Impact of diffusion-weighted MR imaging on the characterization of small hepatocellular carcinoma in the cirrhotic liver

Abstract

Purpose

The purpose of this study was to determine whether or not adding diffusion-weighted magnetic resonance imaging (DWI) to conventional magnetic resonance (MR) imaging sequences improves the characterization of small hepatocellular carcinoma (HCC) (≤2 cm) in the setting of cirrhotic liver compared to conventional sequences alone.

Materials and Methods

A total of 62 cirrhotic liver patients with 82 nodules smaller than 2 cm in diameter were enrolled, and all lesions were pathologically confirmed. For the first reading session, which included precontrast T1- and T2-weighted images and T1 dynamic contrast-enhanced images, preindicated lesions by a study coordinator were characterized by two radiologists. They determined the confidence levels in consensus for the presence of small HCC into four grades. In another session, respiratory-triggered diffusion-weighted MR images (b factor=50, 400 and 800 s/mm²) were added to the previously reviewed images, and the same two radiologists again determined the confidence levels. The diagnostic performance of the combined DWI–conventional sequences set and the conventional sequences alone set was evaluated using receiver operating characteristic curves. Sensitivity and specificity values for characterizing small HCCs were also calculated.

Results

The area under the receiver operating characteristic curve for the second interpretation session (0.86) was significantly higher (P=.038) than that of the first session (0.76). The sensitivity was significantly increased from 75.7% to 87.8% by adding DWI to the conventional sequences (P=.015). No significant differences were observed for specificity values.

Conclusion

Adding DWI to conventional imaging modalities improves the diagnosis of small HCCs in the cirrhotic liver in terms of diagnostic performance and sensitivity by increasing reader confidence.

Introduction

Early diagnosis of hepatocellular carcinoma (HCC) is of the utmost importance because it allows the detection of candidates for curative treatments such as transplantation, resection or local ablation therapy [1], [2]. With recent advances in radiologic techniques and the systematic surveillance of cirrhotic patients, there has been an increase in the detection of small focal nodular lesions. But HCC is a long multistage process, with variable features at the early stages of this tumor, and a definitive diagnosis of a nodular lesion in liver cirrhosis remains a difficult task. Enhancement in the arterial phase and washout in the portal venous and delayed phases are now regarded as distinctive features of HCC in liver cirrhosis [3]. According to the recently revised and updated American Association for the Study of Liver Diseases (AASLD) criteria, for lesions ≥1 cm, a single dynamic imaging study [multiphasic computed tomographic scan or dynamic magnetic resonance imaging (MRI)] showing this typical vascular pattern is enough to confirm the diagnosis of HCC, whereas for nodules <1 cm, an ultrasound follow-up at 3-month intervals is recommended to detect changes in size or a change in the vascular pattern [4]. But some small HCCs, ≤2 cm, can be misdiagnosed and do not satisfy these imaging criteria in up to 45% of cases using dynamic MRI [5] because of significant overlaps between the dynamic imaging findings of benign and malignant lesions in liver cirrhosis. Intense arterial uptake without washout might be present in regenerative nodules, dysplastic nodules (DNs), focal nodular hyperplasia or arterioportal shunts, and up to 57% of small hypervascular HCCs do not show washout on delayed venous phase [6], [7]. Furthermore, a number of truly hypovascular HCCs do exist [8], [9] and represent 17% of HCCs with a diameter of 1 to 2 cm [10]. Alternative approaches, particularly functional MRI such as diffusion-weighted MRI (DWI), are expected to improve the ability to characterize these small lesions. DWI enables the noninvasive characterization of biological tissues based on the diffusion properties of water molecules, and it has become a practical tool for MRI of the liver [11]. Because DWI is fundamentally different from the conventional morphological and hemodynamic-based imaging techniques, DWI may provide additional information on disease-associated histological changes in lesions. In tumorous structures, cell density considerably increases with a decrease in the extracellular space. This is accompanied by a subsequent decrease in mobility, which leads to restricted diffusion [12]. Meanwhile, DWI has been applied to body MRI, including liver imaging for the assessment of focal lesions according to the restricted water diffusion and the low apparent diffusion coefficient (ADC) values for malignant lesions [13], [14], [15], [16]. To the best of our knowledge, only a limited number of studies have been performed on the use of DWI for the specific detection or characterization of HCC in liver cirrhosis [17], [18], [19], [20], and only one study focused on HCCs smaller than 2 cm [17].

The aim of this prospective study was to investigate additional diagnostic contributions of DWI compared to conventional sequences alone for the characterization of small HCCs (≤20 mm) on the cirrhotic liver using qualitative scoring.