Intraductal papillary mucinous neoplasm
Intraductal papillary mucinous neoplasms or tumours (IPMNs or IMPTs) are cystic tumours of the pancreas.
These tumours 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 (see below) appears to present a decade or so earlier on average than branch duct type 5.
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 5,9.
IPMNs are one of a number of mucinous tumours of the pancreas and can be further divided both histologically and with respect to their macroscopic appearance 5. They are uncommon ductal epithelial tumours comprising approximately 10-15% of cystic pancreatic neoplasms.
- 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 localised and mass-like
- may be multifocal 13
- may be macro or microcystic in appearance 5
- typically indolent behaviour 6
- ~5% (range 2-10%) are malignant 11,12
mixed type lesions
- 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:
- 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.
Reported locations of IPMN include 15
- head ~ 50%
- tail ~ 7%
- uncinate process ~ 4%,
- elsewhere throughout pancreas ~ 39%
The characteristic feature is that these tumours communicate with the pancreatic duct or branches, which helps to distinguish these tumours from mucinous cystadenoma / cystadenocarcinoma which do not.
Direct imaging of the pancreatic duct demonstrates variable dilatation (segmental or diffuse or branch) depending on the type. Polypoid mural tumour 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 calibre). Diffuse main duct type has appearances 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.
In some cases, the tumour is very localised and appears cystic. It can, therefore, be difficult to distinguish from peripheral mucinous cystadenoma / cystadenocarcinoma unless convincing communication with the duct system can be demonstrated. They do not calcify.
main duct IPMN (with dilatation of the main duct >5 mm)
- either segments of the pancreatic duct (or the entire duct) are dilated and filled with low density (mucin thus water density) 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, and appear as hyperdense nodules protruding into the mucin-filled dilated ducts
- enhancing nodules following administration of contrast are very concerning
- occasionally mucinous material can be seen to bulge out of a dilated ampulla of Vater (uncommon but essentially pathognomonic)
branch duct IPMN
- 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 mimicks cystic tumours of the pancreas
- its appearance has been termed a bunch of grapes due to its appearance
- microcystic variety has appearances similar to serous cystadenomas, but again communication with the main pancreatic duct is the key to correct diagnosis
See the Tanaka criteria / International consensus guidelines for the management of IPMN and MCN of the pancreas (2012) for further details.
MRCP appearances are similar to those seen on CT.
Mural nodules appear hypointense compared to surrounding fluid and mucin and enhance following administration of contrast, representing one of the worrisome features suggesting malignant degeneration. Mucin globules do not enhance and lie dependently within the duct.
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).
Current consensus criteria recommend resection for main duct IPMNs and varying treatment of branch duct IPMNs, ranging from resection to surveillance, depending on high-risk stigmata and worrisome features (see: Tanaka criteria). Patient co-morbidities and wishes clearly have a major impact on the decision to operate.
If the lesion is proximal (either segmental main duct or branch type) then a Whipple procedure may be performed. If distal then a partial pancreatectomy suffices. Complete resection is curative.
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
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- 8. Roch AM, Parikh JA, Al-Haddad MA et-al. Abnormal serum pancreatic enzymes, but not pancreatitis, are associated with an increased risk of malignancy in patients with intraductal papillary mucinous neoplasms. Surgery. 2014;156 (4): 923-9. doi:10.1016/j.surg.2014.07.010 - Pubmed citation
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- 11. Ohno E, Itoh A, Kawashima H et-al. Malignant transformation of branch duct-type intraductal papillary mucinous neoplasms of the pancreas based on contrast-enhanced endoscopic ultrasonography morphological changes: focus on malignant transformation of intraductal papillary mucinous neoplasm itself. Pancreas. 2012;41 (6): 855-62. doi:10.1097/MPA.0b013e3182480c44 - Pubmed citation
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- 14. Strauss A, Birdsey M, Fritz S et-al. Intraductal papillary mucinous neoplasms of the pancreas: radiological predictors of malignant transformation and the introduction of bile duct dilation to current guidelines. Br J Radiol. 2016;89 (1061): 20150853. doi:10.1259/bjr.20150853 - Pubmed citation
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