Cystic forms of typically solid pancreatic tumors.

In addition to the well-known cystic lesions, the differential diagnosis of pancreatic cysts also includes cystic counterparts (or cystic change in) otherwise typically solid tumors of this organ. Pancreatic endocrine neoplasms (islet cell tumors) and ductal adenocarcinomas sometimes undergo cystic degeneration, the latter usually due to necrosis. Also, although acinar cell carcinoma is typically a solid tumor, its rare cystic counterpart, "acinar cell cystadenocarcinoma," has been reported. A rare variant of pancreatic ductal adenocarcinoma referred to as "large-duct-type" is characterized by microcystic ectasia of the invasive glands and may mimic other cystic tumors at the microscopic level. Secondary tumors, although exceedingly rare, may also potentially fall into the differential diagnosis of pancreatic cysts. Often, the morphological characteristics of these lesions are identical to those of their solid counterparts, and their diagnosis is not difficult if one is aware of their existence. This review focuses on these cystic counterparts of otherwise characteristically solid pancreatic neoplasms. Solid pseudopapillary tumor, in which cystic degeneration is so common that "cystic" has been a part of many alternate terms assigned to this neoplasm, is discussed in another article of this issue of Seminars in Diagnostic Pathology.