ABERRANT INSULINOMA OF THE DUODENAL BULB

A rare insulin-immunoreactive neuroendocrine tumor of the duodenum in a 54 year old male is reported, The incidentally identified tumor was located on the anterior free wall of the duodenal bulb and measured ap proximately 6 mm in diameter, Uncomplicated endoscopic resection of th e tumor was carried out. The lesion exhibited classic histologic featu res of insulinoma of the beta-islet cell type with stromal amyloid dep osition, In addition to positive reactivities of chromogranin A, neuro n-specific enolase, synaptophysin, Leu 7 (CD57), cystatin C, CA15-3 an d cytokeratin, the nonargyrophilic tumor cells were strongly immunorea ctive for insulin and C-peptide, The stromal amyloid was clearly label ed for amylin, A few cells were stained for somatostatin, whereas othe r hormones were negative, Interestingly, a few isolated insulin-positi ve cells were identified in the non-neoplastic duodenal mucosa in the proximity of the tumor, Immunoelectron microscopy using paraffin secti ons disclosed insulin-immunoreactive secretory granules in the cytopla sm, The patient exhibited no signs or symptoms of hypoglycemia. Serum insulin levels were not measured prior to resection, No tumors were de monstrated in the pancreas. Magnetic resonance imaging revealed a 1 cm asymptomatic pituitary mass, in association with moderately elevated serum prolactin levels, The patient is currently being followed up in the outpatient clinic.