Acinar Cell Cystadenoma of the Pancreas: A Benign Neoplasm or Non-Neoplastic Ballooning of Ducts?
Aatur D Singhi, Stephanie Norwood, Ta-Chiang Liu, Christopher Wolfgang, Richard Schulick, Ralph H Hruban. Johns Hopkins Medical Institutions, Baltimore, MD
Background: Acinar cell cystadenoma of the pancreas is a rare cystic lesion. Although it was initially described as the benign counterpart of acinar cystadenocarcinoma, and given the neoplastic designation “-oma,” the nature of this process is unclear. We have collected a series of 6 cases and examine the possible pathogenesis of this entity using immunohistochemistry.
Design: Six resection specimens were collected from our institution between 2004 to 2011. In each case, clinical records, gross reports and H&E-stained slides were reviewed. Immunohistochemical stains for trypsin, chymotrypsin, CK7, CK19, synaptophysin and chromogranin were performed for each case.
Results: The majority of patients were female (5 of 6, 83%) and ranged in age from 18 to 57 years (mean, 41 years). One patient was noted to have a first-degree relative with a similar cystic lesion by imaging. Grossly, the lesions were either multilocular (n=3) or unilocular (n=3), and ranged in size from 2.5 to 15 cm. The cysts involved the head (n=3), body (n=1) or the entire pancreas (n=2). Histologically, the multilocular lesions were characterized by dilated ducts lined by patches of ductal and acinar epithelium. Immunolabeling highlighted the patchy nature of the ductal and acinar cells lining the dilated spaces and suggested that ducts had expanded into and appeared to incorporate the surrounding acinar parenchyma into their walls. In 2 of 3 multilocular lesions, the ducts also involved islets of Langerhans. In some areas, the ducts formed larger locules with incomplete septa as they appeared to fuse with other ducts. In contrast, the unilocular cases were lined by one-to-two cell layers of acinar cells with little intervening ductal epithelium and displayed a thick hyalinized cyst wall. Nuclear atypia and infiltrative growth were absent in all cases.
Conclusions: Acinar cell cystadenoma appears to evolve over multiple stages. We hypothesize that early lesions are marked by ductal dilatation that expands into and eventually incorporates the surrounding acinar and endocrine components of the pancreas. As the ducts increase in size, they begin to fuse forming larger cysts. Later lesions demonstrate a unilocular cyst lined by predominantly acinar epithelium with a thick hyalinized cyst wall. Regardless of the pathogenesis, acinar cell cystadenoma is not a neoplastic lesion as the name implies. We suggest the name should be changed to Cystic Acinar Adenomatoid Transformation (CAAT).
Tuesday, March 20, 2012 9:30 AM
Poster Session III # 263, Tuesday Morning