title: Pile driving into the skull and suspending the bridging veins? An undescribed role of arachnoid granulations.
abstract: OBJECTIVE
  Arachnoid granulations (AGs) occasionally appear to protrude into the calvarial convexity, lying close to the bridging veins (BVs). This study aims to characterize such AGs and BVs using magnetic resonance imaging (MRI).
  
  
  METHODS
  Ninety-five patients were enrolled in this study. Initially, stepwise frontal craniotomy was performed in an injected cadaver head. Next, examinations with contrast MRI were performed involving the whole cranial vault.
  
  
  RESULTS
  In cadaveric dissection, the AGs located in the parasagittal regions appeared as outward protrusions through the dura mater and in contact with the diploic veins. Forming tent-shaped sleeves, these AGs and the continuous arachnoid membranes suspended the BVs coursing just below. A total of 237 AGs were identified on contrast MRI that protruded into the skull, lying close to the BVs. Among them, 78 % were located in parasagittal regions as AG-BV pairs. These pairs were most frequently found in the middle third of the calvarial hemisphere, followed by the anterior and posterior thirds. In 34 %, the BV segments were lodged in the AGs.
  
  
  CONCLUSIONS
  Some AGs located in the parasagittal regions and cerebral convexity pass through the dura mater and pile drive into the skull, which contribute to forming hanging-type arachnoid sleeves suspending the BVs. These structures may underpin the predisposition of BVs to injury following mechanical impacts.
authors.affiliation: Department of Neurological Surgery, Juntendo University Urayasu Hospital, 2-1-1 Tomioka, Urayasu, 279-0021, Chiba, 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, 279-0021, Chiba, Japan.
authors.forename: Yukimasa
authors.initials: Y
authors.lastname: Yasumoto
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D001099:Arachnoid / Q000033:anatomy & histology* / Q000000981:diagnostic imaging*; D002102:Cadaver; D002550:Cerebral Veins / Q000033:anatomy & histology*; D003287:Contrast Media; D004388:Dura Mater / Q000033:anatomy & histology / Q000000981:diagnostic imaging; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008875:Middle Aged; D012189:Retrospective Studies; D012886:Skull / Q000033:anatomy & histology / Q000000981:diagnostic imaging
chemical_list: D003287:Contrast Media
keywords: Arachnoid granulations; Arachnoid membrane; Bridging veins; MRI