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Objectives: To evaluate MRI derived whole-tumour histogram analysis parameters in predicting pancreatic neuroendocrine neoplasm (panNEN) grade and aggressiveness., Methods: Pre-operative MR of 42 consecutive patients with panNEN >1 cm were retrospectively analysed. T1-/T2-weighted images and ADC maps were analysed. Histogram-derived parameters were compared to histopathological features using the Mann-Whitney U test. Diagnostic accuracy was assessed by ROC-AUC analysis; sensitivity and specificity were assessed for each histogram parameter., Results: ADC entropy was significantly higher in G2-3 tumours with ROC-AUC 0.757; sensitivity and specificity were 83.3 % (95 % CI: 61.2-94.5) and 61.1 % (95 % CI: 36.1-81.7). ADC kurtosis was higher in panNENs with vascular involvement, nodal and hepatic metastases (p= .008, .021 and .008; ROC-AUC= 0.820, 0.709 and 0.820); sensitivity and specificity were: 85.7/74.3 % (95 % CI: 42-99.2 /56.4-86.9), 36.8/96.5 % (95 % CI: 17.2-61.4 /76-99.8) and 100/62.8 % (95 % CI: 56.1-100/44.9-78.1). No significant differences between groups were found for other histogram-derived parameters (p >.05)., Conclusions: Whole-tumour histogram analysis of ADC maps may be helpful in predicting tumour grade, vascular involvement, nodal and liver metastases in panNENs. ADC entropy and ADC kurtosis are the most accurate parameters for identification of panNENs with malignant behaviour., Key Points: • Whole-tumour ADC histogram analysis can predict aggressiveness in pancreatic neuroendocrine neoplasms. • ADC entropy and kurtosis are higher in aggressive tumours. • ADC histogram analysis can quantify tumour diffusion heterogeneity. • Non-invasive quantification of tumour heterogeneity can provide adjunctive information for prognostication.

While abutment, encasement or vessel occlusion are identified in most patients with a pancreatic tumor, tumor thrombosis is an uncommon finding. In particular, there are no description in the literature of tumor thrombosis associated with ductal adenocarcinoma, the most common pancreatic tumor. On the other hand, surgical series reveal that tumor thrombosis is associated with about 5% of pancreatic neuroendocrine neoplasms (PanNENs), and literature data suggest that this finding is frequently underreported on pre-operative imaging examinations. Tumor thrombosis may be clinically relevant, causing splenoportomesenteric hypertension, possibly responsible for life-threatening upper gastrointestinal bleeding. Bland thrombosis caused by direct infiltration of peri-pancreatic vessels frequently determines surgical unresectability, even in neuroendocrine tumors; on the opposite, tumor thrombosis associated with PanNENs do not exclude surgery per se, even though both morbidity and mortality can be increased by such condition. Considering the favorable prognosis of PanNENs and the frequent need to treat tumor thrombosis in order to prevent complications or to relieve symptoms, it is of paramount importance for radiologists the knowledge of the variety of findings associated with tumor thrombosis in PanNENs.

Aim: To describe magnetic resonance (MR) imaging features of pancreatic neuroendocrine neoplasms (PanNENs) according to their grade and tumor-nodes-metastases stage by comparing them to histopathology and to determine the accuracy of MR imaging features in predicting their biological behavior., Methods: This study was approved by our institutional review board; requirement for informed patient consent was waived due to the retrospective nature of the study. Preoperative MR examinations of 55 PanNEN patients (29 men, 26 women; mean age of 57.6 years, range 21-83 years) performed between June 2013 and December 2015 were reviewed. Qualitative and quantitative features were compared between tumor grades and stages determined by histopathological analysis., Results: Ill defined margins were more common in G2-3 and stage III-IV PanNENs than in G1 and low-stage tumors ( P < 0.001); this feature had high specificity in the identification of G2-3 and stage III-IV tumors (90.3% and 96%, 95%CI: 73.1-97.5 and 77.7-99.8). The mean apparent diffusion coefficient value was significantly lower in G2-3 and stage III-IV lesions compared to well differentiated and low-stage tumors (1.09 × 10 -3 mm 2 /s vs 1.45 × 10 -3 mm 2 /s and 1.10 × 10 -3 mm 2 /s vs 1.53 × 10 -3 mm 2 /s, P = 0.003 and 0.001). Receiving operator characteristic analysis determined optimal cut-offs of 1.21 and 1.28 × 10 -3 mm 2 /s for the identification of G2-3 and stage III-IV tumors, with sensitivity and specificity values of 70.8/80.7% and 64.5/64% (95%CI: 48.7-86.6/60-92.7 and 45.4-80.2/42.6-81.3)., Conclusion: MR features of PanNENs vary according to their grade of differentiation and their stage at diagnosis and could predict the biological behavior of these tumors., Competing Interests: Conflict-of-interest statement: We have no financial relationships to disclose.