10 year old child with posterior fossa mass. On biopsy following features were seen. What are these dense eosinophilic fibers marked with arrow?

Ans. (a) Rosenthal fibers*Rosenthal fibers are eosinophilic, corkscrew fibers found in pilocytic astrocytoma, the most common primary brain tumor in children. They contain two heat-shock proteins (aB-crystallin and hsp27) as well as ubiquitin.*They are seen in Alexander disease and, pilocytic astrocytoma.