Johns Hopkins Pathology

 
Key Points:
  • Tall, columnar mucin-producing epithelium
  • "Ovarian-type" stroma
Images: Epithelium and "ovarian-type" stroma |

The cysts of mucinous cystic neoplasms, as one would expect from their gross appearance, usually do not communicate microscopically with the pancreatic ducts. The cysts are lined by tall columnar mucin-producing epithelium. These columnar cells have basal nuclei and abundant intracytoplasmic apical mucin, and can form flat sheets or papillae. The epithelium is often focally denuded and several sections may be needed to demonstrate an epithelial lining. The epithelium can be quite bland with uniform small basally placed nuclei, or the epithelium can show significant architectural and cytological atypia with cribriforming, an increased nuclear to cytoplasm ratio, loss of nuclear polarity and pleomorphism. Most remarkably, in a single neoplasm there is often an abrupt, at times striking, transition from completely bland epithelium to epithelium with sigificant atypia.

The walls of the cysts contain a very distinctive "ovarian-type" stroma. This stroma is composed of densely packed spindle cells with sparse cytoplasm and uniform elongated nuclei. The stroma can be partially hyalinized in some mucinous cystic neoplasms, and it is not unusual for the stroma to contain entrapped normal pancreatic tissue including islets of Langerhans and acini.

Non-invasive mucinous neoplasms are categorized into adenomas, borderline neoplasms and carcinoma in situ based on the degree of architectural and cytological atypia of the epithelial cells. Mucinous cystic neoplasms should be categorized based on the worst degree of atypia present in the lesion.

Approximately, one-third of all mucinous cystic neoplasms are associated with invasive carcinoma. These invasive carcinomas are usually a tubular/ductal type of invasive adenocarcinoma. Unidfferentiated carcinomas with osteoclast-like giant cells, invasive adenosquamous carcinomas and colloid carcinomas have also been reported. The diagnosis of an invasive carcinoma should only be made when there is clear-cut invasion into the stroma. This invasion is often associated with a desmoplastic reaction. The invasive and in situ carcinomas in mucinous cystic neoplasms can be very focal. A benign diagnosis cannot be established on biopsy alone, nor can it be established in an adequately examined resected specimen.

Mucicarmine and PAS stains will confirm the presence of substantial quantities of intracellular and extracellular mucin. These are predominantly sulphated acid mucins with some neutral mucins; two-thirds of the neoplasms are alcian blue positive. Gremilius/Churukin-Schenk (argyrophilic) and Fontana-Masson (argentafin) stains will stain scattered endocrine cells at the base of the epithelial cells.

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