Mucinous Cystic Pancreatic Tumor

Published on 19/07/2015 by admin

Filed under Radiology

Last modified 19/07/2015

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 “Macrocystic” pattern: Few (< 6) macrocystic locules, which are relatively large (> 2 cm)

image Usually of simple fluid attenuation, but may be mildly hyperdense due to hemorrhage or protein
image Frequent peripheral curvilinear calcifications or calcifications in septations (16% of cases)
image Presence of thick wall, mural nodularity, or thick septations suggests invasive malignancy
image No apparent communication with main pancreatic duct
• MR: Usually simple fluid signal (high T2; low T1), but may be slightly less T2 hyperintense due to mucin content

image Internal septations (which are T2 hypointense) easier to perceive on MRI compared to CT
image MRCP: No communication with main pancreatic duct

PATHOLOGY

• Tumor shares clinical and pathologic characteristics of biliary tumors, ovarian tumors, and IPMN
• Presence of ovarian stroma lining cyst is key feature for diagnosis of mucinous cystic neoplasm (MCN)

CLINICAL ISSUES

• Strong preponderance in middle-aged women (99%)
• Considered premalignant or frankly malignant: Rate of malignancy in different series ranges between 10-40%
• Risk factors for invasive malignancy: Older age, lesion size, mural nodularity, thick wall, patient symptoms (pain, pancreatitis), and ↑ CEA and CA 19-9
• MCNs typically undergo complete surgical resection with adjuvant chemotherapy for malignant lesions
• Malignant MCNs receive adjuvant chemotherapy after surgical resection
image
(Left) Graphic of a mucinous cystic tumor shows a multiseptate, mucin-filled, cystic mass in the pancreatic tail that displaces the pancreatic duct.

image
(Right) Axial CECT in a 35-year-old woman demonstrates a large complex cystic mass image arising from the pancreatic tail with multiple internal cystic locules and septations, some of which are thick image. This mass was found to be a mucinous cystic neoplasm (MCN) with invasive adenocarcinoma at surgery.
image
(Left) Axial CECT in a 46-year-old woman demonstrates a large, simple-appearing cyst image arising from the upstream pancreatic body.

image
(Right) Axial T2 FS MR in the same patient confirms the lack of complexity within the T2-hyperintense cyst image. MR can sometimes show complexity and suspicious features that might be difficult to identify on CT. This was found to be a MCN with low-grade dysplasia at surgery.

TERMINOLOGY

Synonyms

• Mucinous cystic neoplasm (MCN), mucinous macrocystic neoplasm or adenoma, mucinous cystadenoma or cystadenocarcinoma

Definitions

• Thick-walled, unilocular or multilocular pancreatic tumor composed of large, mucin-containing cysts

image Some sources suggest presence of ovarian stroma within lesion is necessary for diagnosis
• MCN and intraductal papillary mucinous neoplasm (IPMN) are together classified as pancreatic mucinous tumors

IMAGING

General Features

• Best diagnostic clue

image Large, unilocular or multilocular encapsulated cystic mass with septations and thick wall in pancreatic tail
• Location

image Tail of pancreas (more common)
image Presents as single lesion (not multifocal like IPMN)
• Size

image 2-12 cm in diameter

– MCNs usually larger than serous cystadenoma or IPMN
image Size is predictor of biologic behavior

– Lesions < 40 mm found to have low risk of malignancy in recent series
• Morphology

image Typically round/ovoid, but may be ill defined/irregular

Radiographic Findings

• ERCP

image Displacement and narrowing of main pancreatic duct adjacent to tumor
image Can differentiate IPMN (which communicate with main pancreatic duct) from MCN (which do not communicate)

CT Findings

• Unilocular or multilocular encapsulated cyst in pancreatic body/tail with frequent internal septations

image “Macrocystic” pattern: Few (< 6) macrocystic locules that are relatively large (> 2 cm)
• Usually of simple fluid attenuation, but may be mildly hyperdense due to hemorrhage or protein
• Frequent peripheral curvilinear calcifications or calcifications in septations (16% of cases)
• Presence of thick, irregular wall, internal mural nodularity, or thick septations suggest invasive malignancy

image Upstream pancreatic ductal dilatation or atrophy suggest invasive malignancy
• No apparent communication with main pancreatic duct

image In rare instances, some series have suggested possible communication with pancreatic duct in very small minority of lesions

MR Findings

• Typically show simple fluid signal (high T2; low T1), but may be slightly less T2 hyperintense due to mucin content

image May show areas of T1 hyperintensity due to internal hemorrhage, proteinaceous content, or mucin
• Internal septations (typically T2 hypointense) easier to perceive on MR compared to CT
• Calcifications often not visible on MR: If visible, are low signal on all pulse sequences
• Thick, enhancing septations, wall thickening, and mural nodularity on T1WI C+ suggest invasive malignancy
• MRCP: No communication with pancreatic duct
• DWI: No role in differentiating mucinous from nonmucinous lesions or benign from malignant

Ultrasonographic Findings

• Grayscale ultrasound

image Multiloculated cystic mass with echogenic internal septa

– Often associated with thick wall ± mural nodularity
image Can also appear as unilocular anechoic mass

Angiographic Findings

• Conventional

image Predominantly avascular mass
image Cyst wall and solid component

– Show small areas of vascular blush and neovascularity
image Displacement of surrounding arteries and veins by cysts

Imaging Recommendations

• CECT or MR

DIFFERENTIAL DIAGNOSIS

Pancreatic Pseudocyst

• Usually known history of pancreatitis or alcoholism ± imaging stigmata of chronic pancreatitis (pancreatic calcifications, ductal beading, etc.)
• Loculated cyst with adjacent peripancreatic fat stranding/inflammation
• Evolves over time from acute peripancreatic fluid collection into loculated pseudocyst
• Communication with pancreatic duct is frequent (70% of cases) and may be visible on ERCP or MRCP
• Lab data: Increased amylase in cyst and serum
• When occurring in pancreatic tail, may simulate unilocular mucinous cystic neoplasm

Pancreatic Serous Cystadenoma

• Well-circumscribed, lobulated cystic mass most often occurring in pancreatic head
• Classic appearance (“microcystic” or “sponge” lesion): Many small cysts separated by thin septa and with central scar demonstrating calcification

image Calcification more common in serous than mucinous pancreatic neoplasms (38% vs. 16%)
• Macrocystic, oligocystic, and unilocular variants of serous cystadenoma difficult to distinguish from MCN

image Thick wall and mural nodularity unusual with serous cystadenoma

Pancreatic IPMN

• Mucin-producing neoplasms which are classified into 3 types with different risks of malignancy

image Side-branch IPMN: Arise in pancreatic duct side branch and carry risk of invasive malignancy of 17%
image Main pancreatic duct (MPD): Arise in main pancreatic duct and carry high risk of malignancy (58%)
image Combined type IPMN: Features of both side branch and main duct IPMN with prognosis similar to main duct IPMN
• Side-branch or combined type IPMN: Cyst (± nodularity, septations, calcifications) that communicates with pancreatic duct

Cystic Pancreatic Neuroendocrine Tumor

• Cystic neuroendocrine tumors more likely to be non-insulin producing and nonsyndromic
• Cystic lesion without pancreatic ductal dilatation or atrophy

image Differentiate from IPMN/MCN by presence of peripheral hyperenhancement on arterial phase CECT or MR

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