Noninvasive Assessment of Hemodynamic Stress Distribution after Indirect Revascularization for Pediatric Moyamoya Vasculopathy

Arterial spin labeling for moyamoya angiopathy: A preoperative and postoperative evaluation method

Objectives

Studies have shown that arterial spin labeling (ASL) effectively replaces traditional MRI perfusion imaging for detecting cerebral blood flow (CBF) in patients with Moyamoya angiopathy (MMA). However, there are few reports on the relationship between neovascularization and cerebral perfusion in patients with MMA. The aim of this study is to investigate the effects of neovascularization on cerebral perfusion with MMA after bypass surgery.

Methods

We selected patients with MMA in the Department of Neurosurgery between September 2019 and August 2021 and enrolled them based on the inclusion and exclusion criteria. ASL imaging was used to monitor the baseline CBF level before surgery and determine the changes in cerebral vessels at postoperative 1 week and 6 months, respectively. The Alberta stroke grade, modified Rankin Scale (mRS), and digital subtraction angiography images were used to evaluate the effect of postoperative CBF status and prognosis. Ninety hemispheres from 51 patients were included in this study. There were no significant differences in the baseline data of the enrolled patients. At 1 week and 6 months post-surgery, the CBF state in the operation area was significantly changed compared with that at baseline (P < 0.05). The preoperative Alberta score (t = 2.714, P = 0.013) and preoperative mRS score (t = 6.678, P < 0.001) correlated with postoperative neovascularization.

Conclusion

ASL is an effective method for detecting CBF and plays an important role in the long-term follow-up of patients with MMA. Combined cerebral revascularization significantly improves CBF in the operation area both in the short and long terms. Patients with lower preoperative Alberta scores and higher mRS scores were more likely to benefit from combined cerebral revascularization surgery. However, regardless of the type of patient, CBF reconstruction can effectively improve prognosis.

Image-based patient-specific flow simulations are consistent with stroke in pediatric cerebrovascular disease

Moyamoya disease (MMD) is characterized by narrowing of the distal internal carotid artery and the circle of Willis (CoW) and leads to recurring ischemic and hemorrhagic stroke. A retrospective review of data from 50 pediatric MMD patients revealed that among the 24 who had a unilateral stroke and were surgically treated, 11 (45.8%) had a subsequent, contralateral stroke. There is no reliable way to predict these events. After a pilot study in Acta-/- mice that have features of MMD, we hypothesized that local hemodynamics are predictive of contralateral strokes and sought to develop a patient-specific analysis framework to noninvasively assess this stroke risk. A pediatric MMD patient with an occlusion in the right middle cerebral artery and a right-sided stroke, who was surgically treated and then had a contralateral stroke, was selected for analysis. By using an unsteady Navier-Stokes solver within an isogeometric analysis framework, blood flow was simulated in the CoW model reconstructed from the patient's postoperative imaging data, and the results were compared with those from an age- and sex-matched control subject. A wall shear rate (WSR) > 60,000 s-1 (about 12 × higher than the coagulation threshold of 5000 s-1 and 9 × higher than control) was measured in the terminal left supraclinoid artery; its location coincided with that of the subsequent postsurgical left-sided stroke. A parametric study of disease progression revealed a strong correlation between the degree of vascular morphology altered by MMD and local hemodynamic environment. The results suggest that an occlusion in the CoW could lead to excessive contralateral WSRs, resulting in thromboembolic ischemic events, and that WSR could be a predictor of future stroke.

Monitoring Cerebral Perfusion Changes Using Arterial Spin-Labeling Perfusion MRI after Indirect Revascularization in Children with Moyamoya Disease

OBJECTIVE

To assess the role of arterial spin-labeling (ASL) perfusion MRI in identifying cerebral perfusion changes after indirect revascularization in children with moyamoya disease.

MATERIALS AND METHODS

We included pre- and postoperative perfusion MRI data of 30 children with moyamoya disease (13 boys and 17 girls; mean age ± standard deviation, 6.3 ± 3.0 years) who underwent indirect revascularization between June 2016 and August 2017. Relative cerebral blood flow (rCBF) and qualitative perfusion scores for arterial transit time (ATT) effects were evaluated in the middle cerebral artery (MCA) territory on ASL perfusion MRI. The rCBF and relative time-to-peak (rTTP) values were also measured using dynamic susceptibility contrast (DSC) perfusion MRI. Each perfusion change on ASL and DSC perfusion MRI was analyzed using the paired t test. We analyzed the correlation between perfusion changes on ASL and DSC images using Spearman's correlation coefficient.

RESULTS

The ASL rCBF values improved at both the ganglionic and supraganglionic levels of the MCA territory after surgery (p = 0.040 and p = 0.003, respectively). The ATT perfusion scores also improved at both levels (p < 0.001 and p < 0.001, respectively). The rCBF and rTTP values on DSC MRI showed significant improvement at both levels of the MCA territory of the operated side (all p < 0.05). There was no significant correlation between the improvements in rCBF values on the two perfusion images (r = 0.195, p = 0.303); however, there was a correlation between the change in perfusion scores on ASL and rTTP on DSC MRI (r = 0.701, p < 0.001).

CONCLUSION

Recognizing the effects of ATT on ASL perfusion MRI may help monitor cerebral perfusion changes and complement quantitative rCBF assessment using ASL perfusion MRI in patients with moyamoya disease after indirect revascularization.