Diffusion-weighted imaging (DWI) of hepatocellular carcinomas: a retrospective analysis of the correlation between qualitative and quantitative DWI and tumour grade

Highlights

• High DWI SI and low ADC values were associated with more advanced histological grade.

• SI values on DWI could only distinguish well-differentiated HCC from other HCC.

• ADC values could distinguish the different grades of HCC.

Aim

To evaluate the application of qualitative and quantitative diffusion-weighted imaging (DWI) in predicting the histological grade of hepatocellular carcinoma (HCC).

Materials and methods

Two hundred and fifty-four patients with pathologically confirmed HCC who underwent hepatic DWI on a 1.5-T platform (b = 0, 600 s/mm²) were evaluated retrospectively. HCCs were divided into well-, moderately, and poorly differentiated groups. The relationships between naked-eye signal intensity (SI), SI values, apparent diffusion coefficient (ADC) values on DWI, and the histopathological differentiation of HCC were analysed. Receiver operating characteristic (ROC) curves were drawn to determine the optimal operating points (OOPs) of the SI and ADC values to predict the tumour grade.

Results

A weak negative correlation (r=–0.350, p<0.05) was obtained between naked-eye SI and histological grade. There was a significant difference in mean SI values between well- (68.32±31.71) and moderately (102.39±45.55)/poorly (114.55±32.15) differentiated HCC but not between moderately and poorly differentiated HCC. The OOP of the SI value by ROC curve analysis was 66.5 to predict well-differentiated HCC. The mean ADC values of well-, moderately, and poorly differentiated HCC were 1.67±0.13×10⁻³, 1.31±0.16×10⁻³, and 1.08±0.11×10⁻³ mm²/s, respectively, with significant differences between any two combinations of groups. The OOPs of ADC to diagnose well- and poorly differentiated HCC were 1.5×10⁻³ and 1.24×10⁻³ mm²/s, respectively.

Conclusion

Qualitative and quantitative SI and ADC values at DWI may be useful to estimate the histological grade of HCC preoperatively and non-invasively.

Introduction

Hepatocellular carcinoma (HCC) is the most common primary malignant neoplasm of the liver, and the third most common cause of death linked to tumours worldwide,1, 2 with increasing prevalence.1, 3 Surgical resection is one of the most efficient treatments for this disease; however, despite improvements in surgical techniques, the prognosis of HCC is poor due to its high rate of postoperative recurrence, up to 70% at the 5-year follow-up.4, 5 The grade of histological differentiation of HCC is the most important factor influencing early post-surgery recurrence. Patients with poorly differentiated HCC have higher recurrence rates and a poorer prognosis after surgical resection than do those with well- and moderately differentiated HCC.6, 7, 8 Okusaka et al.⁹ reported that wider resection and more frequent follow-up were needed for patients with poorly differentiated HCC. Oishi et al.⁶ concluded that patients with a poorly differentiated HCC >3 cm should not undergo liver transplantation. Thus, preoperative prediction of the histological grade of HCC is pivotal to better treatment planning; however, the histological grade of HCC is not routinely given by biopsy pre-surgery as it is invasive and can result in procedure-related complications.¹⁰ Therefore, preoperative assessment of the histological grade of HCC using non-invasive procedures is of great importance.

Diffusion-weighted imaging (DWI) is the only functional magnetic resonance imaging (MRI) technique, and apparent diffusion coefficient (ADC) values provide a quantitative index of diffusion characteristics. DWI can evaluate water molecule diffusion in vivo and reflects the histopathological condition of organs and tissues by virtue of a high scan speed without the need for a contrast agent. Thus, it is more practical in patients with kidney failure, leading to wider clinical applications. DWI can not only indicate the morphological characteristics of a lesion but also quantitatively analyse its structure and tissue components, making up for the shortcomings of conventional MRI, which can provide only morphological and haemodynamic information. DWI has been widely used for the diagnosis and differential diagnosis of neoplasms in the liver; however, few studies have considered the relationship between quantitative signal intensity (SI) values, ADC values on DWI, and the histological grade of HCC, and studies have been limited by small sample sizes.¹¹ Moreover, results regarding the relationship between ADC values and the histological grade of HCC are contradictory.12, 13, 14, 15, 16 This study evaluated the efficacy of preoperatively predicting the histological grade of HCC using DWI by analysing the relationship between SI measured by the naked eye, SI values, ADC values, and the different histological grades of HCC. The present study had a much larger sample size and examined more indexes than previous studies, resulting in greater significance.