Full pancreatic endocrine differentiation in a mediastinal teratoma.

In a mediastinal teratoma containing pancreatic tissue rich in islet cells, immunofluorescence studies showed a high degree of differentiation of the endocrine tissue. Insulin-, glucagon-, somatostatin-, and pancreatic polypeptide(PP)-containing cells were all consistently represented. They showed the same precise topographic distribution that is seen in normal islets (i.e., a central core of insulin-containing cells with the other cell types in a peripheral position) and that is thought to be important for the integrated function of the islets. This may explain the absence of clinical symptoms of hypoglycemia. In addition, a nonrandom distribution of endocrine cell types, with PP-rich and PP-poor areas, similar to that found in pancreatic regions embryologically derived from the ventral and dorsal anlagen, respectively, was observed. This finding suggests that the unknown mechanisms responsible for the dissimilar endocrine cell contents in pancreatic regions of different embryologic origins were operating in the teratoma.