Answer: Paraganglioma

Histology: This well-demarcated neoplasm is composed of nests of cells in a richly vascular background. The neoplastic cells have a granular cytoplasm and the nuclei have the type of pleomorphism one frequently sees in endocrine neoplasms. The neoplastic cells are synaptophysin positive and immunolabeling for S-100 protein highlights sustentacular cells.

Discussion: Only a handful of paragangliomas have been reported in the pancreas. Grossly these are usually well-demarcated richly vascular and rubbery masses. The neoplastic cells form nests (“zellballen”). True lumen formation is not seen. Large bizarre nuclei of no particular clinical significance can be seen. The neoplastic cells express endocrine markers such as synaptophysin and chromogranin, but usually do not express keratin or pancreatic endocrine hormones. Immunolabeling for S-100 will highlight the sustentacular cells. Little is known about the prognosis of these neoplasms, but the prognosis for patients with one of these neoplasms is believed to be similar to that of patients with extra-pancreatic paragangliomas.