title: Sex differences in intracranial arterial bifurcations.
abstract: BACKGROUND
  Subarachnoid hemorrhage (SAH) is a serious condition, occurring more frequently in females than in males. SAH is mainly caused by rupture of an intracranial aneurysm, which is formed by localized dilation of the intracranial arterial vessel wall, usually at the apex of the arterial bifurcation. The female preponderance is usually explained by systemic factors (hormonal influences and intrinsic wall weakness); however, the uneven sex distribution of intracranial aneurysms suggests a possible physiologic factor-a local sex difference in the intracranial arteries.
  
  
  OBJECTIVE
  The aim of this study was to explore sex variation in the bifurcation anatomy of the middle cerebral artery (MCA) and internal carotid artery (ICA), and the subsequent hemodynamic impact.
  
  
  METHODS
  Vessel radii and bifurcation angles were measured in patients with MCA and ICA bifurcations. Data from a previously published study of 55 patients undergoing diagnostic cerebral digital subtraction angiography at Dalcross Private Hospital in Sydney, Australia, between 2002 and 2003, were available for analysis. The measurements were used to create idealized, averaged bifurcations of the MCA and ICA for females and males. Computational fluid dynamics simulations were performed to calculate hemodynamic forces in the models.
  
  
  RESULTS
  The vessel radii and bifurcation angles of 47 MCA and 52 ICA bifurcations in 49 patients (32 females, 17 males; mean age, 53 years; age range, 14-86 years) were measured. Statistically significant sex differences were found in vessel diameter (males larger than females; P < 0.05), but not in bifurcation angle. Computational fluid dynamics simulations revealed higher wall shear stress in the female MCA (19%) and ICA (50%) bifurcations compared with the male bifurcations.
  
  
  CONCLUSIONS
  This study of MCA and ICA bifurcations in female and male patients suggests that sex differences in vessel size and blood flow velocity result in higher hemodynamic forces acting on the vessel wall in females. This new hypothesis may partly explain why intracranial aneurysms and SAH are more likely to occur in females than in males.
authors.affiliation: Department of Clinical Medicine, University of Tromsø, Norway.
authors.forename: Haakon M
authors.initials: HM
authors.lastname: Lindekleiv
authors.forename: Kristian
authors.initials: K
authors.lastname: Valen-Sendstad
authors.forename: Michael K
authors.initials: MK
authors.lastname: Morgan
authors.forename: Kent-Andre
authors.initials: KA
authors.lastname: Mardal
authors.forename: Kenneth
authors.initials: K
authors.lastname: Faulder
authors.forename: Jeanette H
authors.initials: JH
authors.lastname: Magnus
authors.forename: Knut
authors.initials: K
authors.lastname: Waterloo
authors.forename: Bertil
authors.initials: B
authors.lastname: Romner
authors.forename: Tor
authors.initials: T
authors.lastname: Ingebrigtsen
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000704:Analysis of Variance; D015901:Angiography, Digital Subtraction; D001783:Blood Flow Velocity; D002343:Carotid Artery, Internal / Q000033:anatomy & histology* / Q000000981:diagnostic imaging / Q000502:physiology; D002533:Cerebral Angiography; D005260:Female; D020022:Genetic Predisposition to Disease / Q000453:epidemiology / Q000235:genetics; D006439:Hemodynamics; D018056:Hemorheology; D006801:Humans; D002532:Intracranial Aneurysm / Q000000981:diagnostic imaging / Q000453:epidemiology* / Q000209:etiology; D016014:Linear Models; D008297:Male; D008875:Middle Aged; D020768:Middle Cerebral Artery / Q000033:anatomy & histology* / Q000000981:diagnostic imaging / Q000502:physiology; D008955:Models, Cardiovascular; D020412:Multifactorial Inheritance / Q000235:genetics; D009517:New South Wales / Q000453:epidemiology; D012307:Risk Factors; D012727:Sex Characteristics; D017678:Sex Distribution; D013345:Subarachnoid Hemorrhage / Q000000981:diagnostic imaging / Q000453:epidemiology* / Q000209:etiology