[Piloid astrocytes (spongiocytes) and Rosenthal fibers in multiple sclerosis (author's transl)].

Focal and widespread intense hyperplasia of piloid astrocytes was found in the brain of a 51 year old woman with multiple sclerosis and typical demyelinating lesions. The piloid astrocytosis was confined to older plaques in brain stem, cerebellum and periventricular white matter, but could not be found in telencephalic plaques distant from the ventricular system. The piloid astrocytes and accompanying glial fiber bundles were oriented in alternating direction, thus imitating structural characteristics of spongioblastomas. In the pons, an especially high density of astrocytosis was found with lobulated and giant nuclei and binuclear cells. One large demyelinated plaque in the central white matter of the cerebellum contained numerous Rosenthal fibers between the piloid astrocytes. By their intense glial fiber production, the piloid astrocytes took part of the formation of glial scars. The term spongiocyte is proposed for piloid astrocytes of this highly differentiated type, in order to separate them from the immature spongioblasts of gliogenesis. The pathogenetic mechanism is not clear. It is supposed that during intense reparative astrocytic proliferation the development of atypic reactions is favoured. A primary evocation of this type of reaction by the demyelinating factor itself must also be taken into consideration. The topographic predilection, in our case, of piloid astrocytosis to brain stem and cerebellum indicates a disposition of regions formed by the embryogenetic side plate to reactions of this type.