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* We describe unique features seen in a case of classic acoustic schwannoma. In the central portion of the tumor, abundant Rosenthal fibers and occasional eosinophilic granular bodies were present. Rosenthal fibers are homogeneous eosinophilic structures commonly seen in central nervous system lesions, such as pilocytic astrocytoma, or in the gliotic tissues adjacent to slowly growing neoplasms and some congenital malformations. Eosinophilic granular bodies are also structural markers of slow-growing, welldifferentiated neuroglial neoplasms, such as pleomorphic xanthoastrocytoma, ganglion cell tumors, and pilocytic astrocytoma. To the best of our knowledge, however, these two structures have never before been described in schwannomas.
(Arch Pathol Lab Med 1997;121:1207-1209)
Rosenthal fibers, first described in 1898 by W Rosenthal in a case of syringomyelia and intramedullary ependymoma,1 are bodies formed in the perikarya and processes of astrocytes. They appear as homogeneous, hyaline, eosinophilic structures and may be round, oval, or elongated. These structures are thought to occur as the nonspecific result of damage to astrocytic processes that become swollen and filled with masses of granular electron-dense material that is surrounded by glial filaments.2 Rosenthal fibers stain blue with Mallory's phosphotungstic acid hematoxylin and are immunoreactive for aB-crystallin.3 With glial fibrillary acidic protein (GFAP) immunohistochemistry, the central part of the Rosenthal fiber remains nonreactive, while a rim of GFAP staining is usually present.4 Rosenthal fibers are found in a variety of typically long-standing processes, such as within optic nerve and cerebellar astrocytomas, and in the gliotic brain parenchyma adjacent to hemangioblastomas and craniopharyngiomas or surrounding syringomyelic cavities and vascular malformations. They are also especially prominent in the dysmyelinated areas in Alexander's disease.5 Eosinophilic granular bodies (EGBs) represent cells that contain intermediate filaments, lipid droplets, and granular debris. The core of an EGB is immunoreactive for alpha^sub 1^antitrypsin and alpha^sub 1^-antichymotrypsin, as well as for ubiquitin, (alpha)B-crystallin, and GFAP.6 Eosinophilic granular bodies are also commonly seen in slowly growing neuroglial neoplasms. Recently, we encountered typical Rosenthal fibers within an otherwise classic schwannoma.
REPORT OF A CASE
The patient was a 43-year-old man with a discrete contrastenhancing mass in the right cerebellopontine angle. The mass was completely resected without complications. The biopsy specimen was fixed in 10% neutral-buffered formalin and processed for light microscopy. Paraffin sections were stained with hematoxylin-eosin, periodic acid-Schiff,...