Answer: Intraductal papillary mucinous neoplasm (IPMN), borderline

Histology: The mass consists of a cystic lesion lined by mucinous epithelium involving the main pancreatic duct. The epithelium shows columnar cells with cytologic atypia analogous to that seen in colonic tubular adenoma. No invasive carcinoma is identified.

Discussion: IPMN is a grossly visible cystic lesion that involves the pancreatic duct. IPMN are lined by mucinous epithelium, which distinguishes them from serous cystadenomas. They are graded as adenoma, borderline, or carcinoma in-situ. When the mucinous epithelium shows no atypia, it is given the grade adenoma. When it shows atypia analogous to that seen in colonic tubular adenoma, a borderline grade is given. When the lesion shows marked cytologic atypia with tufting of cells reminiscent of micropapillary architecture, it is classified as carcinoma in-situ. Care should be given to thoroughly sample the lesion, as invasive carcinoma arises in IPMN in about 30% of cases. When there is an invasive carcinoma, it is often of the mucinous (colloid) type, although the usual tubular type may also be seen. Also, patients who have invasive carcinoma associated with an IPMN may follow a more favorable course compared to those with conventional ductal adenocarcinoma without IPMN. PANIN usually involves smaller ducts and does not dilate them to form a cystic mass. In addition, unlike IPMN, they are not grossly identifiable.

References:
Sohn TA, Yeo CJ, Cameron JL, Iacobuzio-Donahue CA, Hruban RH, Lillemoe KD Intraductal papillary mucinous neoplasms of the pancreas: an increasingly recognized clinicopathologic entity. Ann Surg. 2001 Sep;234(3):313-21; discussion 321-2.

Adsay NV, Conlon KC, Zee SY, Brennan MF, Klimstra DS. Intraductal papillary-mucinous neoplasms of the pancreas: an analysis of in situ and invasive carcinomas in 28 patients. Cancer. 2002 Jan 1;94(1):62-77.