Differential diagnosis of non-hypervascular pancreatic neuroendocrine tumor and pancreatic ductal adenocarcinoma by MRI

Abstract

Objective To investigate the value of MR unenhancement and dynamic enhancement scans for distinguishing non-hypervascular pancreatic neuroendocrine tumor (PNET) from pancreatic ductal adenocarcinoma (PDAC). Methods Thirty five patients (45 lesions) with pathologically confirmed PNETs and 52 patients (53 lesions) with PDACs were retrospectively analyzed before surgery. All patients underwent MR unenhanced and dynamic enhanced scans (including arterial, venous and delayed phase). Based on arterial enhancement, PNETs were divided into hypervascular and non-hypervascular lesions. The morphologic characteristics (including location, size, quantity, margin and signal intensity) and enhancement patterns of non-hypervascular PNETs and PDACs were evaluated. Involvement of the pancreatic duct and bile duct, vascular invasion, peripancreatic infiltration and other organs metastasis were observed. Independent sample ttest was used to compare signal intensity ratio of nonhypervascular PNET and PDAC. Chi-square test was used to compare MRI characteristic and secondary signs. Results PNET included 20 hypervascular and 25 nonhypervascular lesions. Enhancement degree of non-hypervascular PNET was higher than PDAC in the arterial, venous and delayed phase (P<0.01). Non-hypervascular PNET showed significantly higher frequencies (P<0.01) of venous hyper-or isoenhancement (20/25), delayed hyper-or isoenhancement (23/25) and a well-defined margin (17/25), but lower frequencies of ductal stricture and dilatation (P<0.01), pancreas atrophy (P<0.05), bile duct stricture (2/25), peripancreatic infiltration (8/25, P<0.01) and vascular invasion (8/25, P<0.05), when compared with PDAC. Conclusion A well-defined margin, hyper-or isoenhancement in the venous and delayed phase,and without ductal dilatation and pancreas atrophy are more common in non-hypervascular PNET, which may be distinguished from PDAC. Key words: Pancreatic neoplasms; Magnetic resonance imaging; Neuroendocrine tumor