MRCP provides excellent 2-dimensional 2D and 3-dimensional 3D depiction of the pancreatic duct anatomy and its abnormalities in patients with pancreatitis as well as neoplasms. Typical imaging sequences used include axial T1-weighted images, with and without fat saturation, using breath-hold or gated respirations. A complete evaluation of the pancreatic parenchyma and pancreatico-biliary ductal system can be performed with the following sequences: T1-weighted gradient echo, T2-weighted T2W axial, and coronal sequences, either fast spin echo FSE or turbo spin echo TSE , 2D and 3D MRCP; and T1-weighted 3D gradient-echo before and after gadolinium.
To adequately visualize the gallbladder and to assess the exocrine response to secretin, the patient should ideally be fasting for 4 hours. Negative oral contrast is administered to reduce the signal from the overlying stomach and duodenum. Axial and coronal T2 images with and without fat saturation should also be obtained.
Dynamic postcontrast images should be obtained 25, 70, and sec after the gadolinium contrast injection. A standard pancreatic protocol also includes MRCP images for further evaluation of pancreatic ductal abnormalities. The 3D fast spin echo sequence can either be acquired as a series of breath holds or during free breathing.
Secretin MRCP is useful in assessment of complex ductal anomalies and to quantitatively or semiquantitatively assess the exocrine function of the pancreas.
On US, the pancreas is slightly echogenic compared to the liver and has a homogenous appearance. On MDCT, the normal pancreas has slightly higher attenuation than the paraspinal muscles and has a lobulated contour. The normal pancreas has the highest intrinsic T1 signal of all abdominal organs and therefore precontrast T1-weighted images are the most sensitive sequence to detect focal lesions, which are often hypointense relative to normal parenchyma and for detection of hemorrhage within inflammatory collections. On T2-weighted images, the pancreas is slightly hyperintense compared to the adjacent muscle, and they are optimally suited for depicting the ductal anatomy, cystic lesions, and islet cell tumors, which are hyperintense compared to normal pancreas.
Acute pancreatitis refers to acute reversible inflammation of pancreatic parenchyma. Approximately , patients with this condition are admitted to the hospital each year in the United States U. Other etiologies include mechanical post ERCP, trauma , metabolic hypercalcemia, hypertriglyceridemia, cystic fibrosis, and hereditary pancreatitis and toxic drugs like HCTZ and aspariginase. The diagnosis of acute pancreatitis is often based on clinical and laboratory evidence. Imaging is therefore performed in patients with pancreatitis not for diagnosis but for the following reasons: i to identify the possible etiology such as gallstones or neoplasm , ii to grade the severity, iii to evaluate complications, and iv to identify possible distinctive imaging features in special types of pancreatitis, such as tropical pancreatitis, autoimmune pancreatitis, or groove pancreatitis.
MDCT is the preferred imaging modality and contrast administration is essential to detect complications, such as parenchymal necrosis, venous thrombosis, and arterial pseudo-aneurysm. A single portal venous phase abdominal MDCT is performed for routine cases,but arterial phase scanning is imperative when pseudoaneurym is suspected. The range of pancreatic findings and the CT grading is depicted in Table 2. Mild or early pancreatitis Grade A is occult on CT and the imaging findings lag behind the clinical and laboratory findings.
Grade B pancreatitis is characterized by diffuse or focal pancreatic enlargement, while peripancreatic inflammatory changes,including blurring of the pancreatic margin, stranding of adjacent fat, and mild decrease in parenchymal density from edema occur inGrade C pancreatitis Figure 4. MRI is typically performed for evaluation of etiologies, such as gallstones or pancreas divisum. The imaging findings include loss of normal T1 hyperintensity with heterogeneous hypointense areas.
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T2 fat-suppressed images may show small amounts of peripancreatic fluid. Accurately detecting pancreatic necrosis is of paramount importance in imaging pancreatitis. Additionally, MRI depicts areas of hemorrhage within necrotic foci as ill-defined areas of high T1 and low T2 signal.
On MDCT, false positive diagnosis can result from areas of decreased attenuation due to focal fatty replacement, edema, or intrapancreatic fluid collections. False negative scans occasionally occur when imaging is performed early in the phase of pancreatic inflammation first hours after symptom onset. Although necrosis occurs early, the false negative rate can be reduced if CT is performed 72 hours after symptom onset. Acute fluid collections often occur in patients with pancreatitis, and the presence of fluid collections increases the CT pancreatitis grade.
Pseudocysts are the most common inflammatory cystic pancreatic lesions and contain necrotic debris from digested retroperitoneal fat. Pseudocysts can have myriad imaging appearances ranging from unilocular to multilocular morphology.
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Enhancement of the cyst wall is commonly seen on MDCT. On MRI, they typically show variable but low signal on T1-weighted images and high signal on T2-weighted images.
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Hemorrhage and debris can cause an atypical appearance leading to an increased T1 signal and decreased T2 signal compared to simple appearing pseudocysts. Gas within a pseudocyst does not prove infection; this imaging finding could also be due to enteric fistula or recent intervention. Percutaneous, endoscopic or open surgical drainage are treatment options. Leakage of the digestive pancreatic enzymes can cause digestion of the wall of the surrounding arteries leading to weakening and pseudoaneurysm formation Figure 8. The splenic artery is most commonly involved, followed by the gastro-duodenal artery, celiac artery, orSMA.
They are at a high risk for hemorrhage and urgent surgical or vascular interventional radiology evaluation is needed. Pancreatic and peripancreatic inflammation can extend to surrounding venous structures leading to thrombosis, which manifests as a filling defect within the affected vessel during the portal venous phase. While traditionally chronic pancreatitis has been thought of as a separate entity from acute pancreatitis, given that recurrent episodes of acute pancreatitis occasionally lead to chronic pancreatitis, acute and chronic pancreatitis are now thought be on a spectrum of a similar disease.
Chronic pancreatitis, which results in irreversible fibrosis, atrophy, and exocrine and endocrine insufficiency of the pancreas, may manifest clinically as malabsorption and diabetes. MDCT is the preferred modality to image chronic pancreatitis owing to better visualization of calcifications Figure 9. Pancreatic calcifications may be parenchymal or ductal in origin.
The gland may become focally or diffusely atrophic. Pancreatic ductal dilatation with a beaded appearance is a characteristic appearance in chronic pancreatitis. Occasionally, chronic pancreatitis may result in an inflammatory pseudomass causing focal enlargement with fibrosis and hypoenhancement and inflammatory narrowing of the common bile duct, which can mimic adenocarcinoma. The presence of calcifications and smooth tapered narrowing of the CBD allow differentiation of inflammatory pseudo mass from adenocarcinoma, which results in abrupt narrowing of the common bile duct.
However, pancreatic calcifications are not well seen on MRI. Inflammatory pseudo mass has a decreased signal intensity on T1-weighted images secondary to fibrosis and decreased protein content of the gland from atrophy. Imaging of the pancreas: Part 1. Appl Radiol. Clinical Departments Imaging of the pancreas: Part 1.
Guimaraes, MD, PhD. Normal anatomy and physiology The pancreas is a retroperitoneal organ located in the anterior pararenal space posterior to the stomach and bounded by the c-loop of duodenum on the right side. Development and variants Embryologically, the pancreas arises from a dorsal and ventral pancreatic bud. Imaging evaluation Plain radiograph Radiography has a limited role in imaging of the pancreas, but it can sometimes depict parenchymal calcifications, which helps in the detection of chronic pancreatitis.
Ultrasound Ultrasound US also has a limited role in pancreatic evaluation as the overlying gas from the transverse colon and stomach makes visualizing pancreatic parenchyma difficult or even impossible. Multidetector CT MDCT is the modality of choice for the evaluation of both inflammatory and neoplastic conditions of the pancreas.
Technique Typical imaging sequences used include axial T1-weighted images, with and without fat saturation, using breath-hold or gated respirations. Normal appearance On US, the pancreas is slightly echogenic compared to the liver and has a homogenous appearance.
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Imaging in acute pancreatitis The diagnosis of acute pancreatitis is often based on clinical and laboratory evidence. Complications Necrosis Accurately detecting pancreatic necrosis is of paramount importance in imaging pancreatitis.
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Vascular complications Leakage of the digestive pancreatic enzymes can cause digestion of the wall of the surrounding arteries leading to weakening and pseudoaneurysm formation Figure 8. Chronic pancreatitis While traditionally chronic pancreatitis has been thought of as a separate entity from acute pancreatitis, given that recurrent episodes of acute pancreatitis occasionally lead to chronic pancreatitis, acute and chronic pancreatitis are now thought be on a spectrum of a similar disease. Imaging findings MDCT is the preferred modality to image chronic pancreatitis owing to better visualization of calcifications Figure 9.
Medicine Radiology. Diagnostic Imaging Free Preview. Documents the strengths and limitations of all the imaging techniques used in patients with pancreatitis Clearly explains how imaging findings derive from the pathophysiology of the disease processes Examines in detail the significance of imaging findings for clinical and therapeutic decision-making Contains numerous informative high-quality illustrations see more benefits.
Buy eBook. Buy Hardcover. Buy Softcover. FAQ Policy. About this book With the aid of numerous high-quality illustrations, this volume explains the strengths and limitations of the different techniques employed in the imaging of pancreatitis. Show all. From the reviews: "I was very keen to read the book. Acute, traumatic and chronic diseases of the pancreas and their complications are discussed in 20 chapters and pages plus a well structured subject index. Show next xx. Read this book on SpringerLink.