Imaging in Mucinous Cystic Neoplasms of the Pancreas
- Author: Ali Nawaz Khan, MBBS, FRCS, FRCP, FRCR; Chief Editor: John Karani, MBBS, FRCR more...
Mucinous cystic neoplasms (MCNs) of the pancreas are uncommon, and their diagnosis, treatment, and prognosis have yet to be uniformly determined in full. Differentiation of cystic lesions of the pancreas is difficult, as they can be benign (serous cystadenomas), inflammatory (pseudocyst of the pancreas), or malignant. The radiologic characteristics of MCNs are demonstrated in the images below.
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. IPMTs are seen in the images below.
MCNs develop predominantly in the tail of the pancreas (>90%). Compared with serous cystic tumors, MCNs are larger (>20 mm in diameter) and less numerous (usually < 6).
The biologic behavior of MCNs 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.
Imaging in differential diagnosis
The differential diagnosis of MCNs includes the following:
Pancreatic pseudocyst or pancreatic fluid collections
Benign pancreatic cysts
Retention pancreatic cysts
Lymphoepithelial cysts (LECs)
Pancreatic dermoid cysts
Pancreatic hematoma and traumatic pancreatitis
Von Hippel-Lindau (VHL) syndrome
Papillary pancreatic tumors
Retroperitoneal neurofibroma or schwannoma
Obstructed roux loop, duodenal diverticula
Gastric/duodenal leiomyosarcoma or leiomyoma
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.
Imaging findings that suggest a diagnosis of pseudocyst rather than of cystic neoplasm include the following: lack of septae, loculations, solid components, or cyst-wall calcifications on computed tomography (CT) scans; 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.
Serous cystadenomas (microcystic adenomas), seen in the images below, 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.
Because of increasing use of cross-sectional imaging, many of these tumors are detected as an incidental, asymptomatic finding.
On cross-sectional images, serous cystadenomas appear as numerous tiny cysts separated by delicate fibrous septa, 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 does 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.
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.
These cysts are usually small (1-2 cm in diameter) and asymptomatic. However, in rare cases, they 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.
Echinococcus granulosis cysts and multilocularis cysts of the pancreas have been described, although pancreatic involvement is exceptionally rare. E. 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. E. multilocularis cysts show an echogenic infiltrative pattern. This diagnosis should be entertained in endemic regions when such a pattern is seen.
Solid and papillary epithelial pancreatic tumors
Solid and papillary epithelial neoplasm of the pancreas may be solid or cystic. These are rare tumors that are often mistaken for mucin-secreting tumors or nonfunctioning adenomas.
Solid and papillary epithelial pancreatic 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 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 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% of 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 may mimic pancreatic neoplasms on sonograms, as they may have 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 or magnetic resonance imaging (MRI) scans. However, a duodenal diverticulum that is entirely filled with fluid may mimic a cystic neoplasm arising from 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 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.
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.
A solitary pancreatic metastasis cannot normally be differentiated from a primary pancreatic tumor on CT scans or sonograms.
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.[1, 2, 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 fine-needle aspiration (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. 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.
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.
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 at least as well on MRI scans as it is on CT scans, with the exception of calcification within the lesion (which MRI has only a limited ability to reveal).
Spiral and/or multisection CT are excellent techniques for 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; most centers now seldom use angiography to assess pancreatic tumors.
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 in 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, is expensive, and poses a problem for 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 nonspecific and invasive. It also requires iodinated contrast medium, with the risk of anaphylaxis and nephrotoxicity.
In a retrospective study of 150 patients with 166 incidentally discovered pancreatic cysts, Das et al recommended that, particulary when cystic lesions are 3.0 cm or less in size and have no intracystic or mural nodules, follow-up imaging optimally be performed 2 years from baseline evaluation. The authors found that most incidentally detected cystic neoplasms of the pancreas did not have significant growth during follow-up.
Plain radiographs may show tumor calcification in 10-15% of cases of microcystic adenomas. Calcification in microcystic adenoma presents as a central cluster arranged in a sunburst or stellate arrangement (as seen in the image below). In mucinous-type tumors, calcification tends to occur at the periphery of the tumor or in the walls of the cysts and to appear curvilinear. CT is more sensitive for detecting calcification than is plain radiography.
Upper GI barium studies are nonspecific and usually show extrinsic displacement of the stomach or duodenum. As most symptomatic cystic neoplasms are large, these findings are not infrequent.
ERCP depicts ductal changes in cystic tumors of the pancreas in approximately 80% of patients. ERCP may show duct displacement, stretching, encasement, duct ectasia, cystic tumor filling, and tumor in the duct as a filling defect and duct obstruction. ERCP in MCN rarely shows cyst communication with pancreatic ducts, but it frequently shows duct displacement by mass effect or ductal obstruction.
ERCP results may establish the diagnosis of IPMT and permit its differentiation from a pseudocyst or cystic neoplasm of the pancreas. It may also help in assessment of the risk of malignancy, evaluation of the extent of disease, acquisition of tissue samples, and enablement therapeutic intervention. ERCP typically shows a patulous ampulla of Vater with discharging mucus, which is often diagnostic for IPMT. Other findings on ERCP include the following: main duct dilation, filling defects (viscid mucus), and communication between cystic areas and the MPD.
Degree of confidence
ERCP can be used to attempt to differentiate mucinous cystadenoma from cystadenocarcinoma. ERCP typically shows a patulous ampulla of Vater with discharging mucus (as demonstrated in the image below), which is often diagnostic for IPMT. Although no finding is an absolute indicator of benign and malignant disease, obstruction occurs in 60% of malignant lesions and in 2.5% of cases of benign disease. It can be assumed that these ductal changes can also be demonstrated by MRCP. ERCP remains the imaging modality of choice for diagnosis of IPMT.
Reflux of contrast material due to mucin blobs or mural nodules may hinder filling of the ducts in IPMT on ERCP, causing diagnostic difficulties.
There are several causes of calcification in the pancreatic bed; these include chronic pancreatitis, pancreatic hemorrhage, abscess, infarction, hyperparathyroidism, cystic fibrosis, and kwashiorkor. Many pancreatic tumors can become calcified, including adenocarcinoma (rare), islet cell tumor, microcystic adenoma–sunburst calcification, MCN (macrocystic cystadenoma), cavernous lymphangioma, hemangioma, and colonic carcinoma metastases.
Abnormalities on upper GI barium series are also nonspecific and can be caused by many neoplastic and nonneoplastic masses near the stomach and duodenum. Pancreatic duct calculi and chronic pancreatitis may mimic IPMT, and vice versa.
This section discusses mucinous cystic neoplasms and, specifically, intraductal papillary mucinous tumors.
Mucinous cystic neoplasms
Nonenhanced CT scans show a well-defined, unilocular or multilocular, externally smooth, round-to-ovoid mass with fluid attenuation. (See the image below.)
The attenuation values of the multilocular cysts vary according to the degree of hemorrhage or protein in the mucoid cysts. Larger cysts may demonstrate small daughter cysts along their internal surface. Typically, they show a well-defined, multilocular cystic mass with thick internal septa separating the different cystic cavities of varying sizes. The cysts are 2-26 cm. (See the images below.)[7, 8]
Visualization of nodular or papillary excrescences with irregular borders of the septa is possible. If present, calcification is curvilinear or punctate and confined to the cyst wall or septa. Contrast-enhanced CT scans show enhancement of the cyst wall, internal septations, mural nodules, and other intracavitary projections. CT may also allow the identification of solid components associated with cystic elements, which are features of borderline or malignant tumors but not benign variants. CT more clearly demonstrates enhancement of cystic walls and septa than do other studies.
Intraductal papillary mucinous tumors
Main ductal IPMTs may be focal or diffuse, findings that are reflected on imaging. However, main duct tumors may be difficult to differentiate from chronic pancreatitis, as the imaging features may be similar. Examples of IPMTs are presented below.
In the early stages of focal or segmental involvement by IPMT, the features may be difficult to differentiate from focal chronic obstructive pancreatitis on cross-sectional imaging. In these cases, the findings on ERCP may be diagnostic. Rarely, segmental pancreatic duct dilatation may acquire a cystic appearance, whereas the MPD and the rest of the pancreas appear normal. Cases with a cystic appearance may mimic a peripheral MCN. However, with a peripheral MCN, the pancreatic duct is almost always normal in appearance.
When the tumor involves the head of the pancreas, imaging reveals upstream dilatation of the pancreatic duct.
IPMT can be more confidently diagnosed when imaging reveals a filling defect in the main duct or a branch pancreatic duct. The filling defects are hyperechoic on sonograms, high-attenuating on CT scans, and hypointense on T2-weighted MRIs relative to the surrounding fluid.
When there is diffuse involvement of the MPD, dilatation is present along the whole length of the pancreatic duct. This dilatation is often associated with diffuse and generally uniform pancreatic atrophy. These features may be difficult to differentiate from those of chronic pancreatitis. However, dilatation of a branch duct is a frequent finding in IPMT, and the presence of mural nodules and mucin blobs is another finding that may be a clue to the diagnosis.
In late cases with advanced disease, mass effect from the tumor may cause common bile duct (CBD) compression and dilatation of the biliary tree and compression or displacement of the stomach and duodenum. Pancreatobiliary fistula may be a late complication. Advanced stages of the disease may be complicated by pseudomyxoma peritonei as a result of dissemination of the disease to the peritoneum and retroperitoneum. Peritoneal seedlings can be identified as small foci that appear hyperechoic on sonography and hyperattenuating on CT.
Branch-duct IPMTs may be easier to identify than main-duct IPMTs, as the former generally appear as mass lesions on imaging. When these lesions are small, they are commonly an incidental finding in patients undergoing imaging for unrelated conditions. Branch IPMT is most frequently encountered in the region of the uncinate process. Branch IPMT may be microcystic or macrocystic.
The microcystic variety may mimic serous cystadenomas/cystadenocarcinomas on imaging, but communication with the MPD (which is frequently dilated) may be a clue to the diagnosis. The macrocystic variety must be differentiated from other cystic masses.
The thickness of the cyst wall and septa is variable with benign tumors; they tend to be thin and regular. In malignant tumors, the walls and septa appear irregular and thick, with solid nodules.
Degree of confidence
CT findings can be highly specific and are usually sufficient for a confident diagnosis. Bulging of the papilla into the duodenal lumen is virtually diagnostic of IPMT and is well demonstrated with CT and MRI.
CT is not useful for differentiating mucinous cystadenoma from cystadenocarcinomas, with the exception that papillary excrescences suggest malignancy and metastases prove malignancy. Mural nodules in IPMT can be difficult to differentiate from mucin blobs, as a clear attachment of the mural nodules to the pancreatic duct wall must be demonstrated; this may be difficult to define. However, mural nodules tend to enhance after the intravenous administration of contrast material, whereas mucin blobs do not.
When IPMT involves the entire MPD, differentiation from chronic pancreatitis may not be possible on imaging.
Kluger et al describe a potential false-positive CT finding for a mucinous cystic neoplasm in the head of the pancreas. The authors present a case of a 49-year-old woman with 2 years of intermittent epigastric pain found to have an 8.5-cm head-of-the-pancreas mass on CT. CT findings were suggestive of a mucinous cystic neoplasm for which she underwent pancreaticoduodenectomy. Histology revealed a bronchogenic cyst of the head of the pancreas.
Bronchogenic cysts of ventral foregut origin can migrate into the abdomen prior to fusion of the diaphragm. These cysts can easily be misinterpreted as benign and malignant retroperitoneal lesions. Both mucinous cystic neoplasms and bronchogenic cysts can undergo malignant transformation. They can also become infected and hemorrhagic; with increasing use of high-resolution cross-sectional imaging, the frequency is likely that more of these lesions would be recognized. The final diagnosis is offered by histology by the presence of ciliated respiratory epithelium and cartilage on pathology, which provides definitive diagnosis.
Magnetic Resonance Imaging
The radiologic findings on cross-sectional imaging correlate well with the macroscopic features of mucinous cystadenoma and cystadenocarcinoma. Cystic lesions in MCN are hypointense or hyperintense on T1-weighted MRIs depending on protein content. Breathing-independent T2-weighted images, such as half-Fourier acquired single-shot turbo spin-echo (HASTE) images, show multiple hyperintense cysts separated by multiple hypointense septa. Intracystic excrescences and mural nodules also have low signal intensity, but they enhance significantly with gadolinium-based contrast agents. (See the images below.)
Gadolinium-based contrast agents (gadopentetate dimeglumine [Magnevist], gadobenate dimeglumine [MultiHance], gadodiamide [Omniscan], gadoversetamide [OptiMARK], gadoteridol [ProHance]) have been linked to the development of nephrogenic systemic fibrosis (NSF) or nephrogenic fibrosing dermopathy (NFD). For more information, see the eMedicine topic Nephrogenic Systemic Fibrosis. The disease has occurred in patients with moderate to end-stage renal disease after being given a gadolinium-based contrast agent to enhance MRI or MRA scans.
NSF/NFD is a debilitating and sometimes fatal disease. Characteristics include red or dark patches on the skin; burning, itching, swelling, hardening, and tightening of the skin; yellow spots on the whites of the eyes; joint stiffness with trouble moving or straightening the arms, hands, legs, or feet; pain deep in the hip bones or ribs; and muscle weakness. For more information, see Medscape.
MRCP allows depiction of pancreatic duct or CBD changes that may be associated with the tumors.
Differentiation between serous and mucinous neoplasms may be difficult on MRIs, as there is variability in the MRI appearance of serous cystadenomas and overlap with mucinous neoplasms. CT criteria can be applied to MRI, except that calcification is often missed on MRI. Most serous tumors require histologic confirmation.
MRCP is useful in differentiating between benign and malignant mucinous tumors, including IPMT of the pancreas. The presence of mural nodules is suggestive of malignancy; however, the absence of mural nodules does not indicate that the tumor is benign.
A maximum MPD diameter of greater than 15 mm and diffuse dilatation of the MPD are suggestive of malignancy in main duct–type tumors. Among branch duct–type tumors, malignant tumors tend to be larger than benign tumors; however, this finding is variable. The presence of MPD dilatation may be helpful in determining malignancy of branch duct-type tumors.
Degree of confidence
MRI is an excellent modality for the depiction of cystic pancreatic masses, showing their internal architecture to advantage.
As with other cross-sectional imaging techniques, several mimics of MCN can be depicted on MRIs. These include benign and malignant neoplastic cysts and cysts of inflammatory origin.
At presentation, mucinous cystic pancreatic neoplasms are usually larger than 5 cm. The walls of mucinous cysts are composed of thick, fibrous stroma that sometimes contain dystrophic calcification. Sonography reveals a large, cystic mass (as seen in the images below) that sometimes contains numerous septa, tumor excrescences, and debris. The tumors may be 2-23 cm, and they usually have sharply marginated walls and smooth borders. The cystic portions show a good through transmission. Sonograms typically show a multilocular, fluid-containing mass with good transmission and strong acoustic enhancement.
Microcystic adenomas (serous cystadenoma), an example of which is seen below, are mostly complex, with numerous internal echoes resulting in the appearance of an externally lobulated solid mass, sometimes with good through transmission. The central scar and calcification may be demonstrated on CT scans but are not well depicted on sonograms.
Although histologic studies remain the criterion standard for the differential diagnosis of pancreatic tumors, Rickes et al concluded in a report that echo-enhanced power Doppler sonography has a high sensitivity and specificity for such diagnosis.
In their study, the authors selected 137 patients with a mean age of 60 years and clinically suspected pancreatic tumors. The patients were assessed with conventional sonography and nonenhanced and echo-enhanced power Doppler sonography. The sensitivity of echo-enhanced power Doppler sonography with respect to diagnosing pancreatic carcinoma was 87%, and its specificity was 94%. The corresponding values for chronic pancreatitis were 85% and 99%, respectively.
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. When the lesion is differentiated from other cystic masses and when the tumors are large and symptomatic, the best course of action is surgical resection. When small cystic lesions are encountered in asymptomatic patients, follow-up EUS may suffice.
Ikeda et al established EUS criteria for the follow-up of small cystic pancreatic lesions. Their guidelines can help in the decision-making process. The authors reported on 31 patients with pancreatic cystic lesions of unknown etiology who were followed-up with semiannual EUS over 3 years. In 87.1% of these patients, the lesions were smaller than 2 cm. The cystic lesions remained stable in 30 patients, and only 1 lesion increased in size. This lesion was resected and was found to be a retention cyst.
The criteria by Ikeda et al include the following: (1) a clear, thin wall; (2) a smooth contour; (3) a round or oval shape; (4) no septum or nodules; (5) an asymptomatic clinical presentation; and (6) no findings of chronic pancreatitis.
With the widespread use of advanced imaging techniques, cystic lesions of the pancreas are now diagnosed relatively frequently. The nature of these lesions varies from benign cysts (serous cystadenoma) or inflammatory processes (pseudocyst) to premalignant (mucinous cystadenoma) or frankly malignant (cystadenocarcinoma) lesions.
The differentiation of various types of pancreatic cysts presents a diagnostic and therapeutic challenge, as the clinical presentation may be vague. Laparoscopic ultrasonography (LAPUS), biopsy of the cystic wall, and analysis of the cystic aspirate significantly contribute to the differential diagnosis of pancreatic cystic lesions.
Degree of confidence
Ultrasonography is an excellent modality in depicting cystic structures and particularly advantageous to show the internal septa, mural nodules, and solid excrescences of the cyst wall. IPMT of the pancreas encompasses a spectrum of pathologies, ranging from benign conditions to malignant disease. IPMT must be differentiated from other cystic neoplasms of the pancreas, as well as from inflammatory cystic lesions.
Because the pancreas is near the gastric and duodenal loop, EUS is ideally suited for imaging the pancreas. Additionally, EUS facilitates FNA of pancreatic cysts and/or a dilated pancreatic duct for cytologic and tumor marker analysis.
LAPUS is expensive and invasive.
There is a wide differential diagnosis of cystic lesions in the pancreas, and therefore, the potential for false-positive results is significant. For smaller cystic lesions, a false-negative finding is possible in obese patients or in patients with gaseous distention.
Sperti et al concluded in a study that fluorodeoxyglucose (FDG) positron emission tomography (PET) is more accurate than CT scanning in identifying malignant pancreatic cystic lesions and should be used, in combination with CT and tumor marker assay, in the preoperative evaluation of patients with pancreatic cystic lesions. In 56 patients with a suspected cystic tumor of the pancreas, values for sensitivity, specificity, and positive and negative predictive values in detecting malignant tumors were, for FDG PET, 94%, 97%, 94%, and 97%, respectively. For CT scanning, these values were 65%, 87%, 69%, and 85%, respectively.
A study by Sendler and associates, however, indicated that PET does not allow the precise exclusion of malignant tumors and that, therefore, the use of invasive diagnostic procedures may not be reduced by employing this modality. In their study, FDG PET was performed in 46 patients admitted to the hospital for pancreatic tumor surgery. The resulting values for sensitivity and specificity were 86% and 67%, respectively.
With FDG PET, there is a potential for false-positive scans as a result of physiologic activity.
Mucinous cystic pancreatic tumors are usually hypovascular on angiography. The only vascularity present is in the walls, septa, and mural nodules. In cystadenocarcinoma, there might be narrowing or obstruction of the splenic artery and vein due to direct tumor encasement or invasion. Angiography may also depict metastases and contiguous organ invasion. (See the image below.)
Approximately 85% of microcystic adenomas are hypervascular or moderately vascular, and 84% are associated with parenchymal lucencies corresponding to cystic areas. The primary angiographic manifestations of microcystic adenomas are arterial displacement, arterial dilatation, and neovascularity; arterial encasement is unusual. Arteriovenous shunting is seen in 40% patients.
Degree of confidence
The findings on angiograms alone are nonspecific, and a similar appearance may occur with other benign and malignant tumors.
Low-grade vascularization may occur in benign and malignant pancreatic tumors. When MCNs have a low-grade vascularity or are avascular, differentiation from a pseudocyst may be difficult. Leiomyosarcoma and other retroperitoneal tumors may invade the pancreas and cause a similar angiographic appearance. Moreover, a variety of angiomatous lesions have been reported within the pancreas, with a potential for false-positive diagnosis of microcystic adenoma.
Hong HS, Kim MJ. [Diagnosis of pancreatic intraductal papillary mucinous neoplasm]. Korean J Gastroenterol. 2008 Oct. 52(4):207-13. [Medline].
Pai M, Habib N, Senturk H, Lakhtakia S, Reddy N, Cicinnati VR, et al. Endoscopic ultrasound guided radiofrequency ablation, for pancreatic cystic neoplasms and neuroendocrine tumors. World J Gastrointest Surg. 2015 Apr 27. 7 (4):52-9. [Medline].
Brugge WR. Diagnosis and management of cystic lesions of the pancreas. J Gastrointest Oncol. 2015 Aug. 6 (4):375-88. [Medline].
Michael H, Gress F. Diagnosis of cystic neoplasms with endoscopic ultrasound. Gastrointest Endosc Clin N Am. 2002 Oct. 12(4):719-33. [Medline].
Telford JJ, Carr-Locke DL. The role of ERCP and pancreatoscopy in cystic and intraductal tumors. Gastrointest Endosc Clin N Am. 2002 Oct. 12(4):747-57. [Medline].
Das A, Wells CD, Nguyen CC. Incidental Cystic Neoplasms of Pancreas: What Is the Optimal Interval of Imaging Surveillance?. Am J Gastroenterol. 2008 Jun 16. [Medline].
Grenacher L, Klauss M. [Computed tomography of pancreatic tumors]. Radiologe. 2009 Feb. 49(2):107-23. [Medline].
Fisher WE, Hodges SE, Yagnik V, Morón FE, Wu MF, Hilsenbeck SG, et al. Accuracy of CT in predicting malignant potential of cystic pancreatic neoplasms. HPB (Oxford). 2008. 10(6):483-90. [Medline].
Hong TM, Lee RC, Chiang JH. Intraductal papillary mucinous tumor of the pancreas: computerized tomography and magnetic resonance imaging features. Kaohsiung J Med Sci. 2003 Feb. 19(2):55-61. [Medline].
Kluger MD, Tayar C, Belli A, Salceda JA, Van Nhieu JT, Luciani A, et al. A foregut cystic neoplasm with diagnostic and therapeutic similarities to mucinous cystic neoplasms of the pancreas. JOP. 2013 Jul 10. 14(4):446-9. [Medline].
Sahani D, Prasad S, Saini S. Cystic pancreatic neoplasms evaluation by CT and magnetic resonance cholangiopancreatography. Gastrointest Endosc Clin N Am. 2002 Oct. 12(4):657-72. [Medline].
Rickes S, Unkrodt K, Neye H. Differentiation of pancreatic tumours by conventional ultrasound, unenhanced and echo-enhanced power Doppler sonography. Scand J Gastroenterol. 2002 Nov. 37(11):1313-20. [Medline].
Schachter PP, Shimonov M, Czerniak A. The role of laparoscopy and laparoscopic ultrasound in the diagnosis of cystic lesions of the pancreas. Gastrointest Endosc Clin N Am. 2002 Oct. 12(4):759-67, vii-viii. [Medline].
Bounds BC. Diagnosis and fine needle aspiration of intraductal papillary mucinous tumor by endoscopic ultrasound. Gastrointest Endosc Clin N Am. 2002 Oct. 12(4):735-45, vii. [Medline].
Sperti C, Pasquali C, Chierichetti F. Value of 18-fluorodeoxyglucose positron emission tomography in the management of patients with cystic tumors of the pancreas. Ann Surg. 2001 Nov. 234(5):675-80. [Medline].
Sendler A, Avril N, Roder JD. [Can the extent of pancreatic tumors be evaluated reliably enough by positron emission tomography (PET)]. Langenbecks Arch Chir Suppl Kongressbd. 1998. 115:1485-7. [Medline].