Ultrastructure of a chemodectoma

Electron microscopic study of a chemodectoma has revealed structural traits consonant with the benign nature of the neoplasm. Nuclei did not demonstrate unusual features. Mitochondria were abundant and large. Smooth‐surfaced endoplasmic reticulum was present as small vesicles dispersed throughout the cell cytoplasm. Rough‐surfaced endoplasmic reticulum varied in development from cell to cell, being prominent in some. Golgi apparatus was similarly variable, but generally inconspicuous. Two aspects were of particular note: (1) It was not possible to recognize with certainty 2 cell types analogous to those present within the animal carotid body; thus cells directly comparable to the sustentacular cells of the latter were not identified; the axonal relationships of the animal carotid body were not encountered; nor were the tumor cells enveloped by cytoplasmic processes, as is the case in the normal animal carotid body; (2) granules were noted within the tumor cells, which resembled the granules observed in cells of known endocrine function (the adrenal medulla, the argentaffin cell, the alpha cells of the pancreas). The presence of these granules within the chemodectoma suggests an endocrine function. Furthermore, if the poor representation of the axonal‐sustentacular cell system observed within this tumor constitutes a true reflection of the structure of human chemoreceptor tissues, it is possible that humoral secretion may have supplanted, in man, the neuronal mechanism whereby this system is able to influence circulatory haemodynamics in animals.