Rosenthal fibers are astrocytic cytoplasmic inclusions, typically found in areas of longstanding gliosis. These elongated or "corkscrew" structures occur within astrocytic processes and are brightly eosinophilic (stain bright pink on the H&E stain) . They represent astrocytic processes swollen with glial filaments and amorphous granular material .
They can be seen in a number conditions, all of which have prominent fibrillary gliosis. Such conditions include :