Intraductal papillary mucinous neoplasm

Intraductal papillary mucinous neoplasms or tumours (IPMNs or IMPTs) are cystic tumours of the pancreas.

Epidemiology

These tumours are most frequently identified in older patients (50-60 years of age) 6. Main duct type (see below) appears to present a decade or so earlier on average than branch duct type 5. There may be a slight female predilection 7.

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 5,9

Pathology

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.

Macroscopic appearance

Divided macroscopically

  • main duct
    • 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

Solid components as well as bile duct dilation 14 are suspicious of malignant transformation.

Histology

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 elevation of these a marker of invasiveness 8

Radiographic features

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.

CT

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 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

MRI

MRI appearances are similar to those seen on CT. Mural nodules appear hypointense compared to surrounding fluid and mucin and enhance following administration of contrast. Mucin globules do not enhance and lie dependently within the duct.

Ultrasound

Ultrasound demonstrates dilated ducts which appear hypoechoic. Mural nodules and mucin globules may appear hyperechoic, and difficult to separate from adjacent pancreatic parenchyma 6.

Diffuse main duct type has appearances essentially indistinguishable from chronic pancreatitis, with duct dilatation and parenchymal atrophy 5.

ERCP

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.

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.

Differential diagnosis

General imaging differential considerations include


Pancreatic pathology
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Article Information

rID: 1521
Section: Pathology
Synonyms or Alternate Spellings:
  • Intraductal papillary mucinous neoplasms
  • Intraductal papillary mucinous neoplasms (IPMN)
  • IPMN
  • IPMT
  • Intraductal papillary mucinous tumour
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    Case 1: at the pancreatic head
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    IPMN of tail of p...
    Case 2: at the pancreatic tail
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    Case 3: with a choledochal cyst
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    Case 4: probable main duct type
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    Case 5: main duct type
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    Case 5: shown on MIP
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    Case 6
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    Case 7: multifocal side branch type
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