title: Endoscopic observation of a slit-valve mechanism in a suprasellar prepontine arachnoid cyst: case report.
abstract: OBJECTIVE
  There are several theories regarding the genesis of arachnoid cysts. However, controversy continues over what mechanisms are involved in the formation of the cysts.
  
  
  METHODS
  A 6-year-old female patient presented with precocious puberty. The results of a neurological examination were unremarkable. Magnetic resonance imaging revealed a large suprasellar prepontine arachnoid cyst.
  
  
  METHODS
  An endoscopic ventriculocystostomy via a right frontal burr hole was performed. During inspection of the cyst, we clearly observed a slit-valve mechanism that was obviously responsible for the formation and enlargement of the cyst. The valve was formed by an arachnoid membrane surrounding the basilar artery. Synchronous with pulsation, the valve opened and closed rapidly.
  
  
  CONCLUSIONS
  A slit-valve mechanism seems to be at least one factor of the genesis of suprasellar prepontine arachnoid cysts.
authors.affiliation: Department of Neurosurgery, Ernst Moritz Arndt University, Greifswald, Germany.
authors.forename: H W
authors.initials: HW
authors.lastname: Schroeder
authors.forename: M R
authors.initials: MR
authors.lastname: Gaab
mesh_terms: D001099:Arachnoid / Q000503:physiopathology; D016080:Arachnoid Cysts / Q000503:physiopathology* / Q000601:surgery; D002648:Child; D019723:Endoscopes; D005260:Female; D006801:Humans; D011149:Pons / Q000503:physiopathology / Q000601:surgery; D011673:Pulsatile Flow / Q000502:physiology; D014696:Ventriculostomy / Q000295:instrumentation*