Morphological and immunohistochemical characterization of granular cells in non-hypophyseal tumours of the central nervous system.

We report 14 biopsy cases of granular cell tumours (GCT) of the central nervous system (CNS) outside the pituitary gland. In six cases the granular cells determined the morphology (actual GCT), the other eight consisted of different CNS tumours with a varying granular cell component. Pronounced immunoreactivity for ubiquitin and alpha-1-antichymotrypsin could be found in all investigated tumours, while GFAP, neuron specific enolase, von Willebrand factor, vimentin, S-100 protein, alpha-1-antitrypsin, actin, and the neurofilaments 68 kDa and 160 kDa showed mostly weak positivity in some cases. Four out of eight GCT showed no immunoreactivity for MIB1; the other four cases had a proliferation index between 0.5% and 15%. Six out of nine cases were positive for p53. We consider granular cells to originate from different cell types. Thus, although morphologically identical, GCT are actually biologically heterogeneous. GCT of the CNS may represent gliomas of mostly astrocytic origin with a metabolically induced transformation of some tumour cells into granular cells.