Incomplete Posterior Circle of Willis: A Risk Factor for Migraine?

Dissecting the Circle of Willis-Migraine connection: A review

Objective

Anatomical variations in the Circle of Willis (CoW) may mediate the prevalence of migraines with aura (MWA) and without aura (MWoA) in patients. The aim of this review is to describe and evaluate contrasting studies to clarify the current understanding of this association within the literature.

Methods

A comprehensive search across PubMed, Google Scholar, and the Cochrane Library resulted in 10 relevant studies that met our selection criteria and examined the association between the CoW and migraine prevalence.

Results

Conflicting results were reported across the prospective and retrospective studies, which varied among different populations and the inclusion classification of CoW variants. Studies that evaluated posterior CoW variations repeatedly reported differential associations between migraines with aura (MWA) and without aura (MWoA), thus revealing a significant association only with the former. Two mechanisms of actions were hypothesized to be attributed to such associations; one hypothesized a resultant cerebral hypovascularization, whilst the other emphasized the role of shear stress in associated small arteries.

Discussion

While some studies reported significant associations between specific CoW variations and migraines, particularly with the posterior CoW variations and MWA, conflicting evidence emphasizes the necessity for further investigations to provide a greater understanding between CoW variations and different migraine subtypes. A consensus calls for future studies to include larger samples over various ethnic populations to overcome the biases encountered within the current field of literature.

Validation of an Oscillation Test for the Sonographic Assessment of Fetal-Type Posterior Cerebral Artery Variants in Migraine Patients with Visual Aura

Anatomic variants of the posterior circle of Willis, including the fetal-type posterior cerebral artery (FPCA), may contribute to the formation of visual aura in migraine. We sought to validate an oscillation test to investigate FPCA frequency in migraine using transcranial color-coded duplex ultrasonography (TCCS). First, the diagnostic accuracy of the oscillation test used to identify FPCA variants by TCCS was assessed in stroke patients with available computed tomography angiography (CTA) as the set gold standard. Second, in a cross-sectional study, patients with migraine with visual aura (MWVA) and migraine without aura (MWOA), as well as healthy controls, were prospectively recruited for sonographic assessment of FPCA variants. We compared FPCA frequency between migraine patients and controls using χ²-testing and performed logistic regression analysis to investigate a potential association between MWVA and the presence of FPCA variants. Specificity, sensitivity and positive and negative predictive values for sonographic identification of FPCA with CTA as the set gold standard were 93%, 77%, 63% and 96% (partial FPCA) and 99%, 78%, 88% and 98% (complete FPCA), respectively. One hundred forty-two migraine patients (39 ± 12 y, 90 MWVA and 52 MWOA) and 49 healthy controls (31 ± 12 y) were recruited. The χ² testing did not reveal significant differences in FPCA frequency as assessed by TCCS (unilateral or bilateral, partial and/or complete) between migraine patients and controls (MWVA: 40/90 or 44.4%, MWOA: 22/52 or 42.3%, controls: 24/49 or 49%, p = 0.79). Similarly, the frequencies of partial FPCA (p = 0.61) and complete FPCA (p = 0.27) did not vary significantly among groups. Logistic regression analysis revealed no interaction effect between migraine diagnosis and FPCA prevalence (any FPCA), when adjusted for age and sex. The sonographic oscillation test can be used as a non-invasive method to identify partial and complete FPCA variants with high specificity and reasonable sensitivity. Our findings suggest that FPCA variants do not contribute to the formation of visual migraine aura.

Hemodynamic modeling of the circle of Willis reveals unanticipated functions during cardiovascular stress

The circle of Willis (CW) allows blood to be redistributed throughout the brain during local ischemia; however, it is unlikely that the anatomic persistence of the CW across mammalian species is driven by natural selection of individuals with resistance to cerebrovascular disease typically occurring in elderly humans. To determine the effects of communicating arteries (CoAs) in the CW on cerebral pulse wave propagation and blood flow velocity, we simulated young, active adult humans undergoing different states of cardiovascular stress (i.e., fear and aerobic exercise) using discrete transmission line segments with stress-adjusted cardiac output, peripheral resistance, and arterial compliance. Phase delays between vertebrobasilar and carotid pulses allowed bidirectional shunting through CoAs: both posteroanterior shunting before the peak of the pulse waveform and anteroposterior shunting after internal carotid pressure exceeded posterior cerebral pressure. Relative to an absent CW without intact CoAs, the complete CW blunted anterior pulse waveforms, although limited to 3% and 6% reductions in peak pressure and pulse pressure, respectively. Systolic rate of change in pressure (i.e., ∂P/∂t) was reduced 15%-24% in the anterior vasculature and increased 23%-41% in the posterior vasculature. Bidirectional shunting through posterior CoAs was amplified during cardiovascular stress and increased peak velocity by 25%, diastolic-to-systolic velocity range by 44%, and blood velocity acceleration by 134% in the vertebrobasilar arteries. This effect may facilitate stress-related increases in blood flow to the cerebellum (improving motor coordination) and reticular-activating system (enhancing attention and focus) via a nitric oxide-dependent mechanism, thereby improving survival in fight-or-flight situations.NEW & NOTEWORTHY Hemodynamic modeling reveals potential evolutionary benefits of the intact circle of Willis (CW) during fear and aerobic exercise. The CW equalizes pulse waveforms due to bidirectional shunting of blood flow through communicating arteries, which boosts vertebrobasilar blood flow velocity and acceleration. These phenomena may enhance perfusion of the brainstem and cerebellum via nitric oxide-mediated vasodilation, improving performance of the reticular-activating system and motor coordination in survival situations.

Profiling cerebrovascular function in migraine: A systematic review and meta-analysis

Previous studies have investigated whether migraine is a circulatory disorder, as migraineurs are at heightened risk of cerebrovascular disease. However, in most cases, systemic vascular function was evaluated, which may not reflect abnormalities in the cerebral circulation. Therefore, we aimed to determine whether cerebrovascular function differs between migraineurs and controls. A systematic literature search was conducted across three electronic databases to search for studies that compared cerebrovascular function in migraineurs to controls. Where applicable, meta-analyses were used to determine standardised mean differences (SMD) between migraineurs and controls. Seventy articles were identified, 40 of which contained quantitative data. Meta-analyses showed pulsatility index (PI) was higher (SMD = 0.23; 95%CI = 0.05 to 0.42, P = 0.01) and cerebrovascular responsiveness (CVR) to hypercapnia was lower (SMD=-0.34; 95%CI=-0.67 to -0.01, P = 0.04) in the posterior circulation of migraineurs, particularly those without aura. The meta-analyses also indicated that migraineurs have higher resting mean blood flow velocity in both anterior (SMD = 0.14; 95%CI = 0.05 to 0.23, P = 0.003) and posterior circulations (SMD = 0.20; 95%CI = 0.05 to 0.34, P = 0.007). Compared to healthy controls, migraineurs have altered cerebrovascular function, evidenced by elevated PI (representing arterial stiffness) and impaired CVR to hypercapnia (representing cerebral vasodilator function). Future studies should investigate whether improvement of cerebrovascular function is able to alleviate migraine.

Advanced Imaging in the Evaluation of Migraine Headaches

The use of advanced imaging in routine diagnostic practice appears to provide only limited value in patients with migraine who have not experienced recent changes in headache characteristics or symptoms. However, advanced imaging may have potential for studying the biological manifestations and pathophysiology of migraine headaches. Migraine with aura appears to have characteristic spatiotemporal changes in structural anatomy, function, hemodynamics, metabolism, and biochemistry, whereas migraine without aura produces more subtle and complex changes. Large, controlled, multicenter imaging-based observational trials are needed to confirm the anecdotal evidence in the literature and test the scientific hypotheses thought to underscore migraine pathophysiology.

Circle of Willis variations in migraine patients with ischemic stroke

OBJECTIVES

Migraine is a risk factor for stroke, which might be explained by a higher prevalence in anatomical variants in the circle of Willis (CoW). Here, we compared the presence of CoW variants in patients with stroke with and without migraine.

MATERIALS AND METHODS

Participants were recruited from the prospective Dutch acute Stroke Study. All participants underwent CT angiography on admission. Lifetime migraine history was assessed with a screening questionnaire and confirmed by an interview based on International Classification of Headache Disorders criteria. The CoW was assessed for incompleteness/hypoplasia (any segment <1 mm), for anterior cerebral artery asymmetry (difference > 1/3), and for posterior communicating artery (Pcom) dominance (Pcom-P1 difference > 1/3). Odds ratios with adjustments for age and sex (aOR) were calculated with logistic regression.

RESULTS

We included 646 participants with stroke, of whom 52 had a history of migraine. Of these, 45 (87%) had an incomplete or hypoplastic CoW versus 506 (85%) of the 594 participants without migraine (aOR: 1.47; 95% CI: 0.63-3.44). There were no differences between participants with and without migraine in variations of the anterior or posterior CoW, anterior cerebral artery asymmetry (aOR: 0.86; 95% CI: 0.43-1.74), or Pcom dominance (aOR: 0.64; 95% CI: 0.32-1.30). There were no differences in CoW variations between migraine patients with or without aura.

CONCLUSION

We found no significant difference in the completeness of the CoW in acute stroke patients with migraine compared to those without.

Completion of the Circle of Willis Varies by Gender, Age, and Indication for Computed Tomography Angiography

OBJECTIVE

The circle of Willis (CoW) is the foremost anastomosis and blood distribution center of the brain. Its effectiveness depends on its completion and the size and patency of its vessels. Gender-related and age-related anatomic variations in the CoW may play an important role in the pathogenesis of cerebrovascular diseases. In this study, we analyzed computed tomography angiograms (CTAs) to assess for differences in CoW completion related to gender, age, and indication for CTA.

METHODS

A total of 834 CTAs were retrospectively analyzed for all CoW vessels to compare the incidence of complete CoW and variation frequency based on gender, age, and indication.

RESULTS

The incidence of complete CoW was 37.1% overall. CoW completion showed a statistically significant decrease with increasing age for all age groups in both men (47.0%, 29.4%, 18.8%) and women (59.1%, 44.2%, 30.9%). Completion was greater in women (43.8%) than in men (31.2%) overall and for all age groups. These gender differences were all statistically significant except for the 18-39 years age group. The most frequent of the 28 CoW variations were absent posterior communicating artery (PCOM) bilaterally (17.1%), right PCOM (15.3%), and left PCOM (10.9%). Ischemic stroke and the 18-39 years age group of hemorrhagic stroke showed a statistically significant reduction in completion relative to trauma.

CONCLUSIONS

The incidence of complete CoW is likely greater in women for all age groups and likely decreases with age in both genders. The most frequently absent vessel is likely the PCOM, either unilaterally or bilaterally. Completion may play a role in ischemic stroke and a subset of patients with hemorrhagic stroke.

Incomplete Circle of Willis: A risk factor for mesial temporal sclerosis?

OBJECTIVE

The aim of this study was to investigate whether there may be a correlation between the anatomical variants of Circle of Willis (CoW) and presence/laterality of mesial temporal sclerosis (MTS).

METHODS

We retrospectively identified the CoW variants on Wada angiograms in 71 patients with pathologically proven MTS. Angiograms were interpreted by two radiologists independently and blinded to clinical data. We divided the anterior and posterior components of the CoW into functionally complete and functionally incomplete groups. We then sought its correlation with the presence and laterality of MTS.

RESULTS

No statistically significant relationship was found between the functional status of the anterior circulation and the laterality of the MTS (p=0.657). Relationship of the posterior incomplete circle to MTS was statistically significant on both sides (p=0.023 for the left, p=0.04 for the right), with an effect size moderate to large for the left side and moderate for the right side. Although the fetal variant appeared to be related to the ipsilateral MTS, it did not reach to a level of statistical significance (p=0.15).

SIGNIFICANCE

The study demonstrates a statistically significant association of the incomplete posterior circulation of the CoW to the presence of ipsilateral MTS. Further studies in larger patient populations may be needed to seek whether an incomplete circulation may facilitate development of MTS, especially affecting the watershed zones.

Anatomical Variants of the Circle of Willis and Brain Lesions in Migraineurs

Background:

Some reports demonstrated vascular alterations in brain magnetic resonance imaging (MRI) in migraineurs and a relationship between circle of Willis (Circle) variants and lacunar brain infarcts. We examined anomalies of the whole circle of Willis and their relationship with vascular brain lesions in migraineurs, to identify any possible vascular mechanism in migraine.

Methods:

We studied, with a cohort controlled study, the circle of Willis in migraineurs seen consecutively in our Headache Center, and in non-headache controls, using angio-MRI of the brain. Statistical analysis used ANOVA, Scheffè's criterion, t-student test.

Results:

We recruited 270 migraineurs (204 without aura (MWOA), 66 with aura (MWA) and 159 controls. Migraineurs presented an anatomical variant in 108 (40%) cases with 34 controls (21.4%) presenting a variant. We found a significant association between MWOA and variants (OR=2.4 CI95% [1.5 to 3.9]) and between MWA and variants (OR=3.2 CI95% [1.6 to 4.1]). Unilateral posterior variants with basilar hypoplasia are statistically associated only with MWA compared to controls (OR=9.2, CI95% [2.3 to 37.2]). Thirty-three percent of MWOA and 24% of MWA sufferers present some kind of brain lesion, included 2% of infra-tentorial lesions. We did not find any statistical association between the presence of Circle variants and ischemic lesions on MRI (OR=1.5 CI95% [0.68; 1.94]), or with infratentorial lacunar lesions (OR=1.58 CI95% [0.48 to 5.24]).

Conclusions:

Anatomical variants of the Circle of Willis are significantly more frequent in migraineurs; posterior anomalies are more frequent in MWA, suggesting a vascular mechanism provoking changes in cerebral blood flow, thereby stimulating cortical spreading depression.

Migraine and stroke: in search of shared mechanisms

BACKGROUND

Migraine, particularly with aura, increases the risk for ischemic stroke, at least in a subset of patients. The underlying mechanisms are poorly understood and probably multifactorial.

METHODS

We carried out an extended literature review of experimental and clinical evidence supporting the association between migraine and ischemic stroke to identify potential mechanisms that can explain the association.

RESULTS

Observational, imaging and genetic evidence support a link between migraine and ischemic stroke. Based on clinical and experimental data, we propose mechanistic hypotheses to explain the link, such as microembolic triggers of migraine and enhanced sensitivity to ischemic injury in migraineurs.

DISCUSSION

We discuss the possible practical implications of clinical and experimental data, such as aggressive risk factor screening and management, stroke prophylaxis and specific acute stroke management in migraineurs. However, evidence from prospective clinical trials is required before modifying the practice in this patient population.

Migraine without aura is not associated with incomplete circle of Willis: a case-control study using high-resolution magnetic resonance angiography

Background

The circle of Willis is an important source of collateral blood flow to maintain adequate cerebral perfusion, particularly in the posterior circulation. Some studies report a relationship between incomplete circle of Willis and migraine, whereas other studies show no difference between the prevalence of incomplete circle of Willis in migraineurs and controls. In the present study we compared the prevalence of incomplete circle of Willis in female migraine patients without aura to female healthy non-migraine controls.

Using 3-Tesla magnetic resonance angiography we recorded three-dimensional time-of-flight angiograms in 85 female participants (48 migraine patients without aura [median age 28 years] and 37 healthy controls [median age 25 years]). The images were subsequently analysed blindly by a neuroradiologist to detect incomplete circle of Willis.

Findings

We found no difference between the prevalence of incomplete circle of Willis in patients, 20/47 (43%), and controls, 15/37 (41%), p = 0.252. Post hoc analysis showed a significant relationship between age and prevalence of incomplete circle of Willis, p = 0.003.

Conclusion

We found no relationship between migraine without aura and incomplete circle of Willis.

Recent progress in migraine pathophysiology: role of cortical spreading depression and magnetic resonance imaging

Migraine is characterised by debilitating pain, which affects the quality of life in affected patients in both the western and the eastern worlds. The purpose of this article is to give a detailed outline of the pathophysiology of migraine pain, which is one of the most confounding pathologies among pain disorders in clinical conditions. We critically evaluate the scientific basis of various theories concerning migraine pathophysiology, and draw insights from brain imaging approaches that have unraveled the prevalence of cortical spreading depression (CSD) in migraine. The findings supporting the role of CSD as a physiological substrate in clinical pain are discussed. We also give an exhaustive overview of brain imaging approaches that have been employed to solve the genesis of migraine pain, and its possible links to the brainstem, the neocortex, genetic endophenotypes, and pathogenetic factors (such as dopaminergic hypersensitivity). Furthermore, a roadmap is proposed to provide a better understanding of pain pathophysiology in migraine, to enable the development of strategies using leads from brain imaging studies for the identification of early biomarkers, efficient prognosis, and treatment planning, which eventually may help in alleviating some of the devastating impact of pain morbidity in patients afflicted with migraine.

Migraine with aura is associated with an incomplete circle of willis: results of a prospective observational study

OBJECTIVE

To compare the prevalence of an incomplete circle of Willis in patients with migraine with aura, migraine without aura, and control subjects, and correlate circle of Willis variations with alterations in cerebral perfusion.

METHODS

Migraine with aura, migraine without aura, and control subjects were prospectively enrolled in a 1∶1∶1 ratio. Magnetic resonance angiography was performed to examine circle of Willis anatomy and arterial spin labeled perfusion magnetic resonance imaging to measure cerebral blood flow. A standardized template rating system was used to categorize circle of Willis variants. The primary pre-specified outcome measure was the frequency of an incomplete circle of Willis. The association between circle of Willis variations and cerebral blood flow was also analyzed.

RESULTS

170 subjects were enrolled (56 migraine with aura, 61 migraine without aura, 53 controls). An incomplete circle of Willis was significantly more common in the migraine with aura compared to control group (73% vs. 51%, p = 0.02), with a similar trend for the migraine without aura group (67% vs. 51%, p = 0.08). Using a quantitative score of the burden of circle of Willis variants, migraine with aura subjects had a higher burden of variants than controls (p = 0.02). Compared to those with a complete circle, subjects with an incomplete circle had greater asymmetry in hemispheric cerebral blood flow (p = 0.05). Specific posterior cerebral artery variants were associated with greater asymmetries of blood flow in the posterior cerebral artery territory.

CONCLUSIONS

An incomplete circle of Willis is more common in migraine with aura subjects than controls, and is associated with alterations in cerebral blood flow.

Migraine: possible role of shear-induced platelet aggregation with serotonin release

BACKGROUND

Migraine patients are at an increased risk for stroke, as well as other thromboembolic events. This warrants further study of the role of platelets in a proportion of migraine patients.

OBJECTIVE

To extend the "platelet hypothesis" using literature data and observations made in a rat model of shear stress-induced platelet aggregation. Such aggregation causes release of serotonin, leading to vasoconstriction during sufficiently strong aggregation and to long-lasting vasodilation when aggregation diminishes. This vasodilation also depends on nitric oxide and prostaglandin formation.

RESULTS

A role for platelet aggregation in a number of migraineurs is indicated by reports of an increased platelet activity during attacks and favorable effects of antiplatelet medication. We hypothesize that in those patients, a migraine attack with or without aura may both be caused by a rise in platelet-released plasma serotonin, albeit at different concentration. At high concentrations, serotonin may cause vasoconstriction and, consequently, the neuronal signs of aura, whereas at low concentrations, it may already stimulate perivascular pain fibers and cause vasodilation via local formation of nitric oxide, prostaglandins, and neuropeptides. Platelet aggregation may be unilaterally evoked by elevated shear stress in a stenotic cervico-cranial artery, by reversible vasoconstriction or by other cardiovascular abnormality, eg, a symptomatic patent foramen ovale. This most likely occurs when a migraine trigger has further enhanced platelet aggregability; literature shows that many triggers either stimulate platelets directly or reduce endogenous platelet antagonists like prostacyclin.

CONCLUSION

New strategies for migraine medication and risk reduction of stroke are suggested.

A simple technique for morphological measurement of cerebral arterial circle variations using public domain software (Osiris)

This article describes a straightforward method to measure the dimensions and identify morphological variations in the cerebral arterial circle using the general-purpose software program Osiris. This user-friendly and portable program displays, manipulates, and analyzes medical digital images, and it has the capability to determine morphometric properties of selected blood vessels (or other anatomical structures) in humans and animals. To ascertain morphometric variations in the cerebral arterial circle, 132 brains of recently deceased fetuses, infants, and adults were dissected. The dissection procedure was first digitized, and then the dimensions were measured with Osiris software. Measurements of each vessel's length and external diameters were used to identify and classify morphological variations in the cerebral arterial circle. The most commonly observed anatomical variations were uni- and bilateral hypoplasia of the posterior communicating artery. This study demonstrates that public domain software can be used to measure and classify cerebral arterial circle vessels. This method could be extended to examine other anatomical regions or to study other animals. Additionally, knowledge of variations within the circle could be applied clinically to enhance diagnostic and treatment specificity.

Adult-onset migraine-related ophthalmoplegia and omolateral fetal-type posterior cerebral artery

A 33-year-old woman with a long history of typical migraine without aura developed a pupillary-involving right third nerve palsy, after a typical migraine attack. The right pupil was 5 mm and showed delayed direct and consensual photomotor responses; the left pupil was 3 mm and reactive. Pupillary reaction to convergence was slow on the right eye. Ptosis, impaired elevation of the eye and weakened adduction were noted in the right eye. CT scan of the brain showed no abnormalities, whereas a CT digital cerebral angiography revealed a fetal-type right posterior cerebral artery (PCA). MRI disclosed thickening and contrast-enhancement of the cisternal portion of the right oculomotor nerve. A lumbar puncture, performed 5 days after the onset of ocular symptoms, yielded acellular cerebrospinal fluid (CSF) with normal protein and glucose levels. Ptosis and diplopia recovered within a week, whereas blurred vision, anisocoria and accommodation deficit subsided after 10 weeks.