Increased proliferative activity due to necroses induced by pre-operative embolization in benign meningiomas

The proliferative behaviour of 35 benign intracranial meningiomas was investigated which were embolized for devascularization 3 to 268 hours prior to surgical exstirpation. The nuclear proliferation antigen Ki-67 was visualized by means of the monoclonal antibody MIB1 on formalin fixed and paraffin embedded tissue. Tumor cells and inflammatory reactions were recognized by means of conventional staining procedures and by immunohistochemical detection of HAM56, LCA, HLA-DR, CD15-epitope and vimentin. Extravasation and proliferation of granulocytes, macrophages, lymphocytes and the degree of expression of MHCII antigens was estimated according to a 7-point ordinal scale. Confirming preliminary observations of others the proliferation index within the perinecrotic tumor rim (PIperinec) exceeded that of intact tissue highly significantly. PIperinec peaked at the third to fourth day after embolization and kept this level until the seventh day. The time course of PIperinec was paralleled by that of macrophages, whereas--expectedly--granulocytes occured earlier and lymphocytes and HLA-DR-positivity somewhat later. The timely relationships suggested that the perinecrotic increase in tumor cell proliferation was mainly due to macrophage-born mitogens. Perinecrotic proliferative activity in embolized meningiomas does not reflect genuine tumor proliferation and should not be used for assessment of the presence or degree of malignancy in a given tumor.