Diffusion-weighted imaging in characterization of cystic pancreatic lesions

Towards a Simplified and Cost-Effective Diagnostic Algorithm for the Surveillance of Intraductal Papillary Mucinous Neoplasms (IPMNs): Can We Save Contrast for Later?

The increased detection of pancreatic cysts in recent years has triggered extensive diagnostic investigations to clarify their potential risk of malignancy, resulting in a large number of patients undergoing numerous imaging follow-up studies for many years. Therefore, there is a growing need for optimization of the current surveillance protocol to reduce both healthcare costs and waiting lists, while still maintaining appropriate sensibility and specificity. Imaging is an essential tool for evaluating patients with intraductal papillary mucinous neoplasms (IPMNs) since it can assess several predictors for malignancy and thus guide further management recommendations. Although contrast-enhanced magnetic resonance imaging (MRI) with magnetic resonance cholangiopancreatography (MRCP) has been widely recommended by most international guidelines, recent results support the use of unenhanced abbreviated-MRI (A-MRI) protocols as a surveillance tool in patients with IPMN. In fact, A-MRI has shown high diagnostic performance in malignant detection, with high sensitivity and specificity as well as excellent interobserver agreement. The aim of this paper is, therefore, to discuss the current available evidence on whether the implementation of an abbreviated-MRI (A-MRI) protocol for cystic pancreatic lesion surveillance could improve healthcare economics and reduce waiting lists in clinical practice without significantly reducing diagnostic accuracy.

DWI Metrics Differentiating Benign Intraductal Papillary Mucinous Neoplasms from Invasive Pancreatic Cancer: A Study in GEM Models

KPC (KrasG12D:Trp53R172H:Pdx1-Cre) and CKS (KrasG12D:Smad4L/L:Ptf1a-Cre) mice are genetically engineered mouse (GEM) models that capture features of human pancreatic ductal adenocarcinoma (PDAC) and intraductal papillary mucinous neoplasms (IPMN), respectively. We compared these autochthonous tumors using quantitative imaging metrics from diffusion-weighted MRI (DW-MRI) and dynamic contrast enhanced (DCE)-MRI in reference to quantitative histological metrics including cell density, fibrosis, and microvasculature density. Our results revealed distinct DW-MRI metrics between the KPC vs. CKS model (mimicking human PDAC vs. IPMN lesion): the apparent diffusion coefficient (ADC) of CKS tumors is significantly higher than that of KPC, with little overlap (mean ± SD 2.24±0.2 vs. 1.66±0.2, p<10−10) despite intratumor and intertumor variability. Kurtosis index (KI) is also distinctively separated in the two models. DW imaging metrics are consistent with growth pattern, cell density, and the cystic nature of the CKS tumors. Coregistration of ex vivo ADC maps with H&E-stained sections allowed for regional comparison and showed a correlation between local cell density and ADC value. In conclusion, studies in GEM models demonstrate the potential utility of diffusion-weighted MRI metrics for distinguishing pancreatic cancer from benign pancreatic cysts such as IPMN.

Quantitative MRI of Pancreatic Cystic Lesions: A New Diagnostic Approach

The commonly used magnetic resonance (MRI) criteria can be insufficient for discriminating mucinous from non-mucinous pancreatic cystic lesions (PCLs). The histological differences between PCLs’ fluid composition may be reflected in MRI images, but cannot be assessed by visual evaluation alone. We investigate whether additional MRI quantitative parameters such as signal intensity measurements (SIMs) and radiomics texture analysis (TA) can aid the differentiation between mucinous and non-mucinous PCLs. Fifty-nine PCLs (mucinous, n = 24; non-mucinous, n = 35) are retrospectively included. The SIMs were performed by two radiologists on T2 and diffusion-weighted images (T2WI and DWI) and apparent diffusion coefficient (ADC) maps. A total of 550 radiomic features were extracted from the T2WI and ADC maps of every lesion. The SIMs and TA features were compared between entities using univariate, receiver-operating, and multivariate analysis. The SIM analysis showed no statistically significant differences between the two groups (p = 0.69, 0.21–0.43, and 0.98 for T2, DWI, and ADC, respectively). Mucinous and non-mucinous PLCs were successfully discriminated by both T2-based (83.2–100% sensitivity and 69.3–96.2% specificity) and ADC-based (40–85% sensitivity and 60–96.67% specificity) radiomic features. SIMs cannot reliably discriminate between PCLs. Radiomics have the potential to augment the common MRI diagnosis of PLCs by providing quantitative and reproducible imaging features, but validation is required by further studies.

Cystic Lesions of the Pancreas: Is Apparent Diffusion Coefficient Value Useful at 3 T Magnetic Resonance Imaging?

OBJECTIVE

The objective of this study is to determine the role of apparent diffusion coefficient (ADC) value at 3T magnetic resonance imaging (MRI) in the characterization of pancreatic cystic lesions.

METHODS

We retrospectively selected a total number of 223 patients with a conclusive diagnosis of pancreatic cystic lesion, previously undergoing MR examination on a 3 T system. The MRI protocol first included axial T1/T2-weighted sequences and magnetic resonance cholangiopancreatography. Diffusion-weighted MRI was performed using a spin-echo echo-planar sequence with multiple b values (0, 150, 500, 1000, and 1500 s/mm2) in all diffusion directions, obtaining an ADC map. Contrast-enhanced T1-weighted sequences were performed during the initial work-up of a pancreatic cystic lesion and when signs of malignancy were suspected during the MRI follow-up. The ADC value of each pancreatic lesion was measured using a monoexponential curve fitting with all the multiple b.

RESULTS

The final diagnosis of our study group included the following: serous cystadenomas (n = 42), mucinous cystadenomas (n = 14), intraductal papillary mucinous neoplasms (IPMNs) (n = 121), IPMNs with signs of malignancy at histopathologic examination (n = 24), pseudocysts (n = 9), other cystic lesions (n = 13). A statistically significant difference was observed between the ADC values of malignant IPMNs and those of each other group of pancreatic lesions (P < 0.001). The ADC value of benign IPMN was significantly higher than that of serous cystadenomas (P = 0.024). A statistically significant difference was observed between the ADCs of all mucinous cystic tumors (benign IPMNs together to mucinous cystadenomas) and the ADCs of serous cystadenomas (P = 0.014).

CONCLUSIONS

Fitted ADC value obtained at 3T MRI may be helpful in the characterization of pancreatic cystic lesions with particular regards of differential diagnosis between mucinous and serous cystic tumors and between malignant and benign IPMNs.

Pancreas MRI Segmentation Into Head, Body, and Tail Enables Regional Quantitative Analysis of Heterogeneous Disease

BACKGROUND

Quantitative imaging studies of the pancreas have often targeted the three main anatomical segments, head, body, and tail, using manual region of interest strategies to assess geographic heterogeneity. Existing automated analyses have implemented whole-organ segmentation, providing overall quantification but failing to address spatial heterogeneity.

PURPOSE

To develop and validate an automated method for pancreas segmentation into head, body, and tail subregions in abdominal MRI.

STUDY TYPE

Retrospective.

SUBJECTS

One hundred and fifty nominally healthy subjects from UK Biobank (100 subjects for method development and 50 subjects for validation). A separate 390 UK Biobank triples of subjects including type 2 diabetes mellitus (T2DM) subjects and matched nondiabetics.

FIELD STRENGTH/SEQUENCE

A 1.5 T, three-dimensional two-point Dixon sequence (for segmentation and volume assessment) and a two-dimensional axial multiecho gradient-recalled echo sequence.

ASSESSMENT

Pancreas segments were annotated by four raters on the validation cohort. Intrarater agreement and interrater agreement were reported using Dice overlap (Dice similarity coefficient [DSC]). A segmentation method based on template registration was developed and evaluated against annotations. Results on regional pancreatic fat assessment are also presented, by intersecting the three-dimensional parts segmentation with one available proton density fat fraction (PDFF) image.

STATISTICAL TEST

Wilcoxon signed rank test and Mann-Whitney U-test for comparisons. DSC and volume differences for evaluation. A P value < 0.05 was considered statistically significant.

RESULTS

Good intrarater (DSC mean, head: 0.982, body: 0.940, tail: 0.961) agreement and interrater (DSC mean, head: 0.968, body: 0.905, tail: 0.943) agreement were observed. No differences (DSC, head: P = 0.4358, body: P = 0.0992, tail: P = 0.1080) were observed between the manual annotations and our method's segmentations (DSC mean, head: 0.965, body: 0.893, tail: 0.934). Pancreatic body PDFF was different between T2DM and nondiabetics matched by body mass index.

DATA CONCLUSION

The developed segmentation's performance was no different from manual annotations. Application on type 2 diabetes subjects showed potential for assessing pancreatic disease heterogeneity.

LEVEL OF EVIDENCE

4 TECHNICAL EFFICACY STAGE: 3.

Diagnostic Performance of Diffusion-Weighted Imaging for Differentiating Malignant From Benign Intraductal Papillary Mucinous Neoplasms of the Pancreas: A Systematic Review and Meta-Analysis

Objectives

To assess the diagnostic accuracy of diffusion-weighted imaging (DWI) in predicting the malignant potential in patients with intraductal papillary mucinous neoplasms (IPMNs) of the pancreas.

Methods

A systematic search of articles investigating the diagnostic performance of DWI for prediction of malignant potential in IPMNs was conducted from PubMed, Embase, and Web of Science from January 1997 to 10 February 2020. QUADAS-2 tool was used to evaluate the study quality. Pooled sensitivity, specificity, diagnostic odds ratio (DOR), positive likelihood ratios (PLR), negative likelihood ratios (NLR), and their 95% confidence intervals (CIs) were calculated. The summary receiver operating characteristic (SROC) curve was then plotted, and meta-regression was also performed to explore the heterogeneity.

Results

Five articles with 307 patients were included. The pooled sensitivity and specificity of DWI were 0.74 (95% CI: 0.65, 0.82) and 0.94 (95% CI: 0.78, 0.99), in evaluating the malignant potential of IPMNs. The PLR was 13.5 (95% CI: 3.1, 58.7), the NLR was 0.27 (95% CI: 0.20, 0.37), and DOR was 50.0 (95% CI: 11.0, 224.0). The area under the curve (AUC) of SROC curve was 0.84 (95% CI: 0.80, 0.87). The meta-regression showed that the slice thickness of DWI (p = 0.02) and DWI parameter (p= 0.01) were significant factors affecting the heterogeneity.

Conclusions

DWI is an effective modality for the differential diagnosis between benign and malignant IPMNs. The slice thickness of DWI and DWI parameter were the main factors influencing diagnostic specificity.

3D quantitative analysis of diffusion-weighted imaging for predicting the malignant potential of intraductal papillary mucinous neoplasms of the pancreas

Purpose

To investigate the predictors of intraductal papillary mucinous neoplasms of the pancreas (IPMNs) with high-grade dysplasia, using 2-dimensional (2D) analysis and 3-dimensional (3D) volume-of-interest-based apparent diffusion coefficient (ADC) histogram analysis.

Material and methods

The data of 45 patients with histopathologically confirmed IPMNs with high-grade or low-grade dysplasia were retrospectively assessed. The 2D analysis included lesion-to-spinal cord signal intensity ratio (LSR), minimum ADC value (ADC_min), and mean ADC value (ADC_mean). The 3D analysis included the overall mean (ADC_{overall mean}), mean of the bottom 10^th percentile (ADC_mean0-10), mean of the bottom 10-25^th percentile (ADC_mean10-25), mean of the bottom 25-50^th percentile (ADC_mean25-50), skewness (ADC_skewness), kurtosis (ADC_kurtosis), and entropy (ADC_entropy). Diagnostic performance was compared by analysing the area under the receiver operating characteristic curve (AUC). Inter-rater reliability was assessed by blinded evaluation using the intraclass correlation coefficient.

Results

There were 16 and 29 IPMNs with high- and low-grade dysplasia, respectively. The LSR, ADC_{overall mean}, ADC_mean0-10, ADC_mean10-25, ADC_mean25-50, and ADC_entropy showed significant between-group differences (AUC = 72-93%; p < 0.05). Inter-rater reliability assessment showed almost perfect agreement for LSR and substantial agreement for ADC_{overall mean} and ADC_entropy. Multivariate logistic regression showed that ADCoverall mean and ADCentropy were significant independent predictors of malignancy (p < 0.05), with diagnostic accuracies of 80% and 73%, respectively.

Conclusion

ADC_{overall mean} and ADC_entropy from 3D analysis may assist in predicting IPMNs with high-grade dysplasia.

The value of MRI in identifying pancreatic neuroendocrine tumour G3 and carcinoma G3

AIM

To explore the magnetic resonance imaging (MRI) differences between pancreatic neuroendocrine tumour grade 3 (pNET-G3) and pancreatic neuroendocrine carcinoma grade 3 (pNEC-G3).

MATERIALS AND METHODS

Between 2009 and 2019, 31 patients underwent pNEN-G3 resection with preoperative MRI in two local hospitals in China. The 31 patients were assigned to a pNET-G3 group (n=13) or a pNEC-G3 group (n=18). The MRI findings between the groups were compared.

RESULTS

There was no statistically significant difference between the two groups in lesion size, clinical characteristics, or laboratory indexes. The lesions showed high or slightly higher signal on diffusion-weighted imaging and decreased apparent diffusion coefficient (ADC) values, which differed between the two groups (p=0.013). The difference between the groups regarding positive enhancement integral, arterial phase and portal phase signal enhancement ratio were statistically significant; however, the delayed phase signal enhancement ratio was not significantly different.

CONCLUSIONS

pNET-G3 and pNEC-G3 showed different characteristics on MRI. In particular, the ADC value and dynamic enhanced imaging could have an important role in distinguishing between the two.

Role of volumetric multiparametric MRI in distinguishing between intraductal papillary mucinous neoplasms and serous cystadenoma

PURPOSE

To evaluate the use of volumetric multiparametric MRI in differentiating pancreatic intraductal papillary mucinous neoplasms (IPMNs) from serous cystadenomas (SCAs) METHODS: Included patients (123 patients with pancreatic cystic neoplasms (PCNs) measuring ≥ 10 mm) were stratified into two groups based on cyst type. Axial cyst size, region of interest (ROI)-based apparent diffusion coefficient (ADC) and volumetric data, including cyst volume, volumetric apparent diffusion coefficient (vADC), and volumetric venous enhancement (vVE) were extracted and compared between the two groups. Univariate and multiple logistic regression was used to develop models for distinguishing between IPMNs and SCAs.

RESULTS

Volume and size of the cysts, vVE and vADC and ROI-ADC were significantly different between the two groups. Cyst volume was significantly larger in SCAs (median = 14.1cm³, IQR 3.5-42.5) than in IPMNs (median = 2.5 cm³, IQR 1.1-6) (p < 0.001). IPMNs had a higher volumetric ADC value in comparison to SCAs (2925 ± 294 × 10^-6 mm²/s vs 2521 ± 202 × 10^-6 mm²/s, p < 0.001). However, IPMNs had lower vVE values compared to SCAs (37 signal intensity (SI) vs 86 SI, p < 0.001). Area under the ROC Curve (AUC) of the model that included vADC and cyst volume had 95% accuracy in distinguishing between the two groups. In comparison, the AUC of the model that included ROI-ADC and axial cyst size had 84% accuracy in distinguishing between the two groups. A threshold of 2615 × 10^-6 mm²/s for volumetric ADC resulted in the identification of IPMNs from SCAs with sensitivity and specificity of 90.8% and 73.5%, respectively.

CONCLUSION

IPMNs had smaller cyst volume, higher volumetric ADC and lower volumetric VE values compared to SCAs. Volumetric multiparametric MRI could be useful in differentiating between the IPMN and SCA groups.

Diffusion-weighted MRI versus FDG-PET/CT for diagnosing pancreatic cancer: an indirect comparison meta-analysis

BACKGROUND

Fluorodeoxyglucose positron emission tomography (FDG-PET)/computed tomography (CT) and diffusion-weighted magnetic resonance imaging (DWI or DW-MRI) are tools for the diagnosis of pancreatic cancer. However, comparison of their diagnostic performance remains unknown.

PURPOSE

To indirectly compare the diagnostic value of DWI and FDG-PET/CT in the detection of pancreatic cancer.

MATERIAL AND METHODS

A literature search of PubMed, Embase, and Cochrane Library electronic databases for articles published through May 2018 yielded 875 articles. For the meta-analysis, we included 26 studies evaluating the efficacy of DWI and FDG-PET/CT for determining pancreatic cancer with a total of 1377 patients. QUADAS (Quality Assessment of Diagnostic Accuracy Studies) was used to assess the study quality. Sensitivity, specificity, positive likelihood ratio (PLR), negative likelihood ratio (NLR), diagnostic odds ratio (DOR), and the area under the receiver operating characteristic curves (AUC) with their 95% confidence intervals were calculated for each individual study.

RESULTS

There were no significant differences between DWI and FDG-PET/CT for sensitivity, specificity, PLR, NLR, or DOR, while DWI AUC was higher than that of FDG-PET/CT for the detection of pancreatic cancer.

CONCLUSION

The diagnostic value of both DWI and FDG-PET/CT were comparable and, hence, both techniques seem to be equally useful tools for the diagnosis of pancreatic cancer.

Radiomics for the Diagnosis and Differentiation of Pancreatic Cystic Lesions

Radiomics, also known as quantitative imaging or texture analysis, involves extracting a large number of features traditionally unmeasured in conventional radiological cross-sectional images and converting them into mathematical models. This review describes this approach and its use in the evaluation of pancreatic cystic lesions (PCLs). This discipline has the potential of more accurately assessing, classifying, risk stratifying, and guiding the management of PCLs. Existing studies have provided important insight into the role of radiomics in managing PCLs. Although these studies are limited by the use of retrospective design, single center data, and small sample sizes, radiomic features in combination with clinical data appear to be superior to the current standard of care in differentiating cyst type and in identifying mucinous PCLs with high-grade dysplasia. Combining radiomic features with other novel endoscopic diagnostics, including cyst fluid molecular analysis and confocal endomicroscopy, can potentially optimize the predictive accuracy of these models. There is a need for multicenter prospective studies to elucidate the role of radiomics in the management of PCLs.

Mucinous Cystadenocarcinoma of the Pancreas with Cyst Infection in a Male Patient

Follow-up computed tomography revealed a 40-mm pancreatic tail cyst in a 59-year-old man with type 1 diabetes mellitus. An intraductal papillary mucinous neoplasm was suspected; mucinous cystic neoplasm (MCN) was not considered because the patient was a man. During follow-up, cyst infection occurred but was improved by conservative treatment. At the 24-month follow up examination, cyst nodules had developed, corresponding to an increase in the carbohydrate antigen 19-9 level. Mucinous cystadenocarcinoma (MCC) was diagnosed pathologically based on distal pancreatectomy. A diagnosis of male MCN/MCC is often delayed, which may lead to a poor prognosis. MCN infection is also rare and poorly recognized. We observed an atypical male case of MCN/MCC.

Advanced MR Imaging Techniques for Pancreas Imaging

Advances in MR imaging with optimization of hardware, software, and techniques have allowed for an increased role of MR in the identification and characterization of pancreatic disorders. Diffusion-weighted imaging improves the detection and staging of pancreatic neoplasms and aides in the evaluation of acute, chronic and autoimmune pancreatitis. The use of secretin-enhanced MR cholangiography improves the detection of morphologic ductal anomalies, and assists in the characterization of pancreatic cystic lesions and evaluation of acute and chronic pancreatitis. Emerging MR techniques such as MR perfusion, T1 mapping/relaxometry, and MR elastography show promise in further evaluating pancreatic diseases.

Comparison of Navigator Triggering Reduced Field of View and Large Field of View Diffusion-Weighted Imaging of the Pancreas

RATIONALE AND OBJECTIVES

The purpose of this study is to compare image quality, presence and grade of artifacts, signal-to-noise ratio, and apparent diffusion coefficient (ADC) values in pancreatic tissue between high-resolution navigator-triggered (NT) restricted field of view (rFOV) FOCUS single-shot (SS) echo-planar imaging (EPI) diffusion-weighted imaging (DWI) and NT large FOV SS-EPI DWI.

MATERIALS AND METHODS

Magnetic resonance imaging examinations were performed with GE 3-T systems using a 32-channel body array coil. Seventeen consecutive patients were imaged. A 5-point scale semiquantitative grading system was used to evaluate image quality and general artifacts. Signal-to-noise ratio and ADC were measured in the head, body, and tail of the pancreas. Statistical analysis was performed using Student t test and Wilcoxon signed rank test, with differences considered significant for P value less than 0.05.

RESULTS

More artifacts were present on large FOV compared with rFOV FOCUS SS-EPI DW images (P < 0.01). Restricted field of view image quality was subjectively better (P < 0.01). No difference in the signal-to-noise ratio was demonstrated between the 2 image datasets. Apparent diffusion coefficient values were significantly lower (P < 0.01) when calculated from rFOV images than large FOV images.

CONCLUSIONS

Our results demonstrate better image quality and reduced artifacts in rFOV images compared with large FOV DWI. Measurements from ADC maps derived from rFOV DWI show significantly lower ADC values when compared with ADC maps derived from large FOV DWI.

Imaging and clinical features of xanthogranulomatous pancreatitis: an analysis of 10 cases at a single institution

PURPOSE

The purpose of the study was to investigate the imaging and clinical features of xanthogranulomatous pancreatitis (XGP).

METHODS

This retrospective series study included 10 patients with pathology-proven XGP. Two radiologists reviewed the computed tomography (CT) and magnetic resonance imaging (MRI) in consensus to determine the morphological features of XGP. The lesion enhancement pattern on dynamic contrast-enhanced scans and the MR signal intensity were also evaluated. Clinical data including symptoms, underlying pancreatic disease, and laboratory findings were reviewed.

RESULTS

Two XGP cases were of a solid type; six were of cystic type, and two were mixed type. XGP usually showed a lobulated contour (90%) and heterogeneous enhancement (100%), with lesion size varying from 2 to 11 cm. Perilesional infiltration was common (90%), but pancreatic duct dilatation was less frequent (30%). Cystic type XGP mostly had an irregular thick wall (83%). On dynamic contrast-enhanced CT/MRI, XGP enhanced progressively from arterial to portal or delayed phases. Lesions appeared hypointense on T1-weighted images (89%) and hyperintense on T2-weighted images (100%). All lesions appeared hyperintense on diffusion-weighted images, with the majority (78%) showing diffusion restriction on apparent diffusion coefficient maps. The patients often had abdominal pain (80%) and underlying pancreatic disease (80%), but mostly had normal or clinically insignificant laboratory findings.

CONCLUSIONS

XGP typically manifests as a clinically silent lobulated heterogeneous mass, with a progressive enhancement pattern and/or irregular thick wall, and diffusion restriction on CT/MRI. Awareness of the imaging and clinical features of XGP may help differentiate it from pancreatic neoplasms, thereby reducing unnecessary surgery.

Functional imaging in pancreatic disease

In addition to the classical morphological evaluation of pancreatic disease, the constant technological advances in imaging techniques based fundamentally on computed tomography and magnetic resonance imaging have enabled the quantitative functional and molecular evaluation of this organ. In many cases, this imaging-based information results in substantial changes to patient management and can be a fundamental tool for the development of biomarkers. The aim of this article is to review the role of emerging functional and molecular techniques based on computed tomography and magnetic resonance imaging in the evaluation of pancreatic disease.

Evaluating the malignant potential of intraductal papillary mucinous neoplasms of the pancreas: added value of non-enhanced endoscopic ultrasound to supplement non-enhanced magnetic resonance imaging

Purpose

To evaluate the diagnostic performance of combining non-enhanced magnetic resonance imaging (MRI) and non-enhanced endoscopic ultrasonography (EUS) for assessing the malignant potential of lesions in patients with intraductal papillary mucinous neoplasms of the pancreas (IPMNs).

Material and methods

Data from 38 patients histopathologically diagnosed with IPMN adenomas or IPMN adenocarcinomas were retrospectively analysed. Preliminary univariate and multivariate analyses were conducted to identify statistically significant associations. Three blinded radiologists evaluated the image sets to assess the diagnostic performance of combined use of non-enhanced MRI and EUS as opposed to non-enhanced MRI alone in distinguishing malignant from benign lesions. Observer performance and interobserver variability were determined using receiver-operating-characteristic curve analysis and weighted κ statistics.

Results

Multivariate analyses identified a significant difference between the abrupt change in the main pancreatic duct (MPD) calibre with distal pancreatic atrophy and the signal intensity of lesion-to-spinal cord ratio on MRI; a significant difference was observed in MPD size on EUS. Diagnostic performance assessments of the image sets did not differ significantly between the blinded radiologists.

Conclusions

The clinical utility of non-enhanced EUS may be attributive in evaluating IPMN that has already been evaluated by non-enhanced MRI.

Radiological Workup of Cystic Neoplasms of the Pancreas

Pancreatic cystic lesions are being detected with increasing frequency because of increased use and improved quality of cross-sectional imaging techniques. Pancreatic cystic lesions encompass non-neoplastic lesions (such as pancreatitis-related collections) and neoplastic tumors. Common cystic pancreatic neoplasms include serous cystadenomas, mucinous cystic neoplasms, intraductal papillary mucinous neoplasms, and solid pseudopapillary tumors. These cystic pancreatic neoplasms may have typical morphology, but at times show overlapping imaging features on cross-sectional examinations. This article reviews the classical and atypical imaging features of commonly encountered cystic pancreatic neoplasms and presents the limitations of current cross-sectional imaging techniques in accurately classifying pancreatic cystic lesions.

Diagnostic accuracy of diffusion restriction in intraductal papillary mucinous neoplasm of the pancreas in comparison with "high-risk stigmata" of the 2012 international consensus guidelines for prediction of the malignancy and invasiveness

Background It is debated whether diagnostic performance of diffusion-weighted imaging (DWI), which is widely used for detection and characterization of various malignant tumors, is comparable with high-risk stigmata of 2012 international consensus guidelines (ICG) for diagnosis of intraductal papillary mucinous neoplasms (IPMNs). Purpose To evaluate the diagnostic accuracy of diffusion restriction in IPMNs for prediction of malignancy and invasiveness in comparison with high-risk stigmata of 2012 ICG. Material and Methods This retrospective study was institutional review board approved and informed consent was waived. A total of 132 patients with surgically proven IPMNs (49 malignant, 83 benign) who underwent gadoxetic acid-enhanced magnetic resonance imaging (MRI), magnetic resonance cholangiopancreatography (MRCP), and DWI with a b-value of 0, 100, and 800 s/mm² using a 3.0 T MR system were included. Two radiologists independently evaluated imaging parameters of high-risk stigmata and worrisome features of 2012 ICG and diffusion restriction in IPMNs. Univariate and multivariate logistic regression analyses and McNemar's test were used for statistical analysis. Results The presence of diffusion restriction in IPMNs was the only independent imaging parameter for prediction of malignancy (odds ratio [OR], 11.98; 95% confidence interval [CI], 3.60-39.87; P < 0.001) and invasiveness (OR, 17.92; 95% CI, 3.91-82.03; P < 0.001) on multivariate analysis. The diagnostic accuracy and specificity of diffusion restriction were significantly improved compared to high-risk stigmata of 2012 ICG to prediction of malignant ( P = 0.006 and P < 0.001, respectively) or invasive IPMNs ( P = 0.009 and P = 0.015, respectively). Conclusion The diffusion restriction in IPMNs could be considered as another high-risk stigma of malignancy and predictor for invasiveness.

Value of apparent diffusion coefficient for predicting malignancy of intraductal papillary mucinous neoplasms of the pancreas

PURPOSE

We aimed to explore the potential value of the whole tumor apparent diffusion coefficient (ADC) for discriminating between benign and malignant intraductal papillary mucinous neoplasms (IPMNs) of the pancreas.

METHODS

Forty-two patients underwent 1.5 T magnetic resonance imaging that included diffusion-weighted imaging (DWI, b=0.500 s/mm2). The mean, minimum, and maximum ADC values were measured for the whole tumor. The differences between benign and malignant IPMNs were calculated for the mean ADC, ADC-min, and ADC-max values. Receiver operating characteristics (ROC) analysis was conducted to evaluate their potential diagnostic performance.

RESULTS

Fifteen of 25 benign IPMNs demonstrated low or iso-signal intensity on DWI with a b value of 500 s/mm2 compared with normal pancreatic parenchyma, whereas all malignant IPMNs demonstrated high signal intensity. The mean value of ADC was significantly higher in benign IPMNs compared with malignant IPMNs (3.39×10-3 mm2/s vs. 2.39×10-3 mm2/s, P < 0.001), with an area under the ROC curve (AUC) of 0.92 (95% confidence interval [CI], 0.79-0.98). The ADC-min value of malignant IPMNs was also significantly lower than that of benign IPMNs (1.24×10-3 mm2/s vs. 2.58×10-3 mm2/s, P < 0.001), with an AUC of 0.94 (95% CI, 0.82-0.99). No marked difference was found between benign and malignant IPMNs for the ADC-max value (3.89×10-3 mm2/s vs. 3.78×10-3 mm2/s, P = 0.299).

CONCLUSION

Lower mean and minimum ADC values of the whole tumor might be potential predictors of malignant IPMNs of the pancreas.

Imaging modalities for characterising focal pancreatic lesions

BACKGROUND

Increasing numbers of incidental pancreatic lesions are being detected each year. Accurate characterisation of pancreatic lesions into benign, precancerous, and cancer masses is crucial in deciding whether to use treatment or surveillance. Distinguishing benign lesions from precancerous and cancerous lesions can prevent patients from undergoing unnecessary major surgery. Despite the importance of accurately classifying pancreatic lesions, there is no clear algorithm for management of focal pancreatic lesions.

OBJECTIVES

To determine and compare the diagnostic accuracy of various imaging modalities in detecting cancerous and precancerous lesions in people with focal pancreatic lesions.

SEARCH METHODS

We searched the CENTRAL, MEDLINE, Embase, and Science Citation Index until 19 July 2016. We searched the references of included studies to identify further studies. We did not restrict studies based on language or publication status, or whether data were collected prospectively or retrospectively.

SELECTION CRITERIA

We planned to include studies reporting cross-sectional information on the index test (CT (computed tomography), MRI (magnetic resonance imaging), PET (positron emission tomography), EUS (endoscopic ultrasound), EUS elastography, and EUS-guided biopsy or FNA (fine-needle aspiration)) and reference standard (confirmation of the nature of the lesion was obtained by histopathological examination of the entire lesion by surgical excision, or histopathological examination for confirmation of precancer or cancer by biopsy and clinical follow-up of at least six months in people with negative index tests) in people with pancreatic lesions irrespective of language or publication status or whether the data were collected prospectively or retrospectively.

DATA COLLECTION AND ANALYSIS

Two review authors independently searched the references to identify relevant studies and extracted the data. We planned to use the bivariate analysis to calculate the summary sensitivity and specificity with their 95% confidence intervals and the hierarchical summary receiver operating characteristic (HSROC) to compare the tests and assess heterogeneity, but used simpler models (such as univariate random-effects model and univariate fixed-effect model) for combining studies when appropriate because of the sparse data. We were unable to compare the diagnostic performance of the tests using formal statistical methods because of sparse data.

MAIN RESULTS

We included 54 studies involving a total of 3,196 participants evaluating the diagnostic accuracy of various index tests. In these 54 studies, eight different target conditions were identified with different final diagnoses constituting benign, precancerous, and cancerous lesions. None of the studies was of high methodological quality. None of the comparisons in which single studies were included was of sufficiently high methodological quality to warrant highlighting of the results. For differentiation of cancerous lesions from benign or precancerous lesions, we identified only one study per index test. The second analysis, of studies differentiating cancerous versus benign lesions, provided three tests in which meta-analysis could be performed. The sensitivities and specificities for diagnosing cancer were: EUS-FNA: sensitivity 0.79 (95% confidence interval (CI) 0.07 to 1.00), specificity 1.00 (95% CI 0.91 to 1.00); EUS: sensitivity 0.95 (95% CI 0.84 to 0.99), specificity 0.53 (95% CI 0.31 to 0.74); PET: sensitivity 0.92 (95% CI 0.80 to 0.97), specificity 0.65 (95% CI 0.39 to 0.84). The third analysis, of studies differentiating precancerous or cancerous lesions from benign lesions, only provided one test (EUS-FNA) in which meta-analysis was performed. EUS-FNA had moderate sensitivity for diagnosing precancerous or cancerous lesions (sensitivity 0.73 (95% CI 0.01 to 1.00) and high specificity 0.94 (95% CI 0.15 to 1.00), the extremely wide confidence intervals reflecting the heterogeneity between the studies). The fourth analysis, of studies differentiating cancerous (invasive carcinoma) from precancerous (dysplasia) provided three tests in which meta-analysis was performed. The sensitivities and specificities for diagnosing invasive carcinoma were: CT: sensitivity 0.72 (95% CI 0.50 to 0.87), specificity 0.92 (95% CI 0.81 to 0.97); EUS: sensitivity 0.78 (95% CI 0.44 to 0.94), specificity 0.91 (95% CI 0.61 to 0.98); EUS-FNA: sensitivity 0.66 (95% CI 0.03 to 0.99), specificity 0.92 (95% CI 0.73 to 0.98). The fifth analysis, of studies differentiating cancerous (high-grade dysplasia or invasive carcinoma) versus precancerous (low- or intermediate-grade dysplasia) provided six tests in which meta-analysis was performed. The sensitivities and specificities for diagnosing cancer (high-grade dysplasia or invasive carcinoma) were: CT: sensitivity 0.87 (95% CI 0.00 to 1.00), specificity 0.96 (95% CI 0.00 to 1.00); EUS: sensitivity 0.86 (95% CI 0.74 to 0.92), specificity 0.91 (95% CI 0.83 to 0.96); EUS-FNA: sensitivity 0.47 (95% CI 0.24 to 0.70), specificity 0.91 (95% CI 0.32 to 1.00); EUS-FNA carcinoembryonic antigen 200 ng/mL: sensitivity 0.58 (95% CI 0.28 to 0.83), specificity 0.51 (95% CI 0.19 to 0.81); MRI: sensitivity 0.69 (95% CI 0.44 to 0.86), specificity 0.93 (95% CI 0.43 to 1.00); PET: sensitivity 0.90 (95% CI 0.79 to 0.96), specificity 0.94 (95% CI 0.81 to 0.99). The sixth analysis, of studies differentiating cancerous (invasive carcinoma) from precancerous (low-grade dysplasia) provided no tests in which meta-analysis was performed. The seventh analysis, of studies differentiating precancerous or cancerous (intermediate- or high-grade dysplasia or invasive carcinoma) from precancerous (low-grade dysplasia) provided two tests in which meta-analysis was performed. The sensitivity and specificity for diagnosing cancer were: CT: sensitivity 0.83 (95% CI 0.68 to 0.92), specificity 0.83 (95% CI 0.64 to 0.93) and MRI: sensitivity 0.80 (95% CI 0.58 to 0.92), specificity 0.81 (95% CI 0.53 to 0.95), respectively. The eighth analysis, of studies differentiating precancerous or cancerous (intermediate- or high-grade dysplasia or invasive carcinoma) from precancerous (low-grade dysplasia) or benign lesions provided no test in which meta-analysis was performed.There were no major alterations in the subgroup analysis of cystic pancreatic focal lesions (42 studies; 2086 participants). None of the included studies evaluated EUS elastography or sequential testing.

AUTHORS' CONCLUSIONS

We were unable to arrive at any firm conclusions because of the differences in the way that study authors classified focal pancreatic lesions into cancerous, precancerous, and benign lesions; the inclusion of few studies with wide confidence intervals for each comparison; poor methodological quality in the studies; and heterogeneity in the estimates within comparisons.

Utility of whole-lesion ADC histogram metrics for assessing the malignant potential of pancreatic intraductal papillary mucinous neoplasms (IPMNs)

PURPOSE

To evaluate whole-lesion ADC histogram metrics for assessing the malignant potential of pancreatic intraductal papillary mucinous neoplasms (IPMNs), including in comparison with conventional MRI features.

METHODS

Eighteen branch-duct IPMNs underwent MRI with DWI prior to resection (n = 16) or FNA (n = 2). A blinded radiologist placed 3D volumes-of-interest on the entire IPMN on the ADC map, from which whole-lesion histogram metrics were generated. The reader also assessed IPMN size, mural nodularity, and adjacent main-duct dilation. Benign (low-to-intermediate grade dysplasia; n = 10) and malignant (high-grade dysplasia or invasive adenocarcinoma; n = 8) IPMNs were compared.

RESULTS

Whole-lesion ADC histogram metrics demonstrating significant differences between benign and malignant IPMNs were: entropy (5.1 ± 0.2 vs. 5.4 ± 0.2; p = 0.01, AUC = 86%); mean of the bottom 10th percentile (2.2 ± 0.4 vs. 1.6 ± 0.7; p = 0.03; AUC = 81%); and mean of the 10-25th percentile (2.8 ± 0.4 vs. 2.3 ± 0.6; p = 0.04; AUC = 79%). The overall mean ADC, skewness, and kurtosis were not significantly different between groups (p ≥ 0.06; AUC = 50-78%). For entropy (highest performing histogram metric), an optimal threshold of >5.3 achieved a sensitivity of 100%, a specificity of 70%, and an accuracy of 83% for predicting malignancy. No significant difference (p = 0.18-0.64) was observed between benign and malignant IPMNs for cyst size ≥3 cm, adjacent main-duct dilatation, or mural nodule. At multivariable analysis of entropy in combination with all other ADC histogram and conventional MRI features, entropy was the only significant independent predictor of malignancy (p = 0.004).

CONCLUSION

Although requiring larger studies, ADC entropy obtained from 3D whole-lesion histogram analysis may serve as a biomarker for identifying the malignant potential of IPMNs, independent of conventional MRI features.

Diffusion-Weighted Magnetic Resonance Imaging in Distinguishing Between Mucin-Producing and Serous Pancreatic Cysts

OBJECTIVE

The aim of this study was to evaluate the feasibility and reproducibility of diffusion-weighted imaging in distinguishing between mucin-producing and serous pancreatic cysts.

METHODS

Forty-four pancreatic cysts (43 patients, 27 women; mean age, 57 years; 26 mucin-producing cysts, 18 serous cysts) that underwent histological examination or cyst analysis after diffusion-weighted magnetic resonance imaging were retrospectively reviewed. Three blinded readers independently evaluated signal intensity and apparent diffusion coefficient (ADC). Intraobserver and interobserver agreements were calculated. Fisher exact test and Welch t test were used to compare signal intensity and ADC values, respectively, with pathological results. Receiver operating characteristic analysis was used to determine diagnostic accuracy of various thresholds for ADC. A P value less than 0.05 was considered statistically significant.

RESULTS

Mean ADC values of the mucin-producing cysts were 3.26 × 10, 3.27 × 10, and 3.35 × 10 mm/s for the 3 readers, respectively. Mean ADC values of the serous cysts were 2.86 × 10, 2.85 × 10, and 2.85 × 10 mm/s for the 3 readers, respectively. Differences in ADC values between the 2 cyst groups were 12.4%, 12.9%, and 14.8% for the 3 readers, respectively (P < 0.001). Intraobserver and interobserver agreement was excellent. A threshold ADC of 3 × 10 mm/s resulted in correct identification of cysts in 77% to 81% of cases, with sensitivity and specificity ranging between 84% and 88% and 66% and 72%, respectively.

CONCLUSIONS

Diffusion-weighted imaging may be a helpful tool in distinguishing between mucin-producing and serous pancreatic cysts.

Imaging patterns of intraductal papillary mucinous neoplasms of the pancreas: an illustrated discussion of the International Consensus Guidelines for the Management of IPMN

Intraductal papillary mucinous neoplasms (IPMN) are being diagnosed with increasing frequency, necessitating an algorithm to help stratify patients into low- and high-risk groups, for follow-up versus more invasive evaluation. New evidence concerning their natural history and overall risk of malignancy has emerged since the 2006 International Association of Pancreatology consensus guidelines, prompting an update in 2012, that distinguishes radiologic 'worrisome features' from 'high-risk stigmata'. The aim of this article is to illustrate, with case examples, the variable imaging patterns of IPMN and how their radiologic features, such as cyst size and mural nodules, are interpreted in the context of the new 2012 guidelines. The 2012 and 2006 guidelines will be compared and discussed with reference to additional studies that have since been published. Despite these guidelines, lingering uncertainty remains about the natural history of IPMN, a source of unease to both radiologists and referring clinicians alike, mandating further refinement of clinical and radiologic parameters predictive of malignancy. Emerging data regarding the risk of extrapancreatic malignancy, as well as synchronous or metachronous pancreatic ductal adenocarcinoma remote in location from a branch duct IPMN are also reviewed. With the expanding research and evolving understanding of this clinicopathologic entity across the globe, radiologists will continue to play an important role in the management of patients with IPMN.

Imaging of pancreatic neoplasms

Ductal adenocarcinoma accounts for 85% to 90% of all solid pancreatic neoplasms, is increasing in incidence, and is the fourth leading cause of cancer-related deaths. There are currently no screening tests available for the detection of ductal adenocarcinoma. The only chance for cure in pancreatic adenocarcinoma is surgery. Imaging has a crucial role in the identification of the primary tumor, vascular variants, identification of metastases, disease response assessment to treatment, and prediction of respectability. Pancreatic neuroendocrine neoplasms can have a distinctive appearance and pattern of spread, which should be recognized on imaging for appropriate management of these patients.

Differential diagnosis of pancreatic cancer by single-shot echo-planar imaging diffusion-weighted imaging

AIM: To investigate the diagnostic ability of single-shot echo-planar imaging (EPI) diffusion-weighted imaging (DWI) to differentiate between malignant and benign pancreatic lesions.

METHODS: A computerized search was performed on PubMed, MEDLINE and EMBASE up to August 2014. Nine studies (10 sets of data) with a total of 304 malignant pancreatic lesions and 188 benign pancreatic lesions were included. The characteristics of each study included the study name, year of publication, magnetic resonance modalities used, patient population, strength of field, pulse time, repetition time, echo time (TE), maximum b factor, mean age, mean body weight, fat suppression, number of benign and malignant lesions, and true positive, true negative, false positive and false negative results. All analyses were performed using Meta-DiSc and Stata 11.0.

RESULTS: The pooled sensitivity and specificity of single-shot EPI DWI were 0.83 (95%CI: 0.79-0.87) and 0.77 (95%CI: 0.70-0.83), respectively. The positive likelihood ratio and negative likelihood ratio were 5.09 (95%CI: 2.19-11.84) and 0.23 (95%CI: 0.15-0.36), respectively. The P value for the χ² heterogeneity for all pooled estimates was < 0.05. From the fitted summary receiver operating characteristic curve, the area under the curve and Q* index were 0.89 and 0.82, respectively. Publication bias was not present (t = 0.58, P = 0.58). Meta-regression analysis indicated that fat suppression, mean age, TE, and maximum b factor were not sources of heterogeneity (all P > 0.05).

CONCLUSION: Single-shot EPI DWI is useful to differentiate between malignant and benign pancreatic lesions. Lesion size ≥ 2 cm is the limit for the diagnosis of early lesions.

Nononcologic applications of diffusion-weighted imaging in the gastrointestinal system

OBJECTIVE

The purpose of this article is to review infectious, inflammatory, and auto-immune-mediated processes in the gastrointestinal system where diffusion-weighted imaging can be helpful as well as pitfalls associated with its use.

CONCLUSION

Diffusion-weighted imaging has become an important and widely used tool in abdominal and pelvic MRI, but it has been used primarily for oncologic applications. As more body MRI protocols are routinely including diffusion-weighted imaging, this sequence can be useful in evaluating an increasing number of nononcologic processes.

Value of diffusion-weighted MRI for differentiating malignant from benign intraductal papillary mucinous neoplasms of the pancreas

OBJECTIVE

The purpose of this study was to evaluate whether the use of diffusion-weighted MRI (DWI) increases diagnostic accuracy in the differentiation of malignant from benign intraductal papillary mucinous neoplasms (IPMNs) of the pancreas over the accuracy of contrast-enhanced MRI with MRCP.

MATERIALS AND METHODS

A total of 61 patients with surgically resected IPMNs (19 malignant, 42 benign) who underwent gadoxetic acid-enhanced MRI, DWI, and MRCP were included. Two blinded observers evaluated two image sets, that is, conventional MRI with MRCP images versus combined conventional MRI with MRCP and DW images, and scored their confidence for malignancy of IPMNs. Qualitative analyses of the IPMNs were also conducted. Diagnostic performance (ROC curve analysis), accuracy, sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) were evaluated. The Fisher exact test was used to compare groups.

RESULTS

The diagnostic performance (area under the ROC curve [Az]) with respect to predicting malignancy of IPMNs improved significantly for both observers after additional review of DW images (p < 0.05). The diagnostic accuracy, sensitivity, specificity, PPV, and NPV of combined conventional and DW images were higher than those of conventional MR images alone. Diffusion restriction was more often present in malignant IPMNs (78.9%) than in benign IPMNs (16.7%) (p < 0.001) with excellent interobserver agreement (ĸ = 0.965).

CONCLUSION

Compared with conventional MRI alone, adding DWI to conventional MRI improves diagnostic accuracy with increased specificity for differentiating malignant from benign IPMNs of the pancreas.

Meta-analysis of quantitative diffusion-weighted MR imaging in differentiating benign and malignant pancreatic masses

There have been numerous studies done to explore the diagnostic performance of quantitative diffusion-weighted (DW) MR imaging to differentiate between benign and malignant pancreatic masses. However, the results have been inconsistent. We performed a meta-analysis to investigate whether DW-MR imaging can differentiate between these two diseases. Databases including MEDLINE, EMBASE and Cochrane Library were utilized to find relevant articles published between January 2001 and January 2014. A Stata version 12.0 and a Meta-Disc version 1.4 were used to describe primary results. Twelve studies with 594 patients, which fulfilled the inclusion criteria, were enrolled for the analysis. The pooled sensitivity and specificity of DW imaging was 0.91 (95% CI: 0.84, 0.95) and 0.86 (95% CI: 0.76, 0.93) respectively. The area under the curve of the summary receiver operating characteristic was 0.95 (95% CI: 0.93, 0.96). The results indicated that DW imaging might be a valuable tool for differentiating benign and malignant pancreatic masses.

Implications of imaging criteria for the management and treatment of intraductal papillary mucinous neoplasms - benign versus malignant findings

OBJECTIVES

Evaluation of computed tomography (CT) and magnetic resonance imaging (MRI) for differentiation of pancreatic intraductal papillary mucinous neoplasm (IPMN) subtypes based on objective imaging criteria.

METHODS

Fifty-eight patients with 60 histologically confirmed IPMNs were included in this retrospective study. Eighty-three imaging studies (CT,n = 42; MRI,n = 41) were analysed by three independent blinded observers (O1-O3), using established imaging criteria to assess likelihood of malignancy (-5, very likely benign; 5, very likely malignant) and histological subtype (i.e., low-grade (LGD), moderate-grade (MGD), high-grade dysplasia (HGD), early invasive carcinoma (IPMC), solid carcinoma (CA) arising from IPMN).

RESULTS

Forty-one benign (LGD IPMN,n = 20; MGD IPMN,n = 21) and 19 malignant (HGD IPMN,n = 3; IPMC,n = 6; solid CA,n = 10) IPMNs located in the main duct (n = 6), branch duct (n = 37), or both (n = 17) were evaluated. Overall accuracy of differentiation between benign and malignant IPMNs was 86/92 % (CT/MRI). Exclusion of overtly malignant cases (solid CA) resulted in overall accuracy of 83/90 % (CT/MRI). The presence of mural nodules and ductal lesion size ≥30 mm were significant indicators of malignancy (p = 0.02 and p < 0.001, respectively).

CONCLUSIONS

Invasive IPMN can be identified with high confidence and sensitivity using CT and MRI. The diagnostic problem that remains is the accurate radiological differentiation of premalignant and non-invasive subtypes.

KEY POINTS

• CT and MRI can differentiate benign from malignant forms of IPMN. • Identifying (pre)malignant histological IPMN subtypes by CT and MRI is difficult. • Overall, diagnostic performance with MRI was slightly (not significantly) superior to CT.

Diffusion-weighted magnetic resonance imaging for evaluating the histological degree of malignancy in patients with intraductal papillary mucinous neoplasm

BACKGROUND

The aim of this study was to evaluate the usefulness of high b-value diffusion-weighted magnetic resonance imaging (DWI) for evaluating the histological degree of malignancy in patients with intraductal papillary mucinous neoplasm (IPMN).

METHODS

A total of 35 patients (mean age 68 ± 10 years, 23 males) who had undergone DWI before surgery were included in this study. Of these 35 patients, 13 had IPMN with low- or intermediate-grade dysplasia, eight had IPMN with high-grade dysplasia, and 14 had IPMN with an associated invasive carcinoma. We evaluated the positive signal rate on DWI and the apparent diffusion coefficient (ADC) value of each pathology.

RESULTS

The positive signal rate on DWI of IPMN with low- or intermediate-grade dysplasia, of IPMN with high-grade dysplasia, and of IPMN with an associated invasive carcinoma were 0% (0/13), 38% (3/8), and 93% (13/14), respectively. The sensitivity, specificity, and accuracy for malignancy (IPMN with high-grade dysplasia or IPMN with an associated invasive carcinoma) using DWI were 73%, 100%, and 83%, respectively. The mean ADC value of malignancy was significantly lower than that of benignity (P = 0.002).

CONCLUSIONS

Diffusion-weighted magnetic resonance imaging, easily applicable in addition to conventional MRI, is considered an efficient modality for evaluating the histological degree of malignancy in patients with IPMN.

Functional MR imaging of the abdomen

In this article, functional magnetic resonance (MR) imaging techniques in the abdomen are discussed. Diffusion-weighted imaging (DWI) increases the confidence in detecting and characterizing focal hepatic lesions. The potential uses of DWI in kidneys, adrenal glands, bowel, and pancreas are outlined. Studies have shown potential use of quantitative dynamic contrast-enhanced MR imaging parameters, such as K(trans), in predicting outcomes in cancer therapy. MR elastography is considered to be a useful tool in staging liver fibrosis. A major issue with all functional MR imaging techniques is the lack of standardization of the protocol.

Morphological and functional evaluation of chronic pancreatitis with magnetic resonance imaging

Magnetic resonance imaging (MRI) techniques for assessment of morphology and function of the pancreas have been improved dramatically the recent years and MRI is very often used in diagnosing and follow-up of chronic pancreatitis (CP) patients. Standard MRI including fat-suppressed T1-weighted and T2-weighted imaging techniques reveal decreased signal and glandular atrophy of the pancreas in CP. In contrast-enhanced MRI of the pancreas in CP the pancreatic signal is usually reduced and delayed due to decreased perfusion as a result of chronic inflammation and fibrosis. Thus, morphological changes of the ductal system can be assessed by magnetic resonance cholangiopancreatography (MRCP). Furthermore, secretin-stimulated MRCP is a valuable technique to evaluate side branch pathology and the exocrine function of the pancreas and diffusion weighted imaging can be used to quantify both parenchymal fibrotic changes and the exocrine function of the pancreas. These standard and advanced MRI techniques are supplementary techniques to reveal morphological and functional changes of the pancreas in CP. Recently, spectroscopy has been used for assessment of metabolite concentrations in-vivo in different tissues and may have the potential to offer better tissue characterization of the pancreas. Hence, the purpose of the present review is to provide an update on standard and advanced MRI techniques of the pancreas in CP.

Added value of diffusion-weighted imaging to MR cholangiopancreatography with unenhanced mr imaging for predicting malignancy or invasiveness of intraductal papillary mucinous neoplasm of the pancreas

PURPOSE

To investigate the added value of diffusion-weighted imaging (DWI) to magnetic resonance cholangiopancreatography (MRCP) with unenhanced MR imaging for predicting the malignancy or invasiveness of intraductal papillary mucinous neoplasms (IPMNs).

MATERIALS AND METHODS

Following Institutional Review Board (IRB) approval, this retrospective study included 52 patients with surgically resected IPMNs and who underwent MRCP, unenhanced MRI, and DWI. Three blinded radiologists evaluated the two image sets, ie, MRCP with unenhanced MR images vs. the combined set with MRCP, unenhanced MR images, and DWI, and scored their confidence for malignancy or for invasiveness of IPMNs. The mean apparent diffusion coefficient (ADC) values of benign IPMNs and of intraductal mucinous carcinomas (IPMCs) were compared. The diagnostic accuracy was calculated using receiver operating characteristic (ROC) curve analysis.

RESULTS

The mean ADC of malignant IPMNs (2.05 ± 0.66 × 10(-3) mm(2) /sec) was significantly lower than that of benign IPMNs (2.95 ± 0.32 × 10(-3) mm(2) /sec, P < 0.0001). Invasive IPMCs (1.51 ± 0.32 × 10(-3) mm(2) /sec) showed significantly lower ADC than that of noninvasive IPMCs (2.67 ± 0.23 × 10(-3) mm(2) /sec, P = 0.0003). The area of diffusion restriction was more frequently seen in malignant IPMNs than in benign IPMNs (P < 0.00001). The addition of DWI to MRCP with unenhanced MRI did not show a significant improvement for predicting malignant IPMN (P> 0.05), but resulted in a tendency to improve the diagnostic accuracy for the prediction of invasive IPMN in two observers (P = 0.072, P = 0.085).

CONCLUSION

The addition of DWI to MRCP with unenhanced MRI may improve the diagnosis of malignant IPMN and further increase the prediction of invasive IPMC.

Advances in the diagnosis of cystic neoplasms of the pancreas

PURPOSE OF REVIEW

Management of pancreatic cystic neoplasms is challenging due to limitations of current diagnostic tests. There is considerable interest in developing an accurate and cost-effective diagnostic test (or panel of tests) to differentiate cyst types and to identify those which would benefit most from surgical resection.

RECENT FINDINGS

Current multidetector computed tomography scans may have improved accuracy to distinguish between mucinous and nonmucinous cysts. Attempts to generate quantitative criteria from cross-sectional imaging to differentiate cyst types have yielded mixed results. DNA mutations and microRNA show promise in the ability to distinguish between mucinous and nonmucinous cysts. Cyst fluid mucin glycoproteins and cytokines may identify those cysts with high malignant potential. Proteomic analysis may yield other biomarker candidates.

SUMMARY

Analysis of DNA mutations and proteins within pancreatic cyst fluid have identified potential biomarkers to aid with the management of patients with pancreatic cystic neoplasms.

Apparent diffusion coefficient measurements in the differentiation between benign and malignant lesions: a systematic review

Objectives

To systematically review the value of apparent diffusion coefficient (ADC) measurement in the differentiation between benign and malignant lesions.

Methods

A systematic search of the Medline/Pubmed and Embase databases revealed 109 relevant studies. Quality of these articles was assessed using the Quality Assessment of the Studies of Diagnostic Accuracy Included in Systematic Reviews (QUADAS) criteria. Reported ADC values of benign and malignant lesions were compared per organ.

Results

The mean quality score of the reviewed articles was 50%. Comparison of ADC values showed marked variation among studies and between benign and malignant lesions in various organs. In several organs, such as breast, liver, and uterus, ADC values discriminated well between benign and malignant lesions. In other organs, such as the salivary glands, thyroid, and pancreas, ADCs were not significantly different between benign and malignant lesions.

Conclusion

The potential utility of ADC measurement for the characterisation of tumours differs per organ. Future well-designed studies are required before ADC measurements can be recommended for the differentiation of benign and malignant lesions. These future studies should use standardised acquisition protocols and provide complete reporting of study methods, to facilitate comparison of results and clinical implementation of ADC measurement for tumour characterisation.

Electronic supplementary material

The online version of this article (doi:10.1007/s13244-012-0175-y) contains supplementary material, which is available to authorized users.

Diagnostic value of diffusion-weighted magnetic resonance imaging compared with fluorodeoxyglucose positron emission tomography/computed tomography for pancreatic malignancy: a meta-analysis using a hierarchical regression model

BACKGROUND AND AIM

To obtain diagnostic performance of diffusion-weighted magnetic resonance imaging (DWI) and fluorine 18 fluorodeoxyglucose (FDG) positron emission tomography/computed tomography (PET/CT) in the detection of pancreatic malignancy.

METHODS

We performed a meta-analysis of all available studies of the diagnostic performance of DWI and PET/CT for pancreatic malignancy. MEDLINE, EMBASE, Cochrane library and some other databases were searched for initial studies. We determined sensitivities and specificities across studies, calculated positive and negative likelihood ratios (LR+ and LR-), and constructed summary receiver operating characteristic curves (SROC) using hierarchical regression models.

RESULTS

Across 16 studies with 804 patients, PET/CT sensitivity was 0.87 (95% confidence interval [CI], 0.82, 0.81) and specificity was 0.83 (95% CI, 0.71, 0.91). Overall, LR+ was 5.84 (95% CI, 4.59, 7.42) and LR- was 0.24 (95% CI, 0.17, 0.33). DWI sensitivity was 0.85 (95% CI, 0.74, 0.92) and specificity was 0.91 (95% CI, 0.71, 0.98). LR+ was 9.53 (95% CI, 2.41, 37.65) and LR- was 0.17 (95% CI, 0.09, 0.32). In subgroup analysis, the sensitivity of enhanced versus unenhanced PET/CT in the detection of pancreatic cancer was 0.91 (95% CI, 0.86, 0.96) versus 0.84 (95% CI, 0.78, 0.90) (P > 0.05), the specificity 0.88 (95% CI, 0.73, 1.00) versus 0.81 (95% CI, 0.69, 0.94) (P > 0.05).

CONCLUSION

Positron emission tomography/computed tomography (PET/CT) was highly sensitive and DWI was a highly specific modality in diagnosing patients with pancreatic malignancy. PET/CT and DWI could play different roles in diagnosing pancreatic carcinoma. Enhanced PET/CT seems to be superior to unenhanced PET/CT. Further larger prospective studies are needed to establish its value for diagnosis in pancreatic cancer.

Cystic tumors of the pancreas: imaging and management

Cystic tumors of the pancreas are a subset of rare pancreatic tumors that vary from benign to malignant. Many have specific imaging findings that allow them to be differentiated from each other. This article (1) reviews the imaging features of the common cystic pancreatic lesions, including serous microcystic adenoma, mucinous cystic tumor, intraductal papillary mucinous tumor, and solid pseudopapillary tumor, and including the less common lesions such as cystic endocrine tumors, cystic metastases, cystic teratomas, and lymphangiomas; and (2) provides comprehensive algorithms on how to manage the individual lesions, with recommendations on when to reimage patients.

Value of diffusion-weighted imaging for the discrimination of pancreatic lesions: a meta-analysis

OBJECTIVE

We aimed to explore the role of diffusion-weighted imaging (DWI) in the discrimination of pancreatic lesions through meta-analysis.

METHODS

The MEDLINE, EMBASE, Cancerlit, and Cochrane Library databases, from January 2001 to August 2011, were searched for studies evaluating the diagnostic performance of DWI in the discrimination of pancreatic lesions. We determined sensitivities and specificities across studies, calculated positive and negative likelihood ratios (LR+ and LR-), and constructed summary receiver operating characteristic curves.

RESULTS

A total of 11 studies with 586 patients, who fulfilled all of the inclusion criteria, were considered for the analysis. No publication bias was found. The pooled sensitivity of DWI was 0.86 [95% (confidence interval (CI), 0.78, 0.91] and the pooled specificity was 0.91 (95% CI, 0.81, 0.96). Overall, LR+ was 9.8 (95% CI, 4.1, 23.3) and LR- was 0.15 (95% CI, 0.09, 0.26). The area under the curve of the summary receiver operating characteristic was 0.94 (95% CI, 0.91-0.96). In subgroup analysis, prospectively designed studies had the highest pooled sensitivity (0.87, 95% CI 0.75, 0.94) and specificity (0.96, 95% CI 0.91, 0.99) (P<0.05). Study sensitivity was not correlated with the prevalence of pancreatic lesions (R=0.1076, P=0.3247).

CONCLUSION

A limited number of small studies suggest that DWI is a potentially technically feasible measure to differentiate malignant from benign pancreatic lesions. However, it is still controversial and is limited in that it can only distinguish certain lesions. High-quality prospective studies on DWI for the discrimination of pancreatic lesions still need to be conducted.