Rosenthal fiber

A Rosenthal fiber is a thick, elongated, worm-like eosinophilic (pink) bundle that is found on H&E staining of the brain in the presence of long standing gliosis, occasional tumors, and some metabolic disorders. Its presence is pathognomonic of either pilocytic astrocytoma (more common) or Alexander's disease (a rare leukodystrophy). The fibers are found in astrocytic processes and are thought to be clumped intermediate filament proteins.

=References=
 * Neuropathology Mini-Course. Chapter 9 - Tumors of the Nervous System
 * Doctor's Doctor - Brain and Spinal Cord
 * Isolation of a major protein component of Rosenthal fibers