuretic hormone secretion n=1 Pseudomembranous enterocolitis n = 1 Pleural effusion n = 1 Pneumonitis n = 1 Functional ileus n = 1

Major complications Grade IIIa

13

Refractory ascites requiring drainage n = 3 Pleural effusion requiring drainage n = 2 Biloma requiring percutaneous drainage n = 12 Atelectasis requiring BIPAP n = 2 Intestinal bleeding n = 3 Intra-abdominal abscess n = 1

Grade IIIb Grade IVa Grade IVb Grade V Total

0 1 0 1

Acute liver injury requiring BIPAP Death from liver failure

29

BIPAP, biphasic positive airway pressure.

Continuous variables are reported as median (i.q.r.) values, and the values for different subgroups were compared with the unpaired t test or the Mann–Whitney U test as appropriate. Categorical variables were expressed as prevalence, and differences in the proportions of different patient groups were compared by performing Fisher’s exact test. P < 0⋅100 in univariable analysis was set for multivariable analysis. The following eight variables were examined as potential risk factors: age, sex, LS value, serum albumin concentration, prothrombin time, platelet count, total bilirubin level and liver damage score. Multivariable logistic regression analysis using these variables was performed to identify independent predictors. A ROC curve was generated to determine the optimal LS cut-off value measured by MRE for predicting morbidity. In the statistical analyses, P < 0⋅050 was considered to indicate statistical significance. Stata® version 13 (StataCorp, College Station, Texas, USA) was used for all statistical analyses.

Results

In the study period, 98 patients were enrolled; two patients with hepatic iron deposition were subsequently excluded. The population for analysis had a median age of 69⋅5 (i.q.r. 62–77) years, and 72 per cent of the patients were men (Table 1). Fifty-one patients (53 per cent) had a normal liver © 2018 BJS Society Ltd Published by John Wiley & Sons Ltd

and 33 had a history of chronic hepatitis B (9 per cent) or C (25 per cent) infection. Ninety patients (94 per cent) were classified as having Child–Pugh grade A disease, and 84 (88 per cent) had liver damage score A. According to histopathological findings, 17 patients (18 per cent) had F4 and 19 (20 per cent) had F3 liver fibrosis. The median LS value was 2⋅8 (i.q.r. 2⋅3–4⋅5) kPa.

Diagnostic performance of liver stiffness value in detecting stage of liver fibrosis The relationship between individual LS values and the METAVIR score is shown in Fig. S1 (supporting information). A positive correlation between LS value and pathological liver fibrotic stage was observed. The diagnostic performance of MRE for different stages of liver fibrosis was evaluated by ROC analysis. For each ROC analysis, the optimal cut-off LS value, corresponding sensitivity and specificity, and AUROC values are shown in Table S1 (supporting information). The AUROC and cut-off values of LS for diagnosis of any stage of fibrosis (F1 or above), significant fibrosis (F2 or above), advanced fibrosis (F3 or above) and cirrhosis (F4) were 0⋅85 and 2⋅8 kPa, 0⋅94 and 2⋅9 kPa, 0⋅94 and 3⋅6 kPa, and 0⋅94 and 4⋅1 kPa respectively. Measurement of the LS value was successful in 96 patients, with no adverse events. MRE had a high power to discriminate between mild fibrosis and severe fibrosis or cirrhosis. www.bjs.co.uk

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LS value (kPa)

8

Multivariable logistic regression analysis to identify preoperative predictors of postoperative major complications of hepatectomy

Table 3

Refractory ascites and pleural effusion Other

6

4

2 F1

F2

F3

F4

METAVIR grade

Scatter graph showing the correlation between liver stiffness (LS) value and METAVIR grade of liver fibrosis in 15 patients with postoperative major complications, six with ascites or pleural effusion and nine with other complications

Age (years) Sex (M versus F) LS value (kPa) Serum albumin (g/dl) Prothrombin time (%) Platelet count (× 103 /μl) Total bilirubin (mg/dl) Liver damage score (A versus B)

Odds ratio

P

0⋅97 (0⋅91, 1⋅04) 1⋅52 (0⋅29, 7⋅98) 1⋅77 (1⋅09, 2⋅87) 0⋅03 (0⋅00, 0⋅40) 1⋅03 (0⋅97, 1⋅10) 1⋅05 (0⋅93, 1⋅18) 37⋅98 (0⋅43, 3318⋅47) 0⋅17 (0⋅01, 2⋅58)

0⋅419 0⋅619 0⋅021 0⋅009 0⋅338 0⋅449 0⋅111 0⋅200

Values in parentheses are 95 per cent confidence intervals. LS, liver stiffness.

Fig. 1

Hepatic resection and perioperative data Perioperative data, tumour characteristics, surgical outcomes and postoperative complications are shown in Tables 1 and 2, and Table S2 (supporting information). Fiftytwo single or multiple partial resections, 17 segmentectomies, 14 right lobectomies and 13 left lobectomies were performed. Among 27 major hepatectomies, five patients (19 per cent) had histological fibrosis above grade F3. Laparoscopic hepatectomy was performed in 29 patients (30 per cent). Intraoperative transfusion was required in 11 hepatectomies (11 per cent) without intraoperative hypotensive episodes (defined as systolic arterial pressure below 80 mmHg). The mortality rate at 90 days or less after surgery was 1 per cent; one patient died from postoperative portal thrombosis and severe liver failure after a right hepatectomy for hepatocellular carcinoma with F4 liver fibrosis due to chronic hepatitis C infection. Preoperative assessment of this patient’s liver function had been relatively favourable: the Child–Pugh grade and liver damage score were both A. The patient’s LS value was 4⋅7 kPa, which is greater than the cut-off value for F4 fibrosis in the present analysis. The overall complication rate was 30 per cent (29 of 96), and the major complication rate was 16 per cent. Five of these 15 major complications (3 refractory ascites, 2 pleural effusion) occurred in patients with liver cirrhosiss (F4) (Fig. 1).

Predictive factors for postoperative major complications The results of univariable and multivariable analysis using preoperative, intraoperative and histological variables © 2018 BJS Society Ltd Published by John Wiley & Sons Ltd

with a potential relationship to postoperative major complications are presented in Tables 1 and 3, and Table S2 (supporting information). Univariable analysis showed that lower serum albumin level (P < 0⋅001), higher LS value (P < 0⋅001), lower platelet count (P = 0⋅030), METAVIR grade F3–4 (P < 0⋅001), blood loss of 540 ml or more (P < 0⋅001) and intraoperative blood transfusion (P = 0⋅013) were associated with major complications. Multivariable analysis using a logistic regression model for predicting major complications showed that independent predictive factors were LS value (P = 0⋅021) and serum albumin concentration (P = 0⋅009). There were no significant differences in tumour locations and other operative variables, including extent of liver resection.

Risk stratification for postoperative major complications by degree of liver fibrosis ROC analysis identified an LS of 4⋅3 kPa as the best cut-off value for predicting major complications (Fig. 2). The median LS value in patients with and those without major complications was 5⋅0 (i.q.r. 4⋅3–5⋅8) and 2⋅5 (2⋅2–3⋅8) kPa respectively. Overall and major complication rates were increased with higher METAVIR grades and LS values.

Probability of major complications based on liver stiffness and preoperative serum albumin A logistic regression model to estimate the probability of major complications was constructed from two preoperative parameters, serum albumin level and LS value, identified as independent predictors by multivariable analysis. The formula for the logistic regression model is: [ ( )] Predicted probability = 0.54 × LS value kPa [ ( )] − 1.80 × serum albumin g∕dl + 3.02

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Discussion

1·00

Sensitivity

0·75 Cut-off value at 4·3 kPa

0·50

0·25

0

0·25

0·50

0·75

1·00

1 −specificity

Receiver operating characteristic (ROC) curve analysis of liver stiffness measurement for detecting postoperative morbidity (Clavien–Dindo grade IIIa or above). The best cut-off value is 4⋅3 kPa (area under the ROC curve 0⋅813, 95 per cent c.i. 0⋅677 to 0⋅948; sensitivity 80 per cent; specificity 82 per cent; positive predictive value 43 per cent; negative predictive value 96 per cent; positive likelihood ratio 4⋅1 per cent; negative likelihood ratio 0⋅3 per cent)

Fig. 2

0

0·2

6

0·4

0·6

0·8

Probability of complications

LS value (kPa)

4

2

0

2·5

3·0

3·5

4·0

4·5

Preoperative serum albumin (g/dl)

Probability of postoperative major complications based on liver stiffness (LS) value and preoperative serum albumin concentration, predicted by a logistic regression model illustrated using contour lines

Fig. 3

Fig. 3 shows that the probability of hepatectomy-related major complications stratified according to LS value and serum albumin level. ROC analysis showed that the discriminative performance of this predictive model (AUROC) was 0⋅84. © 2018 BJS Society Ltd Published by John Wiley & Sons Ltd

This study has demonstrated that LS values measured by MRE were an independent predictor of major complications following elective hepatectomy in the authors’ institution. The best cut-off value of 4⋅3 kPa, comparable to F4 stage fibrosis according to METAVIR grading, had adequate discriminative power for major complications after hepatic surgery, with a sensitivity of 80 per cent and a specificity of 82 per cent. Liver fibrosis is caused by chronic injury to the liver and has been recognized as a significant risk factor for short-term outcomes after hepatectomy2 . The significance of preoperative assessment of liver fibrosis is supported by the present findings: the degree of liver fibrosis varied in study participants, 90 per cent of whom had good hepatic functional capacity; and advanced fibrosis (F3) or cirrhosis (F4) were relevant to surgical short-term outcomes after hepatectomy. Taken together, preoperative assessment of liver fibrosis may be of added value for stratifying the surgical risk of hepatic resection, even in patients with good liver functional capacity. However, liver biopsy is rarely used in preoperative liver assessment by hepatic surgeons because of its invasive nature. Recently, non-invasive ultrasonography and MRE for evaluating liver fibrosis have been developed5 and used for preoperative liver assessment, as also shown in the present study. The finding that LS value was strongly predictive of major complications is consistent with the results of previous studies of ultrasound elastography8,9,19,20 . Compared with ultrasound imaging, MRE may be superior in discriminating liver fibrosis and can be used in obese patients21,22 . Ultrasound elastography had a higher incidence of unreliable measurements than MRE, because a narrow intercostal space is a potential risk factor related to technical failure of ultrasound elastography22 . However, the technical requirements of MRE limit its use in patients with hepatic iron deposition, which is a well known confounding factor of MRE. As elastography can stratify the surgical risk of hepatectomy in patients with good hepatic function capacity, it may become a new preoperative liver function test, providing information that cannot be obtained by conventional liver function tests. Preoperative LS measurement may enable development of a new scale for evaluating portal venous pressure (PVP). Transient elastography has received considerable attention as a non-invasive technology for evaluating portal hypertension23 . Taking into account the fact that PVP measured by the hepatic venous pressure gradient has been adopted for patient selection by the Barcelona Clinic Liver Cancer classification24 , non-invasive MRE may provide hepatic surgeons with a new sensitive scale for www.bjs.co.uk

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discriminating the degree of PVP. In the present study, 33 per cent of major complications (5 of 15), such as refractory ascites and pleural effusion, were observed in patients with F4 liver fibrosis, which may be caused by portal hypertension. For prediction of major complications, a logistic model to estimate the probability of major complications was constructed from two independent predictors: albumin and LS value (albumin–LS model). This risk model is comparable to the albumin–bilirubin or albumin–ICG grade for assessing liver function capacity25,26 . Bilirubin or ICG disappearance has already been used as a biomarker of hepatic functional capacity in the assessment for hepatectomy. Thus, the albumin–LS model is considered as novel in terms of evaluating liver fibrosis, and useful for selecting patients suspected to have high PVP. This study had some limitations, such as a relatively small sample size and heterogeneity of patients. Nevertheless, a subgroup analysis of patients with primary hepatic carcinoma demonstrated that LS value was also identified as an independent predictor of major complications after hepatectomy. The volume of resected liver parenchyma was not an independent risk factor in this study. This finding might be explained by the fact that hepatectomy was performed according to clinical practice guidelines, and a few patients, who were suitable only for partial hepatic resection owing to poorer liver function, were included in the group with major complications. Heterogeneity of hepatectomy type may also have influenced the present results. In fact, no patient with major complications had a laparoscopic hepatectomy. The possibility that the incidence of major complications would be estimated as lower in the laparoscopic group had to be considered, because most laparoscopic hepatectomies were partial resections in the present study. However, a previous study27 found no difference in surgical outcome between open and laparoscopic hepatectomy groups. MRE can quantify liver fibrosis with high diagnostic performance, resulting in risk stratification of hepatectomy. Because the liver is a multifunctional organ, a comprehensive evaluation of preoperative liver function, including MRE, may be required for accurate prediction of the risk of hepatectomy. Acknowledgements

The authors thank Y. Hashimoto and Y. Kiko for histopathological evaluation of liver fibrosis, and S. Seino for technical assistance relating to MRE. They also thank J. Watanabe and M. Makoto for collecting data and inspired guidance. © 2018 BJS Society Ltd Published by John Wiley & Sons Ltd

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Supporting information

Additional supporting information can be found online in the supporting information tab for this article.

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