Myoepithelial hamartoma as a solitary mass in the pancreatic parenchyma: the first case report.

Solid hamartoma of the pancreas is very rare, and only 3 cases have been reported thus far. A patient underwent pancreaticoduodenectomy due to a mass in the head of the pancreas which was suspected to be a borderline malignant tumor, but the histologic diagnosis turned out to be myoepithelial hamartoma (MEH) or adenomyoma. It was characterized by benign duct and glandular structures surrounded by proliferating smooth muscle, and acinus formation was not observed. Immunohistochemical stain for smooth muscle actin (SMA) was positive in spindle cells, and CD34 was negative, differentiating it from the three previously reported cases of solid hamartoma of the pancreas. MEH is an entity that is on the same spectrum as heterotopic pancreas. MEH is rare and has usually been reported in the gastrointestinal tract. To the best of our knowledge, MEH has never been reported in the pancreas. Therefore we report the world's first documented case of MEH of the pancreas.