title: Changes to the geometry and fluid mechanics of the carotid siphon in the pediatric Moyamoya disease.
abstract: BACKGROUND
  The Moyamoya disease is a cerebrovascular disease that causes occlusion of the distal end of the internal carotid artery, leading to the formation of multiple tiny collateral arteries. To date, the pathogenesis of Moyamoya is unknown. Improved understanding of the changes to vascular geometry and fluid mechanics of the carotid siphon during disease may improve understanding of the pathogenesis, prognosis techniques and disease management.
  
  
  METHODS
  A retrospective analysis of Magnetic Resonance Angiography (MRA) images was performed for Moyamoya pediatric patients (MMD) (n = 23) and control (Ctrl) pediatric patients (n = 20). The Ctrl group was composed of patients who complained of headache and had normal MRA. We performed segmentation of MRA images to quantify geometric parameters of the artery. Computational fluid dynamics (CFD) was performed to quantify the hemodynamic parameters.
  
  
  RESULTS
  MMD internal carotid and carotid siphons were smaller in cross-sectional areas, and shorter in curved vascular length. Vascular curvature remained constant over age and vascular size and did not change between Ctrl and MMD, but MMD carotid siphon had lower tortuosity in the posterior bend, and higher torsion in the anterior bend. Wall shear stress and secondary flows were significantly lower in MMD, but the ratio of secondary flow kinetic energy to primary flow kinetic energy were similar between MMD and Ctrl.
  
  
  CONCLUSIONS
  There were alterations to both the geometry and the flow mechanics of the carotid siphons of Moyamoya patients but it is unclear whether hemodynamics is the cause or the effect of morphological changes observed.
authors.affiliation: a Department of Biomedical Engineering , National University of Singapore , Singapore.
authors.forename: Muhammad
authors.initials: M
authors.lastname: Jamil
authors.affiliation: a Department of Biomedical Engineering , National University of Singapore , Singapore.
authors.forename: Germaine Xin Yi
authors.initials: GX
authors.lastname: Tan
authors.affiliation: a Department of Biomedical Engineering , National University of Singapore , Singapore.
authors.forename: Mehnaz
authors.initials: M
authors.lastname: Huq
authors.affiliation: b Hwa Chong Institution , Singapore.
authors.forename: Heidi
authors.initials: H
authors.lastname: Kang
authors.affiliation: b Hwa Chong Institution , Singapore.
authors.forename: Zhi Rui
authors.initials: ZR
authors.lastname: Lee
authors.affiliation: c KK Women's and Children's Hospital , Singapore.
authors.forename: Phua Hwee
authors.initials: PH
authors.lastname: Tang
authors.affiliation: d Fudan Children's Hospital , Shanghai , China.
authors.forename: Xi Hong
authors.initials: XH
authors.lastname: Hu
authors.affiliation: a Department of Biomedical Engineering , National University of Singapore , Singapore.
authors.forename: Choon Hwai
authors.initials: CH
authors.lastname: Yap
mesh_terms: D000293:Adolescent; D002343:Carotid Artery, Internal / Q000473:pathology* / Q000503:physiopathology*; D002648:Child; D002675:Child, Preschool; D005260:Female; D006439:Hemodynamics / Q000502:physiology*; D006801:Humans; D057446:Hydrodynamics; D018810:Magnetic Resonance Angiography; D008297:Male; D009072:Moyamoya Disease / Q000503:physiopathology*; D012189:Retrospective Studies; D033081:Shear Strength; D013314:Stress, Mechanical
keywords: Moyamoya; carotid siphon; hemodynamics; vascular geometry