Nonhypervascular pancreatic neuroendocrine tumors: spectrum of MDCT imaging findings and differentiation from pancreatic ductal adenocarcinoma
Summary Purpose: to determine contrast-enhanced MDCT features to differentiate nonhypervascular pancreatic neuroendocrine tumors (PNETs) from pancreatic ductal adenocarcinomas (PDACs). Methods and materials. We included 74 patients with PNETs and 80 patients with PDACs who underwent preoperative MDCT. Two radiologists evaluated the morphologic characteristic and enhancement patterns of the tumors. Quantitative and qualitative analysis was performed, including evaluation of tumor size, homogeneity, presence of pancreatic duct dilatation and tumor invasion to the adjacent vessels and peripancreatic infiltration. Tumor-to-pancreas enhancement ratio was defined as the Hounsfield units (HU) value of the tumor divided by the HU value of the pancreas. There were two groups: hypervascular PNETs showing hyperenhancement on arterial phase images and nonhypervascular PNETs, showing iso- or hypoenhancement on arterial phase images. Results. Given the data of arterial enhancement, 43 PNETs were hypervascular and 31 were nonhypervascular. Non-hypervascular PNETs, compared with ductal adenocarcinomas, more often had smooth and clear contours and more often had a cystic component in the structure (p <0.001). Calcinations in the structure of ductal adenocarcinomas were absent and were found 150 only in the structure of non-hypervascular PNETs (p <0.01). The ductal adenocarcinomas of the pancreas more often caused dilatation of the main pancreatic duct (p <0.001), invasion into the surrounding fat tissue (p <0.0001) and vessels (p = 0.011). The most accurate MDCT-findings to predict nonhypervascular PNET were the absence of pancreatic duct dilatation and peripancreatic infiltration (79% and 92% accuracy), the presence of intratumoral blood vessels (77%) and relative enhancement intensity in venous phase > 0.9 (76%). Conclusion. Combined assessment of the enhancement and morphologic characteristics can improve the differentiation between nonhypervascular PNETs and PDAC at contrast-enhanced MDCT.