• adc
• cystic neoplasms
• diffusion-weighted imaging
• mr imaging
• pancreas

Introduction
Pancreatic cystic neoplasms are a etherogenous group of lesions, ranging from completely benign processes to invasive malignant tumors: many of these have specific features that are well visualized by cross-sectional imaging. Since biopsy diagnosis is inaccurate in a high proportion of cases, imaging plays an important role in identifying or excluding malignancy. Both CT and MRI allow optimal evaluation of location, morphology, internal architecture and enhancement characteristics of these lesions. MRI imaging and/or CT are indicated in all patients with cystic lesion of the pancreas for the differential diagnosis and for depicting signs suggestive of malignancy. Magnetic Resonance Imaging with MR cholangiopancreatography accurately depicts the morphologic features of the cyst and has the advantage of demonstrating the relationship of the cyst to the pancreatic ductal system. Magnetic Resonance Imaging is potentially able to reduce the number of differential diagnoses because of its intrinsic high soft tissue contrast resolution, being able to depict internal features of the cystic neoplasms, such as septa and cysts contents, and by exploiting the lesion-ductal system relationship, by means of MR/MRCP imaging. However the lesion characterization remains complicated due to an overlap in the radiologic and clinical features and the mimics between this find of lesions. In this setting diffusion-weighted imaging, including apparent diffusion coefficient (ADC) measurement for the quantification of diffusivity, may help in the differential diagnosis of pancreatic cystic neoplasms. The aim of our study is to analyze the potential of DWI-MRI in the differentiation of pancreatic cystic neoplasms.
Material and Methods
We retrospectively selected a total number of 223 patients (130 women and 93 men; age range: 16-88 years; mean age: 64 years;SD:14) with neoplastic and non-neoplastic pancreatic cystic lesions. The lesions were categorized in five groups: serous cystoadenomas, mucinous cystoadenomas, IPMNs, degenerated IPMNs and pseudocysts. All patients underwent MR examination performed on superconductive system operating at 3T. MR imaging protocol included axial T1w/T2w sequences, MRCP, diffusion-weighted MR imaging with multiple b values in all diffusion directions and contrast-enhanced T1-weighted sequences. All ADC values measurements were obtained from the images with multiple-b values and were perfomed for each pancreatic cystic lesions.
Results
Mean ADC value was 2,57x10-3 mm2/s (range 1,10x10-3-3,32x10-3 mm2/s) for serous cystoadenomas (range 1,10x10-3-3,32x10-3 mm2/s) and 2,73x10-3 mm2/s for mucinous cystoadenomas (range 1,13x10-3-3,24x10-3 mm2/s). No significant difference in terms of ADC values was identified between subtypes of IPMNS, in particular the mean ADC value was 2,72x10-3 mm2/s for IPMN-branch duct (range 1,71x10-3-3,70x10-3 mm2/s), 2,81x10-3 mm2/s for IPMN-mixed type (range 2,09x10-3-3,35x10-3 mm2/s) and 2,84x10-3 mm2/s for IPMN-main duct (range 2,29x10-3-3,11x10-3 mm2/s). But we found an average ADC value of all the benign IPMNs was 2,79x10-3 mm2/s and the mean ADC value was significantly lower in degenerated IPMNs (1,83x10-3 mm2/s with the ADC values ranged between 1,02 and 3,20x10-3 mm2/s). The ADC values of pseudocysts ranged from 1,09 to 3,18x10-3 mm2/s with a mean value of 2,67x10-3 mm2/s. A statistically significant difference was observed between the ADC values of degenerated IPMNs and the ADC of each other category (p<0,001), respectively IPMNs (the benign counterpart), serous cystoadenomas, mucinous cystoadenomas and pseudocysts. The statistical analysis showed that the ADC value of IPMN was significantly higher than the ADC of serous cystoadenomas (p=0,0024). Mucinous cysts represent the predominant pre-malignant disease, and these include all subtypes of IPMNs, and mucinous cystoadenomas. A statistically significant difference was observed between the ADC values of the latter category (IPMNs + mucinous cystoadenomas) and the ADC of serous cystoadenomas (p=0,014).
Conclusion
Our data suggest that diffusion-weighted imaging may be helpful in the differential diagnosis of pancreatic cystic neoplasms.