[Ultrastructure of B-cell tumors of the pancreas (insulinomas - insular carcinoid tumors)].

The subcellular organization of 6 B-cell tumours of the human pancreas was studied. The tumour parenchyma consisted of processed light, dark, and moderately electron dense cells containing insulin granules. The presence of villi in the cytoplasm of tumour cells and intranuclear fibrills was demonstrated. The participation of tumour cells in formation of amyloid-like thin-fiber substance filling the intercellular and perivascular spaces was established. The similarity between endothelial cells of tumour vessels and parenchymatous cells was shown. A hypothesis on neuroectodermal origin of the endocrine tissue of the pancreas is supported.