Noninvasive and minimally invasive intraductal papillary mucinous neoplasms of the pancreas

Intraductal papillary mucinous neoplasms of the pancreas are characterized by mucinous dilatation of the duct lined with neoplastic cells forming papillae. Noninvasive intraductal papillary mucinous neoplasms are classified into low-, moderate-, or high-grade dysplasia. The epithelium of the papillae exhibits 4 morphologically distinct types-gastric, intestinal, pancreaticobiliary, and oncocytic-with specific expressions of mucin glycoproteins. Intraductal papillary mucinous neoplasms with low-grade dysplasia comprise papillae resembling gastric foveolae or pyloric glands; those with moderate dysplasia usually comprise papillae exhibiting intestinal features. High-grade intraductal papillary mucinous neoplasms of gastric type exhibit short, complex, and irregular shapes of papillae with highly atypical nuclei. High-grade intraductal papillary mucinous neoplasms of the intestinal type exhibit large villous papillae composed of tall columnar cells with enlarged atypical nuclei, basophilic cytoplasm, and abundant acid mucin; those of the pancreaticobiliary type exhibit fern leaf-like thin branching complex papillae composed of cells with amphophilic to basophilic cytoplasm and high nucleus-to-cytoplasmic ratios. High-grade intraductal papillary mucinous neoplasms of the oncocytic type exhibit arborizing papillae composed of eosinophilic cells containing enlarged round nuclei with prominent nucleoli. Intraductal papillary mucinous neoplasms with minimal invasion have invasion slightly beyond the duct wall. Invasive foci within a 5-mm distance from involved ducts may be a practical criterion for assessing minimal invasion. Patients with low-or moderate-grade intraductal papillary mucinous neoplasms show a fairly good prognosis; almost no patients died owing to the neoplasm. However, patients with high-grade neoplasms and those with minimally invasive neoplasms may show an unfavorable prognosis, with 5-year survival rates of 94% to 98% and 89% to 91%, respectively.