RHABDOID TRANSFORMATION OF TUMOR-CELLS IN MENINGIOMAS - A HISTOLOGIC INDICATION OF INCREASED PROLIFERATIVE ACTIVITY - REPORT OF 4 CASES

Four cases of meningeal tumors in adults (ages ranging from 28 to 84 y ears) are presented. All had the typical gross appearance of meningiom as at operation. In three tumors, areas of meningothelial or fibroblas tic meningiomas showed transition to cell groups of the rhabdoid type. In the fourth case only rhabdoid cells were encountered, possibly rep resenting a total ''take-over'' of a meningioma by rhabdoid elements. In the three cases with mixed pattern, the rhabdoid cells showed more anaplasia and atypism than the conventional meningiomatous elements. I n case 3 this was expressed by very high MIB-1 positivity in the rhabd oid cells and absence of same in the fibroblastic meningiomatous eleme nts. These cases (the first three with certainty, the fourth with a st rong likelihood) indicate that the phenotypic changes to cells with '' rhabdoid'' morphology may involve meningiomas and that such change is associated with aggressive biologic and clinical behavior of the tumor s showing this type of alteration.