Ultrastructural features of intercellular contacts in pancreatic insulinomas

Insulinomas are the most frequent functional pancreatic neuroendocrine tumors. To study the ultrastructural structure intercellular contacts of insulinomas G1-2. Material about tumors of 38 patients who had been in the surgical treatment from 2010 to 2015 was studied. Male to female ratio was 38:62 (10/28). The age range differed from 23 to 71 y.o. The average age was 48.2 years. All the patients had the symptoms of hyperinsulinism determined. In 39% (1 5/38) the MEN syndrome was revealed. All the tumors were clinically benign. The electron and histological study of the removed tumors was conducted. In 39,5% (15/38) the tumor was localized in the head, in 24% - in the tail, in 21% - in the body, and in 5% - in the isthmus. In two cases the lesion affected the body and the tail of the gland (5%), and in another two - it affected the whole gland (5%). Tumor nodule size ranged from 0.8 to 5.5 cm. The average size was 2.0 cm. G1 was present in 84%. G2 was present in six cases. The tumors were composed of monomorphic cells with a low nucleus-cytoplasmic ratio and abundant eosinophilic cytoplasm. Two main ß-cell phenotypes in different stages of functional activity were detected. The first type of cells was “the light cells», which were dominated by the processes of synthesis of granules. The second type was “the dark cells», in which the processes of hormone secretion outside the cell membrane were actively running. The two cell types were connected by the desmosomal junctions. In the area of contact of adjacent cells' cytomembrane the portions of the cytoplasmic fusion with the formation of cytoplasmic bridges were determined. This resulted in the formation of syncytium-like structures. These changes were more common between “the light cells”. Through the cytoplasmic bridges the metabolic processes of nutrients and secretory material occure. Perhaps, it is a condition for the release of granules synchronization processes in the bloodstream, which may explain the cause of hypoglycemic crises. Syncytium-like structure due to the large size cannot penetrate through the fenestrated capillary, eliminating the possibility of the formation of the secondary tumors. Moreover, their production makes it impossible to complete the next cell division. Progression of the tumor stops. The formation of syncytium-like structures may be one of the causes of a conservation of a benign potential in insulinoma.

insulinoma, neuroendocrine tumor, ultrastructure, electronic microscopy, pancreas