Elsevier

Magnetic Resonance Imaging

Volume 30, Issue 7, September 2012, Pages 916-925
Magnetic Resonance Imaging

Original contribution
Imaging features of small (≤3 cm) pancreatic solid tumors on gadoxetic-acid-enhanced MR imaging and diffusion-weighted imaging: an initial experience

https://doi.org/10.1016/j.mri.2012.02.017Get rights and content

Abstract

Objective

The objective was to determine imaging features that distinguish small (≤3cm) solid pancreatic adenocarcinoma, neuroendocrine tumor (NET) and solid pseudopapillary tumor (SPT) on gadoxetic-acid-enhanced magnetic resonance imaging (MRI) and diffusion-weighed imaging (DWI).

Materials and methods

Twenty-four adenocarcinomas, 10 NETs and 8 SPTs were retrospectively included. Two radiologists analyzed morphologic features, signal intensity of the tumors on MR images including DWI (b=800) and dynamic enhancement pattern with consensus. Tumor-to-parenchyma ratio and tumor apparent diffusion coefficients (ADCs) were quantitatively assessed.

Results

All adenocarcinomas had an ill-defined margin and irregular shape, and more frequently had pancreatic duct dilatation compared with other tumors (P<.05). All SPTs and all but one of the adenocarcinomas (95.8%) had no arterial enhancement with progressively increased enhancement, whereas seven NETs (70%) had arterial enhancement with progressively decreased enhancement (P<.01). The mean value of tumor-to-parenchyma ratio on arterial and portal phases was significantly higher for NETs, and the mean value of tumor ADCs was significantly lower for SPTs than for other tumors (P<.05).

Conclusions

Gadoxetic-acid-enhanced MRI may aid in differentiation between small adenocarcinomas, NETs and SPTs based on morphologic features with dynamic enhancement pattern in adenocarcinomas, dynamic enhancement pattern with tumor-to-parenchyma ration on arterial and portal phases in NETs, and dynamic enhancement pattern with lower ADC value in SPTs.

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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