Embryonal neuroepithelial tumors induced by human adenovirus type 12 in rodents. 2. Tumor induction in the central nervous system.

Intracranial inoculation with human adenovirus type 12 (Ad12) induced tumors multicentrically in the brain and spinal cord of 37.2% of hamsters, 30.2% of mice, and in the brains of 91.0% of rats. Brain tumors developed preferentially at the olfactory bulb, lateral ventricular horns, tapetum region, and ventral and dorso-caudal aspects of the fourth ventricle. In the spinal cord, tumor developed on the dorsal aspect and, in hamsters, at the root of the cauda equina. Microtumors were found almost invariably in the subependymal areas and occasionally in the leptomeninges. The histological and ultrastructural features indicated extremely undifferentiated neoplasms analogous with the intraperitoneal tumors described in the companion report. Closely packed small polygonal or tadpole-shaped tumor cells resembled the subependymal cell remnants of normal perinatal brains. Divergent differentiation consisted in an intermingling of a fascicular or palisading arrangement of spongioblastic cells, of incomplete perivascular pseudorosettes and of neuroblastic (Homer Wright type) rosettes. Neither distinct neuronal nor neurogial fibrils were demonstrated. True ependymoblastomatous and medulloepitheliomatous rosettes were rarely encountered. These results indicate that Ad12-induced tumors in the central nervous system are of embryonal neuroectodermal origin and with limited differentiation, leading to divergent phenotypes corresponding to medulloblastoma, neuroblastoma, primitive spongioblastoma, ependymoblastoma and, rarely, medulloepithelioma.