eMedicine Specialties > Radiology > Gastrointestinal

Pancreas, Mucinous Cystic Neoplasm: Imaging

Author: Ali Nawaz Khan, MBBS, FRCS, FRCP, FRCR, LRCP, Chairman of Medical Imaging, Professor of Radiology, NGHA, King Fahad National Guard Hospital, King Abdulaziz Medical City, Riyadh, Saudi Arabia
Coauthor(s): Aali J Sheen, MD, MBChB, FRCS, Consulting Hepatobiliary Surgeon, HepatoBiliary Unit, Manchester Royal Infirmary; Sumaira MacDonald, MBChB, PhD, MRCP, FRCR, Lecturer, Sheffield University Medical School; Endovascular Fellow, Sheffield Vascular Institute; Haren Varia, MB ChB, FRCR, Consultant, Department of Clinical Radiology, Blackpool, Fylde and Wyre NHS Trust
Contributor Information and Disclosures

Updated: Mar 12, 2009

Radiography

Findings

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. In mucinous-type tumors, calcification tends to occur at the periphery of the tumor or in the walls of the cysts and appear curvilinear. CT is more sensitive for calcification.

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. These techniques may also help in assessing the risk of malignancy, evaluating the extent of disease, allowing tissue sampling, and enabling therapeutic intervention.⁵ 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, 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.

False Positives/Negatives

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.

Reflux of contrast material due to mucin blobs or mural nodules may hinder filling of the ducts in IPMT on ERCP, causing diagnostic difficulties.

Computed Tomography

Findings

Mucinous cystic neoplasms

Nonenhanced CT scans show a well-defined, unilocular or multilocular, externally smooth, round-to-ovoid mass with fluid attenuation. 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 its internal surface. Typically, they show a well-defined, multilocular cystic mass with thick internal septae separating the different cystic cavities of varying sizes. The cysts are 2-26 cm.^6,7

Visualization of nodular or papillary excrescences with irregular borders of the septae 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. MCNs develop predominantly in the tail of the pancreas (>90%). CT more clearly demonstrates enhancement of cystic walls and septa than do other studies.

Compared with serous cystic tumors, the cysts in MCNs are larger (>20 mm in diameter) and less numerous (usually <6).CT-guided aspiration of the cyst can provide further diagnostic clues and enable their differentiation from other pancreatic cystic masses (eg, pseudocyst, serous cystadenoma, and solid and pseudopapillary neoplasm). MCN cyst fluid typically has a high viscosity, low amylase levels, and high CEA and carbohydrate antigen (CA) 72-4 levels, and they may show malignant cytology in patients with mucinous cystadenocarcinomas. Periodic acid-Schiff (PAS) and May-Grunwald/Giemsa (MGG) stains are usually positive for extracellular as well as intracellular mucin.

Intraductal papillary mucinous tumors

Main ductal IPMT may be focal or diffuse, the findings of which are reflected on imaging. However, main duct tumors may be difficult to differentiate from chronic pancreatitis, as the imaging features may be similar. 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 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 IPMT may be easier to identify than main-duct IPMT, as the former generally appears 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 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.

False Positives/Negatives

CT is not useful for differentiating mucinous cystadenoma from cystadenocarcinomas except 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.

Magnetic Resonance Imaging

Findings

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.

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 Fibrosing Dermopathy. 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 the FDA Public Health Advisory or Medscape.

MRCP allows depiction of pancreatic duct or CBD changes that may be associated with the tumors.

Hong and associates analyzed the CT and MRI features of IPMT of the pancreas in 8 patients with pathologically proven IPMT of the pancreas (1 papillary hyperplasia, 7 adenocarcinoma).⁸ The patients included 5 men and 3 women aged 42-82 years. Imaging studies included 6 thin-section dynamic CTs, 7 MRIs, 1 MRCP, and ERCP examinations.

The authors found only 1 benign IPMT, which appeared as a unilocular cyst in the pancreatic body with no mural nodules and no dilatation of the MPD. All 7 patients with malignant IPMT had multilocular cysts with papillary projections in the pancreatic head and/or uncinate process accompanied by dilated MPD (5 diffuse, 2 segmental). Communication between the cystic lesions and the MPD were evident in all 7 patients. One patient had small mural nodules in the branch ducts of the pancreatic body, and 5 had a bulging papilla with a patulous orifice. A mass effect resulting in biliary obstruction was shown in 1 patient. One patient had a ruptured cyst with mucin leakage into the right anterior pararenal space after sonography-guided aspiration.

The main imaging feature of IPMT in the 8 reported patients was a multilocular cyst with papillary projections in the pancreatic head and uncinate process. 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.

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.⁹

Degree of Confidence

MRI is an excellent modality for the depiction of cystic pancreatic masses, showing their internal architecture to advantage. MRCP is a noninvasive technique.

False Positives/Negatives

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.

Ultrasonography

Findings

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 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) 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.

Rickes and associates selected 137 patients with a mean age of 60 years and clinically suspected pancreatic tumors.¹⁰ The patients were assessed with conventional sonography and nonenhanced and echo-enhanced power Doppler sonography. An experienced examiner blinded to the patients' clinical diagnoses performed the studies. The exact diagnosis was based on histologic evidence from surgical and fine needle biopsy or on a follow-up of at least 18 months.

Of the 137 patients, 47 had pancreatic cancer; 41 had masses associated with pancreatitis, 17 had neuroendocrine tumors, 12 had cystic lesions of the pancreas, and 10 had other pancreatic diseases. A normal pancreas was found in 10 patients. 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. The authors concluded that echo-enhanced power Doppler sonography has a high sensitivity and specificity in the differential diagnosis of pancreatic tumors. However, histologic study remains the criterion standard.

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 31 patients with pancreatic cystic lesions of unknown etiology who were followed-up with semiannual EUS over 3 years. In 87.1%, 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 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.¹¹

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 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.¹² LAPUS is expensive and invasive.

False Positives/Negatives

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.

Nuclear Imaging

Findings

Sperti and associates assessed the reliability of fluorodeoxyglucose (FDG) positron emission tomography (PET) in distinguishing benign from malignant cystic lesions of the pancreas.¹³ During a 4-year period, 56 patients with a suspected cystic tumor of the pancreas underwent FDG PET in addition to CT, serum CA 19-9 assay, and (in some instances) MRI or ERCP. FDG PET images were visually and semiquantitatively analyzed by using the standard uptake value. The accuracy of FDG PET and CT was determined for preoperative diagnosis of a malignant cyst.

Seventeen patients had malignant tumors. Sixteen patients (94%) had FDG uptake with a standard uptake value of 2.6-12.0. Twelve patients (70%) were correctly identified as having malignancy by means of CT, CA 19-9 assay, or both. Thirty-nine patients had benign tumors. Only 1 mucinous cystadenoma showed increased FDG uptake (standard uptake value of 2.6). Five patients with benign cysts had CT findings of malignancy.

The authors concluded that FDG PET is more accurate than CT 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. A positive result on FDG PET strongly suggests malignancy and, therefore, a need for resection. A negative result shows a benign tumor that may be treated with limited resection or, in select high-risk patients, with biopsy, follow-up, or both.

Degree of Confidence

The preoperative differential diagnosis of cystic lesions of the pancreas remains difficult. The most important determinant of the prognosis is the identification of malignant or premalignant cysts that require resection. FDG PET is a new imaging procedure based on the increased glucose metabolism by tumor cells and has been proposed for use in the diagnosis and staging of pancreatic cancer. Sperti and associates have reported sensitivity, specificity, and positive and negative predictive values in detecting malignant tumors. Values were, respectively, 94%, 97%, 94%, and 97%; and 65%, 87%, 69%, and 85%.

Sendler and associates performed FDG PET in 46 patients admitted to the hospital for pancreatic tumor surgery.¹⁴ The method yielded a sensitivity of 86% and a specificity of 67%. The authors concluded that PET does not allow the precise exclusion of malignant tumors and that, therefore, the use of invasive diagnostic procedures may not be reduced.

False Positives/Negatives

With FDG PET, there is a potential for false-positive scans as a result of physiologic activity. Kato and associates investigated pancreatic cancer with FDG PET. They reported 1 false-negative case (mucinous adenocarcinoma), in which the tumor contained a small number of malignant cells, and 1 false-positive case, in which lymphocytes densely accumulated in the mass in the pancreatic head.

Angiography

Findings

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.

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.

False Positives/Negatives

Low-grade vascularization may occur in both 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.

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