Peculiar changes in Rosenthal fibres in an atypical astrocytoma

A 50-year-old female patient died of an untreatable glioma apoplecticum. At autopsy a strongly vascularized glial tumour was found. The criteria for malignancy according to the WHO classification were only partially fulfilled by this tumour which displayed morphological features of an astrocytoma but could not be further subclassified. By light microscopy, angioma-like vascular proliferations, large cells with brightly eosinophilic cytoplasm, and small cells with hyperchromatic nuclei were found. Most large cells had vesicular, excentrically placed nuclei and contained fibrillary whorls or amorphous, irregular cytoplasmic inclusions. By immunohistochemical staining, using antibodies to glial fibrillary acidic protein (GFAP) the fibrillary whorls were identified as aggregates of glial filaments. The amorphous inclusions lacked GFAP immunoreactivity and appeared in the electron microscope as electron dense material surrounded by a dense network of glial filaments. The abnormal perikaryal inclusions of these atypical astrocytoma cells appeared to be peculiar alterations of Rosenthal fibres closely mimicing Mallory bodies.