Ampullary somatostatinoma. An immunohistochemical and ultrastructural study

Two new cases of ampullary somatostatinoma are reported. In one case the tumor is associated with an increase in somatostatin-positive cells in the adjacent duodenal mucosa. Both tumors show a predominant glandular pattern with many psammomatous calcified bodies. Such bodies seem to arise by calcium phosphate encrustation of intraluminal cellular debris. The neoplastic cells contain two distinct types of intermediate filaments: the first is located along the plasma membrane and reacts to keratin antiserum; the other, appearing as paranuclear aggregates, reacts to neurofilament antiserum. The neoplastic cells show signs of intestinal differentiation (microvilli, glycocalyceal bodies, filamentous core rootlets) as well as of neuroendocrine differentiation (secretory granules, whorls of neurofilaments).