Intraductal papillary mucinous neoplasms or tumors (IPMNs or IMPTs) are epithelial pancreatic cystic tumors of mucin-producing cells that arise from the pancreatic ducts. They are most commonly seen in elderly patients.
On imaging, particularly MRCP, they are characterized by single or multiple unilocular or septated pancreatic cystic lesions communicating with the pancreatic ducts.
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Epidemiology
These tumors are most frequently identified in older patients, 50-60 years of age 6, and thus are sometimes colloquially referred to as the "grandfather lesion". Main duct type appears to present a decade or so earlier on average than branch duct type 5. The sex distribution is roughly balanced with a possible slight male predominance 15.
Clinical presentation
Clinical presentation can be difficult to distinguish from chronic pancreatitis with repeated acute exacerbations. Patients can present with abdominal pain, weight loss, obstructive jaundice, pancreatitis and new-onset diabetes mellitus 5,9.
Pathology
Intraductal papillary mucinous neoplasms are one of a number of mucinous tumors of the pancreas and can be further divided both histologically and with respect to their macroscopic appearance 5. They are uncommon ductal epithelial tumors comprising 10-15% of cystic pancreatic neoplasms.
Location
Reported locations of IPMN include 15:
head ~50%
tail ~7%
uncinate process ~4%
elsewhere throughout the pancreas ~40%
Macroscopic appearance
Divided macroscopically:
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main duct type
reminiscent of chronic pancreatitis
segmental or diffuse distribution
-
highest malignant potential 6
~60% are malignant 10
-
branch duct type
mostly seen in the head and uncinate process
more localized and mass-like
may be multifocal 13
may be macro- or microcystic in appearance 5
-
typically indolent behavior 6
~5% (range 2-10%) are malignant 11,12
-
mixed type
similar to the main duct type in terms of prognosis and overall survival
Solid components, as well as bile duct dilatation 14, are suspicious of malignant transformation.
Microscopic appearance
They are histologically divided into:
adenoma
borderline-malignant
intraductal papillary mucinous adenocarcinoma
Markers
In patients without pancreatitis, abnormal (either elevated or depressed) pancreatic enzyme markers (amylase/lipase) are associated with malignant IPMN, with the elevation of these a marker of invasiveness 8.
Radiographic features
The characteristic feature is that these tumors communicate with the main pancreatic duct or its branches, which helps distinguish them from mucinous cystadenoma/cystadenocarcinoma, which do not.
Calcifications have been reported in retrospective imaging analyzes of resected IPMN at an incidence of ~13% (range 5-20%) 17-21, however, the overall incidence of calcifications in all IPMNs (i.e. resected and unresected) is not known (c.2023) and, interestingly, calcifications are not a criterion in the Kyoto guidelines to help guide whether surgical treatment is appropriate and are much more common in other pancreatic cystic lesions (e.g. serous cystadenomas).
Fluoroscopy
ERCP
Direct imaging of the pancreatic duct demonstrates variable dilatation (segmental, diffuse, or branch) depending on the type. Polypoid mural tumor or amorphous mucinous luminal filling defects may be identified 5.
Mucinous material may be seen protruding from the ampulla of Vater 6.
Ultrasound
Ultrasound may demonstrate small thin-walled pancreatic cysts or dilated hypoechoic ducts (main pancreatic duct over 5 mm in caliber). Diffuse main duct type appears essentially indistinguishable from chronic pancreatitis, with duct dilatation and parenchymal atrophy 5.
Mural nodules and mucin globules may appear hyperechoic and difficult to separate from adjacent pancreatic parenchyma 6.
CT
They present as single or multiple pancreatic cystic hypodense lesions. Dilatation of the main duct over 5 mm concerns the main duct type IPMN. The communication with the pancreatic ducts, particularly the side branch lesions, may be difficult to demonstrate on CT. They do not calcify.
Both a dedicated pancreatic CT protocol and pancreatic MRI/MRCP have been reported as having similar accuracy in the characterization of the pancreatic cystic lesions 16, but guidelines recommend MRI as the modality of choice for IPMN follow-up.
MRI
MRI studies, particularly MRCP, have largely replaced CT in the imaging workup of these lesions.
-
main duct type (with dilatation of the main duct >5 mm)
either segment of the pancreatic duct (or the entire duct) are dilated and filled with low density (mucin thus water signal) material
overlying pancreatic parenchyma may be thinned
if proximal, the distal pancreatic duct may be dilated without direct involvement (cystic neoplasms can have a similar appearance)
solid mural nodules are concerning for malignant transformation, particularly if enhancing following administration of contrast
occasionally mucinous material can be seen to bulge out of a dilated ampulla of Vater (uncommon but essentially pathognomonic)
mucin globules do not enhance and lie dependently within the duct
-
branch duct type
the majority of the gland is normal in appearance, except for a single or multiple side branches demonstrating marked dilatation
cystic mass-like appearance which often mimics cystic tumors of the pancreas
its appearance has been termed a bunch of grapes
microcystic variety has appearances similar to serous cystadenomas, but again communication with the main pancreatic duct is the key to the correct diagnosis
-
mixed type
appears like an advanced branch duct IPMN with main pancreatic duct dilatation over 5 mm
See the Kyoto guidelines for further details.
Treatment and prognosis
Although generally indolent, malignant degeneration does occur, with direct invasion into adjacent organs or, more frequently, dissemination in the peritoneal cavity (pseudomyxoma peritonei).
Consensus criteria recommend resection for main duct type IPMNs and varying treatment of branch duct type IPMNs, ranging from resection to surveillance, depending on high-risk stigmata and worrisome features (see Kyoto guidelines). Patient co-morbidities and wishes clearly have a major impact on the decision to operate.
If the lesion is proximal (either segmental main duct type or branch type), a Whipple procedure may be performed. If distal, a partial pancreatectomy suffices. Complete resection is curative.
Differential diagnosis
General imaging differential considerations include:
-
difficult to distinguish from main duct type on account of dilated duct 5
-
mucinous cystadenoma/cystadenocarcinoma
should not appear to communicate with the main pancreatic duct
-
should not appear to communicate with the main pancreatic duct
appear similar to microcystic branch type IPMN
30-40% have central calcification
Practical points
The radiological report has to be clear regarding imaging worrisome features of these lesions that may guide further surgical intervention:
-
main duct type
main pancreatic duct over 5 mm
presence of contrast-enhancing components
-
branch duct type
main pancreatic duct over 5 mm
cyst diameter ≥3 cm
presence of a contrast-enhancing mural nodule ≥5 mm 16
presence of solid mass 16
thickened and enhancing cyst wall
growth rate ≥5 mm/year
Clinical features to guide surgery may also include:
increased serum CA 19-9 level
-
endoscopic ultrasound (EUS) with FNA sampling
cytology: differentiate between benign and lesions with either high-grade dysplasia or cancer
KRAS/GNAS mutation analyzes 16
-
new onset of 16
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