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Chronic Pancreatitis: Ultrasound, Computed Tomography, and Magnetic Resonance Imaging Features
Chronic Pancreatitis: Ultrasound, Computed Tomography, and Magnetic Resonance Imaging Features Aheed J. Siddiqi, MD and Frank Miller, MD Chronic pancreatitis is a progressive, irreversible inflammatory and fibrosing disease of the pancreas with clinical manifestations of chronic abdominal pain, weight loss, and permanent pancreatic exocrine and endocrine insufficiency. In the United States, a long history of heavy alcohol consumption is the most common cause of chronic pancreatitis. This review discusses the different modalities such as computed tomography, transabdominal and endoscopic ultrasound, magnetic resonance imaging/magnetic resonance cholangiopancreatography, and endoscopic retrograde cholangiopancreatography available to image chronic pancreatitis, along with their advantages and limitations. In addition, topics such as groove pancreatitis and autoimmune pancreatitis are examined, along with a discussion of distinguishing chronic pancreatitis from pancreatic adenocarcinoma. Semin Ultrasound CT MRI 28:384-394 © 2007 Elsevier Inc. All rights reserved.
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hronic pancreatitis is a progressive, irreversible inflammatory and fibrosing disease of the pancreas with clinical manifestations of chronic abdominal pain, weight loss, and permanent pancreatic exocrine and endocrine insufficiency. Often the most predominant clinical feature of chronic pancreatitis is chronic recurrent and intense abdominal pain that can make care of these patients difficult.1 Intractable pain can be recalcitrant to most medical and endoscopic therapies, often requiring a frequent need for narcotics.2 Chronic pancreatitis also is a public health care issue due to associated psychosocial problems, loss of work, narcotic addiction, and consumption of health care resources. In the United States, a long history of heavy alcohol consumption is the most common cause of chronic pancreatitis. Other etiologies included hyperlipidemia, hyperparathyroidism, trauma, cystic fibrosis, and pancreas divisum. Obstruction due to posttraumatic ductal strictures, pseudocysts, or structural changes in the pancreatic duct has also been implicated as a possible etiology. Between 30 and 40% of patients with chronic pancreatitis have no apparent underlying cause and are considered to have “idiopathic” chronic Department of Radiology, Northwestern University Feinberg School of Medicine, Chicago, IL. The authors have no conflicts of interest to disclose. Address reprint requests to: Frank H. Miller, MD, Department of Radiology, Northwestern University Feinberg School of Medicine, 676 N. St. Claire Street, Suite 800, Chicago, IL 60611. E-mail: [email protected].
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pancreatitis.3 In contrast to acute pancreatitis, gallstones are not considered risk factors in the development of chronic pancreatitis. The morphologic changes in the pancreas parenchyma include edema, inflammation, and necrosis, superimposed on a background of chronic changes that include fibrosis, chronic inflammation, and loss of exocrine tissue.3 Histologically, the disease is characterized by parenchymal fibrosis, ductal strictures and dilatation with calcifications, and atrophy of acinar and islet tissue. The clinical diagnosis of chronic pancreatitis, especially in its early stages, is difficult and often frustrating for patients and treating physicians. Laboratory testing and imaging is often performed to aid in diagnosis. Endoscopic retrograde cholangiopancreatography (ERCP) and pancreatic function tests have long been considered the diagnostic gold standards; however, these tests have limitations as will be discussed. Pancreatic biopsy is seldom utilized as it may produce false-negative results (if nondiseased areas of the pancreas are biopsied) as well as potential complications such as fistulas, hemorrhage, and acute pancreatitis. With further experience and improved techniques, modalities such as magnetic resonance imaging (MRI), magnetic resonance cholangiopancreatography (MRCP), and endoscopic ultrasound (EUS) are gaining acceptance as sensitive modalities to diagnose chronic pancreatitis as well as its complications. This review discusses the different modalities available to image chronic pancreatitis, along with their advantages
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and limitations. In addition, topics such as groove pancreatitis and autoimmune pancreatitis are examined, along with a discussion of distinguishing chronic pancreatitis from pancreatic adenocarcinoma.
Computed Tomography of Chronic Pancreatitis Computed tomography (CT) is helpful in the diagnosis of late chronic pancreatitis and associated complications. It is, however, limited in the detection of early chronic pancreatitis. The usual CT findings in chronic pancreatitis are dilatation of the pancreatic duct, pancreatic calcifications, and parenchymal atrophy. Dilatation of the pancreatic duct and its secondary radicles is the most common finding and can be seen in 68% of patients.4 The pattern of dilatation can vary (smooth, beaded, or irregular), with no particular pattern predominating. However, ductal dilatation is a nonspecific finding and can be seen with distal common bile duct cholangiocarcinoma, pancreatic and ampullary carcinomas, and other conditions. Luetmer et al demonstrated good correlation between ERCP and CT for ductal dilatation, with ERCP and CT demonstrating concordant findings in 16/18 patients. ERCP detected ductal dilatation in two patients with normal CT findings.4 CT findings of chronic pancreatitis can also be made based on the size and shape of the gland. Parenchymal atrophy is seen in 54% of patients with chronic pancreatitis.4 However, parenchymal atrophy is neither sensitive nor specific and can be seen as a normal aging process. To complicate matters, focal pancreatic enlargement, a less common nonspecific presentation of chronic pancreatitis, can be seen in 30% of patients.4 Parenchymal changes from pancreatitis, if detected on CT, are late in the disease process. Many patients with severe exocrine insufficiency can have a normal-appearing pancreas on CT. Unfortunately, there is poor correlation between pancreatic morphology and exocrine and endocrine deficiency from chronic pancreatitis. Intraductal pancreatic calcifications are the most specific and reliable CT sign of chronic pancreatitis (Fig. 1). When compared to other modalities, the advantage of CT is in the detection of these calcifications, which can be seen in 50% of patients.4 Calcifications develop due to deposition of calcium carbonate in inspissated intraductal protein plugs. They vary widely in size (tiny, stippled to large, coarse) and distribution (localized to diffuse).5 Calcifications, however, appear late in the disease process or in patients with severe disease.6 CT is an excellent modality to identify complications of chronic pancreatitis such as fluid collections, which can be seen in 30% of patients.4 Fluid collections are mostly seen within or adjacent to the pancreas, although distant sites are also rarely seen. Most fluid collections associated with chronic pancreatitis are well-encapsulated. Free fluid in the vicinity of the pancreas suggests superimposed acute pancreatitis.
Figure 1 Chronic pancreatitis. Coronal contrast-enhanced MDCT image shows multiple diffuse calcifications (arrow) in a patient with chronic pancreatitis due to alcohol abuse.
CT can also evaluate the formation of pseudocysts, which are encapsulated collections of pancreatic enzyme secretions that occur in the pancreas or in the peripancreatic tissue. While most resolve spontaneously, pseudocysts can undergo infection, hemorrhage, gastric or biliary obstruction, or fistulae formation with the gastrointestinal tract. Other potential complications that can be evaluated by CT include pseudoaneuryms of the splenic or pancreaticoduodenal arteries and thrombosis of the portosplenic veins with venous collaterals and gastric varices. Pancreatico-pleural fistula is a rare complication of chronic pancreatitis in which pancreatic secretions from a ruptured pancreatic duct dissect through the aortic and esophageal hiatus or through the diaphragm and can gain access to the mediastinum and pleural spaces (Fig. 2). This can be seen on CT and MRI, with MRCP best equipped to depict the fistula and ductal anatomy in these patients.5 Dilatation of the common bile duct can also be seen in many patients with chronic pancreatitis and is strongly associated with dilatation of the main pancreatic duct.4 There is often an inflammatory mass in the head of the pancreas. In chronic pancreatitis, the dilated common bile duct demonstrates gradual tapering, compared to the abrupt cutoff seen in malignant obstructions. However, there is significant imaging overlap between ductal dilatation from malignancy and focal inflammation associated with chronic pancreatitis, and further diagnostic evaluation is often needed. It is generally accepted that CT can detect chronic pancreatitis in patients with severe or advanced disease. In contrast, ERCP, pancreatic function tests, MRI, and EUS are more sensitive in diagnosing early or mild chronic pancreatitis. In the literature, studies evaluating the CT features of chronic pancreatitis are from the 1980s. Since then, vast improvements in CT technology (multidetector CT with multiple phases of imaging and thinner collimation) has undoubtedly improved the sensitivity in detecting this disease. Reevaluation of chronic pancreatitis and CT is long overdue.7
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Transabdominal and Endoscopic Ultrasound of Chronic Pancreatitis Transabdominal Ultrasound Transabdominal ultrasound has been used for many years to evaluate the pancreas. However, the diagnosis of chronic pancreatitis can be difficult. The limitation of ultrasound is its inability to evaluate the complete pancreas due to patient body habitus and overlying bowel gas. In addition, the majority of the findings on ultrasound are neither sensitive nor specific for the diagnosis. Similar to CT, the early detection of chronic pancreatitis is difficult. Late findings include alterations in size and echogenicity of the gland, pancreatic calcifications, pancreatic duct dilatation and irregularity, and biliary dilatation.7 The classic sonographic sign of chronic pancreatitis is pancreatic calcifications, which are seen as multiple punctate hyperechoic foci in 40% of patients8 (Fig. 3). These may or may not shadow depending on their size but can cause ductal obstruction and lead to persistent recurrent pancreatitis. The degree and pattern of pancreatic calcification can change over time and studies have shown no correlation between exocrine function and the amount of pancreatic calcifications.9,10 Late in the disease process, the pancreatic parenchyma may demonstrate heterogeneous echotexture with mixed areas of hyper- and hypoechogenicity. The hyperechoic regions are likely related to fibrosis and calculi, while the hypoechoic regions are associated with areas of inflammation.8 Most patients demonstrate a normal-sized gland, while, in some patients, the pancreas may be atrophic in advanced disease. Although there is relatively good pancreatic functional and morphologic correlation on ultrasound in advanced pancreatic disease, there is poor correlation for mild-to-moderate and early disease.10 Chronic pancreatitis may also present as a focal hypoechoic mass in up to 40% of patients, associated with irregular dilatation and tortuosity of the pancreatic duct, making
Figure 2 (A-C) Pancreatico-pleural fistula. (A) Axial contrast-enhanced MDCT image shows a small rim-enhancing pancreatic pseudocyst (arrow) dissecting through the diaphragm into the pleural space (curved arrow). (B) Coronal contrast-enhanced MDCT image shows the fluid extending from a disrupted duct (arrow) superiorly into the pleural space. The coronal reformatted images aid in the diagnosis. (C) ERCP confirms the findings on CT, demonstrating the fistulous communication between the pancreatic duct and left pleural space (arrow).
Figure 3 Chronic pancreatitis. Transabdominal sonogram of the pancreas demonstrates a hypoechoic gland with multiple punctate calcifications (arrows) throughout the gland.
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it difficult to distinguish from a pancreatic neoplasm.8 Short strictures in the main pancreatic duct can produce alternating areas of narrowing and dilatation, referred to as the “chain of lakes” sign. When the dilated duct contains calcifications without an obstructing mass, chronic pancreatitis is favored over cancer. However, due to imaging overlap between the two entities, diagnostic procedures such as CT or endoscopic ultrasound-guided biopsies may be required. Like CT, complications of chronic pancreatitis can be seen on ultrasound. Pancreatic pseudocysts are reported in 25 to 40% of patients.8 Some patients present with focal dilatation of the pancreatic or common bile duct or pseudocyst formation as the only indication of chronic pancreatitis. Vascular complications including portosplenic vein thrombosis and subsequent development of collateral varices and arterial pseudoaneuryms can also be detected using Doppler sonography.
Endoscopic Ultrasound EUS was introduced in the early 1980s for the purpose of improved imaging of the pancreas. The proximity of the pancreas to the stomach and duodenum allows high-resolution images of the pancreas with the use of high-frequency transducers. EUS also overcomes the limitations of transabdominal ultrasound, namely, abdominal gas and body fat.11 On EUS, the normal pancreas has homogenous fine granularity and reticulation with smooth margins and without side-branch ectasia. It is slightly more echogenic than the liver. The average pancreatic duct diameter in the body is 1.9 mm and is uniformly tubular with anechoic walls, with normal side branches visible in 32% of patients.12,13 Several new features of chronic pancreatitis that are not seen by CT or transabdominal US have been documented by EUS. These include pancreatic parenchymal and ductal abnormalities. There is often subtle lobularity of the outer gland margin and small cystic changes in the pancreatic parenchyma. Hyperechoic foci or strands and prominent interlobular septa (due to fibrosis) within the pancreas can be seen along with heterogeneous echogenicity of the parenchyma. Ductal abnormalities noted on EUS include hyperechoic margins of the pancreatic duct, side-branch duct ectasia, intraductal stones and main pancreatic duct dilatation (⬎3 mm), and irregularity11 (Fig. 4). CT and transabdominal US lack sufficient resolution for the detection of these subtle parenchymal and ductal abnormalities in cases of early chronic pancreatitis on EUS.13 There are many advantages of EUS compared to ERCP. It has a significant safety advantage over ERCP (which can be complicated by postprocedure pancreatitis) and can also be used for drainage of pancreatic pseudocysts and for celiac plexus blockade for pain control.11 In contrast to ERCP, EUS can also provide a very detailed evaluation of the pancreatic parenchyma. While EUS has the potential of being one of the gold standards for the diagnosis of chronic pancreatitis, a few issues need to be considered. First, diagnostic criteria for chronic pancreatitis are not standardized and there is considerable
Figure 4 (A, B) EUS Chronic pancreatitis. (A) Endoscopic sonogram demonstrates a stone in the pancreatic duct (arrow) with associated shadowing. (B) Endoscopic sonogram shows multiple calcifications (arrow) in the pancreatic head due to chronic pancreatitis. There are areas of hyperechogenicity and hypoechogenicity involving the pancreas. (Images courtesy of Dr. Rameez Alasadi, Department of Gastroenterology, Northwestern University Feinberg School of Medicine, Chicago, IL.)
intra- and interobserver variability in analysis of the findings. In addition, some of the findings seen on EUS to suggest chronic pancreatitis (fibrosis, echogenic septations) may occur normally with aging and therefore constitute false-positive findings. Many have wondered if EUS is “too sensitive” in the diagnosis of chronic pancreatitis.
MRI/MRCP of Chronic Pancreatitis With advancements in MR technology, pancreatic disorders are being increasingly evaluated with this modality. Contributions to improved imaging of the pancreas with reduced imaging time include higher strength field magnets and gradients, phased-array body multicoils, fast scanning techniques such as breath-hold spoiled gradient-echo sequences, dynamic contrast-enhanced imaging, and improved fat-suppression techniques.14
388 In addition, the utilization of MRCP with accurate noninvasive assessment of the pancreatic duct and biliary tract has supplanted ERCP as an initial diagnostic modality. Furthermore, MR angiography and assessment of the peripancreatic vasculature obviate other invasive imaging such as conventional angiography. The MR evaluation of the pancreas, biliary tree, and adjacent vessels can be evaluated as a “one-stop shop exam.”15 The normal pancreas is isointense or slightly hyperintense to the liver on T1-weighted non-fat-suppression images. With fat suppression, the normal pancreas is best displayed as hyperintense to all other solid organs of the abdomen. The intrinsic increased T1 signal intensity is due to the presence of aqueous protein in the glandular elements of the pancreas, which shorten the T1 values of the normal gland.16 The normal T2-weighted signal intensity of the pancreas is similar to the liver and hyperintense compared with the spleen and kidneys. The normal pancreas enhances maximally during the arterial phase after the injection of intravenous gadolinium, in contrast to the liver, which shows minimal enhancement during this phase because of its predominant portal venous supply. There is also rapid washout and, during the portal and delayed phases, the pancreas becomes isointense to the liver.16 The main advantage of MRI compared to imaging modalities is the sensitivity of MR in depicting signal intensity and enhancement abnormalities in early chronic pancreatitis. Due to its excellent soft-tissue contrast, MRI can depict early disease by detecting signal changes before any morphologic changes occur.17 The parenchymal changes of chronic pancreatitis can be divided into early and late findings. The early findings include loss of normal high signal intensity of the pancreas on T1-weighted fat-suppressed images due to decreased proteinaceous fluid content from chronic inflammation and fibrosis.17 In early disease, there is also decreased and heterogeneous enhancement of the pancreas in the arterial phase with progressive enhancement in delayed phases18 (Fig. 5). This is related to loss of normal vascularity of the gland secondary to chronic inflammation and fibrosis.17 These findings are in contrast to CT, which may depict normal appearance and enhancement of the pancreas even in advanced disease. Late parenchymal findings in chronic pancreatitis include atrophy and pseudocyst formation. Parenchymal calcifications are also noted, although this is better appreciated on CT. However, MR better defines intraductal calcifications which may cause pancreatic duct obstruction. MRCP imaging allows excellent visualization of the pancreatic and common bile ducts. The MRCP techniques involve fluid-sensitive sequences such as thin-section T2weighted single-shot fast spin-echo (HASTE/SSFSE) and thick-slab T2-weighted half-Fourier SSFSE MRCP and 3D respiratory-triggered or navigator-triggered techniques. Abnormalities of the pancreatic duct in chronic pancreatitis include irregular dilatation and beading often containing intraductal stones.19 Intraductal stones appear as signal void-
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Figure 5 (A-C) MRI of chronic pancreatitis. (A) Axial T1-weighted fat-suppressed gradient echo MR image shows decreased, heterogenous signal intensity in the pancreas, irregular dilatation of the main pancreatic duct, and a pseudocyst within the pancreatic head. (B, C) There is decreased pancreatic parenchymal enhancement during the arterial phase (B) and delayed enhancement during the venous phase (C) related to fibrosis from chronic pancreatitis.
filling defects surrounded by high signal pancreatic secretions within the duct. In severe cases, the beaded main pancreatic duct with marked dilated side branches may result in the classic “chain of lakes” appearance19 (Fig. 6). Other ductal abnormalities seen on MRCP include clubbing, sacculation and ectasia of the side radicles, strictures, ductal obstruction,
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The Perfect Examination?
Figure 6 Coronal T2-weighted MR image shows a dilated pancreatic duct and secondary radicles (arrow) associated with chronic pancreatitis.
pseudocysts, and fistula formation.20 MRCP can also demonstrate the dilatation of the biliary tract secondary to inflammatory stricture or compression of the bile duct.20 Some investigators report better visualization of the pancreatic duct by obtaining MRCP images after the administration of IV secretin.21 Secretin stimulates the pancreas to secrete fluid and bicarbonate and increase the tone of the sphincter of Oddi and therefore improves visualization and delineation of the main pancreatic duct and its branches. In addition, secretin can also be useful for functional evaluation of exocrine pancreas based on quantification of duodenal filling with chronic pancreatitis showing decreased filling.21,22 Currently, ERCP is considered the standard of reference for imaging the pancreaticobiliary system. However, multiple studies have demonstrated that MRCP fares well in comparison to ERCP, as discussed later. Unlike ERCP, MRI can evaluate the pancreatic parenchyma adjacent to the ductal abnormality as well as the adjacent peripancreatic tissues. MRCP can also demonstrate the dilated duct upstream from an obstructing stone or stricture.19 It is also noninvasive and an alternative for patients who are not good candidates or have failed ERCP.14 MR imaging is also an excellent modality in the evaluation of potential complications of chronic pancreatitis. MR has a high sensitivity for the detection of pseudocysts and the characterization of their contents better than CT. Complex pseudocysts from hemorrhagic or proteinaceous fluid are seen as high signal intensity on T1-weighted images. MRI/ MRCP also can show communication with the pancreatic duct, which may guide therapy. MRI also can evaluate vascular complications including splenic artery pseudoaneurysms (Fig. 7) and splenic or portal vein thrombosis. Potential biliary complications like choledocholithiasis, fistulas, and dilatation and transient obstruction of the common bile duct due to inflammatory strictures can also be evaluated by MRCP.5
While there are multiple modalities available to evaluate chronic pancreatitis, the perfect examination to detect this disease has not been clearly established. In general, when comparing different modalities, it is important to compare them with a gold standard. However, there is no acceptable gold standard for chronic pancreatitis. While histology may be the gold standard, it is invasive and features of chronic pancreatitis are often focally distributed and therefore missed by biopsy. ERCP was considered the gold standard in the past, but its limitations have been previously discussed. MRI/ MRCP and EUS may have supplanted ERCP in their sensitivity for detection of early disease. Comparison of EUS with ERCP in the diagnosis of chronic pancreatitis is being actively investigated, especially in the gastrointestinal literature. In a prospective examination of patients with recurrent pancreatitis, EUS demonstrated abnormalities in 79% of patients, while ERCP and secretin testing demonstrated abnormalities in 45 and 31% of patients, respectively.13 In this study, there was good correlation of EUS with ERCP in normal
Figure 7 (A, B) Splenic artery pseudoaneurysm. (A) Axial T2weighted MR image shows high signal intensity lesion in tail of the pancreas (arrow). (B) Axial T1-weighted fat-suppressed gadoliniumenhanced MR image demonstrates an enhancing splenic artery pseudoaneurysm (arrow) within the pancreatic pseudocyst. The use of contrast material is important to show the lesion is not a cystic lesion (high signal intensity on T2).
390 patients as well as in patients with moderate and severe disease. However, patients with mild disease detected on EUS demonstrated normal findings on ERCP. A combined analysis by Wallace et al of three prospective studies evaluating ERCP and EUS found that there was agreement between ERCP and EUS in 80% of patients with suspected chronic pancreatitis.11 When there was disagreement between the two modalities (20%), the findings were abnormal on EUS and normal on ERCP in the majority of the cases (74%). The authors reported, “it is unknown if EUS is more sensitive to mild changes of CP [chronic pancreatitis] than ERP or if EUS is ‘overdiagnosing’ early CP.”11 The clinical significance of “mild” changes of chronic pancreatitis seen on EUS with normal ERCP and pancreatic function tests has not been established.7 Some studies have evaluated the accuracy of MRI/MRCP comparing it directly to ERCP. Tamura et al demonstrated better visualization and opacification of the main pancreatic duct (especially in the pancreatic tail) by MRCP when compared to ERCP in patients with chronic pancreatitis.23 In this study, MRCP tended to be superior to ERCP in the delineation of the main pancreatic duct and provided high diagnostic accuracy in evaluating pathologic findings. The sensitivity, specificity, and accuracy values for delineating pathologic pancreatic changes at MRCP were 88, 98, and 91%, respectively.23 Takehara et al demonstrated agreement between MRCP and ERCP in ductal dilatation (83-92%), ductal narrowing (70-92%), and detection of filling defects (92-100%).24 Sica et al demonstrated 91% sensitivity of MRCP in visualization of the different pancreatic duct segments and 92% accuracy in characterizing segments as either normal, slightly dilated, or narrowed compared to ERCP. In this study, 42 segments in 19 patients could not be visualized by ERCP and in these patients comparison with MRCP was helpful and complementary.25 As MRCP techniques continue to evolve, this modality will play a more prominent role in all patients with suspected chronic pancreatitis, not just in patients with a contraindication to or failed ERCP. With MRCP and EUS emerging as highly accurate diagnostic modalities to evaluate chronic pancreatitis, a recent study compared these two modalities.26 In this prospective analysis, MRCP and EUS were compared to either ERCP, surgical pathology, and/or long-term clinical follow-up as the gold standard. The findings demonstrated EUS as more sensitive but equally specific compared with MRCP in the diagnosis of chronic pancreatitis. In addition, the combination of EUS and MRCP together had a sensitivity of 98% and a specificity of 100% compared to the “gold standards.” With more prospective studies, these two modalities, individually or in combination, may become the diagnostic gold standard for evaluation of chronic pancreatitis.
Pancreatic Inflammatory Mass versus Pancreatic Cancer Clinical and imaging distinction between chronic pancreatitis and pancreatic cancer can be extremely difficult. Both conditions can present with abdominal pain, obstructive
A.J. Siddiqi and F. Miller jaundice, and weight loss. The imaging appearance can be similar as well. Chronic pancreatitis can present as focal enlargement of the gland due to a chronic inflammatory mass, often in the pancreatic head, simulating pancreatic adenocarcinoma.16 Both can appear as noncalcified focal hypointense (MR) and hypodense (CT) masses with associated dilatation of common bile duct and main pancreatic duct (double-duct sign). Both conditions may also demonstrate ductal strictures, infiltration of the adjacent fat, arterial encasement, and peripancreatic venous obstruction.27,28 There are often no distinguishing features on T1- and T2-weighted MR imaging.29 Specific imaging features that favor an inflammatory mass are nondilated or smoothly tapering pancreatic and bile ducts coursing through the mass (“duct-penetrating” sign)30 (Fig. 8),
Figure 8 (A, B) Duct-penetrating sign. (A) Contrast-enhanced CT shows findings of chronic pancreatitis including pancreatic calcifications, a dilated main duct, and side branches. In the uncinate process, there is a heterogeneous area (arrow) that raised concern for neoplasm, which alternatively may relate to chronic pancreatitis. (B) Axial T2-weighted HASTE image shows a dilated pancreatic duct and branches penetrating through the apparent mass (arrows): “duct-penetrating sign.” This finding suggests chronic pancreatitis over adenocarcinoma. ERCP and biopsy suggested adenocarcinoma and the patient underwent a Whipple procedure. At pathology, this was demonstrated to be chronic pancreatitis without evidence of malignancy.
Chronic pancreatitis irregularity of the pancreatic duct, and the presence of pancreatic calcifications. In contrast, a smoothly dilated pancreatic duct with an abrupt interruption prior to the ampulla favors the diagnosis of cancer. Other features that favor cancer are a mass at the site of obstruction resulting in distal atrophy of the pancreas. With malignancy there is usually a high ratio of the duct caliber to the pancreatic gland width. Chronic pancreatitis tends to have limited atrophy and gradual (nonabrupt) narrowing of the dilated pancreatic duct or bile duct. However, pancreatic adenocarcinoma can be superimposed on patients with chronic pancreatitis and therefore specific findings of chronic pancreatitis may not be sufficient to exclude pancreatic malignancy. In a retrospective review of MR imaging and pathology in patients with chronic pancreatitis and pancreatic cancer, Johnson and Outwater found that both entities presented hypointense masses on T1-weighted imaging with progressive delayed enhancement compared to the rest of pancreas. The two entities could not be distinguished on the basis of time or degree of enhancement. In both conditions, histology revealed abundant fibrosis, accounting for their similar imaging appearance. The authors concluded that “similar gradual pattern of enhancement and overlap in peak enhancement preclude distinction of the two entities on the basis of gadolinium-enhanced MR findings.”31 A mass causing upstream chronic pancreatitis can sometimes be detected on early phase dynamic gadoliniumenhanced images. The cancer is seen as a focal hypointense mass relative to the hypoenhancing region of chronic pancreatitis on early gadolinium-enhanced images. In addition, the duct dilation abruptly terminates at the mass (Fig. 9). A prospective analysis using CA 19-9, US, CT, and CTguided fine-needle aspiration biopsy (FNAB) in 81 patients suspected of having chronic pancreatitis or pancreatic neoplasm demonstrated FNAB to be the most reliable method of differentiating chronic pancreatitis mass from pancreatic adenocarcinoma.32 US had technical limitations (abdominal fat and overlying bowel gas) obscuring the pancreas, which deemed 25% of the examinations as nondiagnostic. Nineteen percent of CT examinations were considered nondiagnostic because a focal mass in the pancreas could not be further characterized as inflammatory or neoplastic. CA 19-9 levels had reasonable sensitivity (81%) and specificity (81%) in distinguishing the two entities. However this is not a sufficient value for a laboratory test in distinguishing between a potential malignancy and guide management. Serum CA 19-9 is more useful as an early marker of relapse in patients who undergo surgery for pancreatic cancer. FNAB had 100% sensitivity and specificity when diagnostic, with only five (6%) cases being nondiagnostic.32 Due to clinical and imaging overlap between chronic pancreatitis and pancreatic adenocarcinoma, a percutaneous CTor EUS-guided FNAB may be required if the distinction cannot be made.
Groove Pancreatitis Groove pancreatitis is a type of focal chronic pancreatitis affecting the pancreatoduodenal groove. The pancreatoduo-
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Figure 9 (A-C) Pancreatic adenocarcinoma. (A) Axial contrast-enhanced CT shows atrophy of the pancreas and duct dilatation within the distal body and tail of the pancreas to the level of a suspected mass, which is difficult to see. No calcifications are seen to suggest chronic pancreatitis. (B) Axial T2-weighted HASTE image shows dilatation of pancreatic duct with abrupt termination (arrow). (C) Axial contrastenhanced T1-weighted fat-suppressed gradient-echo image demonstrates a hypo-enhancing mass in the body of the pancreas (arrow) suspicious for adenocarcinoma, which was subsequently confirmed on biopsy. There is upstream chronic pancreatitis.
denal groove is a potential anatomic space bordered by the pancreatic head medially, the second portion of the duodenum laterally, third portion of duodenum or inferior vena cava posteriorly, and the first portion of the duodenum or gastric antrum anteriorly.33
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Groove pancreatitis is characterized by repeated bouts of acute chronic pancreatitis with fluid and inflammatory cells dissecting into the groove between the pancreas and duodenum.19 It is classified as two forms: the pure form and the segmental form. The pure form affects the groove only, while the pancreatic parenchyma is preserved. Conversely, the segmental form involves the head of the pancreas, although predominant scar tissue can be seen within the groove.34 CT features of this condition include a hypodense lesion within the groove that demonstrates delayed contrast enhancement due to fibrosis.35 On MR imaging, Irie et al described a “sheet-like fibrotic mass” within the groove that is hypointense on T1-weighted images and iso- or hypointense on T2-weighted images relative to the pancreas. There is delayed enhancement that is well demarcated from the normal pancreas parenchyma, which demonstrates brisk enhancement on early postgadolinium imaging36 (Fig. 10). Histologic evaluation demonstrates fibrous scar with hypercellular granulation tissue within this region.36 The fibrotic scar in the groove can lead to disturbances in duodenal mobility, duodenal stenosis, and tubular stenosis of common bile duct, occasionally leading to obstructive jaundice. It is important to differentiate groove pancreatitis from exophytic pancreatic adenocarcinomas that have a significant fibrous component and may also display delayed enhancement. On MRCP, however, groove pancreatitis demonstrates smooth tapering of the distal common bile duct, in contrast to abrupt complete obstruction seen in patients with pancreatic carcinoma.33 However, there can be significant imaging overlap between the two entities and biopsy is often indicated. Differential diagnosis of soft tissue within the pancreaticoduodenal groove includes acute pancreatitis, exophytic pancreatic ductal or duodenal adenocarcinoma, gastrinoma (due to the groove being within the gastrinoma triangle), cholangiocarcinoma, or lymphadenopathy.33
Autoimmune Chronic Pancreatitis Autoimmune pancreatitis (AIP) is a type of chronic pancreatitis with an autoimmune pathogenesis and is associated with other autoimmune-related diseases such as Sjogren’s syndrome, primary sclerosing cholangitis, primary biliary cirrhosis, retroperitoneal fibrosis, ulcerative colitis, and systemic lupus erythematosus.37 It is a relatively recent and increasingly reported clinicopathologic entity, previously given a variety of names such as sclerosing pancreatitis, fibrosing pancreatitis, and nonalcoholic duct-destructive chronic pancreatitis. Sarles et al initially described a type of chronic pancreatitis that was painless or caused less pain than other types of pancreatitis and was associated with clinical hyperglobulinemia, jaundice, and often onset in the elderly.38 Histology revealed an enlarged and “elastic-hard” pancreas due to lymphocyte and plasma cell infiltration with fibrosis.
Figure 10 (A-C) Groove pancreatitis. (A) Contrast-enhanced CT shows a solid mass with small low-density cystic areas (arrow) lying within the pancreaticoduodenal groove. (B) Axial T2-weighted image shows abnormal hypointense mass within the pancreatioduodenal groove. High signal intensity cystic areas are seen within the abnormality (arrow). (C) Gadolinium-enhanced T1-weighted fat-suppressed gradient-echo image shows mild heterogenous enhancement within the mass (arrow), which enhances less than the pancreas (curved arrow) and duodenal wall (arrowhead) due to fibrosis.
In 1995, Yoshida et al proposed the name autoimmune pancreatitis for this entity. The authors further described this entity and demonstrated other abnormalities associated with this entity, which included increased serum gamma globulin or IgG levels and presence of auto-antibodies.39 Most patients
Chronic pancreatitis were asymptomatic or had mild symptoms usually with an absence of acute attacks of pancreatitis. The authors also reported two distinct groups of people that comprised this entity. The first group was predominately females with a mean age of 51 years with associated Sjogren’s syndrome. The second group did not have Sjogren’s syndrome, had a mean age of 63 years, with no sex predisposition.39 Autoimmune pancreatitis has many clinical, laboratory, and imaging characteristics. Patients often present with painless jaundice due to common duct narrowing within the pancreatic head, raising suspicion of a pancreaticobiliary malignancy.40 There is an absence of a history of acute attacks of pancreatitis or history of alcohol abuse. Laboratory analysis demonstrates seropositivity for antinuclear antibodies and hypergammaglobulinemia (increased serum ␥-globulin or IgG levels). On CT and MRI, there is diffuse “sausage-shaped” enlargement of the pancreas with delayed enhancement of the parenchyma.41 There is characteristically a rim-like capsule of low density surrounding the pancreas on both early and delayed enhanced images (Fig. 11). This rim demonstrates sub-
393 tle delayed enhancement.41 Calcifications are usually not seen. Ultrasound demonstrates a diffusely enlarged and hypoechoic pancreas, also with “sausage-like” appearance. On MRI, the pancreas demonstrates abnormal decreased or isointense T1 signal and increased T2 signal intensity compared to liver, with abnormal delayed enhancement on contrast-enhanced sequences. The “capsule-like” rim demonstrates hypointensity on T1- and T2-weighted imaging with delayed enhancement suggesting fibrous tissue.36 On MRCP, there is diffuse or segmental irregular narrowing and strictures of the main pancreatic duct. The common bile duct within the pancreas is often narrowed with extrapancreatic dilatation of the proximal duct, which may present with cholestatic liver dysfunction and hyperbilirubinemia. These features contrast with the findings seen in usual chronic pancreatitis seen as irregularly dilated main pancreatic duct, pancreatic parenchymal atrophy and pancreatic cysts, and calculi. Based on imaging, the differential diagnosis for this entity includes diffuse pancreatic enlargement from malignant lymphoma, plasmacytoma, metastases, diffuse infiltrative pancreatic carcinoma, and Shwachman syndrome.42 However, the above entities often have other different radiologic, clinical, and laboratory characteristics than that of autoimmune pancreatitis. Histopathologic features include massive fibrosis, lymphoplasmacytic infiltration, marked destruction of pancreatic islets and acini, and destruction of the pancreatic ducts with marked cellular infiltration. These findings are pathognomonic for autoimmune pancreatitis.43 The diagnosis of autoimmune chronic pancreatitis is important as the treatment differs from other types of pancreatitis. Autoimmune chronic pancreatitis has an excellent response to steroids. Pancreatic morphologic changes and pancreatic function often recover following steroid therapy.44 The size and enhancement pattern of the pancreas often returns to normal and capsule-like low-density rim disappears.41 Therefore, radiologic recognition of this condition is important to avoid unnecessary surgical resection because it is a reversible process when promptly diagnosed and treated.
References
Figure 11 (A, B) Autoimmune pancreatitis. (A) Axial contrastenhanced CT shows a uniformly enlarged pancreas with a peripancreatic hypodense rim (arrow) suggestive of autoimmune pancreatitis. (B) ERCP image in the same patient demonstrates multiple regions of segmental irregular strictures in the main pancreatic duct (arrows) consistent with autoimmune pancreatitis.
1. Sebastiano PD, di Mola FF, Bockman DE, et al: Chronic pancreatitis: the perspective of pain generation by neuroimmune interaction. Gut 52:907-911, 2003 2. Etemad B, Whitcomb DC: Chronic pancreatitis: diagnosis, classification, and new genetic developments. Gastroenterology 120:682-707, 2001 3. Steer ML, Waxman I, Freeman S: Chronic pancreatitis. N Engl J Med 332:1482-1490, 1995 4. Luetmer PH, Stephens DH, Ward EM: Chronic pancreatitis: reassessment with current CT. Radiology 171:353-357, 1989 5. Miller FH, Keppke A, Balthazar E: Imaging pancreatitis. Chapter 98. In: Gore RM, Levine MS (eds): Textbook of Gastrointestinal Radiology (ed 3). Philadelphia, PA, W.B. Saunders, In press 6. Scuro LA, Cavallini G, Benini L, et al: Pancreatic calcifications in patients with chronic pancreatitis. A sign of long-lasting or severe disease? Int J Pancreatol 6:139-150, 1990 7. Remer EM, Baker ME: Imaging of chronic pancreatitis. Radiol Clin North Am 40:1229-1242, 2002
394 8. Alpern MB, Sandler MA, Kellman GM, et al: Chronic pancreatitis: ultrasonic features. Radiology 155:215-219, 1985 9. Ammann RW, Meunch R, Otto R, et al: Evolution and regression of pancreatic calcification in chronic pancreatitis. Gastroenterology 95: 1018-1028, 1988 10. Lankish PG, Otto J, Erkelenz I, et al: Pancreatic calcifications: no indicator of severe exocrine pancreatic insufficiency. Gastroenterology 90: 617-621,1986 11. Wallace MB, Hawes RH: Endoscopic ultrasound in the evaluation and treatment of chronic pancreatitis. Pancreas 23:26-35, 2001 12. Natterman C, Goldschmidt AJ, Dancygier H: Endosonography in chronic pancreatitis: a comparison between endoscopic retrograde pancreatography and endoscopic ultrasonography. Endoscopy 25:565-570, 1993 13. Catalano MF, Lahoti S, Geenen JE, et al: Prospective evaluation of endoscopic ultrasonography, endoscopic retrograde pancreatography, and secretin test in the diagnosis of chronic pancreatitis. Gastrointest Endosc 48:11-17, 1998 14. Keppke AL, Miller FH: Magnetic resonance imaging of the pancreas: the future is now. Semin Ultrasound CT MRI 26:132-152, 2005 15. Ly JN, Miller FH: MR imaging of the pancreas. A practical approach. Radiol Clin N Am 40:1289-1306, 2002 16. Ito K, Koike S, Matsunaga N: MR imaging of pancreatic diseases. Eur J Radiol 38:78-93, 2001 17. Semelka RC, Shoenut JP, Koreker MA, et al: Chronic pancreatitis: MR imaging features before and after administration of gadopentetate dimeglumine. J Magn Reson Imaging 3:79-82, 1993 18. Semelka RC, Kroeker MA, Shoenut JP, et al: Pancreatic disease: prospective comparison of CT. ERCP, and 1.5-T MR imaging with dynamic gadolinium enhancement and fat suppression. Radiology 181:785-791, 1991 19. Miller FH, Keppke AL, Wadhwa A, et al: MRI of pancreatitis and its complications: part 2, chronic pancreatitis. AJR Am J Roentgenol 183: 1645-1652, 2004 20. Leyendecker JR, Elsayes KM, Gratz BI, et al: MR cholangiopancreatography: spectrum of pancreatic duct abnormalities. AJR Am J Roentgenol 179:1465-71, 2003 21. Matos C, Metens T, Devier J, et al: Pancreatic duct. Morphologic and functional evaluation with dynamic MR pancreatography after secretin stimulation. Radiology 203:435-441, 1997 22. Cappeliez O, Delaye M, Deviere J, et al: Chronic pancreatitis: evaluation of pancreatic exocrine function with MR pancreatography after secretin stimulation. Radiology 215:358-364, 2000 23. Tamura R, Ishibashi T, Takahashi S: Chronic pancreatitis: MRCP versus ERCP for quantitative caliber measurement and qualitative evaluation. Radiology 238:920-928, 2006 24. Takehara Y, Ichijo K, Tooyama N, et al: Breath-hold MR cholangiopancreatography with a long-echo-train fast spin-echo sequence and a surface coil in chronic pancreatitis. Radiology 192:73-78, 1994 25. Sica GT, Braver J, Cooney MJ, et al: Comparison of endoscopic retrograde cholangiopancreatography with MR cholangiopancreatography with patients with pancreatitis. Radiology 210:605-610, 1999
A.J. Siddiqi and F. Miller 26. Pungpapong S, Wallace MB, Woodward TA, et al: Accuracy of endoscopic ultrasound and magnetic resonance cholangiopancreatography for the diagnosis of chronic pancreatitis. A prospective comparison study. J Clin Gastroenterol 41:88-93, 2007 27. Balthazar EJ: Pancreatitis associated with pancreatic carcinoma. Preoperative diagnosis: role of CT imaging in detection and evaluation. Pancreatology 5:330-344, 2005 28. Baker ME: Pancreatic adenocarcinoma: are there pathognomonic changes in the fat surrounding the superior mesenteric artery? Radiology 180:613-614, 1991 29. Jenkins JP, Braganza JM, Hickey DS, et al: Quantitative tissue characterization in pancreatic disease using magnetic resonance imaging. Br J Radiol 60:333-341, 1987 30. Ichikawa T, Sou H, Araki T, et al: Duct-penetrating sign at MRCP: usefulness for differentiating inflammatory pancreatic mass from pancreatic carcinomas. Radiology 221:107-116, 2001 31. Johnson PT, Outwater EK: Pancreatic carcinoma versus chronic pancreatitis: dynamic MR imaging. Radiology 212:213-218, 1999 32. DelMaschio A, Vanzulli A, Sironi S, et al: Pancreatic cancer versus chronic pancreatitis: Diagnosis with CA 19-9 assessment. US, CT and CT-guided fine-needle biopsy. Radiology 178:95-99, 1991 33. Yu J, Fulcher AS, Turner MA, et al: Normal anatomy and disease processes of the pancreatoduodenal groove: imaging features. AJR Am J Roentgenol 183:838-846, 2004 34. Stolte M, Weiss W, Volkholz H, et al: A special form of segmental pancreatitis: groove pancreatitis. Hepatogastroenterology 29:1982008, 1982 35. Itoh S, Yamakawa K, Shimamoto K, et al: CT findings in groove pancreatitis: correlation with histopathological findings. J Comput Assist Tomogr 18:911-915, 1994 36. Irie H, Honda H, Kuroiwa T, et al: MRI of groove pancreatitis. J Comput Assist Tomogr 22:651-655, 1998 37. Ito T, Nakano I, Koyanagi S, et al: Autoimmune pancreatitis as a new clinical entity: three cases of autoimmune pancreatitis with effective steroid therapy. Dig Dis Sci 42:1458-1468, 1997 38. Sarles H, Sarles JC, Cammatee R, et al: Observations on 205 confirmed cases of acute pancreatitis, recurring pancreatitis, and chronic pancreatitis. Gut 6:545-559, 1965 39. Yoshida K, Toki F, Takeuchi T, et al: Chronic pancreatitis caused by an autoimmune abnormality. Proposal of the concept of autoimmune pancreatitis. Dig Dis Sci 40:1561-1568, 1997 40. Kim KP, Kim MH, Song MH, et al: Autoimmune chronic pancreatitis. Am J Gastroenterol 99:1605-1616, 2004 41. Irie H, Honda H, Baba S, et al: Autoimmune pancreatitis: CT and MR characteristics. AJR Am J Roentgenol 170:1323-1327, 1998 42. Furukawa N, Muranaka T, Yasumori K, et al: Autoimmune pancreatitis: radiologic findings in three histologically proven cases. J Comput Assist Tomogr 22:880-883, 1998 43. Kloppel G, Luttges J, Lohr M, et al: Autoimmune pancreatitis: pathological, clinical, and immunological features. Pancreas 27:14-19, 2003 44. Horiuchi A, Kawa S, Hamano H, et al: ERCP features in 27 patients with autoimmune pancreatitis. Gastrointest Endosc 55:494-499, 2002
C
hronic pancreatitis is a progressive, irreversible inflammatory and fibrosing disease of the pancreas with clinical manifestations of chronic abdominal pain, weight loss, and permanent pancreatic exocrine and endocrine insufficiency. Often the most predominant clinical feature of chronic pancreatitis is chronic recurrent and intense abdominal pain that can make care of these patients difficult.1 Intractable pain can be recalcitrant to most medical and endoscopic therapies, often requiring a frequent need for narcotics.2 Chronic pancreatitis also is a public health care issue due to associated psychosocial problems, loss of work, narcotic addiction, and consumption of health care resources. In the United States, a long history of heavy alcohol consumption is the most common cause of chronic pancreatitis. Other etiologies included hyperlipidemia, hyperparathyroidism, trauma, cystic fibrosis, and pancreas divisum. Obstruction due to posttraumatic ductal strictures, pseudocysts, or structural changes in the pancreatic duct has also been implicated as a possible etiology. Between 30 and 40% of patients with chronic pancreatitis have no apparent underlying cause and are considered to have “idiopathic” chronic Department of Radiology, Northwestern University Feinberg School of Medicine, Chicago, IL. The authors have no conflicts of interest to disclose. Address reprint requests to: Frank H. Miller, MD, Department of Radiology, Northwestern University Feinberg School of Medicine, 676 N. St. Claire Street, Suite 800, Chicago, IL 60611. E-mail: [email protected].
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pancreatitis.3 In contrast to acute pancreatitis, gallstones are not considered risk factors in the development of chronic pancreatitis. The morphologic changes in the pancreas parenchyma include edema, inflammation, and necrosis, superimposed on a background of chronic changes that include fibrosis, chronic inflammation, and loss of exocrine tissue.3 Histologically, the disease is characterized by parenchymal fibrosis, ductal strictures and dilatation with calcifications, and atrophy of acinar and islet tissue. The clinical diagnosis of chronic pancreatitis, especially in its early stages, is difficult and often frustrating for patients and treating physicians. Laboratory testing and imaging is often performed to aid in diagnosis. Endoscopic retrograde cholangiopancreatography (ERCP) and pancreatic function tests have long been considered the diagnostic gold standards; however, these tests have limitations as will be discussed. Pancreatic biopsy is seldom utilized as it may produce false-negative results (if nondiseased areas of the pancreas are biopsied) as well as potential complications such as fistulas, hemorrhage, and acute pancreatitis. With further experience and improved techniques, modalities such as magnetic resonance imaging (MRI), magnetic resonance cholangiopancreatography (MRCP), and endoscopic ultrasound (EUS) are gaining acceptance as sensitive modalities to diagnose chronic pancreatitis as well as its complications. This review discusses the different modalities available to image chronic pancreatitis, along with their advantages
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and limitations. In addition, topics such as groove pancreatitis and autoimmune pancreatitis are examined, along with a discussion of distinguishing chronic pancreatitis from pancreatic adenocarcinoma.
Computed Tomography of Chronic Pancreatitis Computed tomography (CT) is helpful in the diagnosis of late chronic pancreatitis and associated complications. It is, however, limited in the detection of early chronic pancreatitis. The usual CT findings in chronic pancreatitis are dilatation of the pancreatic duct, pancreatic calcifications, and parenchymal atrophy. Dilatation of the pancreatic duct and its secondary radicles is the most common finding and can be seen in 68% of patients.4 The pattern of dilatation can vary (smooth, beaded, or irregular), with no particular pattern predominating. However, ductal dilatation is a nonspecific finding and can be seen with distal common bile duct cholangiocarcinoma, pancreatic and ampullary carcinomas, and other conditions. Luetmer et al demonstrated good correlation between ERCP and CT for ductal dilatation, with ERCP and CT demonstrating concordant findings in 16/18 patients. ERCP detected ductal dilatation in two patients with normal CT findings.4 CT findings of chronic pancreatitis can also be made based on the size and shape of the gland. Parenchymal atrophy is seen in 54% of patients with chronic pancreatitis.4 However, parenchymal atrophy is neither sensitive nor specific and can be seen as a normal aging process. To complicate matters, focal pancreatic enlargement, a less common nonspecific presentation of chronic pancreatitis, can be seen in 30% of patients.4 Parenchymal changes from pancreatitis, if detected on CT, are late in the disease process. Many patients with severe exocrine insufficiency can have a normal-appearing pancreas on CT. Unfortunately, there is poor correlation between pancreatic morphology and exocrine and endocrine deficiency from chronic pancreatitis. Intraductal pancreatic calcifications are the most specific and reliable CT sign of chronic pancreatitis (Fig. 1). When compared to other modalities, the advantage of CT is in the detection of these calcifications, which can be seen in 50% of patients.4 Calcifications develop due to deposition of calcium carbonate in inspissated intraductal protein plugs. They vary widely in size (tiny, stippled to large, coarse) and distribution (localized to diffuse).5 Calcifications, however, appear late in the disease process or in patients with severe disease.6 CT is an excellent modality to identify complications of chronic pancreatitis such as fluid collections, which can be seen in 30% of patients.4 Fluid collections are mostly seen within or adjacent to the pancreas, although distant sites are also rarely seen. Most fluid collections associated with chronic pancreatitis are well-encapsulated. Free fluid in the vicinity of the pancreas suggests superimposed acute pancreatitis.
Figure 1 Chronic pancreatitis. Coronal contrast-enhanced MDCT image shows multiple diffuse calcifications (arrow) in a patient with chronic pancreatitis due to alcohol abuse.
CT can also evaluate the formation of pseudocysts, which are encapsulated collections of pancreatic enzyme secretions that occur in the pancreas or in the peripancreatic tissue. While most resolve spontaneously, pseudocysts can undergo infection, hemorrhage, gastric or biliary obstruction, or fistulae formation with the gastrointestinal tract. Other potential complications that can be evaluated by CT include pseudoaneuryms of the splenic or pancreaticoduodenal arteries and thrombosis of the portosplenic veins with venous collaterals and gastric varices. Pancreatico-pleural fistula is a rare complication of chronic pancreatitis in which pancreatic secretions from a ruptured pancreatic duct dissect through the aortic and esophageal hiatus or through the diaphragm and can gain access to the mediastinum and pleural spaces (Fig. 2). This can be seen on CT and MRI, with MRCP best equipped to depict the fistula and ductal anatomy in these patients.5 Dilatation of the common bile duct can also be seen in many patients with chronic pancreatitis and is strongly associated with dilatation of the main pancreatic duct.4 There is often an inflammatory mass in the head of the pancreas. In chronic pancreatitis, the dilated common bile duct demonstrates gradual tapering, compared to the abrupt cutoff seen in malignant obstructions. However, there is significant imaging overlap between ductal dilatation from malignancy and focal inflammation associated with chronic pancreatitis, and further diagnostic evaluation is often needed. It is generally accepted that CT can detect chronic pancreatitis in patients with severe or advanced disease. In contrast, ERCP, pancreatic function tests, MRI, and EUS are more sensitive in diagnosing early or mild chronic pancreatitis. In the literature, studies evaluating the CT features of chronic pancreatitis are from the 1980s. Since then, vast improvements in CT technology (multidetector CT with multiple phases of imaging and thinner collimation) has undoubtedly improved the sensitivity in detecting this disease. Reevaluation of chronic pancreatitis and CT is long overdue.7
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Transabdominal and Endoscopic Ultrasound of Chronic Pancreatitis Transabdominal Ultrasound Transabdominal ultrasound has been used for many years to evaluate the pancreas. However, the diagnosis of chronic pancreatitis can be difficult. The limitation of ultrasound is its inability to evaluate the complete pancreas due to patient body habitus and overlying bowel gas. In addition, the majority of the findings on ultrasound are neither sensitive nor specific for the diagnosis. Similar to CT, the early detection of chronic pancreatitis is difficult. Late findings include alterations in size and echogenicity of the gland, pancreatic calcifications, pancreatic duct dilatation and irregularity, and biliary dilatation.7 The classic sonographic sign of chronic pancreatitis is pancreatic calcifications, which are seen as multiple punctate hyperechoic foci in 40% of patients8 (Fig. 3). These may or may not shadow depending on their size but can cause ductal obstruction and lead to persistent recurrent pancreatitis. The degree and pattern of pancreatic calcification can change over time and studies have shown no correlation between exocrine function and the amount of pancreatic calcifications.9,10 Late in the disease process, the pancreatic parenchyma may demonstrate heterogeneous echotexture with mixed areas of hyper- and hypoechogenicity. The hyperechoic regions are likely related to fibrosis and calculi, while the hypoechoic regions are associated with areas of inflammation.8 Most patients demonstrate a normal-sized gland, while, in some patients, the pancreas may be atrophic in advanced disease. Although there is relatively good pancreatic functional and morphologic correlation on ultrasound in advanced pancreatic disease, there is poor correlation for mild-to-moderate and early disease.10 Chronic pancreatitis may also present as a focal hypoechoic mass in up to 40% of patients, associated with irregular dilatation and tortuosity of the pancreatic duct, making
Figure 2 (A-C) Pancreatico-pleural fistula. (A) Axial contrast-enhanced MDCT image shows a small rim-enhancing pancreatic pseudocyst (arrow) dissecting through the diaphragm into the pleural space (curved arrow). (B) Coronal contrast-enhanced MDCT image shows the fluid extending from a disrupted duct (arrow) superiorly into the pleural space. The coronal reformatted images aid in the diagnosis. (C) ERCP confirms the findings on CT, demonstrating the fistulous communication between the pancreatic duct and left pleural space (arrow).
Figure 3 Chronic pancreatitis. Transabdominal sonogram of the pancreas demonstrates a hypoechoic gland with multiple punctate calcifications (arrows) throughout the gland.
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it difficult to distinguish from a pancreatic neoplasm.8 Short strictures in the main pancreatic duct can produce alternating areas of narrowing and dilatation, referred to as the “chain of lakes” sign. When the dilated duct contains calcifications without an obstructing mass, chronic pancreatitis is favored over cancer. However, due to imaging overlap between the two entities, diagnostic procedures such as CT or endoscopic ultrasound-guided biopsies may be required. Like CT, complications of chronic pancreatitis can be seen on ultrasound. Pancreatic pseudocysts are reported in 25 to 40% of patients.8 Some patients present with focal dilatation of the pancreatic or common bile duct or pseudocyst formation as the only indication of chronic pancreatitis. Vascular complications including portosplenic vein thrombosis and subsequent development of collateral varices and arterial pseudoaneuryms can also be detected using Doppler sonography.
Endoscopic Ultrasound EUS was introduced in the early 1980s for the purpose of improved imaging of the pancreas. The proximity of the pancreas to the stomach and duodenum allows high-resolution images of the pancreas with the use of high-frequency transducers. EUS also overcomes the limitations of transabdominal ultrasound, namely, abdominal gas and body fat.11 On EUS, the normal pancreas has homogenous fine granularity and reticulation with smooth margins and without side-branch ectasia. It is slightly more echogenic than the liver. The average pancreatic duct diameter in the body is 1.9 mm and is uniformly tubular with anechoic walls, with normal side branches visible in 32% of patients.12,13 Several new features of chronic pancreatitis that are not seen by CT or transabdominal US have been documented by EUS. These include pancreatic parenchymal and ductal abnormalities. There is often subtle lobularity of the outer gland margin and small cystic changes in the pancreatic parenchyma. Hyperechoic foci or strands and prominent interlobular septa (due to fibrosis) within the pancreas can be seen along with heterogeneous echogenicity of the parenchyma. Ductal abnormalities noted on EUS include hyperechoic margins of the pancreatic duct, side-branch duct ectasia, intraductal stones and main pancreatic duct dilatation (⬎3 mm), and irregularity11 (Fig. 4). CT and transabdominal US lack sufficient resolution for the detection of these subtle parenchymal and ductal abnormalities in cases of early chronic pancreatitis on EUS.13 There are many advantages of EUS compared to ERCP. It has a significant safety advantage over ERCP (which can be complicated by postprocedure pancreatitis) and can also be used for drainage of pancreatic pseudocysts and for celiac plexus blockade for pain control.11 In contrast to ERCP, EUS can also provide a very detailed evaluation of the pancreatic parenchyma. While EUS has the potential of being one of the gold standards for the diagnosis of chronic pancreatitis, a few issues need to be considered. First, diagnostic criteria for chronic pancreatitis are not standardized and there is considerable
Figure 4 (A, B) EUS Chronic pancreatitis. (A) Endoscopic sonogram demonstrates a stone in the pancreatic duct (arrow) with associated shadowing. (B) Endoscopic sonogram shows multiple calcifications (arrow) in the pancreatic head due to chronic pancreatitis. There are areas of hyperechogenicity and hypoechogenicity involving the pancreas. (Images courtesy of Dr. Rameez Alasadi, Department of Gastroenterology, Northwestern University Feinberg School of Medicine, Chicago, IL.)
intra- and interobserver variability in analysis of the findings. In addition, some of the findings seen on EUS to suggest chronic pancreatitis (fibrosis, echogenic septations) may occur normally with aging and therefore constitute false-positive findings. Many have wondered if EUS is “too sensitive” in the diagnosis of chronic pancreatitis.
MRI/MRCP of Chronic Pancreatitis With advancements in MR technology, pancreatic disorders are being increasingly evaluated with this modality. Contributions to improved imaging of the pancreas with reduced imaging time include higher strength field magnets and gradients, phased-array body multicoils, fast scanning techniques such as breath-hold spoiled gradient-echo sequences, dynamic contrast-enhanced imaging, and improved fat-suppression techniques.14
388 In addition, the utilization of MRCP with accurate noninvasive assessment of the pancreatic duct and biliary tract has supplanted ERCP as an initial diagnostic modality. Furthermore, MR angiography and assessment of the peripancreatic vasculature obviate other invasive imaging such as conventional angiography. The MR evaluation of the pancreas, biliary tree, and adjacent vessels can be evaluated as a “one-stop shop exam.”15 The normal pancreas is isointense or slightly hyperintense to the liver on T1-weighted non-fat-suppression images. With fat suppression, the normal pancreas is best displayed as hyperintense to all other solid organs of the abdomen. The intrinsic increased T1 signal intensity is due to the presence of aqueous protein in the glandular elements of the pancreas, which shorten the T1 values of the normal gland.16 The normal T2-weighted signal intensity of the pancreas is similar to the liver and hyperintense compared with the spleen and kidneys. The normal pancreas enhances maximally during the arterial phase after the injection of intravenous gadolinium, in contrast to the liver, which shows minimal enhancement during this phase because of its predominant portal venous supply. There is also rapid washout and, during the portal and delayed phases, the pancreas becomes isointense to the liver.16 The main advantage of MRI compared to imaging modalities is the sensitivity of MR in depicting signal intensity and enhancement abnormalities in early chronic pancreatitis. Due to its excellent soft-tissue contrast, MRI can depict early disease by detecting signal changes before any morphologic changes occur.17 The parenchymal changes of chronic pancreatitis can be divided into early and late findings. The early findings include loss of normal high signal intensity of the pancreas on T1-weighted fat-suppressed images due to decreased proteinaceous fluid content from chronic inflammation and fibrosis.17 In early disease, there is also decreased and heterogeneous enhancement of the pancreas in the arterial phase with progressive enhancement in delayed phases18 (Fig. 5). This is related to loss of normal vascularity of the gland secondary to chronic inflammation and fibrosis.17 These findings are in contrast to CT, which may depict normal appearance and enhancement of the pancreas even in advanced disease. Late parenchymal findings in chronic pancreatitis include atrophy and pseudocyst formation. Parenchymal calcifications are also noted, although this is better appreciated on CT. However, MR better defines intraductal calcifications which may cause pancreatic duct obstruction. MRCP imaging allows excellent visualization of the pancreatic and common bile ducts. The MRCP techniques involve fluid-sensitive sequences such as thin-section T2weighted single-shot fast spin-echo (HASTE/SSFSE) and thick-slab T2-weighted half-Fourier SSFSE MRCP and 3D respiratory-triggered or navigator-triggered techniques. Abnormalities of the pancreatic duct in chronic pancreatitis include irregular dilatation and beading often containing intraductal stones.19 Intraductal stones appear as signal void-
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Figure 5 (A-C) MRI of chronic pancreatitis. (A) Axial T1-weighted fat-suppressed gradient echo MR image shows decreased, heterogenous signal intensity in the pancreas, irregular dilatation of the main pancreatic duct, and a pseudocyst within the pancreatic head. (B, C) There is decreased pancreatic parenchymal enhancement during the arterial phase (B) and delayed enhancement during the venous phase (C) related to fibrosis from chronic pancreatitis.
filling defects surrounded by high signal pancreatic secretions within the duct. In severe cases, the beaded main pancreatic duct with marked dilated side branches may result in the classic “chain of lakes” appearance19 (Fig. 6). Other ductal abnormalities seen on MRCP include clubbing, sacculation and ectasia of the side radicles, strictures, ductal obstruction,
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The Perfect Examination?
Figure 6 Coronal T2-weighted MR image shows a dilated pancreatic duct and secondary radicles (arrow) associated with chronic pancreatitis.
pseudocysts, and fistula formation.20 MRCP can also demonstrate the dilatation of the biliary tract secondary to inflammatory stricture or compression of the bile duct.20 Some investigators report better visualization of the pancreatic duct by obtaining MRCP images after the administration of IV secretin.21 Secretin stimulates the pancreas to secrete fluid and bicarbonate and increase the tone of the sphincter of Oddi and therefore improves visualization and delineation of the main pancreatic duct and its branches. In addition, secretin can also be useful for functional evaluation of exocrine pancreas based on quantification of duodenal filling with chronic pancreatitis showing decreased filling.21,22 Currently, ERCP is considered the standard of reference for imaging the pancreaticobiliary system. However, multiple studies have demonstrated that MRCP fares well in comparison to ERCP, as discussed later. Unlike ERCP, MRI can evaluate the pancreatic parenchyma adjacent to the ductal abnormality as well as the adjacent peripancreatic tissues. MRCP can also demonstrate the dilated duct upstream from an obstructing stone or stricture.19 It is also noninvasive and an alternative for patients who are not good candidates or have failed ERCP.14 MR imaging is also an excellent modality in the evaluation of potential complications of chronic pancreatitis. MR has a high sensitivity for the detection of pseudocysts and the characterization of their contents better than CT. Complex pseudocysts from hemorrhagic or proteinaceous fluid are seen as high signal intensity on T1-weighted images. MRI/ MRCP also can show communication with the pancreatic duct, which may guide therapy. MRI also can evaluate vascular complications including splenic artery pseudoaneurysms (Fig. 7) and splenic or portal vein thrombosis. Potential biliary complications like choledocholithiasis, fistulas, and dilatation and transient obstruction of the common bile duct due to inflammatory strictures can also be evaluated by MRCP.5
While there are multiple modalities available to evaluate chronic pancreatitis, the perfect examination to detect this disease has not been clearly established. In general, when comparing different modalities, it is important to compare them with a gold standard. However, there is no acceptable gold standard for chronic pancreatitis. While histology may be the gold standard, it is invasive and features of chronic pancreatitis are often focally distributed and therefore missed by biopsy. ERCP was considered the gold standard in the past, but its limitations have been previously discussed. MRI/ MRCP and EUS may have supplanted ERCP in their sensitivity for detection of early disease. Comparison of EUS with ERCP in the diagnosis of chronic pancreatitis is being actively investigated, especially in the gastrointestinal literature. In a prospective examination of patients with recurrent pancreatitis, EUS demonstrated abnormalities in 79% of patients, while ERCP and secretin testing demonstrated abnormalities in 45 and 31% of patients, respectively.13 In this study, there was good correlation of EUS with ERCP in normal
Figure 7 (A, B) Splenic artery pseudoaneurysm. (A) Axial T2weighted MR image shows high signal intensity lesion in tail of the pancreas (arrow). (B) Axial T1-weighted fat-suppressed gadoliniumenhanced MR image demonstrates an enhancing splenic artery pseudoaneurysm (arrow) within the pancreatic pseudocyst. The use of contrast material is important to show the lesion is not a cystic lesion (high signal intensity on T2).
390 patients as well as in patients with moderate and severe disease. However, patients with mild disease detected on EUS demonstrated normal findings on ERCP. A combined analysis by Wallace et al of three prospective studies evaluating ERCP and EUS found that there was agreement between ERCP and EUS in 80% of patients with suspected chronic pancreatitis.11 When there was disagreement between the two modalities (20%), the findings were abnormal on EUS and normal on ERCP in the majority of the cases (74%). The authors reported, “it is unknown if EUS is more sensitive to mild changes of CP [chronic pancreatitis] than ERP or if EUS is ‘overdiagnosing’ early CP.”11 The clinical significance of “mild” changes of chronic pancreatitis seen on EUS with normal ERCP and pancreatic function tests has not been established.7 Some studies have evaluated the accuracy of MRI/MRCP comparing it directly to ERCP. Tamura et al demonstrated better visualization and opacification of the main pancreatic duct (especially in the pancreatic tail) by MRCP when compared to ERCP in patients with chronic pancreatitis.23 In this study, MRCP tended to be superior to ERCP in the delineation of the main pancreatic duct and provided high diagnostic accuracy in evaluating pathologic findings. The sensitivity, specificity, and accuracy values for delineating pathologic pancreatic changes at MRCP were 88, 98, and 91%, respectively.23 Takehara et al demonstrated agreement between MRCP and ERCP in ductal dilatation (83-92%), ductal narrowing (70-92%), and detection of filling defects (92-100%).24 Sica et al demonstrated 91% sensitivity of MRCP in visualization of the different pancreatic duct segments and 92% accuracy in characterizing segments as either normal, slightly dilated, or narrowed compared to ERCP. In this study, 42 segments in 19 patients could not be visualized by ERCP and in these patients comparison with MRCP was helpful and complementary.25 As MRCP techniques continue to evolve, this modality will play a more prominent role in all patients with suspected chronic pancreatitis, not just in patients with a contraindication to or failed ERCP. With MRCP and EUS emerging as highly accurate diagnostic modalities to evaluate chronic pancreatitis, a recent study compared these two modalities.26 In this prospective analysis, MRCP and EUS were compared to either ERCP, surgical pathology, and/or long-term clinical follow-up as the gold standard. The findings demonstrated EUS as more sensitive but equally specific compared with MRCP in the diagnosis of chronic pancreatitis. In addition, the combination of EUS and MRCP together had a sensitivity of 98% and a specificity of 100% compared to the “gold standards.” With more prospective studies, these two modalities, individually or in combination, may become the diagnostic gold standard for evaluation of chronic pancreatitis.
Pancreatic Inflammatory Mass versus Pancreatic Cancer Clinical and imaging distinction between chronic pancreatitis and pancreatic cancer can be extremely difficult. Both conditions can present with abdominal pain, obstructive
A.J. Siddiqi and F. Miller jaundice, and weight loss. The imaging appearance can be similar as well. Chronic pancreatitis can present as focal enlargement of the gland due to a chronic inflammatory mass, often in the pancreatic head, simulating pancreatic adenocarcinoma.16 Both can appear as noncalcified focal hypointense (MR) and hypodense (CT) masses with associated dilatation of common bile duct and main pancreatic duct (double-duct sign). Both conditions may also demonstrate ductal strictures, infiltration of the adjacent fat, arterial encasement, and peripancreatic venous obstruction.27,28 There are often no distinguishing features on T1- and T2-weighted MR imaging.29 Specific imaging features that favor an inflammatory mass are nondilated or smoothly tapering pancreatic and bile ducts coursing through the mass (“duct-penetrating” sign)30 (Fig. 8),
Figure 8 (A, B) Duct-penetrating sign. (A) Contrast-enhanced CT shows findings of chronic pancreatitis including pancreatic calcifications, a dilated main duct, and side branches. In the uncinate process, there is a heterogeneous area (arrow) that raised concern for neoplasm, which alternatively may relate to chronic pancreatitis. (B) Axial T2-weighted HASTE image shows a dilated pancreatic duct and branches penetrating through the apparent mass (arrows): “duct-penetrating sign.” This finding suggests chronic pancreatitis over adenocarcinoma. ERCP and biopsy suggested adenocarcinoma and the patient underwent a Whipple procedure. At pathology, this was demonstrated to be chronic pancreatitis without evidence of malignancy.
Chronic pancreatitis irregularity of the pancreatic duct, and the presence of pancreatic calcifications. In contrast, a smoothly dilated pancreatic duct with an abrupt interruption prior to the ampulla favors the diagnosis of cancer. Other features that favor cancer are a mass at the site of obstruction resulting in distal atrophy of the pancreas. With malignancy there is usually a high ratio of the duct caliber to the pancreatic gland width. Chronic pancreatitis tends to have limited atrophy and gradual (nonabrupt) narrowing of the dilated pancreatic duct or bile duct. However, pancreatic adenocarcinoma can be superimposed on patients with chronic pancreatitis and therefore specific findings of chronic pancreatitis may not be sufficient to exclude pancreatic malignancy. In a retrospective review of MR imaging and pathology in patients with chronic pancreatitis and pancreatic cancer, Johnson and Outwater found that both entities presented hypointense masses on T1-weighted imaging with progressive delayed enhancement compared to the rest of pancreas. The two entities could not be distinguished on the basis of time or degree of enhancement. In both conditions, histology revealed abundant fibrosis, accounting for their similar imaging appearance. The authors concluded that “similar gradual pattern of enhancement and overlap in peak enhancement preclude distinction of the two entities on the basis of gadolinium-enhanced MR findings.”31 A mass causing upstream chronic pancreatitis can sometimes be detected on early phase dynamic gadoliniumenhanced images. The cancer is seen as a focal hypointense mass relative to the hypoenhancing region of chronic pancreatitis on early gadolinium-enhanced images. In addition, the duct dilation abruptly terminates at the mass (Fig. 9). A prospective analysis using CA 19-9, US, CT, and CTguided fine-needle aspiration biopsy (FNAB) in 81 patients suspected of having chronic pancreatitis or pancreatic neoplasm demonstrated FNAB to be the most reliable method of differentiating chronic pancreatitis mass from pancreatic adenocarcinoma.32 US had technical limitations (abdominal fat and overlying bowel gas) obscuring the pancreas, which deemed 25% of the examinations as nondiagnostic. Nineteen percent of CT examinations were considered nondiagnostic because a focal mass in the pancreas could not be further characterized as inflammatory or neoplastic. CA 19-9 levels had reasonable sensitivity (81%) and specificity (81%) in distinguishing the two entities. However this is not a sufficient value for a laboratory test in distinguishing between a potential malignancy and guide management. Serum CA 19-9 is more useful as an early marker of relapse in patients who undergo surgery for pancreatic cancer. FNAB had 100% sensitivity and specificity when diagnostic, with only five (6%) cases being nondiagnostic.32 Due to clinical and imaging overlap between chronic pancreatitis and pancreatic adenocarcinoma, a percutaneous CTor EUS-guided FNAB may be required if the distinction cannot be made.
Groove Pancreatitis Groove pancreatitis is a type of focal chronic pancreatitis affecting the pancreatoduodenal groove. The pancreatoduo-
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Figure 9 (A-C) Pancreatic adenocarcinoma. (A) Axial contrast-enhanced CT shows atrophy of the pancreas and duct dilatation within the distal body and tail of the pancreas to the level of a suspected mass, which is difficult to see. No calcifications are seen to suggest chronic pancreatitis. (B) Axial T2-weighted HASTE image shows dilatation of pancreatic duct with abrupt termination (arrow). (C) Axial contrastenhanced T1-weighted fat-suppressed gradient-echo image demonstrates a hypo-enhancing mass in the body of the pancreas (arrow) suspicious for adenocarcinoma, which was subsequently confirmed on biopsy. There is upstream chronic pancreatitis.
denal groove is a potential anatomic space bordered by the pancreatic head medially, the second portion of the duodenum laterally, third portion of duodenum or inferior vena cava posteriorly, and the first portion of the duodenum or gastric antrum anteriorly.33
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Groove pancreatitis is characterized by repeated bouts of acute chronic pancreatitis with fluid and inflammatory cells dissecting into the groove between the pancreas and duodenum.19 It is classified as two forms: the pure form and the segmental form. The pure form affects the groove only, while the pancreatic parenchyma is preserved. Conversely, the segmental form involves the head of the pancreas, although predominant scar tissue can be seen within the groove.34 CT features of this condition include a hypodense lesion within the groove that demonstrates delayed contrast enhancement due to fibrosis.35 On MR imaging, Irie et al described a “sheet-like fibrotic mass” within the groove that is hypointense on T1-weighted images and iso- or hypointense on T2-weighted images relative to the pancreas. There is delayed enhancement that is well demarcated from the normal pancreas parenchyma, which demonstrates brisk enhancement on early postgadolinium imaging36 (Fig. 10). Histologic evaluation demonstrates fibrous scar with hypercellular granulation tissue within this region.36 The fibrotic scar in the groove can lead to disturbances in duodenal mobility, duodenal stenosis, and tubular stenosis of common bile duct, occasionally leading to obstructive jaundice. It is important to differentiate groove pancreatitis from exophytic pancreatic adenocarcinomas that have a significant fibrous component and may also display delayed enhancement. On MRCP, however, groove pancreatitis demonstrates smooth tapering of the distal common bile duct, in contrast to abrupt complete obstruction seen in patients with pancreatic carcinoma.33 However, there can be significant imaging overlap between the two entities and biopsy is often indicated. Differential diagnosis of soft tissue within the pancreaticoduodenal groove includes acute pancreatitis, exophytic pancreatic ductal or duodenal adenocarcinoma, gastrinoma (due to the groove being within the gastrinoma triangle), cholangiocarcinoma, or lymphadenopathy.33
Autoimmune Chronic Pancreatitis Autoimmune pancreatitis (AIP) is a type of chronic pancreatitis with an autoimmune pathogenesis and is associated with other autoimmune-related diseases such as Sjogren’s syndrome, primary sclerosing cholangitis, primary biliary cirrhosis, retroperitoneal fibrosis, ulcerative colitis, and systemic lupus erythematosus.37 It is a relatively recent and increasingly reported clinicopathologic entity, previously given a variety of names such as sclerosing pancreatitis, fibrosing pancreatitis, and nonalcoholic duct-destructive chronic pancreatitis. Sarles et al initially described a type of chronic pancreatitis that was painless or caused less pain than other types of pancreatitis and was associated with clinical hyperglobulinemia, jaundice, and often onset in the elderly.38 Histology revealed an enlarged and “elastic-hard” pancreas due to lymphocyte and plasma cell infiltration with fibrosis.
Figure 10 (A-C) Groove pancreatitis. (A) Contrast-enhanced CT shows a solid mass with small low-density cystic areas (arrow) lying within the pancreaticoduodenal groove. (B) Axial T2-weighted image shows abnormal hypointense mass within the pancreatioduodenal groove. High signal intensity cystic areas are seen within the abnormality (arrow). (C) Gadolinium-enhanced T1-weighted fat-suppressed gradient-echo image shows mild heterogenous enhancement within the mass (arrow), which enhances less than the pancreas (curved arrow) and duodenal wall (arrowhead) due to fibrosis.
In 1995, Yoshida et al proposed the name autoimmune pancreatitis for this entity. The authors further described this entity and demonstrated other abnormalities associated with this entity, which included increased serum gamma globulin or IgG levels and presence of auto-antibodies.39 Most patients
Chronic pancreatitis were asymptomatic or had mild symptoms usually with an absence of acute attacks of pancreatitis. The authors also reported two distinct groups of people that comprised this entity. The first group was predominately females with a mean age of 51 years with associated Sjogren’s syndrome. The second group did not have Sjogren’s syndrome, had a mean age of 63 years, with no sex predisposition.39 Autoimmune pancreatitis has many clinical, laboratory, and imaging characteristics. Patients often present with painless jaundice due to common duct narrowing within the pancreatic head, raising suspicion of a pancreaticobiliary malignancy.40 There is an absence of a history of acute attacks of pancreatitis or history of alcohol abuse. Laboratory analysis demonstrates seropositivity for antinuclear antibodies and hypergammaglobulinemia (increased serum ␥-globulin or IgG levels). On CT and MRI, there is diffuse “sausage-shaped” enlargement of the pancreas with delayed enhancement of the parenchyma.41 There is characteristically a rim-like capsule of low density surrounding the pancreas on both early and delayed enhanced images (Fig. 11). This rim demonstrates sub-
393 tle delayed enhancement.41 Calcifications are usually not seen. Ultrasound demonstrates a diffusely enlarged and hypoechoic pancreas, also with “sausage-like” appearance. On MRI, the pancreas demonstrates abnormal decreased or isointense T1 signal and increased T2 signal intensity compared to liver, with abnormal delayed enhancement on contrast-enhanced sequences. The “capsule-like” rim demonstrates hypointensity on T1- and T2-weighted imaging with delayed enhancement suggesting fibrous tissue.36 On MRCP, there is diffuse or segmental irregular narrowing and strictures of the main pancreatic duct. The common bile duct within the pancreas is often narrowed with extrapancreatic dilatation of the proximal duct, which may present with cholestatic liver dysfunction and hyperbilirubinemia. These features contrast with the findings seen in usual chronic pancreatitis seen as irregularly dilated main pancreatic duct, pancreatic parenchymal atrophy and pancreatic cysts, and calculi. Based on imaging, the differential diagnosis for this entity includes diffuse pancreatic enlargement from malignant lymphoma, plasmacytoma, metastases, diffuse infiltrative pancreatic carcinoma, and Shwachman syndrome.42 However, the above entities often have other different radiologic, clinical, and laboratory characteristics than that of autoimmune pancreatitis. Histopathologic features include massive fibrosis, lymphoplasmacytic infiltration, marked destruction of pancreatic islets and acini, and destruction of the pancreatic ducts with marked cellular infiltration. These findings are pathognomonic for autoimmune pancreatitis.43 The diagnosis of autoimmune chronic pancreatitis is important as the treatment differs from other types of pancreatitis. Autoimmune chronic pancreatitis has an excellent response to steroids. Pancreatic morphologic changes and pancreatic function often recover following steroid therapy.44 The size and enhancement pattern of the pancreas often returns to normal and capsule-like low-density rim disappears.41 Therefore, radiologic recognition of this condition is important to avoid unnecessary surgical resection because it is a reversible process when promptly diagnosed and treated.
References
Figure 11 (A, B) Autoimmune pancreatitis. (A) Axial contrastenhanced CT shows a uniformly enlarged pancreas with a peripancreatic hypodense rim (arrow) suggestive of autoimmune pancreatitis. (B) ERCP image in the same patient demonstrates multiple regions of segmental irregular strictures in the main pancreatic duct (arrows) consistent with autoimmune pancreatitis.
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