DOI: 10.1148/rg.253045104
RadioGraphics 2005;25:671-685
© RSNA, 2005
Imaging Diagnosis of Cystic Pancreatic Lesions: Pseudocyst versus Nonpseudocyst1
Young H. Kim, MD, PhD,
Sanjay Saini, MD,
Dushant Sahani, MD,
Peter F. Hahn, MD, PhD,
Peter R. Mueller, MD and
Yong H. Auh, MD, PhD
1 From the Department of Radiology, UMass Memorial, University of Massachusetts Medical School, 55 Lake Ave North, Worcester, MA 01655 (Y.H.K.); the Department of Radiology, Massachusetts General Hospital, Harvard Medical School, Boston, Mass (S.S., D.S., P.F.H., P.R.M.); and the Department of Radiology, New York Presbyterian Hospital, Cornell University, New York, NY (Y.H.A.). Presented as an education exhibit at the 2003 RSNA Scientific Assembly. Received May 14, 2004; revision requested July 26 and received September 21; accepted September 22. All authors have no financial relationships to disclose.
Address correspondence to Y.H.K. (e-mail: kimy{at}ummhc.org).
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Abstract
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Although the clinical, radiologic, and pathologic features of cystic pancreatic lesions are well known, preoperative diagnosis is difficult. Differentiation between a pancreatic pseudocyst and a cystic pancreatic neoplasm is crucial in determining the proper treatment. Careful evaluation of the patient’s clinical history is important for accurate diagnosis of a pseudocyst. Clinical scenarios include a pseudocyst developing after acute pancreatitis and a pseudocyst superimposed on chronic pancreatitis. However, a pseudocyst in a patient with no clinical history of pancreatitis poses a diagnostic problem. The differential diagnosis of a neoplastic cystic lesion of the pancreas includes serous cystadenoma, mucinous cystic neoplasms, intraductal papillary mucinous tumor, and solid and papillary epithelial neoplasm. Definitive diagnosis is often possible when the lesion has a typical radiologic appearance, but in many cases characterization with imaging alone is impossible. Thin-section computed tomography with multiplanar reformation, magnetic resonance cholangiopancreatography, and endoscopic ultrasonography have emerged as modalities that can provide additional diagnostic information. Familiarity with the range of imaging appearances and awareness of the diagnostic strengths and limitations of each imaging modality are important for accurate diagnosis and management of cystic pancreatic lesions.
© RSNA, 2005
Abbreviations: ERCP = endoscopic retrograde cholangiopancreatography, IPMT = intraductal papillary mucinous tumor, SPEN = solid and papillary epithelial neoplasm
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LEARNING OBJECTIVES FOR TEST 4
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After reading this article and taking the test, the reader will be able to:
- Identify the radiologic findings of pancreatic pseudocysts.
- Describe the radiologic findings of cystic pancreatic neoplasms.
- Discuss the findings that allow differential diagnosis between pancreatic pseudocysts and cystic pancreatic neoplasms.
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Introduction
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Pseudocysts are the most common cystic lesions of the pancreas. All other cystic lesions including cystic neoplasms represent only 10%–15% of pancreatic cysts (1). Recently, wide application of computed tomography (CT) and ultrasound (US) in asymptomatic and mildly symptomatic patients has increased detection of incidental cystic lesions of the pancreas so that the differential diagnosis of pancreatic cystic lesions has become more challenging. In addition, recent awareness of intraductal papillary mucinous tumor (IPMT) has resulted in increasing numbers of reported cases (2). Differentiating pancreatic pseudocysts from nonpseudocysts is important for determining treatment.
It is well known that radiologic imaging alone has limited accuracy in differentiating between pseudocysts and nonpseudocysts due to similarities in the imaging findings of the lesions (3,4). Thin-section CT and magnetic resonance (MR) cholangiopancreatography have gained popularity for the potential advantages of visualizing communication between the main pancreatic duct and a cystic lesion noninvasively. Endoscopic US has emerged as a modality that can provide anatomic structure in greater detail and facilitate aspiration biopsy of smaller lesions (5). When radiologic imaging findings and results of cyst fluid analysis with or without biopsy are interpreted in conjunction with a careful patient history, diagnostic accuracy may be increased substantially.
The purpose of this article is to illustrate the spectrum of imaging findings of cystic pancreatic lesions and highlight the roles, advantages, and limitations of various imaging modalities in the differential diagnosis of pancreatic cystic lesions, with particular emphasis on pseudocysts versus nonpseudocysts.
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Pancreatic Pseudocyst
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Most cystic masses of the pancreas encountered in clinical practice are postinflammatory pseudocysts. Pancreatic pseudocysts are defined as localized amylase-rich fluid collections located within the pancreatic tissue or adjacent to the pancreas and surrounded by a fibrous wall that does not possess an epithelial lining (6,7). The CT findings of a pseudocyst include a round or oval fluid collection with a thin, barely perceptible wall or thick wall that shows evidence of contrast enhancement (7,8). They develop most often as a complication of acute or chronic pancreatitis and may develop secondary to pancreatic trauma or surgery (9). Although a prior history of pancreatitis cannot by itself justify the diagnosis of pancreatic pseudocyst, careful evaluation of the patient’s clinical history is important for the accurate diagnosis of pseudocyst. Clinical scenarios include a pseudocyst developing after identifiable acute pancreatitis (Figs 1–4), a pseudocyst resulting from an acute incident superimposed on chronic pancreatitis (Fig 5), and a pseudocyst with an uncertain or no known previous clinical history of pancreatitis (Fig 6).
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Figure 1a. Developing pseudocyst in a 63-year-old woman with epigastric pain. (a) Unenhanced CT scan shows an edematous pancreas and an ill-defined, acute fluid collection surrounding the tail of the pancreas (arrow) with peripancreatic inflammatory changes, an appearance compatible with acute pancreatitis. (b) On a follow-up contrast-enhanced CT scan obtained 1 month later, the lesion appears as a bilobed cystic mass with a septum in the pancreatic body and tail (arrow). The peripancreatic inflammatory changes are markedly decreased. (c) On a follow-up CT scan obtained 2 years later, the lesion appears as a unilocular, low-attenuation fluid collection with a well-defined thin wall (arrow). This is the typical appearance of a postinflammatory pseudocyst.
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Figure 1b. Developing pseudocyst in a 63-year-old woman with epigastric pain. (a) Unenhanced CT scan shows an edematous pancreas and an ill-defined, acute fluid collection surrounding the tail of the pancreas (arrow) with peripancreatic inflammatory changes, an appearance compatible with acute pancreatitis. (b) On a follow-up contrast-enhanced CT scan obtained 1 month later, the lesion appears as a bilobed cystic mass with a septum in the pancreatic body and tail (arrow). The peripancreatic inflammatory changes are markedly decreased. (c) On a follow-up CT scan obtained 2 years later, the lesion appears as a unilocular, low-attenuation fluid collection with a well-defined thin wall (arrow). This is the typical appearance of a postinflammatory pseudocyst.
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Figure 1c. Developing pseudocyst in a 63-year-old woman with epigastric pain. (a) Unenhanced CT scan shows an edematous pancreas and an ill-defined, acute fluid collection surrounding the tail of the pancreas (arrow) with peripancreatic inflammatory changes, an appearance compatible with acute pancreatitis. (b) On a follow-up contrast-enhanced CT scan obtained 1 month later, the lesion appears as a bilobed cystic mass with a septum in the pancreatic body and tail (arrow). The peripancreatic inflammatory changes are markedly decreased. (c) On a follow-up CT scan obtained 2 years later, the lesion appears as a unilocular, low-attenuation fluid collection with a well-defined thin wall (arrow). This is the typical appearance of a postinflammatory pseudocyst.
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Figure 2a. Progressive evolution and spontaneous resolution of a pancreatic pseudocyst in a 31-year-old man with left upper quadrant pain. (a) Initial contrast-enhanced CT scan shows an edematous pancreas and peripancreatic inflammatory changes, an appearance compatible with acute pancreatitis. (b) Follow-up CT scan obtained 2 months later shows a relatively thick-walled cyst in the pancreatic tail (arrow). This lesion represents a maturing pseudocyst. (c) CT scan obtained 4 months later shows resolution of the pseudocyst.
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Figure 2b. Progressive evolution and spontaneous resolution of a pancreatic pseudocyst in a 31-year-old man with left upper quadrant pain. (a) Initial contrast-enhanced CT scan shows an edematous pancreas and peripancreatic inflammatory changes, an appearance compatible with acute pancreatitis. (b) Follow-up CT scan obtained 2 months later shows a relatively thick-walled cyst in the pancreatic tail (arrow). This lesion represents a maturing pseudocyst. (c) CT scan obtained 4 months later shows resolution of the pseudocyst.
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Figure 2c. Progressive evolution and spontaneous resolution of a pancreatic pseudocyst in a 31-year-old man with left upper quadrant pain. (a) Initial contrast-enhanced CT scan shows an edematous pancreas and peripancreatic inflammatory changes, an appearance compatible with acute pancreatitis. (b) Follow-up CT scan obtained 2 months later shows a relatively thick-walled cyst in the pancreatic tail (arrow). This lesion represents a maturing pseudocyst. (c) CT scan obtained 4 months later shows resolution of the pseudocyst.
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Figure 3a. Infected necrosis and pancreatic abscess in a 35-year-old man with acute pancreatitis, abdominal pain, and mild leukocytosis. (a) Contrast-enhanced CT scan shows a heterogeneous hypoattenuating fluid collection with peripheral irregularity in the pancreatic body and tail (arrow). Three weeks after conservative treatment, a spiking fever and marked leukocytosis developed. (b) CT scan obtained 3 weeks after conservative treatment shows an interval increase in the size of the fluid collection, which contains high-attenuation debris (arrow). The presence of infection was confirmed by means of percutaneous aspiration. The patient remained asymptomatic after percutaneous drainage. (c) Follow-up CT scan obtained 2 months later shows a decrease in the size of the fluid collection (arrow), which appears as a small residual cystic mass in the pancreatic tail.
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Figure 3b. Infected necrosis and pancreatic abscess in a 35-year-old man with acute pancreatitis, abdominal pain, and mild leukocytosis. (a) Contrast-enhanced CT scan shows a heterogeneous hypoattenuating fluid collection with peripheral irregularity in the pancreatic body and tail (arrow). Three weeks after conservative treatment, a spiking fever and marked leukocytosis developed. (b) CT scan obtained 3 weeks after conservative treatment shows an interval increase in the size of the fluid collection, which contains high-attenuation debris (arrow). The presence of infection was confirmed by means of percutaneous aspiration. The patient remained asymptomatic after percutaneous drainage. (c) Follow-up CT scan obtained 2 months later shows a decrease in the size of the fluid collection (arrow), which appears as a small residual cystic mass in the pancreatic tail.
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Figure 3c. Infected necrosis and pancreatic abscess in a 35-year-old man with acute pancreatitis, abdominal pain, and mild leukocytosis. (a) Contrast-enhanced CT scan shows a heterogeneous hypoattenuating fluid collection with peripheral irregularity in the pancreatic body and tail (arrow). Three weeks after conservative treatment, a spiking fever and marked leukocytosis developed. (b) CT scan obtained 3 weeks after conservative treatment shows an interval increase in the size of the fluid collection, which contains high-attenuation debris (arrow). The presence of infection was confirmed by means of percutaneous aspiration. The patient remained asymptomatic after percutaneous drainage. (c) Follow-up CT scan obtained 2 months later shows a decrease in the size of the fluid collection (arrow), which appears as a small residual cystic mass in the pancreatic tail.
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Figure 4. Hemorrhagic pseudocyst in a 45-year-old man who experienced an episode of abdominal pain but had no clinical findings suggestive of infection. Contrast-enhanced CT scan shows a cystic mass containing an area of high attenuation (arrow), a finding consistent with recent hemorrhage.
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Figure 5a. Chronic pancreatitis with an intrapancreatic pseudocyst in a 42-year-old man with a history of alcoholic pancreatitis. (a) Contrast-enhanced CT scan shows a dilated pancreatic duct (arrows) with mild pancreatic atrophy, an appearance compatible with chronic pancreatitis. (b) CT scan shows a round mass with diffuse low attenuation in the pancreatic head (curved arrow). The mass represents a pseudocyst. Note the dilated pancreatic duct (straight arrow). (c) Contrast-enhanced CT scan shows pancreatic calcifications (arrow), a finding compatible with chronic pancreatitis.
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Figure 5b. Chronic pancreatitis with an intrapancreatic pseudocyst in a 42-year-old man with a history of alcoholic pancreatitis. (a) Contrast-enhanced CT scan shows a dilated pancreatic duct (arrows) with mild pancreatic atrophy, an appearance compatible with chronic pancreatitis. (b) CT scan shows a round mass with diffuse low attenuation in the pancreatic head (curved arrow). The mass represents a pseudocyst. Note the dilated pancreatic duct (straight arrow). (c) Contrast-enhanced CT scan shows pancreatic calcifications (arrow), a finding compatible with chronic pancreatitis.
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Figure 5c. Chronic pancreatitis with an intrapancreatic pseudocyst in a 42-year-old man with a history of alcoholic pancreatitis. (a) Contrast-enhanced CT scan shows a dilated pancreatic duct (arrows) with mild pancreatic atrophy, an appearance compatible with chronic pancreatitis. (b) CT scan shows a round mass with diffuse low attenuation in the pancreatic head (curved arrow). The mass represents a pseudocyst. Note the dilated pancreatic duct (straight arrow). (c) Contrast-enhanced CT scan shows pancreatic calcifications (arrow), a finding compatible with chronic pancreatitis.
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Figure 6a. Incidentally detected pancreatic pseudocyst in a 77-year-old woman with no known history of pancreatitis. (a) Image obtained with thin-section (2.5-mm section thickness) contrast-enhanced multidetector CT shows an ovoid hypoattenuating mass without internal septa or mural nodules in the pancreatic tail (arrow). (b) Curved coronal reformatted view shows the relationship of the mass (arrow) to the pancreatic parenchyma. The multiplanar capabilities of multidetector CT are particularly useful for surgical planning.
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Figure 6b. Incidentally detected pancreatic pseudocyst in a 77-year-old woman with no known history of pancreatitis. (a) Image obtained with thin-section (2.5-mm section thickness) contrast-enhanced multidetector CT shows an ovoid hypoattenuating mass without internal septa or mural nodules in the pancreatic tail (arrow). (b) Curved coronal reformatted view shows the relationship of the mass (arrow) to the pancreatic parenchyma. The multiplanar capabilities of multidetector CT are particularly useful for surgical planning.
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Classic Postinflammatory Pancreatic Pseudocyst
In the clinical setting of acute pancreatitis, observing peripancreatic inflammatory changes on initial CT scans and an evolving peripancreatic fluid collection that develops a wall or capsule provides a sufficient diagnostic clue to the diagnosis of pancreatic pseudocyst (Fig 1). After an acute attack, the pseudocyst develops during a period of 4–6 weeks. Pseudocysts may be followed conservatively if they are smaller than 6 cm in diameter or the patient is asymptomatic because pseudocysts can resolve spontaneously (Fig 2 ) (10). Unilocular pseudocysts occur more frequently than multilocular pseudocysts. Pseudocysts usually have a smooth thin wall or a thick wall with uniform thickness. Complications related to pseudocysts include infection, hemorrhage, rupture, and obstruction of other abdominal organs. Secondary infection of the pseudocyst is a dreaded complication due to its high rate of morbidity and mortality, requiring drainage by radiologic, endoscopic, or surgical decompression (11). Radiologic differential diagnosis of infected necrosis, pancreatic abscess, or hemorrhage within the cyst from a simple uncomplicated pseudocyst cannot be made without clinical information (Figs 3, 4).
Pancreatic Pseudocyst Superimposed on Chronic Pancreatitis
Chronic pancreatitis is most often caused by alcoholism. Conditions such as hyperlipidemia or hyperparathyroidism, trauma, and chronic obstruction of the pancreatic duct can also be associated with chronic pancreatitis. Pancreatic pseudocysts can occur in association with chronic pancreatitis as chronic pseudocysts or can result from acute exacerbation of pancreatitis or chronic pancreatitis. In the former case, a distinct clinical history of acute pancreatitis may be lacking and the pseudocyst is often detected incidentally, in comparison with the latter case (12). The recognition of a pancreatic pseudocyst resulting from chronic pancreatitis is usually easy when there are associated stigmata of chronic pancreatitis such as parenchymal calcifications or ductal stones, ductal dilatation, and atrophy of the parenchyma (Fig 5). However, without these findings, pseudocysts will be very difficult to distinguish from IPMT.
Pancreatic Pseudo-cyst without an Antecedent Episode of Acute Pancreatitis
Detection of incidental pancreatic cysts in an asymptomatic patient poses a diagnostic problem. Incidental pancreatic cysts are smaller than symptomatic cysts and are unlikely to be pseudocysts (2). Cystic pancreatic neoplasm should be considered in the differential diagnosis of a pancreatic cyst, even in patients with a history of pancreatitis, if no recent episode of acute pancreatitis can be documented on clinical or imaging grounds. For pancreatic pseudocysts without an antecedent episode of acute pancreatitis and radiologic evidence of pancreatitis, US-, CT-, or endoscopic US–guided aspiration or biopsy or at least a follow-up study should be recommended (Fig 6).
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Cystic Neoplasms
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Cystic pancreatic neoplasms are uncommon but important because they are increasingly being detected and are difficult to distinguish from pseudocysts, which are encountered far more frequently. Cystic pancreatic neoplasms are generally associated with symptoms, as are most pancreatic pseudocysts, but an increasing number of incidental pancreatic cysts are being found (2). The differential diagnosis of a neoplastic cystic lesion of the pancreas encompasses a wide variety of neoplasms, including serous cystadenoma, mucinous cystic neoplasm, IPMT, solid and papillary epithelial neoplasm (SPEN), and cystic islet cell tumor. Definitive diagnosis is often possible when the lesions show typical radiologic appearances, but in many cases characterization by imaging alone is impossible. Although improved radiologic technology provides more detailed anatomic information on many lesions, it produces more challenges because the average size of detected lesions has steadily decreased and imaging characterization becomes more difficult for smaller lesions.
Serous Cystadenoma
Serous cystadenoma, also referred to as microcystic cystadenoma, is typically found in women over the age of 60 years with nonspecific complaints of abdominal pain or weight loss or more commonly as an incidental finding. Typical serous cystadenomas are composed of multiple cysts varying in size from 0.2 to 2.0 cm, and the size of the tumors ranges in greatest dimension from 1.4 to 27 cm (5). A central stellate scar with calcification, which is known to be characteristic of serous cystadenoma, may sometimes be observed (4). Internally, the cyst has a honeycombed appearance compatible with innumerable cysts (Fig 7). At US, the lesion may appear as a solid echogenic mass due to interfaces produced by the numerous cysts. It may appear as a solid mass at CT, depending on the size of the cysts and the amount of fibrous tissue (Fig 8).
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Figure 7a. Serous cystadenoma in a 45-year-old woman with right upper quadrant pain. (a) Contrast-enhanced CT scan shows a low-attenuation mass with a honeycomb appearance in the pancreatic head and uncinate process (arrow). The honeycomb appearance is produced by numerous tiny cystic structures. (b) US scan shows that the mass has low echogenicity due to the interfaces between the tiny cysts. Note the increased through transmission posterior to the mass. (c) Photograph of the cut surface of the specimen shows innumerable cysts.
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Figure 7b. Serous cystadenoma in a 45-year-old woman with right upper quadrant pain. (a) Contrast-enhanced CT scan shows a low-attenuation mass with a honeycomb appearance in the pancreatic head and uncinate process (arrow). The honeycomb appearance is produced by numerous tiny cystic structures. (b) US scan shows that the mass has low echogenicity due to the interfaces between the tiny cysts. Note the increased through transmission posterior to the mass. (c) Photograph of the cut surface of the specimen shows innumerable cysts.
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Figure 7c. Serous cystadenoma in a 45-year-old woman with right upper quadrant pain. (a) Contrast-enhanced CT scan shows a low-attenuation mass with a honeycomb appearance in the pancreatic head and uncinate process (arrow). The honeycomb appearance is produced by numerous tiny cystic structures. (b) US scan shows that the mass has low echogenicity due to the interfaces between the tiny cysts. Note the increased through transmission posterior to the mass. (c) Photograph of the cut surface of the specimen shows innumerable cysts.
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Figure 8a. Incidentally detected serous cystadenoma in a 75-year-old man. (a) Pancreatic phase image obtained with thin-section (1.25-mm section thickness) contrast-enhanced multidetector CT shows a lobulated hypoattenuating mass in the pancreatic tail (white arrow). Enhancing vessels within fine septa (black arrow) enter the mass from the periphery. (b) Curved coronal reformatted view obtained through the pancreas shows no obvious communication between the tumor (arrow) and a normal pancreatic duct (arrowhead).
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Figure 8b. Incidentally detected serous cystadenoma in a 75-year-old man. (a) Pancreatic phase image obtained with thin-section (1.25-mm section thickness) contrast-enhanced multidetector CT shows a lobulated hypoattenuating mass in the pancreatic tail (white arrow). Enhancing vessels within fine septa (black arrow) enter the mass from the periphery. (b) Curved coronal reformatted view obtained through the pancreas shows no obvious communication between the tumor (arrow) and a normal pancreatic duct (arrowhead).
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Asymptomatic serous cystadenomas do not require surgical excision because they are rarely malignant. Tumors smaller than 2 cm have been reported and are more likely to be serous cystadenomas (5). Macrocystic or oligocystic serous cystadenoma is a variant of serous cystadenoma that is very difficult to differentiate from mucinous cystadenoma (Fig 9) (13). Location in the pancreatic head, lobulated contour, and lack of wall enhancement have been reported to be specific for macrocystic serous cystadenoma in comparison with mucinous cystic tumor. Lobulated contours have been reported to be a specific finding in comparison with pseudocyst (14).
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Figure 9a. Oligocystic serous cystadenoma in a 56-year-old woman with epigastric pain. (a, b) US scan (a) and CT scan (b) show a well-demarcated cystic mass with peripheral internal septa (arrow) in the pancreatic head. Note the peripheral septum with calcification (arrow in b). (c) Endoscopic pancreatogram shows the pancreatic duct splayed by the tumor. No communication exists between the lesion and the main duct. (d) Photograph of the external surface of the surgical specimen shows the lobulated, multiseptate cystic mass.
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Figure 9b. Oligocystic serous cystadenoma in a 56-year-old woman with epigastric pain. (a, b) US scan (a) and CT scan (b) show a well-demarcated cystic mass with peripheral internal septa (arrow) in the pancreatic head. Note the peripheral septum with calcification (arrow in b). (c) Endoscopic pancreatogram shows the pancreatic duct splayed by the tumor. No communication exists between the lesion and the main duct. (d) Photograph of the external surface of the surgical specimen shows the lobulated, multiseptate cystic mass.
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Figure 9c. Oligocystic serous cystadenoma in a 56-year-old woman with epigastric pain. (a, b) US scan (a) and CT scan (b) show a well-demarcated cystic mass with peripheral internal septa (arrow) in the pancreatic head. Note the peripheral septum with calcification (arrow in b). (c) Endoscopic pancreatogram shows the pancreatic duct splayed by the tumor. No communication exists between the lesion and the main duct. (d) Photograph of the external surface of the surgical specimen shows the lobulated, multiseptate cystic mass.
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Figure 9d. Oligocystic serous cystadenoma in a 56-year-old woman with epigastric pain. (a, b) US scan (a) and CT scan (b) show a well-demarcated cystic mass with peripheral internal septa (arrow) in the pancreatic head. Note the peripheral septum with calcification (arrow in b). (c) Endoscopic pancreatogram shows the pancreatic duct splayed by the tumor. No communication exists between the lesion and the main duct. (d) Photograph of the external surface of the surgical specimen shows the lobulated, multiseptate cystic mass.
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Mucinous Cystic Neoplasms
Mucinous cystic neoplasms are the most common cystic tumors of the pancreas. The large cystic spaces are lined by tall, mucin-producing columnar cells. Mucinous cystic neoplasms may be unilocular or mutilocular and are commonly detected only after achieving a large size. Solid papillary excrescences sometimes protrude from the wall into the interior of these tumors. The absence of excrescences does not exclude malignancy.
Multiple enhancing septations and solid intramural nodules are typical radiologic findings of mucinous cystic neoplasms (Fig 10). Peripheral calcification, which can be seen in 10%–25%, is an important characteristic for mucinous cystic neoplasms and can be used to differentiate them from serous cystadenomas, which are known to have central calcification (4,15). Endoscopic US can depict the internal architecture of the cystic mass, including internal septa and tiny solid components, better than conventional CT, depending on the location of the tumor and patient body habitus. The tumors are round to oval with a smooth external surface. Secondary cysts along the internal wall are common (Fig 11). Occasionally, communication between the pancreatic duct and the cystic neoplasm is present.
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Figure 11. Mucinous cystadenoma in a 47-year-old woman with left upper quadrant pain. Contrast-enhanced CT scan shows a large cystic tumor with small cysts clustered at its periphery (arrow).
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There is a spectrum of mucinous cystic neoplasms from benign to malignant, but the confident exclusion of malignancy is rarely possible on the basis of imaging findings alone (Fig 12). Mucinous cystic tumors should always be resected because they are all potentially malignant. When the cyst is small in an asymptomatic patient, cyst aspiration and analysis of the cyst fluid can be helpful in differential diagnosis (2) (Fig 13).
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Figure 12. Mucinous cystadenocarcinoma in a 52-year-old woman with epigastric pain. Despite the absence of a history of pancreatitis, the thin cyst wall led to the presumptive diagnosis of a pseudocyst. CT scan shows a thin-walled cyst in the pancreatic tail. There is a tiny peripheral intramural nodular structure (arrow), which was initially overlooked. At surgery, the lesion proved to be a mucinous cystadenocarcinoma.
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Figure 13a. Incidentally detected mucinous cystadenoma in a 65-year-old woman. (a) Contrast-enhanced CT scan shows an ovoid hypoattenuating mass with barely visible septa in the pancreatic head (arrow). (b) Endoscopic US scan shows the complex cystic mass with multiple internal septa (arrow). Endoscopic US–guided fine-needle aspiration was performed, and cytologic analysis revealed abundant mucin with scant glandular epithelial cells, findings suggestive of a mucin-producing tumor. At surgery, the lesion proved to be a mucinous cystadenoma.
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Figure 13b. Incidentally detected mucinous cystadenoma in a 65-year-old woman. (a) Contrast-enhanced CT scan shows an ovoid hypoattenuating mass with barely visible septa in the pancreatic head (arrow). (b) Endoscopic US scan shows the complex cystic mass with multiple internal septa (arrow). Endoscopic US–guided fine-needle aspiration was performed, and cytologic analysis revealed abundant mucin with scant glandular epithelial cells, findings suggestive of a mucin-producing tumor. At surgery, the lesion proved to be a mucinous cystadenoma.
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Mucinous Cystic Neoplasm Misdiagnosed as a Pseudocyst
Owing to partial volume averaging with the hypoattenuating cyst fluid, the fine internal septa and small intramural nodules may not be visible at conventional contrast-enhanced CT. This explains why mucinous cystic neoplasm sometimes is misdiagnosed as a pseudocyst (4) (Fig 12). The application of thin-section imaging with multidetector CT has been known to depict internal anatomic details more clearly, which possibly avoids misdiagnosis (16). The large size of unilocular cysts excludes the diagnosis of IPMT.
Intraductal Papillary Mucinous Tumor
IPMT is characterized by the papillary proliferation of pancreatic ductal epithelium and production of mucin. It is characterized by cystic dilatation of a main or a side branch duct that contains thick mucoid secretions. Patients present with nonspecific abdominal symptoms and sometimes hyperamylasemia. IPMTs typically occur in elderly patients and are more common in men. Although the incidence of IPMT seems to be increasing, the likely explanation is increased use of imaging and awareness of this disease entity.
IPMTs are classified into the main duct type, branch duct type, and combined type. Accordingly, imaging findings vary depending on the type of the tumor. The side branch duct type is the most commonly mistaken for mucinous cystic tumor or pseudocyst. Typical location (uncinate process), typical appearance (grapelike locular appearance), and communication with the duct at endoscopic retrograde cholangiopancreatography (ERCP) usually separate it from other lesions in the pancreas (17). A markedly dilated uncinate branch filled with mucus is a typical feature of a side branch IPMT.
There has been debate over use of ERCP as an initial imaging modality of choice (17). ERCP is regarded as the modality of choice in the diagnosis of IPMT for its ability to depict the bulging ampulla of Vater, mucin pouring from the papilla, and communication between the pancreatic duct and the cyst cavity (17). Communication between the duct and the abnormal cystic structure can be shown with thin-section helical CT (Fig 14) or with MR imaging and MR cholangiopancreatography (Fig 15) (16,18). Although the classic diagnostic role of ERCP has been challenged to some extent by combined use of MR cholangiopancreatography and endoscopic US in the evaluation of IPMT, ERCP has a distinctive diagnostic role where the diagnosis is not clear on cross-sectional images (Fig 16).
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Figure 14a. Multiple branch duct type of IPMT. (a) Contrast-enhanced CT scan shows multiple cystic masses (straight arrow) in the pancreatic head and body. Note the dilated pancreatic duct (curved arrow). (b) Curved coronal reformatted view obtained along the pancreatic tail shows a communication between a cystic mass and the dilated distal pancreatic duct (arrow).
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Figure 14b. Multiple branch duct type of IPMT. (a) Contrast-enhanced CT scan shows multiple cystic masses (straight arrow) in the pancreatic head and body. Note the dilated pancreatic duct (curved arrow). (b) Curved coronal reformatted view obtained along the pancreatic tail shows a communication between a cystic mass and the dilated distal pancreatic duct (arrow).
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Figure 15a. Branch duct type of IPMT. (a) MR cholangiopancreatogram shows a cystic pancreatic mass (arrow). It is not clear whether there is a communication between the mass and the pancreatic duct. (b) Axial T2-weighted MR image (3,860/1,930 [repetition time msec/echo time msec]) shows a communication between the mass and the pancreatic duct (arrowhead).
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Figure 15b. Branch duct type of IPMT. (a) MR cholangiopancreatogram shows a cystic pancreatic mass (arrow). It is not clear whether there is a communication between the mass and the pancreatic duct. (b) Axial T2-weighted MR image (3,860/1,930 [repetition time msec/echo time msec]) shows a communication between the mass and the pancreatic duct (arrowhead).
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Figure 16a. Combined main duct and branch duct type of IPMT in a 55-year-old man with vague abdominal pain. (a) ERCP image shows dilatation of the main and branch pancreatic ducts. Note the intraductal filling defects due to mucus (arrows). (b) MR cholangiopancreatogram shows a filling defect within the dilated main pancreatic duct (arrow). Note the dilated branch ducts in the pancreatic head and uncinate process.
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Figure 16b. Combined main duct and branch duct type of IPMT in a 55-year-old man with vague abdominal pain. (a) ERCP image shows dilatation of the main and branch pancreatic ducts. Note the intraductal filling defects due to mucus (arrows). (b) MR cholangiopancreatogram shows a filling defect within the dilated main pancreatic duct (arrow). Note the dilated branch ducts in the pancreatic head and uncinate process.
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Solid and Papillary Epithelial Neoplasm
SPENs, also known as solid and pseudopapillary tumors, papillary and cystic tumors, or solid-cystic tumors, are histologically distinctive neoplasms of low malignant potential with a favorable prognosis. SPEN is typically found in young women and has a predilection for Asian and black patients. Most patients present with nonspecific signs and symptoms including nausea, vomiting, and abdominal pain or fullness. The tumor tends to be a large, well-circumscribed, and slowly growing mass. The tumor may have a variety of internal appearances, from purely cystic to completely solid, but is usually surrounded by a thick, well-defined rim (Fig 17). The appearance of the internal architecture typically depends on the degree of hemorrhage and necrosis of the tumor.
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Figure 17a. SPEN in a 32-year-old woman with epigastric pain. (a) Contrast-enhanced CT scan shows a mixed solid and cystic mass in the pancreatic head (arrows). (b) Axial T1-weighted MR image (500/20) shows areas of high signal intensity due to hemorrhage within the mass (arrow). (c) Photograph of the cut surface of the gross specimen shows the solid mass with irregular cystic degeneration and hemorrhage. Note the thick fibrous capsule.
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Figure 17b. SPEN in a 32-year-old woman with epigastric pain. (a) Contrast-enhanced CT scan shows a mixed solid and cystic mass in the pancreatic head (arrows). (b) Axial T1-weighted MR image (500/20) shows areas of high signal intensity due to hemorrhage within the mass (arrow). (c) Photograph of the cut surface of the gross specimen shows the solid mass with irregular cystic degeneration and hemorrhage. Note the thick fibrous capsule.
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Figure 17c. SPEN in a 32-year-old woman with epigastric pain. (a) Contrast-enhanced CT scan shows a mixed solid and cystic mass in the pancreatic head (arrows). (b) Axial T1-weighted MR image (500/20) shows areas of high signal intensity due to hemorrhage within the mass (arrow). (c) Photograph of the cut surface of the gross specimen shows the solid mass with irregular cystic degeneration and hemorrhage. Note the thick fibrous capsule.
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Multidetector CT and MR Imaging with MR Cholangiopancreatography
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The improved multiplanar capability, thin collimation, and ability to optimize parenchymal enhancement of multidetector CT not only improve the detection rate of the cystic pancreatic lesion but may enhance diagnostic accuracy by depicting fine internal architecture and the anatomic relationship between the main pancreatic duct and the cystic lesions (19). MR imaging with additional performance of MR cholangiopancreatography can be similar in diagnostic value to multidetector CT with thin sections in the examination of patients with IPMT, especially by depicting communication between the cystic lesions and the main pancreatic duct (20).
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Image-guided Fine-Needle Aspiration Biopsy
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Preoperative cyst fluid analysis and biopsy of the solid portion of the cystic mass can be obtained by conventional US- or CT-guided percutaneous needle aspiration or by an endoscopic US–guided technique. Analysis of the cystic contents includes viscosity, enzymes (amylase, lipase), tumor markers (carcinoembryonic antigen [CEA], cancer antigen 19-9 [CA 19-9]), and cytologic findings, which may help differentiate between neoplastic cysts and pseudocysts. False-negative results from sampling errors are not uncommon (21). Interpretation of the results must be done in conjunction with a careful history and interpretation of radiologic findings (22,23). When the nature of the pancreatic cyst cannot be definitively established by fluid analysis or cytologic analysis, surgical resection is indicated.
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Endoscopic US and US-guided Fine-Needle Aspiration or Biopsy
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Endoscopic US has emerged as a useful diagnostic tool in the evaluation of pancreatic cystic lesions. It provides more detailed anatomic information about the cyst than conventional US and allows the sampling of both cyst fluid and any solid component in smaller lesions (Figs 18–21). By allowing incorporation of the morphologic appearance at endosonography, results of cytologic analysis, and results of tumor marker analysis, endoscopic US can provide additional diagnostic clues (5).
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Figure 18a. Serous cystadenoma in a 77-year-old woman with right upper quadrant pain. (a) Contrast-enhanced CT scan shows a hypoattenuating mass in the pancreatic head (arrow). Septa in the mass are barely visible. (b) Endoscopic US scan shows a central fibrous scar and a stellate configuration of the septa. At surgery, the lesion proved to be a serous cystadenoma.
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Figure 18b. Serous cystadenoma in a 77-year-old woman with right upper quadrant pain. (a) Contrast-enhanced CT scan shows a hypoattenuating mass in the pancreatic head (arrow). Septa in the mass are barely visible. (b) Endoscopic US scan shows a central fibrous scar and a stellate configuration of the septa. At surgery, the lesion proved to be a serous cystadenoma.
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Figure 19a. Mucinous cystadenoma in a 38-year-old woman with recurrent abdominal pain. (a) Contrast-enhanced CT scan shows a well-defined, round, hypoattenuating mass in the pancreatic tail (arrow). Note the fine internal septa (arrowheads). (b) Endoscopic US scan shows the multiple septa in the mass.
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Figure 19b. Mucinous cystadenoma in a 38-year-old woman with recurrent abdominal pain. (a) Contrast-enhanced CT scan shows a well-defined, round, hypoattenuating mass in the pancreatic tail (arrow). Note the fine internal septa (arrowheads). (b) Endoscopic US scan shows the multiple septa in the mass.
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Figure 20a. Incidentally detected mucinous cystadenocarcinoma in a 60-year-old man. (a) Contrast-enhanced CT scan shows a multilocular cystic mass in the pancreatic head (arrow). (b) Endoscopic US scan shows the complex solid and cystic mass. Aspiration of the cyst demonstrated mucin, but the acellular aspirates did not allow exclusion of either a cystic neoplasm or a pseudocyst. At surgery, the lesion proved to be a mucinous cystadenocarcinoma.
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Figure 20b. Incidentally detected mucinous cystadenocarcinoma in a 60-year-old man. (a) Contrast-enhanced CT scan shows a multilocular cystic mass in the pancreatic head (arrow). (b) Endoscopic US scan shows the complex solid and cystic mass. Aspiration of the cyst demonstrated mucin, but the acellular aspirates did not allow exclusion of either a cystic neoplasm or a pseudocyst. At surgery, the lesion proved to be a mucinous cystadenocarcinoma.
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Figure 21a. Intraductal papillary mucinous adenocarcinoma in a 76-year-old man with fever and obstructive jaundice. (a) Contrast-enhanced CT scan shows a markedly dilated side branch duct with wall thickening (arrow). (b) Endoscopic US scan shows the dilated side branch duct with nodular wall thickening, an appearance suggestive of a complex solid and cystic mass. Aspiration biopsy of the nodular wall demonstrated an adenocarcinoma with abundant background mucin. Arrows = aspiration needle. At surgery, the lesion proved to be an intraductal papillary mucinous adenocarcinoma.
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Figure 21b. Intraductal papillary mucinous adenocarcinoma in a 76-year-old man with fever and obstructive jaundice. (a) Contrast-enhanced CT scan shows a markedly dilated side branch duct with wall thickening (arrow). (b) Endoscopic US scan shows the dilated side branch duct with nodular wall thickening, an appearance suggestive of a complex solid and cystic mass. Aspiration biopsy of the nodular wall demonstrated an adenocarcinoma with abundant background mucin. Arrows = aspiration needle. At surgery, the lesion proved to be an intraductal papillary mucinous adenocarcinoma.
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Abstract
LEARNING OBJECTIVES FOR TEST...
