Role of diffusion-weighted MR imaging in predicting the grade of nonfunctional pancreatic neuroendocrine tumors

The purpose of this study was to describe the magnetic resonance imaging (MRI) findings including diffusion-weighted MRI of nonfunctional pancreatic neuroendocrine tumors (PanNETs) and their hepatic metastases, and investigate the relationships between MRI features and histopathological findings for each grade of PanNETs.A total of 30 patients were included. There were 14 men and 16 women with a mean age of 61.60±11 (SD) years (range: 31-81years). PanNET lesions were analyzed qualitatively (signal intensities, contrast enhancement, lesion margins, presence of metastasis and characteristics of metastases) and quantitatively (signal intensity ratios, contrast enhancement indices and normalized apparent diffusion coefficient [ADC]). The relationships between MRI findings and histopathological findings were evaluated.Among 30 nonfunctional PanNETs, 11 were high-grade tumors, 10 were intermediate and 9 were low-grade tumors. All high grade PanNETs showed low to intermediate signal on T2-weighted images and ill-defined borders. All intermediate grade PanNETs had intermediate and 6 low grade PanNETs have high signal on T2-weighted images. Patients with hepatic metastases from high grade PanNETs had cystic component in 8/10 (80%) and wash-out in 7/10 (70%) whereas intermediate grade PanNETs had none (P0.05). The normalized ADC values of high grade PanNETs was lower than those of intermediate and low grade PanNETs (P0.05).The presence of cystic component or contrast wash-out in hepatic metastases correlates with high grade PanNETs. The pre-operative MRI combined with DWI has an important role in grading and surgical planning of PanNETs.