A 52-year-old woman underwent an abdominal MRI for an incidentally found cystic mass within the pancreatic tail (Figure 1A-C). She had no inciting symptoms related to the pancreatic lesion, and medical and surgical history were noncontributory. All laboratory values were within normal range.
Cystic pancreatic mass
Intraductal papillary mucinous neoplasm (IPMN)
Pseudocyst
Serous cystadenoma
Mucinous cystic neoplasm
Solid pseudopapillary tumor with cystic degeneration
Ductal adenocarcinoma with cystic changes
As the utilization of cross-sectional imaging continues to rise, the number of incidentally identified cystic lesions of the pancreas also increases. The goal of the radiologist is to categorize such lesions on the continuum from overtly benign to frankly malignant. This differentiation is important for clinical management, often meaning the difference between continued imaging follow-up or surgical resection. The differential diagnosis for a pancreatic cystic lesion includes a number of inflammatory and neoplastic processes. The clinical and imaging manifestations are discussed below with an emphasis on distinguishing features.
IPMNs occur most commonly in the seventh and eighth decades with an equal incidence in men and women.1,2 Macroscopically, they are classified as main duct, branch duct, or mixed lesions and invariably result in ductal dilation as they produce an abundance of extracellular mucin.3,4 Microscopically, they can be divided into subcategories ranging from benign adenomas to aggressive malignancy. Given their mucinous nature, IPMNs will appear hypoechoic on ultrasound (US), hypoattenuated on computed tomography (CT), and T2 hyperintense on MRI.
Main duct IPMNs carry a higher risk for malignancy and are described based on the degree and length of ductal dilatation without additional causes for obstruction. According to the 2012 consensus statement, main duct dilatation of > 5 mm should be suspicious, 5-9 mm of dilatation is considered a worrisome feature, and > 10 mm of dilatation is high-risk stigmata.5 Additionally, ductal dilatation can be classified as either segmental or diffuse based on the length of dilation. Although uncommon, bulging of mucinous material from the dilated ampulla of Vater is considered pathognomonic and typically seen only on endoscopic retrograde cholangiopancreatography (ERCP). Additional concerning imaging findings include abrupt increase in ductal dilatation with distal parenchymal atrophy and the presence of mural nodules.
Branch duct IPMNs may have dilatation of a single or multiple side branches with the majority of the pancreatic tissue appearing otherwise normal. Multiple microcysts are characteristic, lending to the imaging appearance of a bunch of grapes. Worrisome features of a branch duct IPMN include size > 3 cm, nonenhancing intracystic nodules, and enhancing thickened walls.5 If an enhancing mural nodule is present, this should be considered high-risk stigmata.5
If no suspicious features are present, continued surveillance is recommended. With worrisome findings, patients should proceed to endoscopic US with sampling of the cystic fluid and evaluation of serum tumor markers. The decision for imaging follow-up vs. surgical resection should be based on results of these tests.5 Lesions demonstrating high-risk stigmata should proceed directly to surgical resection, if able.
Pseudocysts are seen in 10% to 12% of interstitial edematous pancreatitis cases and can have variable imaging appearance.6 They typically appear as unilocular, round or ovoid, well-circumscribed pancreatic or peripancreatic fluid collections that present after 4 weeks of symptom onset. They may demonstrate thin or thick enhancing walls and can be multiple or solitary. On US, pseudocysts are anechoic or hypoechoic with variable dependent debris. CT attenuation and MR signal characteristics will vary depending on the contents of the pseudocyst and the presence or absence of infection. In approximately 50% of cases, a communication with the main pancreatic duct is present and is best be seen on magnetic resonance cholangiopancreatography (MRCP).1,4 Recurrence is common if this communication persists.
In rare cases, gas within the cyst may be seen indicating either spontaneous fistulization with the adjacent gastrointestinal tract or superimposed infection. If no overt imaging findings of infection are present and it remains a strong clinical concern, sampling of the fluid percutaneously or through endoscopy can be performed.
Pseudocysts are treated when superimposed infection is present, if they are large (generally > 4-6 cm), or if local mass effect is creating clinical issues such as gastric outlet obstruction, hydronephrosis or biliary obstruction. There may be spontaneous resolution if the cysts are > 4-6 cm.2,4
Serous cystadenoma is a benign primary cystic mass of the pancreas that favors the pancreatic head. They are commonly seen in patients > 60 years old and have a well-known female predilection, as well as an association with von Hippel Lindau disease.4
These lesions can be solitary, multiple, or diffuse and are classified as polycystic, honeycomb, or oligocystic with 0.1 - 2 cm locules.4 These locules are lined by glycogen-rich cuboidal epithelium organized by multiple fibrous septa often radiating from a central scar. Calcification of this scar can occur and aids diagnosis, when present. The cystic components are fluid attenuation on CT and follow fluid signal on MRI with the fibrous septae demonstrating delayed enhancement on postcontrast images. Although these lesions are commonly < 1 cm, they can be > 5 cm at times. No communication with the pancreatic duct should be seen.
Further evaluation with enodoscopic sampling is useful in confirming the benign etiology of this lesion when cross-sectional imaging is not diagnostic. Asymptomatic lesions < 4 cm can be followed closely with CT or MRI. However, if there is significant interval growth, or the patient becomes symptomatic, surgical resection should be strongly considered.
Mucinous cystic neoplasms are found almost exclusively in middle-aged women with a peak-incidence occurring in the fifth decade.1,7 These lesions account for nearly 10% of all pancreatic cystic neoplasms and have malignant potential with degeneration into mucinous cystadenocarcinomas.
On imaging, mucinous cystic neoplasms appear as solitary, well-circumscribed, spherical tumors ranging from 6-11 cm.1 These lesions are classically macrocystic (80%) and unilocular without communication with the pancreatic duct.1 On unenhanced CT, curvilinear, peripheral calcifications may be seen in 15% of cases and are highly specific.8 MRI commonly reveals a mildly septated fluid signal lesion with a low T1 and T2 signal capsule.4,7 The capsule is usually thick with progressive enhancement on dynamic postcontrast images.1,7 Findings suggestive of malignancy include a thickened calcified wall, internal septations, cyst size > 6 cm, and solid mural nodules or internal enhancing soft tissue elements.7
Pancreatic resection is the treatment of choice for all mucinous cystic neoplasms regardless of size due to the high risk of malignant degeneration. An estimated one-third of mucinous cystic neoplasms harbor an invasive carcinoma at the time of diagnosis.1,7,8
Solid pseudopapillary tumors are uncommon pancreatic neoplasms most frequently found in young women with a peak incidence occurring between the second and third decades of life.1,7-9 These tumors are considered both solid and cystic due their tendency to undergo intratumoural hemorrhage.8 They have malignant potential transforming into solid pseudopapillay carcinomas.
On imaging, solid pseudopapillary tumors typically present as large, solitary, centrally cystic lesions with a solid enhancing capsule.8 The thick, fibrous capsule demonstrates delayed enhancement on postcontrast images.1,7,8 Peripheral calcifications may also be identified in nearly 30% of cases, best seen on noncontrast CT.8 MR demonstrates heterogeneous T1 and T2 signal intensity with areas of high T1 signal secondary to hemorrhage.1,8,10 These tumors are treated surgically with malignant degeneration seen in 15% of cases.1,7
Pancreatic ductal adenocarcinoma should also be considered in the differential diagnosis of cystic pancreatic lesions. Although the majority of ductal adenocarcinomas are solid tumors, cystic changes occur in nearly 8% of cases, making this presentation uncommon, but not rare.7,10,11 This tumor is an aggressive malignancy with a high mortality portending less than a 5% 5-year survival rate.7,9,10
Complex cystic changes either adjacent to or within a ductal adenocarcinoma can represent neighboring pseudocysts, internal tumor necrosis, or side-branch ductal obstruction.7 Differentiation between the previously discussed cystic neoplasms can usually be made by the classic infiltrative pattern of ductal adenocarcinoma.7,11 In addition, the presence of vascular invasion, distal pancreatic atrophy, and upstream pancreatic ductal dilatation may also be seen, further supporting the diagnosis of pancreatic ductal adenocarcinoma.7,11
Intraductal papillary mucinous neoplasm (side branch)
Knowledge of the clinical and imaging manifestations of various cystic pancreatic lesions allows for an accurate and efficient creation of a targeted list of differential considerations. Patient age, location of the lesion, and presenting symptoms are all important distinguishing features for cystic masses within the pancreas. The primary goal for the radiologist is to appropriately categorize the lesion along a continuum from overtly benign to frankly malignant. Additional diagnostic data can be obtained with serum tumor markers, and percutaneous or endoscopic fluid or tissue sampling as needed.
Ries S, Giese J, Kreuer S. Cystic Pancreatic Masses. J Am Osteopath Coll Radiol. 2016;5(2):23-25.
Dr. Ries, Dr. Giese, and Dr. Kreuer work with the Department of Diagnostic Radiology, Botsford Hospital, Farmington Hills, MI.
