[The intraneural endocrine cell--the starting point of the origin of carcinoid tumors?].

Endocrine cells are demonstrable by electron microscopy in the lamina propria of the appendix mucosa. They are always in direct contact with a nerve fibre. The endocrine cell (types EC1, and EC2) and the polyaxonal non-myelinated nerve fibres are separated from the interstitial connective tissue by a common continuous basal lamina. The term "ECZ-NF complex" is suggested by the author to describe this morphological and functional unit. The intraneural endocrine cells may be derived from neuroendocrine-programmed ectoblasts according to Pearse (1977). These intraneural endocrine cells may comprise an additional extraepithelial cellular part of the "diffuse neuroendocrine system". The electron microscopic demonstration of similarly structured "eZ-NF complexes" (polypeptide-producing endocrine cell and nerve fibre) in connection with the demonstration of small nerve fibres within carcinoids of appendix, caecum and rectum allows us to propose a hypothetical pathogenesis of gastrointestinal carcinoids from these intraneural endocrine cells.