<prompt> 10 year old child with posterior fossa mass. On biopsy following features were seen. What are these dense eosinophilic fibers marked with arrow?Rosenthal fibersThe Alzheimer type II astrocyteCorpora amylaceaNone  <response>: Ans. a Rosenthal fibersRosenthal 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. 