title: Radiologic differentiation of intracranial epidermoids from arachnoid cysts.
abstract: OBJECTIVE
  Intracranial epidermoids (cholesteatomas) mimic arachnoid cysts in their radiologic characteristics, especially in the cerebellopontine angle. It is essential to differentiate the two conditions because they warrant different therapeutic interventions. The objective of this study is to elucidate the different radiologic characteristics of the conditions.
  
  
  METHODS
  This was a retrospective study of 4 patients referred for a differential diagnosis and management of intracranial cystic lesions to the Departments of Neurotology/Neurosurgery and Neuroradiology in a tertiary referral university hospital.
  
  
  METHODS
  Four patients of different age groups with cystic intracranial lesions, diagnosed epidermoid or arachnoid cysts, were chosen. A retrospective analysis of their case charts, radiologic and surgical interventions, and follow-up records was undertaken.
  
  
  METHODS
  The imaging techniques used included computerized tomographic scans, magnetic resonance imaging (MRI) with T1, T2, proton-density, and gadolinium-enhanced T1 images. In addition, special MRI sequences were used that included fluid-attenuated inversion recovery and echo planar diffusion scanning. All the patients underwent an audiovestibular evaluation.
  
  
  RESULTS
  Both lesions are characteristically well demarcated and have a homogeneous low density, similar to cerebrospinal fluid on computerized tomographic scan, showing no contrast enhancement. On MRI, epidermoids and arachnoid cysts usually appear hypointense on T1-weighted images and hyperintense on T2-weighted images. On fluid-attenuated inversion recovery, an arachnoid cyst tends to follow cerebrospinal fluid intensity, whereas an epidermoid becomes hyperintense. There are occasions when an epidermoid may appear as a low-intensity lesion on fluid-attenuated inversion recovery. This dilemma is resolved with the use of echo planar diffusion scanning, on which an epidermoid remains bright.
  
  
  CONCLUSIONS
  The authors recommend the use of fluid-attenuated inversion recovery and diffusion sequence MRI when definitive radiologic diagnosis of cystic intracranial lesions becomes difficult with routine computerized tomographic scanning and MRI.
authors.affiliation: Departments of Otolaryngology-Head and Neck Surgery, Queen Elizabeth Hospital, Birmingham University, Birmingham, England, UK. sunildutt@hotmail.com
authors.forename: Sunil N
authors.initials: SN
authors.lastname: Dutt
authors.forename: Showkat
authors.initials: S
authors.lastname: Mirza
authors.forename: Swarupsinh V
authors.initials: SV
authors.lastname: Chavda
authors.forename: Richard M
authors.initials: RM
authors.lastname: Irving
mesh_terms: D000328:Adult; D000368:Aged; D016080:Arachnoid Cysts / Q000000981:diagnostic imaging* / Q000473:pathology* / Q000601:surgery; D001927:Brain Diseases / Q000000981:diagnostic imaging* / Q000473:pathology* / Q000601:surgery; D003937:Diagnosis, Differential; D004814:Epidermal Cyst / Q000000981:diagnostic imaging* / Q000473:pathology* / Q000601:surgery; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D012189:Retrospective Studies; D014057:Tomography, X-Ray Computed