Characterization of refractile eosinophilic granular cells in oligodendroglial tumors

Refractile eosinophilic granular cells (rEGCs), which are distinct from the previously reported eosinophilic granular cells in oligodendroglial tumors, were characterized. The granules of rEGCs showed intense eosinophilia and prominent refractility, and were arranged in clusters or piled up in the perikaryon. The rEGCs tended to distribute in the vicinity of fibrovascular stroma and collagenous areas. They appeared in oligodendroglial tumors with numerous minigemistocytes and gliofibrillary oligodendrocytes. More rEGCs were present in WHO grade III oligodendroglial tumors. Histochemically, the granules stained blue with Kluver-Barrera and vividly red with Masson's trichrome stain, but negative with periodic acid-Schiff reagent. Almost all of the rEGCs were immunopositive for glial fibrillary acidic protein (GFAP) and heat shock protein 27 (HSP27), and some of them showed immunopositivity with alphaB-crystallin. No MIB-1 immunopositivity of rEGCs was found. Ultrastructurally, the rEGCs had many ellipsoidal structures associated with bundles of glial fibers in the cytoplasm. The morphological features of granules of rEGCs were similar to those of Rosenthal fibers except for the size and shape of the structure. We considered that the rEGCs originated from overexpression and accumulation of alphaB-crystallin and HSP27 in GFAP-positive oligodendroglial cells due to various pathological conditions. The presence of the rEGCs in the oligodendrogliomas may suggest more aggressive clinical behavior of tumors.