[On the classification of experimental brain tumours (author's transl)]

The classification of experimental brain tumours is essential for mutual understanding and for comparison with human CNS tumours. The histogenetic principle of human neurooncology should be applied to the classification of experimental tumours, too. In rats different quantities of experimental tumours have been classified as ependymonas by various authors. The aim of our morphological investigation is to elucidate the reasons of the differences. The tumours were induced with ethyl- or methylnitrosourea in newborn or adult rats or by trnasplacentar application. Serial sections through the cerebrum of 57 rats were performed to detect early tumour stages and to study their localization within the brain. In other rats the brain and spinal cord were investigated in selected areas.

174 small tumours, most of them less than 2 mm in diameter were found. Early tumour stages never involved the ependyma of the ventricular walls or of the central canal of the spinal cord. These tumours exhibited a strong activity of acid phosphatase whereas the ependymal cells were inactive. No true rosettes, cilia or blepharoblasts were seen in the tumours. No perivascular zones, free of nuclei were found. In literature the experimental ependymomas have been diagnosed on grounds of row-like arrangements of tumour cells. We found similar peculiar structures in large experimental oligodendrogliomas and glioblastomas. Our findings suggest that the classification of experimental brain tumours as ependymomas is not justified in many of the cases published in literature. To avoid misinterpretation of experimental results in their significance for human neurooncology the criteria of the histogenetic classification should be applied thoroughly.