Grading of intracranial tumors following the WHO classification.

The grading scheme contained in the WHO classification "Histological Typing of CNS Tumors" has been introduced after long and controversial discussions. Of the three major systems for grading intracranial tumors which were at hand, Zülch's is closest to the WHO system. The criteria for, and general remarks about, the WHO system for the evaluation of malignancy grades are delineated. Their almost complete concordance with Zülch's "horizontal" scheme is emphasized, although some minor differences are mentioned. It is the author's belief, which may, however not be theoretically fully justified, that this system has been applied successfully since the publication of WHO classification. Opposition to WHO grading mostly reflects general pessimism about the possibility of gaining information concerning proliferation from morphology. However, the analysis of therapeutic trials in the last decades has shown that histological grade is of great predictive value. This correlation can be improved by the broad and exact application of the system.