Pancreatic IPMN

 Well-defined cystic lesion with variable morphology: Unilocular, multicystic, or tubular


image Communication with adjacent main pancreatic duct is key to diagnosis (may be more visible on MR than CT)

image Dilatation of adjacent main pancreatic duct should raise concern for main duct involvement

image Multiplicity is strong clue to diagnosis: Often multiple small cysts scattered throughout pancreas


• Main duct IPMN
image Markedly dilated, tortuous MPD often with bulging ampulla filled with fluid (mucin)

image Dilatation may be segmental or diffuse

image Polypoid nodularity in MPD suspicious for malignancy

image Amorphous calcifications may be seen within duct

image Pancreas often atrophic overlying dilated duct

• Combined IPMN
image Cystic lesion in contiguity with dilated MPD (shares imaging features of main duct and side branch IPMN)




CLINICAL ISSUES




• EUS cyst aspiration: Elevated cyst fluid CEA (> 192 ng/mL)

• Most patients asymptomatic (incidental imaging finding), but can result in repetitive bouts of pancreatitis

• Risk of transformation into invasive carcinoma, with main duct involvement associated with ↑ risk of malignancy

• Management of IPMN based on 2012 IAP guidelines
image Worrisome features: Cyst size ≥ 3 cm, MPD dilatation 5-9 mm, peripheral wall thickening, nonenhancing mural nodularity, abrupt change in main duct caliber with upstream pancreatic atrophy

image High-risk features: MPD dilatation ≥ 1 cm, enhancing solid mural nodularity, or biliary obstruction

image
(Left) Graphic shows combined main and side branch IPMN with gross dilatation of all ducts by mucin, which pours out of a bulging papilla into the duodenum. The parenchyma in the pancreatic head is atrophic.


image
(Right) Coronal MRCP with MIP reconstruction nicely demonstrates 2 discrete side branch IPMNs image and their direct connection with the adjacent normal sized pancreatic duct.

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(Left) Coronal MRCP with MIP reconstruction demonstrates multiple cysts throughout the pancreas compatible with multiple side branch IPMN. Multifocality is characteristic of IPMN, and multiple discrete cystic lesions are often present in the same patient.


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(Right) Coronal CECT demonstrates innumerable pancreatic cysts, compatible with multiple side branch IPMN. No suspicious individual cyst or solid mass was seen, but EUS findings were suspicious, and the patient was found to have invasive carcinoma at surgery.


TERMINOLOGY


Abbreviations




• Intraductal papillary mucinous neoplasm (IPMN)


Synonyms




• Intraductal papillary mucinous tumor, intraductal mucin-hypersecreting neoplasm, ductectatic mucinous cystadenoma/carcinoma


Definitions




• Mucin-producing papillary tumor arising from epithelium of main pancreatic duct (MPD) or pancreatic duct side branches


IMAGING


General Features




• Best diagnostic clue
image Side branch type: Cystic lesion with direct communication with adjacent MPD on CECT/MRCP

image MPD type: Dilated MPD with bulging papilla and enhancing soft tissue nodularity within duct lumen

• Location
image Side branch lesion: Predisposition for uncinate process and head, but can occur anywhere in pancreas

image MPD lesion: Either diffuse or segmental involvement of pancreatic duct, but most often involves body and tail

• Size
image Side branch cysts: Variable, but most side branch IPMN measure 5-20 mm

• Morphology
image IPMN: Subdivision of mucin-producing tumors (along with mucinous cystic neoplasm)

image Classified into 3 types
– Side branch pancreatic duct (BPD) type: Focal lobulated “multicystic” dilatation of branch ducts

– Main pancreatic duct (MPD) type: Diffuse dilatation of main pancreatic duct

– Combined type: Dilatation of both BPD and MPD


CT Findings




• Side branch IPMN
image Well-defined cystic lesion with variable morphology: Unilocular, multicystic (with grape-like clusters or tubes and arcs), or tubular

image Communication with adjacent MPD is key to diagnosis, but may not always be possible to demonstrate
– May be more apparent on multiplanar reformations

– Dilatation of adjacent main pancreatic duct should raise concern for main duct involvement

image Multiplicity is strong clue to diagnosis: Often multiple small cysts scattered throughout pancreas

image Calcifications in 20%, but no correlation with malignancy

• Main duct IPMN
image Markedly dilated, tortuous MPD without evidence of distal obstructing mass and often with “bulging” ampulla filled with fluid (mucin) at duodenal sweep
– Dilatation may be segmental or diffuse

– Possibility of main duct IPMN should be considered when duct measures ≥ 5 mm

image Presence of polypoid enhancing nodularity within MPD lumen is very suspicious for malignancy

image Amorphous calcifications may be seen within duct

image Pancreas often atrophic overlying dilated duct

• Combined IPMN
image Cystic lesion in contiguity with dilated MPD (shares imaging features of main duct and side branch IPMN)

• Concerning imaging features based on 2012 International Association of Pancreatology (IAP) guidelines
image Worrisome features: Cyst size ≥ 3 cm in any dimension, MPD dilatation between 5-9 mm, peripheral wall thickening or enhancement, nonenhancing mural nodularity, abrupt change in main duct caliber with distal pancreatic atrophy, lymphadenopathy

image High-risk features: MPD dilatation ≥ 1 cm, enhancing solid mural nodularity, or biliary obstruction


MR Findings




• Little data directly comparing CT and MR, but MR likely superior for identifying small cysts and multifocal disease, visualizing communication between cyst and main duct, and assessing main duct involvement
image Superior soft tissue resolution of MR may allow better assessment of subtle mural nodularity

• Side branch IPMN typically hyperintense on T2WI and low signal on T1WI, and can appear unilocular, multicystic, tubular, or as grape-like cluster of cysts
image Presence of dilated adjacent main pancreatic duct concerning for main duct involvement
– MRCP may be more accurate than CT for assessing main duct size and internal mural nodularity

• Direct communication with main pancreatic duct easier to identify on thin-section 3D MRCP images
image Enlargement of cyst following administration of secretin may be secondary sign of communication with main duct

• Malignant IPMN may have lower ADC values on DWI compared to benign IPMN, but not widely clinically utilized (due to overlap in ADC values)


Ultrasonographic Findings




• Conventional ultrasound lacks spatial resolution to identify high-risk or worrisome imaging features

• Endoscopic ultrasound (EUS): Now considered important part of evaluation of pancreatic cysts in specialized centers
image Spatial resolution of EUS may help identify suspicious morphologic features (e.g., mural nodularity) not visible on CT/MR, and can help guide FNA and cyst aspiration
– May identify communication between cyst and MPD

image 2012 IAP guidelines recommend EUS with cyst aspiration for cysts with worrisome imaging features 
– Cyst size ≥ 3 cm, MPD dilatation 5-9 mm, peripheral wall thickening, nonenhancing mural nodularity, etc.


Radiographic Findings




• ERCP
image Direct visualization of patulous, bulging, “fish-mouth” ampulla with mucin extruding through ampulla (due to mucin hypersection) in main duct IPMN

image Can directly demonstrate dilatation of MPD (in main duct IPMN) or communication of side branch IPMN with MPD

image Filling defects within duct (either nodular or band-like) may represent mucin or papillary tumors


Imaging Recommendations




• Best imaging tool
image MR or CECT are best initial noninvasive modalities

image EUS utilized for lesions with suspicious imaging features


DIFFERENTIAL DIAGNOSIS


Chronic Pancreatitis




• Dilated, beaded, irregular main pancreatic duct with intraductal calculi and parenchymal atrophy/calcifications

• Significant imaging/clinical overlap with main duct IPMN


Pancreatic Ductal Carcinoma




• Hypodense mass with abrupt cutoff of pancreatic duct and upstream MPD dilatation/parenchymal atrophy

• Small occult lesion obstructing MPD may appear identical to main duct IPMN


Pancreatic Pseudocyst




• Cystic lesions that may communicate with MPD and can mimic side branch IPMN

• Usually known clinical history of pancreatitis (or risk factors) and inflammatory changes surrounding cyst

Nov 16, 2016 | Posted by in GASTROINTESTINAL IMAGING | Comments Off on Pancreatic IPMN

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