title: A novel reference coordinate system to locate the inferomedial point of the transverse-sigmoid sinus junction.
abstract: BACKGROUND
  A coordinate system was previously developed to identify landmarks on the skull surface to help locate the transverse-sigmoid sinus junction in order to reduce surgical morbidity in retrosigmoid craniotomy; however, in practice we found that this system has important flaws.
  
  
  OBJECTIVE
  To develop and evaluate a novel reference coordinate system to precisely locate the inferomedial point of the transverse-sigmoid sinus junction (IMTS) and evaluate the effect of gender and skull side (left or right).
  
  
  METHODS
  Forty-two adult skulls (84 sides) were obtained for analyses. The X-axis was defined by point A (where the upper edge of the zygomatic arch joins with the frontal process of the zygomatic bone) and point B (where the upper edge of the zygomatic arch blends posterosuperiorly into the supramastoid crest). The Y-axis was defined by the line perpendicular to the X-axis and extending across the tip of the mastoid. The x and y coordinates of IMTS (IMTS-x and IMTS-y) were measured in this coordinate system.
  
  
  RESULTS
  There were 20 male skulls and 22 female skulls. The mean IMTS-x measurements were significantly higher on the right side compared with the left side in both males and females. For the left skull side, the mean IMTS-y measurements were significantly lower in females compared with males.
  
  
  CONCLUSIONS
  This novel reference coordinate system may be a reliable and practical method for identifying the IMTS during retrosigmoid craniotomy. There are significant differences in location of the axes with regard to gender and skull side.
authors.affiliation: Department of Neurosurgery, First Affiliated Hospital of Xi'an Jiaotong University, 277 West Yanta Road, Xi'an, Shaanxi, 710061, China.
authors.forename: Rui-chun
authors.initials: RC
authors.lastname: Li
authors.forename: Kuo
authors.initials: K
authors.lastname: Li
authors.forename: Lei
authors.initials: L
authors.lastname: Qi
authors.forename: Gao-feng
authors.initials: GF
authors.lastname: Xu
authors.forename: Wan-fu
authors.initials: WF
authors.lastname: Xie
authors.forename: Mao-de
authors.initials: MD
authors.lastname: Wang
authors.forename: Gang
authors.initials: G
authors.lastname: Bao
mesh_terms: D000328:Adult; D059925:Anatomic Landmarks; D003392:Cranial Sinuses / Q000033:anatomy & histology / Q000601:surgery; D003399:Craniotomy / Q000379:methods; D005260:Female; D006801:Humans; D008297:Male; D008416:Mastoid / Q000033:anatomy & histology*; D008875:Middle Aged; D012886:Skull / Q000033:anatomy & histology* / Q000601:surgery; D054064:Transverse Sinuses / Q000033:anatomy & histology* / Q000601:surgery; D015050:Zygoma / Q000033:anatomy & histology*