Granular cell tumors in the cerebral hemispheres are rare and of unknown origin. Two large aggressive cerebral neoplasms composed mainly of granular cells and also containing neoplastic astrocytes were studied histologically, ultrastructurally and immunohistochemically. In both instances, transitional forms between astrocytes and typical granular cells were demonstrated. In the second case which consisted of a central core of typical glioblastoma surrounded by a thick shell of granular cells, the latter spread in a fashion that is characteristic of intrinsic tumors of the central nervous system by forming abundant secondary structures of Scherer, particularly under the pia and around cortical blood vessels. All the evidence indicates that in these two cases granular cells were transformed neoplastic astrocytes. Paradoxically, many granular cells exhibited benign cytological features that belied their malignant nature.
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