Christine Hoeffel

Diffusion-weighted MR Imaging of the Pancreas: Current Status and Recommendations

Advances in image quality over the past few years, mainly due to refinements in hardware and coil systems, have made diffusion-weighted ( DW diffusion weighted ) magnetic resonance (MR) imaging a promising technique for the detection and characterization of pancreatic conditions. DW diffusion weighted MR imaging can be routinely implemented in clinical protocols, as it can be performed relatively quickly, does not require administration of gadolinium-based contrast agents, and enables qualitative and quantitative assessment of tissue diffusivity (diffusion coefficients). In this review, acquisition parameters, postprocessing, and quantification methods applied to pancreatic DW diffusion weighted MR imaging will be discussed. The current common clinical uses of DW diffusion weighted MR imaging (ie, pancreatic lesion detection and characterization) and the less-common applications of DW diffusion weighted MR imaging used for the diagnosis of pancreatic parenchymal diseases will be reviewed. Also, the limitations of the technique, mainly image quality and reproducibility of diffusion parameters, as well as future directions for pancreatic DW diffusion weighted MR imaging will be discussed. The utility of apparent diffusion coefficient ( ADC apparent diffusion coefficient ) measurement for the characterization of pancreatic lesions is now well accepted but there are a number of limitations. Future well-designed, multicenter studies are needed to better determine the most appropriate use of ADC apparent diffusion coefficient in the area of pancreatic disease.

Characterization of focal pancreatic lesions using normalized apparent diffusion coefficient at 1.5-Tesla: Preliminary experience

PURPOSE To compare the capabilities of apparent diffusion coefficient (ADC) and normalized ADC using the pancreatic parenchyma as reference organ in the characterization of focal pancreatic lesions. PATIENTS AND METHODS Thirty-six patients with focal pancreatic lesions (malignant, n=18; benign tumors, n=10; focal pancreatitis, n=8) underwent diffusion-weighted MR imaging (DWI) at 1.5-Tesla using 3 b values (b=0, 400, 800 s/mm(2)). Lesion ADC and normalized lesion ADC (defined as the ratio of lesion ADC to apparently normal adjacent pancreas) were compared between lesion types using nonparametric tests. RESULTS Significant differences in ADC values were found between malignant (1.150 × 10(-3)mm(2)/s) and benign tumors (2.493 × 10(-3)mm(2)/s) (P=0.004) and between benign tumors and mass-forming pancreatitis (1.160 × 10(-3)mm(2)/s) (P=0.0005) but not between malignant tumors and mass-forming pancreatitis (P=0.1092). Using normalized ADC, significant differences were found between malignant tumors (0.933 × 10(-3)mm(2)/s), benign tumors (1.807 × 10(-3)mm(2)/s) and mass-forming pancreatitis (0.839 × 10(-3)mm(2)/s) (P<0.0001). CONCLUSION Our preliminary results suggest that normalizing ADC of focal pancreatic lesions with ADC of apparently normal adjacent pancreatic parenchyma provides higher degrees of characterization of focal pancreatic lesions than the conventional ADC does.

Diffusion‐weighted MRI in Crohn's disease: Current status and recommendations

Over the past years, technological improvements and refinements in magnetic resonance imaging (MRI) hardware have made high‐quality diffusion‐weighted imaging (DWI) routinely possible for the bowel. DWI is promising for the detection and characterization of lesions in Crohns disease (CD) and has been advocated as an alternative to intravenous gadolinium‐based contrast agents. Furthermore, quantification using the apparent diffusion coefficient may have value as a biomarker of CD activity and has shown promise. In this article we critically review the literature pertaining to the value of DWI in CD for detection, characterization, and quantification of disease activity and complications. Although the body of supportive evidence is growing, it is clear that well‐designed, multicenter studies are required before the role of DWI in clinical practice can be fully established. J. Magn. Reson. Imaging 2016;44:1381–1396.

Magnetic resonance imaging of cystic pancreatic lesions in adults: an update in current diagnostic features and management

Magnetic resonance (MR) imaging has become a widespread diagnostic solving tool for the detection and characterization of a large range of pancreatic cystic lesions. Benign and malignant cystic lesions of the pancreas including serous microcystic adenoma, mucinous cystic tumor, intraductal papillary mucinous tumor, solid pseudopapillary tumor, and also the less common lesions such as cystic endocrine tumors, cystic metastases, and lymphangiomas have suggestive MR imaging presentation that allows them to be differentiated from each other. Knowledge of MR imaging findings of cystic pancreatic lesions is critical to help suggest the diagnosis and chose the best therapeutic approach. The purpose of this review is to discuss and illustrate MR imaging features that are helpful for pancreatic cystic lesion detection and characterization and to provide an update in current MR imaging diagnostic features and management.

ADC normalization: A promising research track for diffusion-weighted MR imaging of the abdomen

Diffusion-weighted magnetic resonance imaging (DW-MRI) is a technique that helps quantify the movement of water molecules at a cellular level. DW-MRI is sensitive to the thermally driven random motion of water protons, which is dependent of their interactions with cell membranes and macromolecules. Consequently, the diffusion of water in tissues reflects at various degrees a combination of tissue cellularity, tortuosity of extracellular spaces, integrity of cell membranes and viscosity of fluids. When present, high cellularity, necrosis, inflammation and fibrosis substantially alter the diffusion properties of water and, thus, affect the returned signal. To date, two models have been applied to abdominal imaging using DW-MRI [1]. One is the mono-exponential model, which is the most commonly used in daily practice. The other one is a bi-exponential model, which accounts for separating tissue diffusivity and tissue microcapillary perfusion. The bi-exponential model is based on the intravoxel incoherent motion (IVIM) theory that was introduced by Le Bihan et al. as a joint method to measure perfusion and diffusion [1]. Multiple b value IVIM models (i.e., more than 10 b values) based on the bi-exponential fitting theory are complex and time consuming because of a long post-processing time and show high degrees of variability and reproducibility, especially for the perfusion related parameter D* [2,3]. Consequently, bi-exponential post-processing using multiple b values is not routinely performed although it is being widely evaluated in research [3—7]. Dramatic advances in image quality during recent years, mainly due to substantial refinements in hardware and coil systems, have made DW-MRI a promising technique for the detection and characterization of a wide range of pathologic condition in the abdomen and pelvis [8—17]. The implementation of ultrafast MRI techniques, such as echo-planar imaging (EPI) combined with parallel imaging using multicoil state-of-the-art MRI scanners, has made DW-MRI of the abdomen a feasible option in clinical practice. Scan acquisitions can be performed relatively quickly, does not require administration of gadolinium-chelate and enables qualitative and quantitative assessment of tissue diffusivity (diffusion coefficients). Beyond detection and characterization, DW-MRI shows also promise for monitoring abdominal cancer response to therapy [9]. Although DW-MRI has received considerable attention and has been subjected to marked developments in the area of liver disease, by contrast less has been made regarding the pancreas. One reason may be that the pancreas is a deep, central and relatively small organ in the abdomen, far from coil elements so that DW-MRI of this organ may be rendered difficult because of signal loss by comparison with the liver. However, a careful selection of technical parameters for DW-MRI image acquisition may contribute to increase the pancreatic signal. Signal-to-noise ratio may be improved by using a minimum TE, by increasing the number of averages, and decreasing bandwidth. Another reason may be that encouraging results achieved with DW-MRI in the liver are not mirrored by those obtained in the pancreas.

Gastrointestinal cancers in inflammatory bowel disease: An update with emphasis on imaging findings.

Inflammatory bowel diseases (IBD) are associated with an increased risk of gastrointestinal cancers depending on the specific type of IBD, the extent of the disease and its location. Patients with IBD and extensive colonic involvement are at increased risk of colorectal cancer whereas patients with Crohn disease have an increased risk for small-bowel and anal carcinoma. These cancers preferentially develop on sites of longstanding inflammation. In regards to colon cancer, several key pathogenic events are involved, including chromosomal instability, microsatellite instability and hypermethylation. The risk for colon cancer in IBD patients correlates with longer disease duration, presence of sclerosing cholangitis, pancolitis, family history of colorectal cancer, early onset of the disease and severity of bowel inflammation. Identification of increased colorectal cancer risk in individual IBD patients has led to formal surveillance guidelines. Conversely, although an increased risk for other types of cancer has been well identified, no specific formal screening recommendations exist. Consequently, the role of the radiologist is crucial to alert the referring gastroenterologist when a patient with IBD presents with unusual imaging findings at either computed tomography (CT) or magnetic resonance (MR) imaging. This review provides an update on demographics, molecular, clinical and histopathological features of gastrointestinal cancers in IBD patients including colorectal carcinoma, small bowel adenocarcinoma, neuroendocrine tumors and anal carcinoma, along with a special emphasis on the current role of CT and MR imaging.

Carcinoid tumors of the small-bowel: Evaluation with 64-section CT-enteroclysis

PURPOSE To describe the imaging presentation of carcinoid tumors of the small-bowel at 64-section CT-enteroclysis and determine the sensitivity of this technique for tumor detection. PATIENTS AND METHODS The 64-section CT-enteroclysis examinations of 22 patients with histopathologically proven small-bowel carcinoid tumors and those of 6 patients with suspected recurrence after small-bowel resection for carcinoid tumor were reviewed. Images were analyzed with respect to imaging presentation. Sensitivity, specificity, and accuracy, of 64-section CT-enteroclysis for the diagnosis of carcinoid tumor of the small-bowel were estimated with 95% confidence intervals (CIs). RESULTS Twenty-five carcinoid tumors were confirmed in 22 patients (prevalence, 22/28; 79%). Overall sensitivity for carcinoid tumor detection was 76% (19/25; 95%CI: 55-91%) on a per-lesion basis. On a per-patient basis, 64-section CT-enteroclysis had a sensitivity of 86% (19/22; 95%CI: 65-97%), a specificity of 100% (6/6; 95%CI: 54-100%) and an accuracy of 89% (25/28; 95%CI: 72-98%) for the diagnosis of carcinoid tumor. Focal small-bowel wall thickening, mesenteric stranding, and mesenteric mass were found in 20/22 (91%), 18/22 (82%) and 15/22 (68%) patients with pathologically confirmed tumors. CONCLUSION 64-Section CT-enteroclysis shows highly suggestive features for the diagnosis of carcinoid tumor of the small-bowel and achieves high degrees of sensitivity for tumor detection.

Solid-pseudopapillary tumor of the pancreas: MR imaging findings in 21 patients

PURPOSE Solid-pseudopapillary tumor (SPT) of the pancreas is a rare, low-grade malignancy, which mostly occurs in adolescent and young adult females. The goal of this study was to retrospectively analyze the magnetic resonance (MR) imaging presentation of SPT of the pancreas. METHODS We retrospectively reviewed the preoperative MR imaging examinations and the medical, surgical and histopathological records of 21 patients who underwent surgery for SPT of the pancreas. MR imaging included T1-weighted, T2-weighted, and gadolinium chelate-enhanced MR imaging. In addition, 10 patients had diffusion-weighted (DW) MR imaging. MR examinations were retrospectively reviewed for location, size, morphological features and signal intensity of the tumors. RESULTS Nineteen women and 2 men (median age, 23 years; range, 14-59) were included. Seven patients (7/21; 33%) presented with abdominal symptoms. The median largest tumor diameter was 53mm (range, 32-141 mm). SPTs were located in the pancreatic head, body, and tail in 9 (9/21; 43%), 5 (5/21; 24%) and 7 (7/21, 33%) patients, respectively. All patients (21/21; 100%) had a single SPT. SPTs were more frequently oval (12/21; 57%), predominantly solid (12/21; 57%), fully encapsulated (16/21; 76%), larger than 30 mm (21/21; 100%), hypointense on T1-weighted MR images (21/21, 100%), hyperintense on T2-weighted MR images (21/21; 100%) and with an enhancing capsule after gadolinium-chelate administration (21/21; 100%). CONCLUSIONS There is trend of appearance for SPT of the pancreas on MR imaging but that variations may be observed in a number of cases. SPT uniformly presents as a single, well-demarcated and encapsulated pancreatic mass.

Update on imaging of Peutz-Jeghers syndrome

Peutz-Jeghers syndrome (PJS) is a rare, autosomal dominant disease linked to a mutation of the STK 11 gene and is characterized by the development of benign hamartomatous polyps in the gastrointestinal tract in association with a hyperpigmentation on the lips and oral mucosa. Patients affected by PJS have an increased risk of developing gastrointestinal and extra-digestive cancer. Malignancy most commonly occurs in the small-bowel. Extra-intestinal malignancies are mostly breast cancer and gynecological tumors or, to a lesser extent, pancreatic cancer. These polyps are also at risk of acute gastrointestinal bleeding, intussusception and bowel obstruction. Recent guidelines recommend regular small-bowel surveillance to reduce these risks associated with PJS. Small-bowel surveillance allows for the detection of large polyps and the further referral of selected PJS patients for endoscopic enteroscopy or surgery. Video capsule endoscopy, double balloon pushed enteroscopy, multidetector computed tomography and magnetic resonance enteroclysis or enterography, all of which are relatively new techniques, have an important role in the management of patients suffering from PJS. This review illustrates the pathological, clinical and imaging features of small-bowel abnormalities as well as the role and performance of the most recent imaging modalities for the detection and follow-up of PJS patients.

Toward a Preoperative Classification of Lymph Node Metastases in Patients with Small Intestinal Neuroendocrine Tumors in the Era of Intestinal-Sparing Surgery

Introduction: In patients with small intestinal neuroendocrine tumors (siNETs), surgical resection of the primary tumor and associated mesenteric lymph nodes (LNs) is recommended, but is not well standardized and can be risky in patients with superior mesenteric vessel involvement. Objective: We aimed to evaluate the correlation between the length of resected small bowel and the number of removed LNs, and to propose a preoperative morphological classification of siNET-associated LNs. Methods: The records of patients operated on for siNETs at two expert centers between August 2005 and November 2013 were analyzed. Two specialist radiologists reviewed the preoperative imaging and classified mesenteric LNs into five stages according to their proximity to the trunk and/or branches of the superior mesenteric artery. Results: 72 patients were included. The mean number of removed LNs was 12 ± 15 and the length of removed small intestine was 53 ± 43 cm. No correlation existed between the length of small bowel resection and the number of removed LNs. Overall, 9 (12%), 13 (18%), 36 (50%), 14 (19%) and 0 patients were classified into LN stages 0, I, II, III and IV. The correlation rate between the two observers was 0.98. Patients with LN stage III (hardly resectable) had more removed LNs than those with LN stages 0, I or II (easily removable). Conclusion: Optimal lymphadenectomy is not always associated with extended small bowel resection. In the era of small bowel-sparing surgery, the preoperative classification of mesenteric LNs could help to standardize the surgical management of patients with siNETs.