MENINGIOMA - CLASSIFICATION AND GRADING

Meningiomas account for the most frequent primary intracranial neoplas ms in adults. In 1993, the so-called atypical meningioma has additiona lly been introduced in the revised edition of the WHO Classification o f Tumors of the Central Nervous System and should characterize meningi omas with an increased propensity to recur. Since the given qualitativ e histological criteria apply both to the ''atypical'' and anaplastic meningioma, mere histological grading appears somewhat critical. There fore, additional parameters were tested for their contribution to meni ngioma grading: First of all, we succeeded in defining 3 meningioma '' grades'' by calculating corresponding 95% confidence intervals for the morphometrically assessed Ki-67 indices of 160 meningiomas in total,t he validity of which was proved by comparison with the ''recurrence''- free intervals. Histologically, atypical meningiomas were distinguishe d by a ''syncytial'', poorly structured growth pattern and macronucleo li. Only occasionally, nuclear pleomorphism, necroses and mitotic figu res were found. Cytogenetics revealed, in 50% of the ''atypical'' and anaplastic meningiomas, partial loss of the short arm of one chromosom e 1 (1p-). Histochemically, we could demonstrate, that the tissue non- specific type of alkaline phosphatase (ALPL), which is coded on chromo some 1 p, is a convenient recurrence-and progression-associated marker enzyme for meningiomas with 1 p-loss (loss of enzyme activity in 30/3 9 of intermediate and 8/8 anaplastic meningiomas). We favor to address the WHO ''atypical'' meningioma as meningioma of the intermediate typ e, since the attribute ''atypical'' in the context of histological dia gnoses is highly susceptible to misinterpretations.