title: Vestibular schwannoma or tanycytic ependymoma: Immunohistologic staining reveals.
abstract: BACKGROUND
  The cerebellopontine angle (CPA) is a common location for primary tumors, most often vestibular schwannomas, and also meningiomas, dermoids, and a host of other neoplasms. Our case report illustrates how radiologic and histopathologic presentations of an unusual variant of ependymal neoplasm can be diagnostically challenging and how accurate diagnosis can affect treatment protocols.
  
  
  METHODS
  Our patient had a CPA mass that was a variant of ependymoma known as tanycytic ependymoma that mimicked vestibular schwannoma radiologically and during intraoperative pathologic examination. Diagnosis as a World Health Organization (WHO) grade II tanycytic ependymoma was supported by its appearance on evaluation of the permanent sections, its diffuse immunoreactivity for glial fibrillary acidic protein (GFAP), and the perinuclear dot-and-ring-like staining for epithelial membrane antigen (EMA).
  
  
  CONCLUSIONS
  Our patient's CPA mass initially believed to be a vestibular schwannoma on preoperative evaluation, surgical appearance, and intraoperative pathologic consultation was then correctly diagnosed as a WHO grade II tanycytic ependymoma on permanent histologic sections with the assistance of immunohistochemical stains, including EMA. After this definitive diagnosis, our patient's adjuvant treatment was adjusted. Earlier diagnosis could have provided guidance for goals of resection and prompt initiation of adjuvant treatment.
authors.affiliation: Department of Neurosurgery, University of Cincinnati (UC) College of Medicine, Cincinnati, OH, USA.
authors.forename: Anthony
authors.initials: A
authors.lastname: Divito
authors.affiliation: Department of Neurosurgery, University of Cincinnati (UC) College of Medicine, Cincinnati, OH, USA ; Comprehensive Stroke Center at UC Neuroscience Institute, OH, USA ; Mayfield Clinic, Cincinnati, OH, USA.
authors.forename: Jeffrey T
authors.initials: JT
authors.lastname: Keller
authors.affiliation: Department of Pathology and Laboratory Medicine, University of Cincinnati (UC) College of Medicine, Cincinnati, OH, USA.
authors.forename: Matthew
authors.initials: M
authors.lastname: Hagen
authors.affiliation: Department of Neurosurgery, University of Cincinnati (UC) College of Medicine, Cincinnati, OH, USA ; Comprehensive Stroke Center at UC Neuroscience Institute, OH, USA ; Mayfield Clinic, Cincinnati, OH, USA.
authors.forename: Mario
authors.initials: M
authors.lastname: Zuccarello
keywords: Cerebellopontine angle; diagnosis; epithelial membrane antigen staining; tanycytic ependymoma