Intraductal papillary mucinous neoplasm

Last revised by Joshua Yap on 4 Jun 2024

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. 

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 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

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.

Reported locations of IPMN include 15:

  • head ~50%

  • tail ~7%

  • uncinate process ~4%

  • elsewhere throughout the pancreas ~40%

Divided macroscopically:

  • 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.

They are histologically divided into:

  • adenoma

  • borderline-malignant

  • intraductal papillary mucinous adenocarcinoma

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

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).

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 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.

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 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.

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.

General imaging differential considerations include:

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:

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