Chemically induced esthesioneuroepithelioma: ultrastructural findings.

Tumors of the olfactory epithelium of rats were induced with two different nitrosamines: 2,6-dimethylnitrosomorpholine and N-nitrosopiperidine. Both carcinogens yielded identical tumors consisting of small, undifferentiated, neuroblastic cell elements without specialized cell contact. Cell processes contained microtubuli, centrioles, and neurosecretory granules. Two kinds of rosettes were encountered frequently: neuroblastic Homer Wright rosettes consisted of undifferentiated cells, surrounding a minute lumen filled with amorphous material; and Flexner rosettes showed a higher degree of maturation. Inside their central lumen, cell processes with characteristic features of olfactory sensory cells (basal bodies, cilia, centrioles, microtubuli) could be demonstrated. The stem cell of this tumor is most likely the undifferentiated light basal cell inside the olfactory epithelium, since its ultrastructural appearance and its cytoskeleton are alike. At least under neoplastic conditions, this stem cell may likewise differentiate into epithelial cells, since transition to squamous cell carcinomas has been observed. In view of their overwhelming similarity to their human counterpart, the induced tumors are most likely to represent esthesioneuroepitheliomas.