Review Article

Intraductal papillary mucinous tumor of the pancreas☆

Nomenclature

Since the initial description of IPMT, various names have been given to this disease, some of which are still used (Table 1).

Pathology

IPMT may involve the main pancreatic duct (main duct type [MDT-IPMT]), in either a diffuse or segmental manner, or the tumor may arise in a branch duct (branch duct type [BDT-IPMT]). The hallmarks of IPMT are diffuse or segmental ductal dilation in the absence of a stricture of the main or branch duct, intraductal growth of mucin-producing epithelial lining cells that have a “flat” or papillary-villous appearance, and protrusion and dilation of the major and/or minor papilla from which mucous

Epidemiology and etiology

Because IPMT is a relatively rare entity only recently described in detail, its epidemiology remains unclear. The true incidence of IPMT in the population is unknown, although surgical series suggest that it accounts for between 8% and 20% of pancreatic resections for malignancy.4, 18 There is a perception among gastroenterologists and surgeons that the incidence of this entity is rising. Whether this represents a true increase or reflects increased use and improved accuracy of abdominal

Pathogenesis

IPMTs are clearly premalignant lesions, with up to 50% of patients having invasive carcinoma at operation.9, 26, 27 A hyperplasia-adenoma-carcinoma sequence has been proposed for the pathogenesis of IPMT based on histopathologic and molecular biology studies.8, 28, 29, 30 The natural history of this proposed sequence is unknown, although the progression is thought to be extremely slow. A case has been reported of noninvasive adenocarcinoma in an IPMT in which the tumor was resected 27 years

Molecular pathogenesis

Despite advancing knowledge of the molecular basis of pancreatic ductal adenocarcinoma, little is known about the molecular abnormalities in the less common IPMT. Available data suggest that the evolution of neoplasia in IPMT follows molecular pathways that are similar but distinct from those of pancreatic ductal adenocarcinoma (Table 5).

Clinical features

IPMT occurs most commonly in men in the age range of 60 to 70 years. Most patients have a long history of recurrent acute pancreatitis (30%-80%) or symptoms that mimic chronic obstructive pancreatitis. Symptoms are likely caused by intermittent obstruction of the main pancreatic duct. Other symptoms include weight loss (46%), anorexia (20%), and steatorrhea (17%). Jaundice and vomiting occur in about 10% of cases. Many patients are asymptomatic and the tumor is found incidentally when an

Differential diagnosis

IPMT is often misdiagnosed initially based on clinical findings as chronic obstructive pancreatitis, MCT of the pancreas, or pancreatic ductal adenocarcinoma. Conventional imaging studies such as CT and transabdominal US often cannot distinguish these distinct clinical entities. Misdiagnosis or delay in diagnosis may result in inappropriate therapy and such errors favor the carcinomatous process.

Although the surgical pathologist can rely on the presence or absence of ovarian-type stroma to

Diagnosis

A variety of imaging methods are available for the diagnosis of IPMT, including the identification of malignant transformation. There is no “imaging method of choice” because each has advantages and disadvantages; optimally, a combination of methods will usually be required for diagnosis and preoperative assessment including staging.

Preoperative assessment of extent and invasiveness: Is it important?

Patients with an IPMT that are surgically resected have a good prognosis. Because a large proportion of IPMT do not contain foci of invasive carcinoma, and because there is evidence to suggest a long course before malignancy develops, surgery is not required for all patients, especially if imaging and other studies favor the presence of a benign tumor. Nonsurgical approaches might be used more frequently if there were reliable methods for detecting malignancy.

Smoking, excessive use of alcohol,