Supratentorial recurrences of gliomas. Morphological studies in relation to time intervals with oligodendrogliomas.

On the basis of a three stage grading system we report 23 stage one recurrent oligodendrogliomas (O 1), and 29 stage two recurrent oligodendrogliomas (O 2). In the O 1 group after the first interval 15 became O 2 and 2 became glioblastomas. Twenty tumours of the O 2 group after the first interval were not changed, three became oligodendroglioma-astrocytomas stage 2, and six became glioblastomas. The time relation for the recurrent phase in the primary O 1 group is calculated as 42 months, and in the primary O 2 group as 22 months, but this is without significance. For the development of malignancy, especially for the change to glioblastoma, a prominent participation by transformed local astrocytes seems to be essential. Postoperative irradiation most probably does not favour malignant change. A prolongation of the expectation of life by radiotherapy is not noticed.