Ultrastructural characteristics of duodenal somatostatinomas. II. Granules and vesicles.

Ultrastructural findings of granules and vesicles appearing in tumor cells of somatostatinoma are reported. Except for D granules, one granule and four kinds of vesicles were discerned. Some tumor cells had granules of the exocrine type which were similar to those of the chief cells of the stomach. Very small clear vesicles (YO and KO) had accumulated mainly in the apical region of the somatostatinoma cells. Both vesicles were round, unit-membrane bounded and clear in the center, each measuring about 90 and 30 nm in diameter. The cored vesicles normally seen in the sympathetic system were revealed. Doughnut vesicles characterized by double contour membranes were detected together with the cored vesicles. A mixture of exocrine cells of the chief cell-type in the paraneuroma has not been previously reported. And we have as yet very little information as to the doughnut vesicle.