Original contributionImpact of diffusion-weighted MR imaging on the characterization of small hepatocellular carcinoma in the cirrhotic liver
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.
Section snippets
Study population
This study was conducted in agreement with French law (4 March 2002) and the Declaration of Helsinki [21]. The ethics committee at our institute deemed that ethical approval for this study was not required.
Between November 2008 and August 2010, all consecutive cirrhotic patients who underwent MRI of the liver including DWI sequences for characterization of undetermined lesions 2 cm or smaller previously detected during surveillance were eligible for enrolment in this study. Patients were
Characteristics of the lesions
Final diagnoses of the 82 nodules stratified by size are summarized in Table 2. The mean size of the nodules was 14.4±3.8 mm (range, 8–20 mm).
A total of 66 lesions from 53 patients were verified as HCCs. The histopathological grade was available for 65 HCCs. Another 16 lesions in 14 patients were non-HCC lesions (including five patients who also had HCC at the same time). With regard to the number of eligible lesions smaller than 2 cm per patient, 50 patients had one lesion, 6 patients had two
Discussion
The results of our study demonstrated that, in addition to conventional MRI sequences, visual evaluation of DWI sequences yielded a significantly higher diagnostic performance and sensitivity for the diagnosis of small HCCs in patients with liver cirrhosis, especially for well-differentiated HCCs. According to the increased confidence level for the sustained hyperintensity with increasing b factors for most of the small HCCs in our study, the DWI sequences compensated dynamic contrast-enhanced
Acknowledgements
We acknowledge Melisa Bakir, radiology technician, GIE IRM Lyon Nord 103 Grande rue de la Croix-Rousse 69004 Lyon, for technical support.
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