Computational analysis of hemodynamics using a two-dimensional model in moyamoya disease

Effect of moyamoya disease on the basilar artery and adjacent arteries on CTA

Background

Computed tomographic angiography (CTA) is rarely used to explore the effect of moyamoya disease (MMD) on the basilar artery (BA) and its adjacent arteries.

Methods

Participants were divided into a control group and an MMD group. The relevant parameters were measured. Statistical analyses included the t-test, chi-squared test, and linear regression analysis.

Results

In the control group of 100 healthy people, the average age was 54.51 ± 13.40 years, and the ratio of males to females was 0.89:1. In the MMD group of 100 patients, the average age was 53.95 ± 11.31 years, and the ratio of males to females was 1.13:1. In the MMD group, the CTA score of the anterior circulation of the bilateral hemispheres was 7.57 ± 2.36. According to the statistical analyses, (1) in the control group, the BA apex tended to lean to the right in healthy participants; (2) in the MMD group, the BA was closer to the midline, and the angle between the BA and anterior inferior cerebellar artery was reduced, indicating that the BA was relatively elevated; (3) in the MMD group, the diameters of the BA, PCA and vertebral artery were larger than those in the control group; and (4) MMD patients with posterior cerebral atery (PCA) involvement had higher CTA scores of the anterior circulation.

Conclusions

MMD can cause the BA to move toward the midline and upward and enlarge major vessels of the posterior circulation. The PCA tends to be involved in MMD patients with higher CTA scores in the anterior circulation.

Computational Modelling of Cerebral Blood Flow Rate at Different Stages of Moyamoya Disease in Adults and Children

Moyamoya disease is a cerebrovascular disorder which causes a decrease in the cerebral blood flow rate. In this study, a lumped parameter model describing the pressures and flow rates in the heart chambers, circulatory system, and cerebral circulation with the main arteries in the circle of Willis, pial circulation, cerebral capillaries, and veins was used to simulate Moyamoya disease with and without coarctation of the aorta in adults and children. Cerebral blood flow rates were 724 mL/min and 1072 mL/min in the healthy adult and child cardiovascular system models. The cerebral blood flow rates in the adult and child cardiovascular system models simulating Moyamoya disease were 676 mL/min and 1007 mL/min in stage 1, 627 mL/min and 892 mL/min in stage 2, 571 mL/min and 831 in stage 3, and 444 and 537 mL/min in stage 4. The cerebral blood flow rates were 926 mL/min and 1421 mL/min in the adult and child cardiovascular system models simulating coarctation of the aorta. Furthermore, the cerebral blood flow rates in the adult and child cardiovascular system model simulating Moyamoya disease with coarctation of the aorta were 867 mL/min and 1341 mL/min in stage 1, 806 mL/min and 1197 mL/min in stage 2, 735 mL/min and 1121 in stage 3, and 576 and 741 mL/min in stage 4. The numerical model utilised in this study can simulate the advancing stages of Moyamoya disease and evaluate the associated risks with Moyamoya disease.

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.

Case-Control Study of Cephalometrics in Patients with Moyamoya

OBJECTIVE

To determine whether cranial metrics consistently differed between patients with moyamoya and age-, sex-, and race-matched controls.

METHODS

Patients diagnosed with moyamoya disease by cerebral angiogram were obtained from a prospectively collected database through the Department of Neurosurgery at the University of Kansas Medical Center. Control patients matched by decade of age, sex, and race were collected through a deidentified hospital database by International Classification of Diseases-9 and 10 codes for ischemic stroke to identify patients with computed tomography angiograms. Imaging studies for both groups were analyzed to obtain 6 skull metrics: maximum anterior to posterior distance, maximum biparietal distance, bregma to occiput distance, right carotid canal diameter (CCD), left CCD, and cephalic index.

RESULTS

Forty-five patients were identified in each cohort. Measurements of mean anterior to posterior skull diameter, mean biparietal skull diameter, bregma to occiput distances, and calculated cephalic index did not demonstrate a statistically significant difference between patients with moyamoya and control patients. Right carotid canal mean diameter was 4.8 mm for the moyamoya group and 5.4 mm for the control group, with a significant raw mean difference of -0.61 mm (95% confidence interval, -0.95 to -0.27). Left CCD was 4.7 mm for the moyamoya group and 5.5 mm for the control group, resulting in a significant raw mean difference of -0.76 mm (95% confidence interval, -1.09 to -0.43).

CONCLUSIONS

This study identified 2 skull parameters as statistically different in patients with moyamoya compared with a matched control group of patients with ischemic stroke: right CCD and left CCD.

Moyamoya syndrome as a manifestation of varicella-associated cerebral vasculopathy-case report and review of literature

BACKGROUND

Varicella-associated cerebral vasculopathy (VACV) is a serious complication of Varicella zoster virus (VZV) infection. VACV has protean manifestations, with varying clinical, radiological features and prognosis.

CASE DESCRIPTION

Moyamoya syndrome (MMS) with VACV is reported in few cases in the past. All the patients were in paediatric age group, presenting with multiple episodes of transient ischemic attacks (TIAs) and infarct. Our case was a 10-year-old Indian girl with ischemic stroke due to VACV who was treated with intravenous acyclovir. She presented 11 months later with multiple episodes of TIAs. Her angiogram showed bilateral moyamoya vasculature. Acetazolamide challenge study revealed areas of hypoperfusion. Previously reported such cases had been treated medically with steroids and antiplatelets. Most of these patients had resolution of motor symptoms after long follow-up; however, this period was marred by recurrent symptoms. Our patient underwent cerebral revascularisation procedure, following which her TIAs resolved, there was improvement in her limb power and, according to her parents, her performance in school has improved at 2-year follow-up.

CONCLUSION

MMS can be a manifestation of VACV and should be suspected in paediatric patient of non-east Asian population. These patients require treatment with intravenous acyclovir to inactivate the virus. Those with TIAs should undergo cerebral revascularisation procedures. Medical management should be reserved for patients with adequate collaterals.

Posterior Cerebral Artery Insufficiency in Pediatric Moyamoya Disease

The majority of clinical studies on moyamoya disease (MMD) have focused on anterior circulation. The disease involvement of posterior circulation in MMD, mainly in the posterior cerebral artery (PCA), has been mentioned since the early 1980s, and it has been repeatedly emphasized as one of the most important factors related to poor prognosis in MMD. However, its clinical features and outcome have only been elucidated during the last few years. In this review, the angiographic definition of PCA stenosis is summarized. The clinical features are elucidated as being either early-onset or delayed-onset, according to the time of PCA stenosis diagnosis in reference to the anterior circulation revascularization surgeries. The surgical strategy and hypothesis on the mechanism of PCA stenosis is also briefly mentioned. It appears that some MMD patients may show PCA stenosis during the early or late course of the disease and that the presenting symptoms may vary. Because the hemodynamic compromise caused by PCA stenosis may respond well to surgical treatment, clinicians should be aware of the condition, especially during follow-up of MMD patients.

Moyamoya Syndrome: A Window of Moyamoya Disease

Moyamoya-like vasculopathy develops in association with various systemic diseases and conditions, which is termed moyamoya syndrome. Relatively common diseases and conditions are related to moyamoya syndrome, including neurofibromatosis type 1, Down syndrome, thyroid disease, and cranial irradiation. Moyamoya syndrome shares phenotypical characteristics with idiopathic moyamoya disease. However, they differ in other details, including clinical presentations, natural history, and treatment considerations. The study of moyamoya syndrome can provide clinicians and researchers with valuable knowledge and insight. Although it is infrequently encountered in clinical practice, moyamoya-like vasculopathy can severely complicate outcomes for patients with various underlying diseases when the clinician fails to expect or diagnose moyamoya syndrome development. Furthermore, moyamoya syndrome could be used as a doorway to more enigmatic moyamoya disease in research. More comprehensive survey and investigation are required to uncover the secrets of all the moyamoya-like phenomena.

Morphology and related hemodynamics of the internal carotid arteries of moyamoya patients

BACKGROUND

Morphological studies investigating the intracranial-extradural internal carotid artery with moyamoya disease have not been reported. We designed this case-control study to investigate the morphological differences of the internal carotid artery with moyamoya disease, and to clarify the contributions of these differences to the resultant fluid dynamics.

METHODS

Patients with moyamoya disease and normal controls were assigned to each group. The vascular tortuosity of internal carotid artery was measured with three-dimensional rendering using magnetic resonance angiography. By computational fluid dynamics, hemodynamic characteristics were simulated and compared between two groups.

RESULTS

Distances were measured from the carotid canal to the siphon. A shorter actual distance was observed in the moyamoya group (p = 0.0170). Vascular tortuosity was significantly low in moyamoya patients showing lower curvature angles in the petrous and intra-cavernous segments (p = 0.0012). Less blood flowed (p < 0.0001) through the narrower internal carotid artery (p < 0.0001) in the moyamoya group at the carotid canal level. The blood flow velocities were not significantly different (p = 0.2332). Faster blood flow and higher wall shear stress in the internal carotid artery bifurcation were verified with computational fluid dynamics.

CONCLUSIONS

Significant morphological differences were confirmed to exist in the intracranial-extradural internal carotid artery of moyamoya patients. These differences might influence the hemodynamics around the bifurcation of the internal carotid artery.

Genetic Analysis of RNF213 c.14576G>A Variant in Nonatherosclerotic Quasi-Moyamoya Disease

BACKGROUND

Quasi-moyamoya disease (MMD) and MMD (definite MMD) have similar cerebral angiographic features, but whether these related diseases have similar etiology or genetic background remains unclear. Recently, we have reported that the recently identified MMD susceptibility gene variant RNF213 c.14576G>A (rs112735431) was associated with atherosclerotic intracranial major artery stenosis/occlusion. The present study investigated the occurrence of RNF213 c.14576G>A in patients with nonatherosclerotic quasi-MMD.

METHODS

This study was a 2-hospital-based case-control study conducted at the Department of Neurosurgery, The University of Tokyo Hospital and Kanto Neurosurgical Hospital. A total of 87 Japanese patients who agreed to participate in this study were enrolled among both new and revisiting outpatients from October 2011 to December 2013 as follows: 78 patients with definite MMD and 9 patients with nonatherosclerotic quasi-MMD.

RESULTS

The 9 patients with nonatherosclerotic quasi-MMD included 3 patients with previous irradiation, 2 with hyperthyroidism, 1 with Turner syndrome, 1 with meningitis, 1 with Behçet disease, and 1 with idiopathic pachymeningitis. The 78 patients with definite MMD included 66 patients (84.6%) with the c.14576G>A variant (64 heterozygotes and 2 homozygous). In contrast, no patients with nonatherosclerotic quasi-MMD had the variant.

CONCLUSIONS

Nonatherosclerotic quasi-MMD did not have RNF213 c.14576G>A variant. Moyamoya disease and related diseases might be classified by genetic analysis of the RNF213 c.14576G>A genotype. Further larger studies are required to confirm the present findings.

Loss of α1β1 soluble guanylate cyclase, the major nitric oxide receptor, leads to moyamoya and achalasia

Moyamoya is a cerebrovascular condition characterized by a progressive stenosis of the terminal part of the internal carotid arteries (ICAs) and the compensatory development of abnormal "moyamoya" vessels. The pathophysiological mechanisms of this condition, which leads to ischemic and hemorrhagic stroke, remain unknown. It can occur as an isolated cerebral angiopathy (so-called moyamoya disease) or in association with various conditions (moyamoya syndromes). Here, we describe an autosomal-recessive disease leading to severe moyamoya and early-onset achalasia in three unrelated families. This syndrome is associated in all three families with homozygous mutations in GUCY1A3, which encodes the α1 subunit of soluble guanylate cyclase (sGC), the major receptor for nitric oxide (NO). Platelet analysis showed a complete loss of the soluble α1β1 guanylate cyclase and showed an unexpected stimulatory role of sGC within platelets. The NO-sGC-cGMP pathway is a major pathway controlling vascular smooth-muscle relaxation, vascular tone, and vascular remodeling. Our data suggest that alterations of this pathway might lead to an abnormal vascular-remodeling process in sensitive vascular areas such as ICA bifurcations. These data provide treatment options for affected individuals and strongly suggest that investigation of GUCY1A3 and other members of the NO-sGC-cGMP pathway is warranted in both isolated early-onset achalasia and nonsyndromic moyamoya.

Posterior cerebral artery involvement in moyamoya disease: initial infarction and angle between PCA and basilar artery

PURPOSE

Moyamoya disease (MMD) is a chronic cerebrovascular occlusive disease, and progressive involvement of the posterior cerebral artery (PCA) has been reported. However, majority of MMD articles are presenting classic anterior circulation related issues. This study investigates the preoperative factors related to the long-term outcome of posterior circulation in MMD.

METHODS

Retrospective review of 88 MMD patients (166 PCAs in either hemisphere) without symptomatic disease involvement of PCA at initial diagnosis was done. Data at initial diagnosis regarding age, presence of infarction, status of the PCA, type of posterior communicating artery, and the angle between PCA and basilar artery were reviewed. Progressive stenosis of PCA was evaluated by symptom or radiological imaging during follow up.

RESULTS

During an average follow up of 8.3 years, 29 out of 166 (18 %) evaluated PCAs showed progressive disease involvement. The average time of progression from the initial operation was 4.9 years, with the latest onset at 10.8 years. The patients who showed progressive stenosis of the PCA tended to be younger, present with infarction, have smaller angle between PCA and basilar artery, and have asymptomatic stenosis of the PCA at initial presentation. However, multivariate analysis confirmed only the presence of initial infarction and a smaller angle between PCA and basilar artery to be significantly associated with progressive stenosis of PCA.

CONCLUSIONS

Involvement of PCA in MMD may occur in a delayed fashion, years after the completion of revascularization of anterior circulation. Persistent long-term follow-up regarding the posterior circulation is recommended.

Local hemodynamic disturbance accelerates early thrombosis of small-caliber expanded polytetrafluoroethylene grafts

OBJECTIVE

Small-caliber expanded polytetrafluoroethylene (ePTFE) grafts cannot be used widely in the clinical situation because of early thrombosis and occlusion. This unsolved and under-recognized problem warrants further investigation.

METHODS

Grafts of uncoated ePTFE (n = 6) and anti-CD34-coated ePTFE (n = 6) were implanted unilaterally into the carotid artery in 12 domestic pigs. Ultrasonography was used to test the proximal and distal anastomotic stoma morphology, diameters and blood velocities. A thrombosis instrument was used to examine the blood coagulation state. After seven days, the pigs were sacrificed and the implanted grafts were excised for general and histological analysis. Computational fluid dynamics was used to investigate the blood flow fields of the implanted grafts and to calculate parameters that might be indicative of thrombosis.

RESULTS

Thrombosis was detected in 10 of 12 (83.3%) implanted ePTFE grafts, 5 in uncoated grafts and 5 in anti-CD34-coated grafts. Endothelial cell coverage was observed in both uncoated and anti-CD34-coated grafts. No obvious abnormalities in anastomotic stoma or blood coagulation state were observed. Computer-based local hemodynamic simulation showed the low flexibility of synthetic ePTFE grafts caused obvious coarctation. Local wall pressure, velocity and wall shear stress were much higher than in the contralateral normal vessel.

CONCLUSIONS

The patency of small-caliber ePTFE grafts for clinical use is impaired by early thrombosis due to mixed causes. Local hemodynamic disturbance was the most powerful predictor of early thrombosis. Decreasing local hemodynamic disturbance, improving the quality of anastomotic stoma, selecting reasonable anticoagulation strategies and promoting rapid endothelialization may increase the long-term patency of small-caliber vascular grafts.