title: Immobile cerebral veins in the context of positional brain shift: an undescribed risk factor for acute subdural hemorrhage.
abstract: BACKGROUND
  Changes in head position are thought to cause a degree of brain shift in the intracranial cavity. However, little is known on the concurrent shift of the cerebral veins. The present study aimed to investigate the positional shift of the cerebral veins that accompanies brain shift.
  
  
  METHODS
  Sagittal T2-weighted magnetic resonance imaging was performed on 21 consecutive patients lying in the supine and prone positions, using the same sequence. For each patient, imaging data were obtained for the two positions as a pair of images with morphologically best-matched cerebral contours.
  
  
  RESULTS
  The subarachnoid spaces in the parasagittal frontal convexity showed variable reductions related to a postural change from a supine to a prone position, with a mean percent reduction (%Δ) of 17.8 ± 11.7%. Additionally, cerebral cisterns ventral to the brainstem and upper cervical cord were reduced in most patients when lying in a prone position, with a mean %Δ of 16.6 ± 8.7%. In contrast, none of these 130 pairs of identical venous segments located in the parasagittal cerebral convexity showed positional shift. Cadaveric dissections found that the major cortical veins were superficially upheld by the arachnoid membranes.
  
  
  CONCLUSIONS
  The parasagittal major cortical and bridging veins do not seem to show positional shifts. Positional change in the posterior-anterior direction causes a shearing between the frontal cortices and the distributing veins and can be a risk factor for acute subdural hemorrhage, in case of severe head trauma.
authors.affiliation: Department of Neurological Surgery, Juntendo University Urayasu Hospital, 2-1-1 Tomioka, Urayasu, Chiba, 279-0021, Japan. shotaro@juntendo-urayasu.jp.
authors.forename: Satoshi
authors.initials: S
authors.lastname: Tsutsumi
authors.affiliation: Division of Radiological Technology, Medical Satellite Yaesu Clinic, Tokyo, Japan.
authors.forename: Hideo
authors.initials: H
authors.lastname: Ono
authors.affiliation: Department of Neurological Surgery, Juntendo University Urayasu Hospital, 2-1-1 Tomioka, Urayasu, Chiba, 279-0021, Japan.
authors.forename: Yukimasa
authors.initials: Y
authors.lastname: Yasumoto
mesh_terms: D000328:Adult; D000368:Aged; D002543:Cerebral Hemorrhage; D002550:Cerebral Veins / Q000033:anatomy & histology*; D005260:Female; D019416:Head Movements / Q000502:physiology*; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008875:Middle Aged; D056888:Patient Positioning; D012189:Retrospective Studies; D012307:Risk Factors
keywords: Arachnoid membrane; MRI; Parasagittal cortical and bridging veins; Postural brain shift