Pancreatic IPMN

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

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

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

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

• Main duct IPMN

Markedly dilated, tortuous MPD often with bulging ampulla filled with fluid (mucin)

Dilatation may be segmental or diffuse

Polypoid nodularity in MPD suspicious for malignancy

Amorphous calcifications may be seen within duct

Pancreas often atrophic overlying dilated duct

• Combined IPMN

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

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

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

(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.

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

(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.

(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

Side branch type: Cystic lesion with direct communication with adjacent MPD on CECT/MRCP

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

• Location

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

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

• Size

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

• Morphology

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

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

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

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

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

Calcifications in 20%, but no correlation with malignancy

• Main duct IPMN

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

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

Amorphous calcifications may be seen within duct

Pancreas often atrophic overlying dilated duct

• Combined IPMN

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

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

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

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

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

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

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