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- Materials and methods
Hepatocellular carcinoma (HCC) is the fifth most common cancer worldwide and the third most common cause of cancer mortality.1 Recent trends show a rising incidence of HCC in developed countries including US.2, 3 This is probably a reflection of the increasing rate of hepatitis C-associated cirrhosis and the epidemics of obesity and diabetes.3, 4The presence of cirrhosis constitutes an important predisposing factor for development of HCC.5 In 80–90% of the cases, HCC arises in a background of cirrhosis.6 The annual incidence of HCC in patients with compensated cirrhosis ranges from 2% to 6%,7 whereas the incidence in noncirrhotic livers is 0.4%.8 HCC is also the leading cause of death in cirrhotic patients. The 5-year survival rate for treated populations is estimated between 50% and 75%, whereas survival rates of 20–50% are observed for untreated patients.9
Although the current practice guidelines recommend screening for HCC in patients with cirrhosis using ultrasonography every 6–12 months, the verification of HCC requires the presence of arterial hypervascularity and delayed venous washout for ≥2 cm lesions using computerised tomography or magnetic resonance imaging.10 However, the use of these modalities may not have a significant impact on early detection as compared with ultrasound. Recent cross-sectional studies using transient elastography suggest that increased liver stiffness value may be a potential risk factor for HCC among individuals with cirrhosis as compared with disease controls without HCC.11, 12 However, the strict assessment of hepatic parenchymal areas uninvolved with HCC may be difficult to perform using transient elastography, as this method can only assess a fractional component of total hepatic parenchyma involving the right lateral liver.13 Furthermore, the relationship between increased liver stiffness and presence of HCC in patients with moderate to severe obesity remains unknown.14, 15 The influence of portal hypertension and hepatic decompensation on liver stiffness may also complicate determining the level of association between liver stiffness value thresholds and risk for developing HCC.
Magnetic resonance elastography (MRE) is a novel technique that can provide in vivo measurements of tissue elasticity in various organs including the liver. Recent studies have demonstrated systematic associations between mean liver stiffness value and degree of hepatic fibrosis assessed by liver histology.16–18 In addition, malignant hepatic lesions have significantly greater mean liver stiffness values as compared with benign tumours in patients with and without chronic liver disease. Notably, the liver stiffness of HCC lesions can be even higher in value than parenchymal areas involved with histological cirrhosis.19
The main aim of our study was to determine if liver stiffness values of nonmalignant hepatic parenchyma assessed using MRE were higher in subjects with compensated cirrhosis and HCC as compared with matched controls without HCC. The rationale for pursuing these objectives is based on the ability of MRE to assess hepatic parenchymal areas distant to HCC lesions including areas medial to the right liver.
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- Materials and methods
Thirty subjects with HCC and compensated cirrhosis (cases), and 60 subjects with compensated cirrhosis alone (controls) comprised the study cohort. The mean age for patients with HCC was 65 ± 11 years (range, 45–85) and 73% were men. The mean BMI was 27.7 ± 5.8 kg/m². For control subjects, the mean age was 59 ± 12 years (range, 27–82) and 60% were men. The mean BMI in this group was 30.7 ± 6.6 kg/m². Liver disease aetiologies among cases were chronic viral hepatitis (57%), non-alcoholic fatty liver disease (33%) and alcohol (10%). For controls, the aetiologies of liver disease were chronic viral hepatitis (55%), non-alcoholic fatty liver disease (26%) and alcohol (14%) (Table 1).
Table 1. Demographical and clinical features cases and controls
| ||Cirrhosis with HCC (n = 30)||Cirrhosis without HCC (n = 60)||P-value|
|Age (years)||65 ± 11||59 ± 12||0.02|
|BMI (kg/m2)||27.7 ± 5.8||30.6 ± 6.6||0.03|
|ALT (U/L)||79 ± 60.||83 ± 74||N.S.|
|AST (U/L)||112 ± 79||68 ± 42||0.0016|
|Albumin (mg/dL)||3.6 ± 0.5||4.6 ± 0.5||0.022|
|Bilirubin (mg/dL)||2.2 ± 4.9||1.3 ± 1.2||N.S.|
|Platelet (109/L)||170.7 ± 167||124.58 ± 66.9||N.S.|
|INR||1.2 ± 0.3||1.1 ± 0.1||N.S.|
| Viral hepatitis||68||55||N.S.|
At initial diagnosis, 28 (93%) patients had single HCC lesions with a mean size of 5.2 cm (range, 2–14 cm). Eleven subjects (37%) were found with single HCC lesions <3 cm. No subject had radiographical evidence of portal vein invasion by tumour. However, two subjects were affected by occlusion of the right portal vein suspicious for tumour invasion. Three patients underwent TACE (n = 1), RFA (n = 1) and surgical resection (n = 1) respectively, as treatment for HCC prior to assessment with MRE. The diagnosis of HCC was established with biopsy or surgery in 16 cases, with the remaining 12 cases verified by validated radiological criteria.
Association between clinical variables and HCC
Univariate analysis demonstrated that HCC was positively associated with age (P = 0.02), serum AST level (P = 0.0016) and serum albumin level (P = 0.002). BMI was significantly higher in controls as compared with cases (P = 0.03). There were no differences between cases and controls in terms of gender, ALT, alkaline phosphatase, INR, total bilirubin and platelet count. (Table 1).
Association between liver stiffness of uninvolved hepatic parenchymal regions and HCC
Magnetic resonance elastography was successfully performed in all cases and controls without any technical difficulty, including those individuals with moderate to severe obesity (Figure 1). Among individuals with HCC, the mean liver stiffness values within hepatic parenchymal regions distant from tumour involvement were 6.3 ± 2.1 kPa. In controls, the mean liver stiffness value was similar to cases with HCC (6.1 ± 2.3 kPa, P = 0.7). Subgroup analysis of subjects with chronic viral hepatitis did not identify any significant differences between cases and controls (data not shown). Figure 2 shows the individual mean liver stiffness values from cases and controls.
Figure 1. Magnetic resonance elastography of the liver in patients with cirrhosis and cirrhosis with hepatocellular carcinoma (HCC). Anatomical images of a patient with cirrhosis and a patient with cirrhosis and HCC are shown in the far left column. The middle column shows wave image data in the liver, superimposed on the corresponding anatomical images. The resulting elastograms are shown in the far right column. The elastograms show that the mean liver stiffness of corresponding areas of hepatic parenchyma not involved with HCC is similar (6.5 vs. 6.4 kPa respectively). Note the stiffness of the HCC lesion is 12.6 kPa.
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Figure 2. Mean liver stiffness values in patients with hepatocellular carcinoma (HCC) and cirrhosis (cases) and patients with cirrhosis alone (controls). Liver stiffness is not significantly higher in cases than in the control group.
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Relationship between clinical variables and liver stiffness of uninvolved hepatic parenchymal regions
The correlation between age, BMI, AST, albumin and mean liver stiffness was assessed for cases and controls. Although statistically significant relationships between individual variables and the presence of HCC were observed, there was no strong association between these variables and mean liver stiffness in cases or controls (Figure 3).
Figure 3. No correlations were observed between mean liver stiffness and (a) age, (b) BMI, (c) AST or (d) albumin among cases and control groups.
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- Materials and methods
The results of our preliminary study show that mean liver stiffness assessed using MRE in hepatic parenchymal regions uninvolved with tumour is not significantly higher in patients with early to intermediate stage HCC as compared with control subjects without HCC, adjusting for age, aetiology of liver disease and the presence of compensated cirrhosis. This relationship persisted when examining a subgroup of patients with moderate to severe obesity who might be at higher risk for HCC. Furthermore, the mean liver stiffness of uninvolved hepatic parenchyma was not influenced by gender, AST, total bilirubin, albumin or platelet count values in both patient groups.
In 80–90% of cases, the development of HCC occurs in the setting of advanced histological fibrosis.1, 5, 6, 10 Hence, there is great interest in recognising novel factors that may improve the ability to facilitate early detection of HCC in patients with cirrhosis. The non-invasive assessment of chronic liver injury using ultrasound-based transient elastography provides excellent diagnostic accuracy for identifying the presence of advanced fibrosis and cirrhosis11, 20–22 primarily among individuals with chronic viral hepatitis. Subsequently, these investigations also examined the potential relationship between liver stiffness measurement and presence of HCC. Foucher et al.11 demonstrated that patients at stage 3 and 4 hepatic fibrosis and mean liver stiffness values ≥53 kPa were more likely to present with HCC as compared with similar patients with lower mean stiffness values. At a diagnostic cutoff value of 53.7 kPa, the sensitivity for detecting HCC was 37%, specificity 87%, positive predictive value 30% and negative predictive value 90%. Masuzaki et al.12 demonstrated that the stratum-specific likelihood ratio for the presence of HCC was 5 when a mean liver stiffness value ≥25 kPa was observed among patients with chronic hepatitis C. Notably, there may have been some patients developing HCC in the absence of cirrhosis, which suggests that inflammation may have been the dominant histological explanation for increased liver stiffness. Nahon et al.14 also reported that patients with HCC had significantly higher liver stiffness measurement values using transient elastography compared with subjects without HCC. Recently, a prospective cohort study of 866 patients demonstrated an independent relationship between liver stiffness and the probability for developing HCC over time.15 However, some cases developing HCC lacked evidence for cirrhosis, whereas others may have had elevations in liver stiffness because of decompensated liver disease.23
The results of our study are divergent from previous case–control studies using ultrasound-based transient elastography to assess the association between liver stiffness and HCC.11, 12, 14, 15 Several caveats about our study need to be emphasised. Only one study looked at subjects with underlying chronic liver diseases other than viral hepatitis.14 In all of the reported studies, the strict assessment of liver stiffness in multiple areas of hepatic parenchyma uninvolved with tumour was not performed based on limitations with transient elastography for examining areas beyond the lateral right liver lobe. In contrast, MRE has the ability to calculate liver stiffness over the entire cross-sectional area of hepatic parenchyma visualised on imaging. In addition, it remains possible that liver stiffness values measured using ultrasound transient elastography could have been influenced by peritumoral oedema and thus resulting in a higher than actual liver stiffness measurement in some instances.
Subjects with obesity have not been systematically assessed with TE to determine the relationship between liver stiffness value and probability for HCC. Earlier investigations have shown the role of obesity in the development of HCC due to its association with metabolic syndrome, which is a risk factor for NAFLD.24–26 There is accumulating evidence that hepatic steatosis increase the risk of HCC in patients with hepatitis C.27, 28 To date, there has not been a significant obstacle for MRE based on the presence of obesity. In our study, the mean BMI of all patients was 29.65 ± 6.43 kg/m² and no technical difficulties were encountered secondary to BMI. In contrast, the study by Foucher et al.11 examined patients with a mean BMI between 24 and 25 kg/m2. Although prior investigations have shown that obesity is an independent risk factor for development of HCC,24–26 our study was not designed or powered to specifically address this question.
Age at presentation and gender are important risk factors for the development of chronic liver disease.29 Serum ALT elevation has also been previously shown to be associated with an increased risk for HCC independent of liver disease aetiology.30 In this study, we found that patients with cirrhosis and HCC were older, and had increased AST with reduced albumin values compared with controls with cirrhosis alone. However, no correlation was found between liver stiffness and the variables age, BMI, AST and albumin.
The lack of correlation between liver stiffness and BMI supports prior studies, which have shown that degree of steatosis does not significantly affect liver stiffness. However, several studies have shown that liver stiffness value can be significantly influenced by hepatic inflammation described indirectly by elevated serum aminotransferase levels.31, 32 Although the cases in our study had higher serum AST values than controls, the correlation between serum AST and liver stiffness value was not found to be significant in this study.
Several questions were raised by our study. As with other case–control studies, we are not able to establish a cause and effect relationship between HCC and liver stiffness. Our sample size was relatively small, and not all of the known aetiologies of liver disease were represented. For example, the precision for assessing statistical significance of correlations between age and AST levels with liver stiffness could have been improved with a larger sample size. However, an increase in case:control ratio beyond 1:3 or 1:4 would not result in any further appreciable gains in study power. Furthermore, we intentionally recruited individuals with compensated cirrhosis to eliminate the confounding effect of decompensated cirrhosis on liver stiffness. Of note, there were some baseline differences between cases and controls in our study. Although cases were 6 years older on average than controls, we prespecified that matching on age would occur within 5 years as the number of available controls was limited in our study. The average BMI was lower in cases with HCC than for controls. The clinical significance of this difference, however, is not felt to be highly influential as we have previously reported that BMI does not independently affect or influence liver stiffness measurement by MRE.17 Mean serum AST levels were higher for cases as well; however, the average background liver stiffness was not significantly higher than for controls. We would have expected higher average liver stiffness values for cases if the serum AST values reflected moderate to severe hepatic inflammation, which does not appear to be the case. The lower mean serum albumin level in cases is of interest. Although there was no evidence for ascites in these subjects, it raises a question about the unique contribution of albumin as a marker of hepatic function and its potential effect on liver stiffness. Future studies are planned to examine this association. Although histological confirmation was not available for each tumour nodule, the remaining patients without a previous biopsy had accepted radiological criteria for a diagnosis of HCC in the setting of cirrhosis.
Planar wave imaging for MRE was performed with a 2D wave inversion. The inversion process does not take into account propagation of waves at an angle relative to the plane of section. With reference to small structures, this problem can potentially yield liver stiffness values that may be incorrectly low owing to partial volume and edge effects in the inversion algorithm. This problem generally occurs whenever a lesion is smaller than the wavelength of the shear wave used. Therefore, one may have to use a higher-frequency and smaller wavelength acoustic waves to accurately estimate the stiffness of smaller structures. High-frequency waves, however, are more attenuated than lower-frequency waves in the liver.
In contrast to previous studies using ultrasound transient elastography, we did not observe a systematic association between liver stiffness assessed using MRE and the presence of HCC in patients with compensated cirrhosis. Furthermore, these results suggest that using elastography imaging in clinical practice for patients with compensated cirrhosis to individualise screening and surveillance for HCC cannot be strongly recommended at the present time.