title: Imaging of posterior fossa epidermoid tumors.
abstract: OBJECTIVE
  Epidermoid tumors have similar radiologic characteristics with arachnoid cysts on routine imaging techniques. Since they warrant different therapeutic interventions, it is essential to differentiate the two pathologies and to assess operative results.
  
  
  OBJECTIVE
  The purpose of this study is to define the MR characteristics of epidermoid tumors in posterior fossa particularly on fluid-attenuated inversion recovery (FLAIR) and diffusion-weighted imaging (DWI).
  
  
  METHODS
  During a 10-year period, we operated 19 cases with epidermoid tumor of posterior fossa. The localization of the epidermoids was cerebellopontine angle in 16 patients, within the fourth ventricle in 2 patients and pineal region in 1 patient. Neuroimaging included CT in all patients, conventional MR in 14 patients and FLAIR and DWI in the last 6 patients.
  
  
  RESULTS
  In the first 13 cases, diagnosis of epidermoid tumor was difficult on CT and conventional MR. Epidermoids appeared as heterogeneous hyperintense lesions on FLAIR and homogenous hyperintense lesions on DWI in the last 6 patients. While total resection of the tumor was achieved in 17 patients, subtotal resection was performed in 2 patients. Histopathological examinations of the specimens revealed epidermoid tumor in all cases.
  
  
  CONCLUSIONS
  Advances in neuroradiology provide us advantages for planning the treatment modalities in epidermoid tumors of the posterior fossa. The difficulties in preoperative differential diagnosis and judgment for reoperation in the postoperative course have been decreased particularly via FLAIR and DWI.
authors.affiliation: Department of Neurosurgery, Gulhane Military Medical Academy, 06018 Etlik, Ankara, Turkey. drssirin@yahoo.com
authors.forename: Sait
authors.initials: S
authors.lastname: Sirin
authors.forename: Engin
authors.initials: E
authors.lastname: Gonul
authors.forename: Serdar
authors.initials: S
authors.lastname: Kahraman
authors.forename: Erdener
authors.initials: E
authors.lastname: Timurkaynak
mesh_terms: D000328:Adult; D016080:Arachnoid Cysts / Q000175:diagnosis; D002294:Carcinoma, Squamous Cell / Q000175:diagnosis* / Q000601:surgery; D003388:Cranial Fossa, Posterior / Q000473:pathology* / Q000601:surgery; D003937:Diagnosis, Differential; D038524:Diffusion Magnetic Resonance Imaging; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007089:Image Enhancement; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D018365:Neoplasm, Residual / Q000175:diagnosis; D011183:Postoperative Complications / Q000175:diagnosis; D012680:Sensitivity and Specificity; D019292:Skull Base Neoplasms / Q000175:diagnosis* / Q000601:surgery; D014057:Tomography, X-Ray Computed