title: Epithelioid ependymoma: a new variant of ependymoma: report of three cases.
abstract: OBJECTIVE
  To describe the pathological features of three very similar and unusual primary central nervous system tumors that are not readily recognized as conventional ependymomas but which, by ultrastructural examination, have an ependymomatous character.
  
  
  METHODS
  Three distinctive tumors were found in a review of our files for cases of ependymoma. In each case, hematoxylin and eosin-stained sections were reviewed, and immunostains for epithelial membrane antigen, cytokeratin, vimentin, and glial fibrillary acidic protein were performed on formalin-fixed, paraffin-embedded sections. Electron microscopy was performed in each case.
  
  
  RESULTS
  The tumors had a diffuse myxoid background, often containing tightly clustered cells that mimicked multinucleated giant cells, but lacking perivascular pseudorosettes or central lumen rosettes. Glial fibrillary acidic protein and vimentin immunostains did not reveal perivascular processes. Epithelial membrane antigen immunostains showed a dot-like cytoplasmic immunoreactivity in some cell clusters in two of the three cases. Cytokeratin was negative in all three cases. However, ultrastructurally, the cells of each tumor had extensive surface microvilli; the giant cell-like clusters had cells with extensive close appositions, some junctions, and, in two cases, lumina with microvilli. Two of the patients were adults (both with temporal lobe tumors), and one patient was 13 years old and had a cervical spinal cord intramedullary tumor. Each tumor was sharply circumscribed from adjacent central nervous system tissue but was not encapsulated. One of the cases in an adult was mitotically highly active; this tumor recurred locally 4 years after initial gross total excision.
  
  
  CONCLUSIONS
  These tumors are unusual variants of ependymoma. This pattern of ependymoma is sufficiently distinctive to be recognized in hematoxylin and eosin stains once the architecture of the epithelioid clusters is appreciated.
authors.affiliation: Department of Pathology, Division of Neuropathology, and the Cancer Research Center, New York University School of Medicine, New York, New York 10016, USA. george.kleinman@med.nyu.edu
authors.forename: George M
authors.initials: GM
authors.lastname: Kleinman
authors.forename: David
authors.initials: D
authors.lastname: Zagzag
authors.forename: Douglas C
authors.initials: DC
authors.lastname: Miller
mesh_terms: D000293:Adolescent; D000328:Adult; D001932:Brain Neoplasms / Q000473:pathology* / Q000601:surgery / Q000648:ultrastructure; D004806:Ependymoma / Q000473:pathology* / Q000601:surgery / Q000648:ultrastructure; D015622:Epithelioid Cells / Q000473:pathology* / Q000648:ultrastructure; D005260:Female; D006801:Humans; D008297:Male; D013120:Spinal Cord Neoplasms / Q000473:pathology* / Q000601:surgery / Q000648:ultrastructure