title: Differential diagnosis of intracranial ring enhancing cystic mass lesions--role of diffusion-weighted imaging (DWI) and diffusion-tensor imaging (DTI).
abstract: OBJECTIVE
  To evaluate the contribution of DWI and DTI to the differential diagnosis of cerebral ring enhancing lesions by describing DWI and ADC (apparent diffusion coefficient) findings and measuring the two DTI parameters mean diffusivity (MD) and fractional anisotropy (FA).
  
  
  METHODS
  A total of 17 patients presenting with 26 rim enhancing cysts were investigated with DWI and DTI. Parameter maps of the DTI metrics MD and FA were calculated and quantified using regions of interest (ROIs).
  
  
  RESULTS
  Five patients suffered from abscesses with a total of 10 cysts, 9 from glioblastomas with 10 cysts, and 3 from metastases with 6 cysts. All abscess cavities showed hyperintense DWI signal intensity compared to normal appearing white matter (NAWM), low ADC, low MD and high FA. Eight out of 10 glioblastoma cysts and all 6 metastatic cysts revealed hypointensity on DWI, high ADC, high MD and low FA (p<0.0001 compared to abscess group). DWI findings of 2/10 glioblastoma cysts overlapped with those of abscesses showing hyperintensity on DWI, low ADC and low MD and hence mimicked abscesses. FA of these 2 glioblastoma cysts was significantly lower than in abscess cavities (p=0.032).
  
  
  CONCLUSIONS
  The findings of reduced diffusion compared to NAWM and increased FA within a ring enhancing cyst strongly indicate a cerebral abscess. In contrast, the majority of neoplastic cysts revealed high diffusion and low FA. Reduced diffusion is also found in a very small number of tumour cysts, but in these low FA refers to a non-infectious origin and thus helps distinguishing from infectious abscess.
authors.affiliation: Institut of Radiology, Ortenau Klinikum Lahr-Ettenheim, 77933 Lahr, Germany. reiche.w@t-online.de <reiche.w@t-online.de>
authors.forename: Werner
authors.initials: W
authors.lastname: Reiche
authors.forename: Volker
authors.initials: V
authors.lastname: Schuchardt
authors.forename: Thomas
authors.initials: T
authors.lastname: Hagen
authors.forename: Kamil A
authors.initials: KA
authors.lastname: Il'yasov
authors.forename: Peter
authors.initials: P
authors.lastname: Billmann
authors.forename: Johannes
authors.initials: J
authors.lastname: Weber
mesh_terms: D000368:Aged; D016880:Anisotropy; D001921:Brain / Q000473:pathology*; D001922:Brain Abscess / Q000175:diagnosis* / Q000473:pathology; D001932:Brain Neoplasms / Q000473:pathology*; D003560:Cysts / Q000175:diagnosis* / Q000473:pathology; D003937:Diagnosis, Differential; D038524:Diffusion Magnetic Resonance Imaging / Q000379:methods*; D056324:Diffusion Tensor Imaging; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008297:Male; D008875:Middle Aged