Effects of Size and Shape (Aspect Ratio) on the Hemodynamics of Saccular Aneurysms: A Possible Index for Surgical Treatment of Intracranial Aneurysms

Effects of Size and Shape (Aspect Ratio) on the Hemodynamics of Saccular Aneurysms: A Possible... AbstractOBJECTIVE:The present study was undertaken to explore the relationship between the characteristic geometry of aneurysms prone to rupture and the blood flow patterns therein, using microsurgically produced aneurysms that simulated human middle cerebral artery aneurysms in scale and shape.METHODS:We measured in vivo velocity profiles using our 20-MHz, 80-channel, Doppler ultrasound velocimeter. We produced small (≤5 mm, 5 cases) and large (6-13 mm, 12 cases) aneurysms with round, dumbbell, or multilobular shapes.RESULTS:The fundamental patterns of intra-aneurysmal flow were composed of inflow, circulating flow, and outflow. The inflow, which entered the aneurysm only during the systolic phase, was strongly influenced by the position and size of the neck and the flow ratio into the distal branches. The outflow was usually nonpulsatile and of low velocity. The circulating flow depended on the aspect ratio (depth/neck width). A single recirculation zone was observed in aneurysms with aspect ratios of less than 1.6. This circulation did not seem to extend to areas with aspect ratios greater than this value; in aneurysms with aspect ratios of more than 1.6, a much slower circulation was observed near the dome. Furthermore, in the dome of dumbbell-shaped aneurysms and daughter aneurysms, no flow was detected. Intra-aneurysmal flow was determined by the aspect ratio, rather than the aneurysm size.CONCLUSION:The localized, extremely low-flow condition that was observed in the dome of aneurysms with aspect ratios of more than 1.6 is a common flow characteristic in the geometry of ruptured aneurysms, so great care should be taken for patients with unruptured intracranial aneurysms with aspect ratios of more than 1.6. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Neurosurgery Oxford University Press

Effects of Size and Shape (Aspect Ratio) on the Hemodynamics of Saccular Aneurysms: A Possible Index for Surgical Treatment of Intracranial Aneurysms

Effects of Size and Shape (Aspect Ratio) on the Hemodynamics of Saccular Aneurysms: A Possible Index for Surgical Treatment of Intracranial Aneurysms

Effects of Size and Shape (Aspect Ratio) on the Hemodynamics of Saccular Aneurysms: A Possible Index for Surgical Treatment of Intracranial Aneurysms Hiroshi Ujiie, M.D., Hiroyuki Tachibana, C.E., Osamu Hiramatsu, C.E., Andrew L. Hazel, Ph.D., Takeshi Matsumoto, Ph.D., Yasuo Ogasawara, Ph.D., Hiroshi Nakajima, M.D., Tomokatsu Hori, M.D., Kintomo Takakura, M.D., Fumihiko Kajiya, M.D., Ph.D. Department of Neurosurgery (H U , HN, TH, KT), Neurological Institute, Tokyo W om en's Medical University, Tokyo, )apan; Department of Medical Engineering (HT, O H , TM, YO, FK), Kawasaki Medical School, Kurashiki, japan; and Department of Applied Mathematics and Theoretical Physics (ALH), University of Cambridge, Cambridge, England OBJECTIVE: The present study was undertaken to explore the relationship between the characteristic geometry of aneurysms prone to rupture and the blood flow patterns therein, using microsurgically produced aneurysms that simulated human middle cerebral artery aneurysms in scale and shape. METHODS: W e measured in vivo velocity profiles using our 20-MHz, 80-channel, Doppler ultrasound velocimeter. We produced small (<5 mm, 5 cases) and large (6-13 mm, 12 cases) aneurysms with round, dumbbell, or multilobular shapes. RESULTS: The fundamental patterns of intra-aneurysmal flow were composed of inflow, circulating flow, and outflow. The inflow, which entered the aneurysm only during the systolic phase, was strongly influenced by the position and size of the neck and the flow ratio into the distal branches. The outflow was usually nonpulsatile and of low velocity. The circulating flow depended on the aspect ratio (depth/neck width). A single recirculation zone was observed in aneurysms with aspect ratios of less than 1.6. This circulation did not seem to extend to areas with aspect ratios greater than this value; in aneurysms with aspect ratios of more than 1.6, a much slower circulation was observed near the dome. Furthermore, in the dome of...
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Publisher
Congress of Neurological Surgeons
Copyright
© Published by Oxford University Press.
ISSN
0148-396X
eISSN
1524-4040
D.O.I.
10.1097/00006123-199907000-00028
Publisher site
See Article on Publisher Site

Abstract

AbstractOBJECTIVE:The present study was undertaken to explore the relationship between the characteristic geometry of aneurysms prone to rupture and the blood flow patterns therein, using microsurgically produced aneurysms that simulated human middle cerebral artery aneurysms in scale and shape.METHODS:We measured in vivo velocity profiles using our 20-MHz, 80-channel, Doppler ultrasound velocimeter. We produced small (≤5 mm, 5 cases) and large (6-13 mm, 12 cases) aneurysms with round, dumbbell, or multilobular shapes.RESULTS:The fundamental patterns of intra-aneurysmal flow were composed of inflow, circulating flow, and outflow. The inflow, which entered the aneurysm only during the systolic phase, was strongly influenced by the position and size of the neck and the flow ratio into the distal branches. The outflow was usually nonpulsatile and of low velocity. The circulating flow depended on the aspect ratio (depth/neck width). A single recirculation zone was observed in aneurysms with aspect ratios of less than 1.6. This circulation did not seem to extend to areas with aspect ratios greater than this value; in aneurysms with aspect ratios of more than 1.6, a much slower circulation was observed near the dome. Furthermore, in the dome of dumbbell-shaped aneurysms and daughter aneurysms, no flow was detected. Intra-aneurysmal flow was determined by the aspect ratio, rather than the aneurysm size.CONCLUSION:The localized, extremely low-flow condition that was observed in the dome of aneurysms with aspect ratios of more than 1.6 is a common flow characteristic in the geometry of ruptured aneurysms, so great care should be taken for patients with unruptured intracranial aneurysms with aspect ratios of more than 1.6.

Journal

NeurosurgeryOxford University Press

Published: Jul 1, 1999

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