Acinar Cell Cystadenoma of the Pancreas

Abstract

Acinar cell cystadenoma (ACA) of the pancreas was initially described as a non-neoplastic cyst of the pancreas and, at that time, referred to as "acinar cystic transformation." In subsequent studies, these lesions were given the designation of "-oma," despite the relative lack of evidence supporting a neoplastic process. To characterize these lesions further, we examined the clinical, pathologic, and immunohistochemical features of 8 ACAs. The majority of patients were female (7 of 8, 88%) and ranged in age from 18 to 57 years (mean, 43 y). Grossly, the cysts involved the head (n=5), body (n=1), or the entire pancreas (n=2). ACAs were either multilocular (n=4) or unilocular (n=4) and ranged in size from 1.8 to 15 cm (mean, 6.8 cm). Histologically, multilocular ACAs were lined by patches of acinar and ductal epithelium. Immunolabeling, including double-labeling for cytokeratin 19 and chymotrypsin, highlighted the patchy pattern of the ductal and acinar cells lining the cysts. In some areas, the cysts with patches of acinar and ductal differentiation formed larger locules with incomplete septa as they appeared to fuse with other cysts. In contrast, the unilocular cases were lined by 1 to 2 cell layers of acinar cells with little intervening ductal epithelium. Nuclear atypia, mitotic figures, necrosis, infiltrative growth, and associated invasive carcinoma were absent in all cases. In addition, we assessed the clonal versus polyclonal nature of ACAs, occurring in women, using X-chromosome inactivation analysis of the human androgen receptor (AR) gene. Five of 7 cases were informative and demonstrated a random X-chromosome inactivation pattern. Clinical follow-up information was available for all patients, and follow-up ranged from 10 months to 7.8 years (mean, 3.6 y), with no evidence of recurrence or malignant transformation. We hypothesize that early lesions are marked by acinar dilatation that expands into and incorporates smaller ductules and later larger ducts. As the cysts increase in size, they fuse forming larger cysts. Later lesions demonstrate a unilocular cyst lined by predominantly acinar epithelium with scattered ductal cells. The term cystadenoma, with its neoplastic connotation, does not seem to accurately reflect the histologic, immunohistochemical, or molecular features of these lesions. We suggest readopting the term "acinar cystic transformation" until the non-neoplastic versus neoplastic origin of these lesions can be resolved.

Fine Needle Aspiration Cytology of Acinar Cell Cystadenoma of the Pancreas

“…In some cases, eosinophilic secretions can be demonstrated in the lumen [2,4]. By immunohistochemistry, the cells with acinar differentiation are positive for trypsin, chymotrypsin, cytokeratin 19 and cytokeratin 7, the latter demonstrating stronger positivity in the epithelial areas with ductal differentiation [2,3,4,5]. Ultrastructurally, the cells contain dark round granules in the apical portion of their cytoplasm.…”

“…Histomorphologically, both unilocular and multilocular ACCs are lined by a single or dual layer of epithelium that can range from flattened to cuboidal. The epithelial cells are cytologically bland with basally located regular nuclei that lack atypia or mitoses [2,3,4,5]. The cytoplasm shows at least focal evidence of acinar differentiation [2,3,4] in the form of apically located coarse, brightly eosinophilic zymogen granules.…”

“…The latter may involve the pancreas in a diffuse fashion [3,4]. Histomorphologically, both unilocular and multilocular ACCs are lined by a single or dual layer of epithelium that can range from flattened to cuboidal.…”

“…Grossly, ACCs can be either unilocular or multilocular [1,2,3,4,5,6]. The latter may involve the pancreas in a diffuse fashion [3,4].…”

“…Some patients may present with abdominal pain and discomfort [3,4], while others are asymptomatic [4,5]. ACC is regarded as neoplastic lesion by the majority of authors, although some believe it may arise from cystic dilatation of pancreatic acini [3]. …”