Original contributionImaging features of small (≤3 cm) pancreatic solid tumors on gadoxetic-acid-enhanced MR imaging and diffusion-weighted imaging: an initial experience
Introduction
The applications of gadoxetic-acid (Gd-EOB-DTPA; gadoxetic acid disodium, Primovist, Bayer-Schering HealthCare AG)-enhanced imaging and diffusion-weighted imaging (DWI) in liver magnetic resonance imaging (MRI) are emerging issues in the fields of contrast media and imaging technology, respectively [1], [2], [3], [4]. Considering the dual requirement of liver imaging, namely, the detection and characterization of focal liver lesions, gadoxetic acid is increasingly used for liver MRI because it provides hemodynamic information on focal liver lesions during the early vascular–interstitial phase and enhances lesion detection with the hepatobiliary phase [1], [2], [3]. The application of DWI to hepatobiliary–pancreas imaging has become popular due to recent advances in MR technology, particularly in coil systems [1], [4]. Since DWI is quick to perform and can be easily incorporated into a standard clinical protocol, it is now routinely conducted.
Compared with conventional gadolinium chelates or gadobenate dimeglumine, gadoxetic acid has peculiar characteristics including its relatively weak, short activity as an extracellular space contrast (ECS) agent and early, strong action as a hepatocyte-selective agent [5], [6], [7], [8]. Therefore, a concern in using gadoxetic acid is that there may be discordance in the enhancement patterns of abdominal organ and tumors between conventional gadolinium chelates and gadoxetic acid, which could lead to confusion in lesion characterization. It has been reported that the course of enhancement of normal pancreas on gadoxetic-acid-enhanced MRI differs from that on gadobutrol-enhanced imaging [6]. Thus, the enhancing patterns of small solid pancreatic tumors on gadoxetic-acid-enhanced MRI can differ from those on MRI with ECS agent. Given that gadoxetic acid has been widely applied to hepatobiliary–pancreas MRI because of its benefit for evaluating hepatic tumors, it is highly relevant to investigate the imaging features of small solid pancreatic tumors on gadoxetic-acid-enhanced MRI. In our institution, during the past 3 years, we tried to expand the application range of gadoxetic acid to pancreatic tumors.
In addition, the useful role of DWI in differentiating pancreatic cancers from mass-forming pancreatitis, detection of pancreatic adenocarcinoma, and detection and localization of small insulinoma has been studied on several reports, and the use of high-b-value DWI allowed the detection of pancreatic adenocarcinoma with a sensitivity of 96.2% and a specificity of 98.6% [9], [10], [11], [12]. But Wang et al. reported the variable mean apparent diffusion coefficient (ADC) values of adenocarcinomas and neuroendocrine tumor (NET) according to tumor grade, tumor cellularity and extracellular fibrosis [13], [14]. Therefore, imaging features of small solid pancreatic tumors on DWI with ADC map could be also affected by specific tumor types such as adenocarcinoma, NET, etc.
To the best of our knowledge, no study has been conducted to investigate imaging features of most common small solid tumors such as adenocarcinoma, NET and solid pseudopapillary tumor (SPT) in the pancreas on gadoxetic-acid-enhanced MRI and DWI. Accordingly, we conducted our study to determine the imaging features for distinguishing small (≤3 cm) solid pancreatic tumors such as adenocarcinoma, NET and SPT on gadoxetic-acid-enhanced MRI and DWI.
Section snippets
Materials and methods
Institutional review board approval was obtained, and informed patient consent was waived because of the retrospective nature of our study.
Results
Qualitative analysis is presented in Table 1. All adenocarcinomas had an ill-defined margin and irregular shape compared with NETs (P=.024, P<.001) and SPTs (P<.001, both) (Fig. 1). Adenocarcinomas had more frequent pancreatic duct dilatation than NETs (P<.001) and SPTs (P<.001) (Fig. 1). All SPTs and all but one of the adenocarcinomas (95.8%) had no arterial enhancement with progressively increased enhancement, but seven NETs (70%) had arterial enhancement with progressively decreased
Discussion
According to the results of our study, small adenocarcinomas can be characterized by an ill-defined margin and irregular shape, presence of pancreatic duct dilatation and no arterial enhancement with progressively increased enhancement on dynamic enhanced T1-weighted images, reaffirming results of previous studies [15], [16]. Small NETs can be characterized by arterial enhancement with progressively decreased enhancement on dynamic enhanced T1-weighted images and high tumor-to-parenchyma ratio
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