Vascular responses to abrupt blood flow change after bypass surgery for complex intracranial aneurysms
Bypass surgery for complex intracranial aneurysms (IAs) results in drastic blood flow changes in intracranial arteries. The aim of the study was to elucidate how vessels adapt to blood flow changes after bypass surgery with phase-contrast magnetic resonance imaging (PC-MRI).
This is a prospective observational study to assess changes of the blood flow in intracranial arteries after bypass surgery for IAs. Flow rates and vessel diameters were measured with PC-MRI in 52 intracranial arteries of 7 healthy volunteers and 31 arteries of 8 IA patients who underwent bypass surgery. Wall shear stress (WSS) was calculated with the Hagen-Poiseuille formula. In 18 arteries of 5 patients, the same measurement was performed 1, 3, and 12 months after surgery.
PC-MRI showed a strong positive correlation between the flow rate and the third power of vessel diameter in both healthy volunteers (r = 0.82, P < 0.0001) and IA patients (r = 0.90, P < 0.0001), indicating the constant WSS. Of the 18 arteries in 5 patients, WSS increased in 7 arteries and decreased in 11 arteries immediately after surgery. In the WSS-increased group, WSS returned to the preoperative value in the third postoperative month. In the WSS-decreased group, WSS increased in the 12th month, but did not return to the preoperative level.
In a physiological state, WSS was constant in intracranial arteries. Changed WSS after bypass surgery tended to return to the preoperative value, suggesting that vessel diameter and flow rate might be controlled so that WSS remains constant.
KeywordsIntracranial aneurysm Bypass surgery Phase contrast Magnetic resonance imaging Wall shear stress
Phase-contrast magnetic resonance imaging
Wall shear stress
- EC-IC bypass
Internal carotid artery
Middle cerebral artery
Superficial temporal artery
Superior cerebellar artery
Number of excitations
Field of view
Analysis of variance
Smooth muscle cell
The authors would like to thank Yoshifumi Hayashi M.D. and Hirotaka Yoshida M.D. at Kitahara International Hospital, Tokyo, Japan, for PC-MRI measurements of healthy volunteers.
This work was supported in part by Grants-in-aid for Scientific Research (grant numbers: 24592150 and 15H04952) from the Japan Society for the Promotion of Science and The Ministry of Education, Culture, Sports, Science, and Technology of Japan.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional research committee and with the 1964 Helsinki declaration and its later amendments. This study was approved by the Institutional Review Board at our institutes.
Informed consent was obtained from all individual participants included in the study.
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