title: Characterizing saccular aortic arch aneurysms from the geometry-flow dynamics relationship.
abstract: Low wall shear stress (WSS) has been reported to be associated with accelerated atherosclerosis, aneurysm growth, or rupture. We evaluated the geometry of aortic arch aneurysms and their relationship with WSS by using the 4-dimensional flow magnetic resonance imaging to better characterize the saccular aneurysms.
  
  
  
  We analyzed the geometry in 100 patients using multiplanar reconstruction of computed tomography. We evaluated WSS and vortex flow using 4-dimensional flow magnetic resonance imaging in 16 of them, which were compared with 8 age-matched control subjects and eight healthy young volunteers.
  
  
  
  Eighty-two patients had a saccular aneurysm, and 18 had a fusiform aneurysm. External diameter/aneurysm length ratio and sac depth/neck width ratio of the fusiform aneurysms were constant at 0.76 ± 0.18 and 0.23 ± 0.09, whereas those of saccular aneurysms, especially those involving the outer curvature, were higher and more variable. Vortex flow was always present in the aneurysms, resulting in low WSS. When the sac depth/neck width ratio was less than 0.8, peak WSS correlated inversely with luminal diameter even in the saccular aneurysms. When this ratio exceeded 0.8, which was the case only with the saccular aneurysms, such correlation no longer existed and WSS was invariably low.
  
  
  
  Fusiform aneurysms elongate as they dilate, and WSS is lower as the diameter is larger. Saccular aneurysms dilate without proportionate elongation, and they, especially those occupying the inner curvature, have higher and variable sac depth/neck width ratio. When this ratio exceeds 0.8, WSS is low regardless of diameter, which may explain their malignant clinical behavior.
authors.affiliation: First Department of Surgery, Hamamatsu University School of Medicine, Shizuoka, Japan. Electronic address: D14022@hama-med.ac.jp.
authors.forename: Kayoko
authors.initials: K
authors.lastname: Natsume
authors.affiliation: First Department of Surgery, Hamamatsu University School of Medicine, Shizuoka, Japan.
authors.forename: Norihiko
authors.initials: N
authors.lastname: Shiiya
authors.affiliation: Department of Radiology, Hamamatsu University School of Medicine, Shizuoka, Japan.
authors.forename: Yasuo
authors.initials: Y
authors.lastname: Takehara
authors.affiliation: Department of Radiology, Hamamatsu University School of Medicine, Shizuoka, Japan.
authors.forename: Masataka
authors.initials: M
authors.lastname: Sugiyama
authors.affiliation: Department of Internal Medicine III, Hamamatsu University School of Medicine, Shizuoka, Japan.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Satoh
authors.affiliation: First Department of Surgery, Hamamatsu University School of Medicine, Shizuoka, Japan.
authors.forename: Katsushi
authors.initials: K
authors.lastname: Yamashita
authors.affiliation: First Department of Surgery, Hamamatsu University School of Medicine, Shizuoka, Japan.
authors.forename: Naoki
authors.initials: N
authors.lastname: Washiyama
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001013:Aorta, Thoracic / Q000000981:diagnostic imaging / Q000473:pathology / Q000503:physiopathology*; D017545:Aortic Aneurysm, Thoracic / Q000145:classification / Q000000981:diagnostic imaging / Q000473:pathology / Q000503:physiopathology*; D001027:Aortography / Q000379:methods; D001783:Blood Flow Velocity; D000072226:Computed Tomography Angiography; D004108:Dilatation, Pathologic; D005260:Female; D006439:Hemodynamics; D006801:Humans; D018810:Magnetic Resonance Angiography; D008297:Male; D008875:Middle Aged; D008955:Models, Cardiovascular; D055420:Perfusion Imaging / Q000379:methods; D011379:Prognosis; D012039:Regional Blood Flow; D012189:Retrospective Studies
keywords: 4D-Flow; MRI; hemodynamics; saccular aneurysm; thoracic aorta aneurysm