eMedicine Specialties > Radiology > Gastrointestinal
Pancreas, Mucinous Cystic Neoplasm
Updated: Mar 12, 2009
Introduction
Background
Mucinous cystic neoplasms (MCNs) of the pancreas are uncommon, and their diagnosis, treatment and prognosis have yet to be fully uniformly determined. Differentiation of cystic lesions of the pancreas is difficult, as they can be benign (serous cystadenomas), inflammatory (pseudocyst of the pancreas), or malignant.
Pancreatic intraductal papillary mucinous tumor (IPMT). Contrast-enhanced CT scans through the pancreas show gross dilatation of the pancreatic duct. At surgery, IPMT was confirmed.
Pancreatic microcystic adenoma. Plain radiograph shows tumor calcification in a microcystic adenoma (left upper quadrant). Calcification in the microcystic adenoma presents as a central cluster arranged in a sunburst or stellate arrangement. Central calcification is better evaluated with CT than with radiography. (See Image 16 in Multimedia.)
Mucinous pancreatic tumors can be subdivided into peripheral and ductal tumors according to the site of origin. The peripheral type of mucinous cystic tumors includes mucin-producing cystadenoma and cystadenocarcinoma. The ductal types originate from the main pancreatic duct (MPD) or its branches. Intraductal tumors have been referred to by different names; however, since 1997, the unified term intraductal papillary mucinous tumor (IPMT) has been adopted.
ERCP typically shows a patulous ampulla of Vater with discharging mucus, which is often diagnostic for IPMT.
The biologic behavior of these tumors is variable, and different histologic patterns frequently coexist in the same tumor. The tumors may be entirely benign, as are mucinous cystadenomas or intraductal papillary mucinous adenomas. Some tumors are borderline, showing cellular dysplasia, whereas others are frankly malignant. Malignant cystadenocarcinoma and intramedullary mucinous carcinomas may be further subdivided into noninvasive and invasive types.
Other cystic neoplasms of the pancreas include papillary cystic tumors, cystic islet cell tumor, acinar cystadenocarcinoma, and lymphangioma. Accurate diagnosis for a cystic neoplasm of the pancreas is therefore important, as treatment depends on the tumor type because of variations in the biology and natural history of the lesions.
Pathophysiology
Histologic features
Serous cystadenomas are generally benign and well circumscribed, consisting of single or multiple cysts 1-25 cm in diameter.
Pseudocysts of the pancreas are inflammatory and commonly arise as a secondary event to acute pancreatitis. Pseudocysts can become infected and exhibit signs of necrosis and hemorrhage.
Mucinous cystic tumors of the pancreas, so-called macrocystic cystadenomas or cystadenocarcinomas, which predominate in the body and tail of the pancreas, have a strong female predilection. MCNs are the most common of cystic pancreatic tumors, accounting for 45-50% of tumors. They are multiloculated tumors with a characteristic smooth glistening surface. They arise from oversecretion of the mucus by the hyperplastic columnar lining of the ducts. The cysts contain thickened viscous material, which can also be hemorrhagic.
The individual cyst is 2-26 cm in diameter, with large tumors being more often malignant than smaller ones. The cyst walls are dense and fibrous with occasional calcification. These tumors display a wide range of clinicopathologic spectrum ranging from benign to frankly malignant. The tumors are classified by histology as benign, borderline, or malignant based on degree of dysplastic changes. This classification is well correlated with the prognosis and suggests that all these tumors be treated as potentially malignant. Accurate diagnosis requires examination of extensive samples of cyst epithelium followed by complete surgical resection.
Mucinous cysts are commonly precancerous and microscopically are recognized to have 3 distinct layers: (1) the innermost layer, which is the epithelial lining (hyperplastic, dysplastic); (2) the middle layer, which is the densely cellular mesenchymal stroma; and (3) the outermost layer, which is the hyalinized connective tissue.
These tumors may demonstrate histologic features of either malignant or benign mucinous epithelium; they are probably considered malignant or potentially malignant, partly because of the limited clinicopathologic experience with these tumors. The degree of atypia of the epithelial lining and the dilatation of the ducts can help determine the malignant nature of the cyst. In some cases, only foci of malignant change occur within a mucinous cyst. This, added to its indolent nature, makes accurate diagnosis and differentiation from the benign serous cystadenoma difficult. Mucinous cysts can invade the surrounding pancreatic parenchyma, which results in symptoms and signs of pancreatic cancer.
IPMT is a papillary neoplasm that arises within the MPD or its branches. The tumors hypersecrete mucin, which often leads to duct dilatation and/or chronic obstructive pancreatitis. IPMTs are premalignant and may histologically demonstrate areas ranging from hyperplasia to carcinoma within a single tumor. The tumors generally show intraluminal, longitudinal growth, but it is slow to invade periductal tissues radially and slow to metastasize. IPMTs are most commonly localized to the head of the pancreas, but they may occur at any site along the pancreatic ductal system. Ductal dilatation is often impressive and may mimic MCNs on CT scans.
Intraductal papillary mucinous neoplasm is recognized as predominantly a solid tumor with a central cyst. The cystic variety consists microscopically of cystlike spaces with papillary protrusions.
Classification of IPMTs
Nakamura and associates have proposed a new classification for IPMTs. In previous studies of the expression of MUC1 (for membrane-bound–type mucin) and MUC2 (for intestinal-type secretory mucin) in pancreatic tumors, invasive ductal carcinoma (IDC) usually showed MUC1+ and MUC2 - expression, whereas IPMT showed MUC1 - and MUC2 + expression.
However, other studies show that many IPMTs have MUC1 - and MUC2 - expression. In the study by Nakamura et al, the clinicopathologic features of 18 tumors with MUC2 + IPMTs and 32 MUC2 - IPMTs and their potential for malignancy were compared. Most of the MUC2 + IPMTs were composed of dark, columnar cells, whereas most MUC2 - were composed of clear columnar cells. The incidence of carcinomatous change and invasive proliferation of the carcinoma in MUC2 + tumors was significantly higher than in MUC2 - tumors.
The clinical outcome for the patients with IPMT and the MUC2 + pattern tended to be worse than for those with IPMT and the MUC2 - pattern, though the overall outcome for the 2 types of IPMT was significantly better than for those with IDC. Because of the differences in mucin-expression patterns and in the morphologic appearance and potential for malignancy between the 2 types of IPMT, the authors believe that they belong to different neoplastic lineages. Therefore, it may be reasonable to classify them as different entities, although the classification by the World Health Organization (WHO) includes a single clinicopathologic entity of IPMT forming an adenoma-carcinoma sequence. The authors concluded that classification of IPMTs by MUC2 expression pattern may be of value in the better assessment of the biologic behavior of IPMTs and their potential for malignancy.
Frequency
United States
Cystic tumors of the pancreas are relatively uncommon, accounting for 10% of cystic lesions of the pancreas and 1% of pancreatic neoplasms. MCNs, serous cystadenomas, and IPMT account for more than 90% of the primary cystic neoplasms of the pancreas, but other nonserous and nonmucous entities with cystic appearance are also known. Cystic neoplasms of the pancreas are an increasing entity.
International
No data suggest that the international incidence of mucinous pancreatic tumors is different from that in the United States.
Mortality/Morbidity
The long-term survival of patients with these tumors is generally better than that of patients with adenocarcinoma of the pancreas, and aggressive resection of the tumors is required in most patients. The prognosis is good after curative resection for serous cystadenomas and MCNs of the pancreas.
- There has been a recent trend to resect all cystic neoplasms, without attempts to preoperatively determine the exact histologic subtype. Five-year survival rates are excellent (>95%) for patients with benign or borderline MCNs, and long-term survival is also expected for 50-75% of patients with fully resected malignant tumors.
- The prognosis for unresectable malignant tumors is as bad as that of an unresected ductal adenocarcinoma. Resection of most of these tumors can be performed with resultant low morbidity and mortality rates. Several studies confirm these findings (see Recurrence and Survival and prognosis in the Intervention section).
Sex
Women are predominantly affected, with a female-to-male ratio of 4:1 for MCN.
- Most reported case series demonstrate that IPMTs occur primarily in men with a mean age of 65 years, in contrast to the female predominance in MCN.
- MPD IPMT has an equal sex distribution.
Age
The mean age of patients is 55 years for MCN and 65 years for IPMT.
Anatomy
The pancreas is a lobulated retroperitoneal organ. It has a slender configuration and a length of 12-20 cm, depending on the patient's build. It weighs 60-100 g but often shows atrophy in the elderly. It does not have a true capsule and merges with the retroperitoneal fat; this feature accounts for its lobulated contour, which is more evident on CT than on sonography. This contour becomes more prominent with age.
As with other organs, the pancreas shows craniocaudal movement with respiration. However, being retroperitoneal and limited above by the celiac-axis origin from the aorta, the pancreas shows far less movement than the liver, spleen, and kidneys. Movement between inspiration and expiration is usually less than 1 cm, but movement up to 3.5 cm has been reported.
The pancreas lies on the posterior abdominal wall with its head in the C of the duodenal loop. The body and tail extend obliquely upward to the left, the pancreatic tail lying in the lienorenal ligament adjacent to the spleen and the upper pole of the left kidney. The head of the pancreas has an uncinate process that extends posteroinferiorly around the superior mesenteric vein at the portal vein origin. The uncinate process extends inferior to the main body of the pancreas; thus, it is important to scan the full extent of the pancreas, or carcinoma of the uncinate process may be missed.
The pancreas lies in the anterior pararenal space. The head lies within the curve of the duodenal loop with the inferior vena cava (IVC) and right renal vessels lying posteriorly. The common bile duct (CBD) receives the MPD as it passes through the pancreatic head and then drains into the second part of the duodenum at the ampulla of Vater. The gastroduodenal artery may be seen anteriorly at the pancreatic head and neck. The head of the pancreas is the most bulbous part of the gland, which then narrows at the neck.
The union of the superior mesenteric and splenic veins forming the portal vein posteriorly marks the anatomic position of the pancreatic neck. The pylorus and gastroduodenal artery lie anteriorly. The lesser sac lies anterior to the body of pancreas, while the splenic vein runs along its posterosuperior surface. The tail of the pancreas is related to the spleen, left adrenal glands, and upper pole of the left kidney.
Presentation
Clinical findings
Signs and symptoms
In 50% of cases, MCNs occur as an incidental finding as a cystic mass in patients with no prior history of jaundice. Patients can also present with vague symptoms, such as nonspecific abdominal pain and possibly a mass effect. Patients with malignant changes may have a history of weight loss and jaundice. As mentioned, diagnostic methods are important because of the known indolent nature of MCNs. Furthermore, mucinous cystadenoma, cystadenocarcinoma, and IPMTs must be differentiated from serous cystadenoma, as all have differing biologic characteristics.1
levels of cystic carcinoembryonic antigen (CEA) can be increased in the mucin content of the cysts, which proportionally rises with the degree of malignancy of the tumor. Although mucinous pancreatic tumors are often hypervascular, GI bleeding is infrequent. In most cases, bleeding is from gastric varices, which develop from splenic vein obstruction as a result of compression or venous invasion from the tumor. Rarely, bleeding can be the result of direct stomach or duodenal invasion by the tumor. A frequent clinical finding is a palpable, firm, and nontender abdominal mass, which the patient often detects before he or she seeks medical help.
MCNs of the pancreas are low-grade malignant tumors with an insidious natural history. They can present with malignant symptoms of weight loss and jaundice. In severe cases, an acute illness occurs as a result of CBD obstruction. The main focus of investigation relies on diagnostic accuracy, as early and complete resection can offer a possibility of cure.
Pancreatitis and jaundice secondary to ductal obstruction are common in IPMTs of the pancreas. However, the incidence and severity of the complications of obstruction are not well documented. Pancreatic or CBD obstruction in IPMT may result in acute, life-threatening disease. Patients frequently present with abdominal pain or pancreatitis, and they may be found to have a past history of recurrent pancreatitis. Aggressive surgical therapy is warranted before development of complications of ductal obstruction or progression of tumor.2
Rarely, IPMT manifests as new-onset diabetes. However, more frequently, IPMT is detected on cross-sectional imaging performed for the evaluation of nonspecific abdominal pain.
Associated abnormalities
A variety of abnormalities have been reported in association with mucinous pancreatic cystic tumors. These include hypertension, diabetes mellitus, peptic ulcer, and biliary disease. The incidence of other neoplasms and deep venous thrombosis is also increased.
Differential diagnosis
The differential diagnosis includes the following: pancreatic pseudocyst or pancreatic fluid collections, serous cystadenomas, pancreatic abscess, benign pancreatic cysts, retention pancreatic cysts, parasitic cysts, lymphoepithelial cysts (LECs), pancreatic dermoid cysts, pancreatic hematoma and traumatic pancreatitis, von Hippel-Lindau (VHL) syndrome, papillary pancreatic tumors, dysontogenic cysts, pseudoaneurysms, retroperitoneal neurofibroma or schwannoma, obstructed roux loop, duodenal diverticula, gastric/duodenal leiomyosarcoma or leiomyoma, pancreatic sarcoma, pancreatic lymphoma, pancreatic metastases, and pancreatic tuberculosis.
Pancreatic pseudocyst or pancreatic fluid collections
Fluid collections occur in as many as 50% of cases of acute pancreatitis. Pseudocysts are usually seen as anechoic fluid spaces on sonograms, but they may show internal echoes if they contain necrotic tissue or clot. Small fluid collections are often transient, and fluid collections smaller than 5 cm in diameter may be treated conservatively. They may dissect tissue planes; therefore, they can appear at a distance from the pancreas.
Patients with pseudocysts often report a history of acute or chronic pancreatitis. However, patients with cystic tumors lack this history.
Imaging findings that suggest a diagnosis of pseudocyst rather than cystic neoplasms include the following: lack of septae, loculations, solid components, or cyst-wall calcifications on CT; hypovascularity on angiograms; and communication between the cyst and pancreatic ducts on endoscopic retrograde cholangiopancreatography (ERCP). Most pseudocysts are extrapancreatic, whereas pancreatic cystic neoplasms are intrapancreatic.
Fine-needle aspiration (FNA) of pseudocyst contents reveals high levels of amylase. When in doubt, it is better to resect a pseudocyst than to observe or drain a pancreatic cystic neoplasm, which allows tumor progression to unresectability, metastasis, and death.
Serous cystadenomas
Serous cystadenomas (microcystic adenomas) are the second most common cystic tumors of the pancreas. The clinical presentation of serous cystadenomas is similar to that of mucinous cystic pancreatic tumors.
An association with VHL disease has been described. Most patients present with nonspecific symptoms of vague abdominal pain or discomfort, but many have a palpable mass. These tumors can be large, with a size of 1-25 cm. Because of increasing use of cross-sectional imaging, many of these tumors are detected as an incidental, asymptomatic finding.
On gross pathologic inspection, serous cystadenomas consist of well-circumscribed, externally lobulated pancreatic tumors. On cross-sectional images, these appear as numerous tiny cysts separated by delicate fibrous septae, which give them a honeycomb appearance. The cysts are filled with clear, watery fluid and are often arranged around a central stellate scar, which may be calcified. On CT scans, sunburst central calcification in a spongy mass is pathognomonic of this tumor, but this finding occurs only in 10% of patients. Endoscopic ultrasonography (EUS) allows better resolution of the honeycomb structure than CT. At times, the cysts may be large, a feature that makes it difficult to differentiate these cysts from MCNs.
Hypervascularity may be demonstrated on angiograms, and some tumors occur with intra-abdominal hemorrhage. Analysis of the cyst fluid characteristically reveals low viscosity and low levels of CEA, with negative cytologic results for malignant cells, as the vast majority of serous cystadenomas are benign.
Serous cystadenocarcinomas have been described, but they are exceedingly rare and account for fewer than 1% of known cases. It is safe to observe small, asymptomatic serous cystadenomas, as the risk of malignant degeneration is extremely small. Some serous cystadenomas show continued growth; therefore, surgery is indicated, because complications such as hemorrhage, obstructive jaundice, pancreatic insufficiency, or gastric outlet obstruction can result.
Surgical resection is the treatment of choice for symptomatic tumors and tumors that show continuous growth. Many of these tumors may require a Whipple procedure or distal pancreatectomy, depending on the anatomic location. Distal pancreatectomy may be performed and the spleen can be preserved, given the absence of malignant potential.
Pancreatic abscess
Pancreatic abscess is usually secondary to infection of a pseudocyst, but in rare cases, it can occur as a result of direct spread from renal or colonic infection. Typically, a pancreatic abscess occurs 2-4 weeks after an episode of acute pancreatitis.
On images, these abscesses may appear similar to pseudocysts. Generally, the appearance depends on their age. In the acute phase, the changes may be subtle, with only loss of normal pancreatic contour associated with obliteration of the pancreatic outline and the peripancreatic vascular and other soft tissue spaces. These changes may be indistinguishable from those found in severe acute pancreatitis. In the subacute and chronic stages, when central necrosis occurs, an anechoic or complex cystic mass is usually seen. A debris level may be observed in the dependent portion of the abscess. In the subacute or chronic phase, through transmission is usually good except when gas is present within the abscess. In the presence of gas, the abscess may become echogenic and may shadow.
The walls of subacute and chronic pancreatic abscess have variable features. The walls may be thick, irregular, and well defined, or the abscess may have no definable wall at all. The sonographic findings are nonspecific, but in the appropriate clinical setting, a diagnosis of an abscess may be suggested and confirmed by means of percutaneous aspiration or CT.
Benign pancreatic cysts
Unlike cysts in the liver and kidneys, asymptomatic simple pancreatic cysts are uncommon. Most congenital pancreatic cysts are discovered in infants and children. Pancreatic cysts occur in a small percentage of patients with autosomal dominant polycystic kidney disease. Macroscopic pancreatic cysts are occasionally seen in patients with cystic fibrosis.
On sonograms, congenital cysts appear as well-defined, anechoic masses with good through transmission. The walls are smooth with no intramural excrescences or septations. Associated renal and hepatic cysts may be seen. Congenital cysts normally occur on the background of an otherwise normal-looking pancreas.
The differential diagnosis includes cystic neoplasms, pancreatic pseudocysts, and acquired cysts. Most congenital cysts occur in children, whereas cystic neoplasms occur in adults. Patients with pseudocysts often have a previous history of acute pancreatitis, and the lesions are often seen on a background of inflammatory pancreatic disease. Congenital pancreatic pseudocysts have been described in neonates; these lesions sometimes reach giant proportions.
Like pseudocysts, retention cysts are a complication of pancreatitis, usually a chronic, calcific type occurring in alcoholic patients. Alcohol causes precipitation of protein within the pancreatic duct, resulting in a protein plug that blocks the duct. Such blockage leads to proximal duct dilatation, forming a cyst.
These cysts are usually small (1-2 cm in diameter) and asymptomatic. However, in rare cases, these cysts may reach enormous proportions and no longer remain within the confines of the pancreas. Retention cysts have also been reported with ampullary stenosis and pancreatic carcinoma. Ultrasonography may reveal the underlying pancreatic abnormality (calcific pancreatitis) and small cysts in continuity with a dilated pancreatic duct. Stigmata of alcoholic liver disease may be present.
Parasitic cysts
Both echinococcus granulosis and multilocularis cysts of the pancreas have been described, though pancreatic involvement is exceptionally rare. Echinococcus granulosis cysts may be unilocular, multilocular, or complex cystic.
On imaging alone, differentiation of these and other cystic masses is difficult. Serologic tests may be useful in the appropriate clinical setting. Echinococcus multilocularis cysts show an echogenic infiltrative pattern. This diagnosis should be entertained in endemic regions when such a pattern is seen.
Lymphoepithelial cysts
LECs of the pancreas are extremely rare. The pathologic features of LEC are well-defined, epithelia-lined cysts surrounded by a rim of lymphoid tissue. They present predominantly in middle-aged or elderly males with nonspecific symptoms such as abdominal pain and diarrhea. Ultrasonography, particularly EUS, is a sensitive means of diagnosing pancreatic cysts.
LECs are mainly cystic structures. However, they are not completely transonic, and they do contain some debris as a result of their keratin content. Cystic neoplasms and pseudocysts may have a similar appearance. As with some pseudocysts, an elevated CEA level is found in LEC aspirates; therefore, an elevated CEA level is not reliably predictive of malignancy.
Pancreatic dermoid cysts
Dermoid cysts within the pancreas are rare, but they do have some distinctive features. Besides the cystic component teeth, fat, bone and calcification may be found in these masses. However, it is not always possible to differentiate these masses from other neoplasms.
Pancreatic hematoma and traumatic pancreatitis
Although the pancreas moves with respiration, it is similar to other retroperitoneal organs in that it is relatively fixed compared to overlying bowel. Therefore, the pancreas is prone to injury due to blunt abdominal trauma when it is compressed against the spine. The pancreas is involved in 3-12% of abdominal injuries as a result of seat-belt or steering-column impact.
A mortality rate as high as 20% has been reported with pancreatic injuries, as these are often associated with trauma to other organs, such as the duodenum. Injury to the duodenum may give rise to an intramural hematoma obstructing the bowel lumen. Delayed retroperitoneal perforation of the duodenum may be present. Injury to the pancreas may also cause contusion or rupture. Rupture may be complete or incomplete, but both frequently cause pancreatitis and fluid collections or pseudocysts.
Pseudocysts usually form anteriorly, but they may be adjacent to any part of the gland and, occasionally, distant. Pancreatic lacerations are diagnosed when the loss of contiguity is present, but this finding may be masked by inflammation. Although sonography is excellent for showing fluid collections, patients are often immobile and often have gaseous distention, making CT a more suitable diagnostic study. Moreover, CT permits imaging of the retroperitoneum.
VHL syndrome
VHL syndrome is an autosomal dominant condition with variable penetrance and delayed expression. (For example, it is reported in identical twins.) Tumors and/or cysts occur in the central nervous system, genitourinary system, liver, spleen, pancreas, and adrenal glands. Cysts are found throughout the pancreas and vary from a few millimeters to 10 cm. These cysts are benign and usually give rise to symptoms when the CBD is obstructed.
Microcystic adenoma (serous cystadenoma) is associated with VHL syndrome and is an externally lobulated mass consisting of multiple small cysts separated by thick-walled stroma. The cysts are lined by cuboidal epithelium that is rich in glycogen but contains no mucin. These tumors are benign and not premalignant; they give rise to symptoms due to mass effect when they are large.
Mucinous cystadenoma is premalignant and is not associated with VHL. Microcystic adenoma may appear solid on sonograms because of the multiple interfaces caused by the cysts of varying sizes, mostly small ones. Other pancreatic tumors reported with VHL include adenoma, hemangioblastoma, and adenocarcinoma of the pancreas and ampulla of Vater. Islet cell tumors appear to be unrelated to pancreatic cystic disease in VHL. These lesions are frequently associated with pheochromocytoma.
A number of endocrinopathies have been reported with pancreatic islet cell tumors in VHL. These tumors are solid initially, but as they grow, central necrosis may occur. They may contain calcification. Because of their small size at presentation, they may not be visualized on sonograms. However, intraoperative sonography is extremely useful in identifying and staging these tumors.
Solid and papillary epithelial pancreatic tumors
Solid and papillary epithelial neoplasm of the pancreas may be solid or cystic. These are rare tumors often mistaken for mucin-secreting tumors or nonfunctioning adenomas. They represent a low-grade malignancy, which affects women 9 times more often than men; the average patient age is 27 years.
These tumors are most often located in the pancreatic tail. They are large, well-encapsulated masses with areas of hemorrhage and necrosis. On sonograms, they appear as heterogeneous, round, solid masses with a cystic necrotic center and dystrophic calcification, which may shadow.
Dysontogenic cysts
Dysontogenic cysts are hamartomatous cysts that are often associated with renal cysts, cerebellar angiomas, and encephaloceles. Imaging reveals a large, thin-walled cyst with a mulberry configuration.
Pseudoaneurysms
Pseudoaneurysms are usually not truly intrapancreatic, and they may be confused with a pancreatic cyst. These aneurysms are a complication of pancreatitis in 3.5-10% patients. Doppler sonography may show turbulent arterial flow within a pseudoaneurysm, whereas color flow Doppler sonography shows bidirectional flow and swirling within the anechoic mass. Doppler imaging may permit tentative identification of the artery feeding the pseudoaneurysm.
Retroperitoneal neurofibroma or schwannoma
These tumors may be hyperechoic or hypoechoic/cystic lesions with sporadic internal echoes. This is a common feature in larger tumors in which cystic degeneration and hemorrhage has occurred. The tumors are retroperitoneal but may mimic pancreatic masses.
Obstructed Roux loop
Obstructed Roux loop after pancreatic cancer or bile duct surgery may appear as a cystic mass in the pancreatic bed. Sonography demonstrates an obstructed Roux loop as well as a patent biliary-enteric anastomosis. Echoes due to gas with or without comet-shaped artifacts are usually demonstrated.
Duodenal diverticula
Duodenal diverticula may mimic pancreatic neoplasms on sonograms, as they may have both complex and cystic appearances and may cause obstructive jaundice. Duodenal diverticula are a common finding and typically asymptomatic. When filled with gas or a combination of fluid and gas, duodenal diverticula are easily recognized on CT scans or MRIs. However, a duodenal diverticulum that is entirely filled with fluid may mimic a cystic neoplasm arising from the head of the pancreas.
Macari and associates described 7 patients with duodenal diverticula in whom initial CT or MRI findings were suggestive of a cystic neoplasm in the head of the pancreas. Recognizing the location in which duodenal diverticula characteristically arise and identifying small amounts of intradiverticular gas when present may aid diagnosis in patients with duodenal diverticula. With careful sonography, it is possible to demonstrate the presence of air in the diverticulum and its continuity with the duodenum. ERCP results may be diagnostic.
Gastric/duodenal leiomyosarcoma and leiomyoma
These tumors represent complex masses with a multicystic component. They may be confused with pancreatic masses, but careful scanning usually suggests their origin in bowel.
Pancreatic sarcoma
Pancreatic sarcoma is a rare tumor of the mesenchymal supporting structures of the pancreas. It is a relatively sonolucent mass and may be mistaken for a fluid collection or pseudocyst. Sonographic results may be normal, or sonograms may demonstrate a retroperitoneal mass, which is relatively sonolucent compared with the surrounding tissues. Therefore, this lesion may be confused with a cystic pancreatic mass.
Pancreatic lymphoma
Primary pancreatic lymphoma is rare. The clinical presentation is not unlike that of pancreatic carcinoma. Sonography may reveal a homogeneous, sonolucent, or complex mass. These masses are usually echo-poor and may mimic cystic lesions. As the prognosis of a pancreatic lymphoma is favorable, its differentiation from a carcinoma is crucial. The correlation of sonographic, CT, and angiographic findings may result in a correct diagnosis. However, if doubt exists, sonography-guided biopsy may reveal the true nature of the mass.
Pancreatic metastases
A variety of tumors may metastasize to the pancreas. Patients may present with acute pancreatitis due to pancreatic duct obstruction. The initial findings in this instance may be those of inflammatory disease of the pancreas complicated by pseudocysts and pancreatic ascites. Most metastases are solid, but cystic metastases may occur, particularly those from cystadenocarcinoma of the ovary and melanoma. A solitary pancreatic metastasis cannot normally be differentiated from a primary pancreatic tumor on CT scans or sonograms.
Pancreatic tuberculosis
Pancreatic tuberculosis is extremely rare and is frequently misdiagnosed as a pancreatic neoplasm.
Liu et al described a 33-year-old man with a 6-month history of vague, intermittent right epigastric pain and weight loss. They found a solitary pancreatic cystic mass and diagnosed it as pancreatic cystadenocarcinoma. Abdominal sonograms showed an irregular, hypoechoic lesion of 6.6 X 4.4 cm in the head of the pancreas. The lesion was avascular on color Doppler flow images. Attempts to obtain pathologic evidence of the lesion by sonography-guided percutaneous FNA failed, and an exploratory laparotomy and incisional biopsy revealed a caseous abscess of the head of the pancreas without typical changes of tuberculous granuloma. However, results of acid-fast staining were positive.
Preferred Examination
Ultrasonography is generally the first imaging technique in a patient with epigastric symptoms. This is an excellent modality for the diagnosis of cystic pancreatic masses. Sonography also provides an opportunity for guided intervention, such as aspiration and biopsy. Doppler sonography provides an added benefit in the evaluation of hypervascular tumors and vascular thrombosis/occlusion associated with pancreatic tumors. Echo-enhanced power Doppler sonography has high sensitivity and specificity in the differential diagnosis of pancreatic tumors.3
From the current data, EUS appears to be reliable in distinguishing between most benign lesions and neoplastic cystic lesions. In equivocal cases or in cases in which malignancy is highly suspected, EUS-guided FNA gives the best diagnostic yield, as it permits the acquisition of cytologic samples and cystic fluid for the analysis of various tumor markers.
Occasionally, despite complete evaluation of a cystic mass, the type of cyst may remain indeterminate.4 Although expensive and invasive, laparoscopic sonography, biopsy of the cyst wall, and analysis of the cystic aspirate significantly contribute to the differential diagnosis of pancreatic cystic lesions. Plain radiographs are often obtained to look for pancreatic calcification. Upper GI barium studies may be performed in the context of epigastric pain. With pancreatic tumors, barium studies may depict extrinsic displacement of the stomach and duodenum.
Spiral and/or multisection CT is an excellent modality in imaging the pancreas, providing superb spatial resolution and anatomic detail. With thin collimation and arterial and venous phases and multiplanar and/or 3-dimensional (3D) reconstructions excellent detail of the vascular anatomy is depicted, and most centers now seldom use angiography to assess pancreatic tumors.
ERCP is the examination of choice for visualizing pancreatic and biliary duct anatomy, ductal displacement, ductal encasement, intraductal tumor, and filling of the tumor cavity with contrast material. ERCP results may establish a diagnosis of IPMT and permit its differentiation from a pseudocyst or cystic neoplasm of the pancreas. These techniques may also be used to assess the risk of malignancy and the extent of disease. They also allow tissue sampling and enable therapeutic intervention.5
Angiography provides evidence of neovascularity, venous compression/invasion, and invasion of contiguous organs. CT shows tumor calcification and is an excellent modality for the detection of local and distant metastases. Although CT and MRI cannot be used to differentiate mucin content from pancreatic juice, communication between the cystic lesion and the dilated MPD and a bulging papilla with a patulous orifice are characteristics of IPMT. The internal architecture of mucinous tumors is displayed equally well, if not better, with MRI than with CT; the exception is the limited ability of MRI to reveal calcification within the lesion. MRI is an evolving modality and appears to be an excellent technique for the diagnosis of cystic pancreatic tumors. MRIs are usually helpful in differentiating between pseudocysts and cystic neoplasms.
Magnetic resonance cholangiopancreatography (MRCP) can depict biliary and pancreatic duct anatomy noninvasively, and it helps with the diagnosis of intraductal tumors.
Limitations of Techniques
Visceral gas, patient habitus, and operator dependency limit the value of sonography. Laparoscopic ultrasonography is invasive. Plain radiographs and upper GI barium studies are nonspecific, and similar findings may be encountered in a variety of pathologies. CT carries a significant ionizing radiation burden and uses iodinated contrast material with a risk of anaphylaxis and nephrotoxicity. MRI is not universally available and is expensive, and it also causes problems in patients with claustrophobia.
Cross-sectional studies, including ultrasonography, CT, and MRI, cannot be used to distinguish between mucinous cystadenoma and cystadenocarcinoma unless the tumor has metastasized or invaded neighboring organs. Angiography is once again nonspecific and invasive. It also requires iodinated contrast medium, with the risk of anaphylaxis and nephrotoxicity.
Differential Diagnoses
| Pancreas, Adenocarcinoma | Pancreatic Pseudocysts |
| Pancreas, Islet Cell Tumors | Von Hippel-Lindau Syndrome |
| Pancreas, Serous Cystadenoma | |
| Pancreatic Cancer | |
| Pancreatic Necrosis and Pancreatic
Abscess |
Other Problems to Be Considered
Pancreatic pseudocyst or pancreatic fluid collection
Serous (microcystic) cystadenoma
Pancreatic abscess
Benign pancreatic cyst
Retention pancreatic cyst
Parasitic cyst
Lymphoepithelial cyst
Pancreatic dermoid cyst
Pancreatic hematoma and traumatic pancreatitis
von Hippel-Lindau disease
Solid and papillary epithelial neoplasm
Dysontogenic cyst
Pseudoaneurysm
Retroperitoneal neurofibroma or schwannoma
Obstructed roux loop
Duodenal diverticula
Gastric, duodenal leiomyosarcoma, or leiomyoma
Pancreatic sarcoma
Pancreatic lymphoma
Pancreatic metastasis
Pancreatic tuberculosis
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References
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Further Reading
Related eMedicine topics
Pancreas, Intraductal Papillary Mucinous Neoplasm
Pancreas, Serous Cystadenoma
Pancreas, Adenocarcinoma
Biliary Cystadenoma/Cystadenocarcinoma
Papillary Tumors
Clinical guidelines
ASGE Guideline: The Role of Endoscopy in the Diagnosis and the Management of Cystic Lesions
and Inflammatory Fluid Collections of the Pancreas
ASGE Guideline: The Role of ERCP in Diseases of the Biliary Tract and the Pancreas
Clinical trials
EUS-Guided Pancreatic Injection of Cyst (EPIC) Trial
Keywords
mucinous cystic neoplasm of pancreas, MCN, macrocystic cystadenoma, cystadenocarcinoma, mucinous duct ectasia, mucinous ductal ectasia, papillary adenocarcinoma, ductectatic tumor, intraductal mucin-secreting neoplasm, mucinous villous adenomatosis, intraductal mucin-producing tumor, intraductal cystadenoma, pancreatic duct villous adenoma, intraductal papillary neoplasms, intraductal papillary mucinous tumor, IPMT, MUC1, MUC2
