We retrospectively reviewed all Chinese Han patients with intracranial aneurysms who were evaluated or treated at Beijing Tiantan Hospital between January 2020 and December 2021. All aneurysms were diagnosed using digital subtraction angiography (DSA). Intracranial aneurysm rupture (IAR) was diagnosed based on computed tomography (CT) evidence of subarachnoid hemorrhage. Institutional review board approval was obtained. Among the 3,514 patients who were evaluated or treated, 1,170 patients harboring 1,059 UIAs and 236 ruptured intracranial aneurysms (RIAs) were included for analysis after applying our exclusion criteria. Figure 1 shows the study flowchart and exclusion criteria in detail.

A semi-structured telephone interview (Table 1) was performed by trained interviewers to determine smoking habits, drinking habits, presence of facial flushing when drinking (23–25). Medical history data was collected from treating physicians through interviews with patients and/or family members. Participants were defined as ever-drinkers if they had ever consumed an alcoholic beverage during their lifetime and as never-drinkers if they had never done so. Ever-drinkers were asked about AFS using the following question: ‘Do you have a propensity to experience facial flushing immediately after drinking a glass of beer or an equivalent alcoholic beverage?’ If the answer was “yes, “they were categorized as having AFS; those who answered “no” were categorized as not having AFS. Habitual alcohol drinking was defined as drinking alcohol more than 5 days a week (24). Current and past smokers were defined as smokers. Patients were considered to have diabetes if they had a previously measured 2-h blood glucose concentration ≥ 200 mg/dl after oral glucose tolerance testing or if they were using insulin or oral hypoglycemic drugs. Patients were considered hypertensive if they had a history of untreated hypertension, used antihypertensive medication, or had been diagnosed with hypertension by a physician. Patients were considered to have hyperlipidemia if they had a history of hyperlipidemia, used anti-lipidemic medications, or had been diagnosed with hyperlipidemia by a physician. Patients were considered to have heart disease if they had a history of myocardial infarction, angina pectoris, percutaneous transluminal coronary angioplasty, or coronary artery bypass graft surgery (26).

Two experienced neurointerventionalists evaluated the morphological features of aneurysms using three-dimensional rotational digital subtraction angiography (DSA). The aneurysm size, neck size, and parent artery diameter were measured, and aneurysm shape and location were documented. The maximum cross-sectional diameter, vertical distance between the aneurysm dome and neck, and maximum horizontal diameter were defined as aneurysm size, height, and width, respectively. Aspect ratio (AR) was calculated as the ratio of aneurysm height to neck diameter. Height/width ratio (HWR) was calculated as the ratio of aneurysm height to aneurysm width. Size ratio (SR) was calculated as the ratio of aneurysm size to parent artery diameter. Additionally, the mean vessel diameter was determined by averaging the diameters of two vessel segments upstream of the aneurysm (D1 at the proximal neck and D2 at the upstream 1.5 × D1), (27). A bifurcation aneurysm was defined as originating from an arterial junction (28). These morphological parameters were used to characterize the aneurysms and were analyzed according to established conventions. The measurements were performed by the two neurointerventionalists to ensure consistency, and the inter-observer agreement was assessed.

Continuous variables were analyzed using appropriate statistical tests based on their distribution, such as means with standard deviation for normally distributed variables and median with interquartile range for non-normally distributed variables. Categorical variables were presented as numbers with frequency and compared using chi-square or Fisher’s exact test as appropriate. To assess the relationship between clinical and aneurysm characteristics and aneurysmal rupture, univariate and multivariate logistic regression analyses were performed to calculate odds ratios (ORs) with 95% confidence intervals (CIs). SPSS software version 25 (IBM Corp., Armonk, NY, United States) was used for all statistical analyses. Statistical significance was considered at a p-value less than 0.05.

In the univariate analyses (Table 5), female sex (OR 1.63; 95% CI, 1.22–2.17), history of ischemic stroke (OR 0.42; 95% CI, 0.25–0.72), smoking (OR 1.68; 95% CI, 1.25–2.25), habitual alcohol drinking (OR 1.97; 95% CI, 1.43–2.70), AFS (OR 0.49; 95% CI, 0.34–0.72), aneurysm size ≥ 7 mm (OR 3.39; 95% CI, 2.53–4.53), bifurcation location (OR 6.63; 95% CI, 4.46–9.85), posterior circulation location (OR 1.93; 95% CI, 1.18–2.79), irregular shape (OR 4.04; 95% CI, 2.97–5.49), aneurysm AR (OR 1.60; 95% CI, 1.31–1.97), aneurysm SR (OR 1.51; 95% CI, 1.38–1.64), and aneurysm HWR (OR 2.67; 95% CI, 1.76–4.06) were significantly associated with IAR.

In the multivariate analysis (Table 5), AFS (OR 0.50, 95% CI 0.35–0.71), history of ischemic stroke (OR 0.38; 95% CI, 0.22–0.65), aneurysm size ≥ 7 mm (OR 2.17; 95% CI, 1.46–3.24), bifurcation location (OR 4.9; 95% CI, 3.6–8.32), irregular shape (OR 2.87; 95% CI, 2.05–4.01), and aneurysm SR (OR 1.25, 95% CI 0.96–2.46) were independent predictors of aneurysmal rupture.

Because of the significant interaction between AFS and habitual alcohol drinking, we performed an analysis with patients stratified according to both categories. Among patients who did not habitually drink alcohol, the prevalence of ruptured aneurysm in the AFS and no AFS subgroups was 13.9 and 19.9%, respectively, and the odds of IAR were significantly higher in those without AFS (OR 1.54; 95% CI, 1.07–2.21; p = 0.02). Among habitual drinkers, the prevalence of IAR in the AFS and no AFS subgroups was 11.6 and 33.8%, respectively, and the odds of IAR were also significantly higher in those without AFS (OR 3.88; 95% CI, 1.55–9.75; p < 0.001; Figure 2B). Univariate analysis (Table 6) showed that hypertension (OR 1.54; 95% CI, 1.06–2.22), history of ischemic stroke (OR 0.37; 95% CI, 0.18–0.77), and AFS (OR 0.63; 95% CI, 0.44–0.92) were significantly associated with IAR in patients without a drinking habit; in the multivariate analysis, AFS (OR 0.69; 95% CI, 0.49–0.96) was independently associated with IAR. In habitual alcohol drinkers, multivariate analysis showed that AFS (OR 0.11; 95% CI, 0.03–0.45) was also independently associated with IAR.

Our study is the first to identify AFS as a possible new clinical marker for assessing the risk of intracranial aneurysm rupture. Conventional factors like history of ischemic stroke, bifurcation location, irregular shape, aneurysm size ≥ 7 mm, and aneurysm SR were also independently associated with aneurysmal rupture.

Facial flushing in patients with AFS occurs because of expansion of facial blood vessels and a temporary increase in facial blood flow after drinking alcohol (29). The underlying cause is accumulation of acetaldehyde, an alcohol metabolite (30). A subset of Asians, including the Chinese Han population, have a mutation in the ALDH2 gene that generates inactive ALDH2, an enzyme that scavenges and detoxifies acetaldehyde and other toxic aldehydes (12). These Asians have a higher prevalence of facial flushing than those without the mutation (31, 32). Epidemiological surveys have shown that ALDH2 gene polymorphisms are strongly linked to an increased incidence of stroke and cardiovascular risk factors (33). Several studies have identified the ALDH2*2 allele as an independent risk factor for ischemic stroke and cerebral infarction in the Chinese population (22, 34). Additionally, studies have indicated that the ALDH2*1 allele appears to be a significant risk factor for ischemic stroke (35), multiple lacunar infarction (36), and stroke (37, 38) in Asian populations.

AFS is a reliable proxy marker for ALDH2 genetic variants in East Asian populations and can be used to identify subjects with ALDH2 deficiency (16–18). In our study, we identified patients with AFS using an alcohol flushing questionnaire and found that AFS was negatively associated with IAR in a population of Chinese Han patients with intracranial aneurysms. One possible explanation for this is that the prevalence of habitual drinkers without AFS is higher than that of patients with AFS. Patients with AFS may experience facial flushing, headache, palpitations, and nausea after drinking alcohol. These adverse physiological reactions to alcohol consumption can reduce the patient’s dependence on alcohol and reduce alcohol intake (12, 15, 39). We compared the clinical characteristics of patients with and without AFS and showed that prevalence of habitual drinking and aneurysm rupture were higher in patients without AFS. Notably, previous studies, including the work by Can et al. (40), have found a significant correlation between alcohol use and the risk of IAR. ALDH2 polymorphisms might be linked to aneurysmal rupture because of their association with alcohol drinking behavior. Wang et al. (37) showed that the ALDH2*2 allele, which is phenotypically expressed as AFS, has a protective effect against stroke in Han Chinese individuals with a history of heavy alcohol consumption. The study also found that excessive alcohol intake can worsen ischemic brain injury by suppressing ALDH2 gene activity (39). However, AFS was independently associated with IAR in our multivariate logistic regression model, which adjusted for all other rupture risk factors, including habitual drinking. Analysis with patients grouped according to drinking habits showed that AFS was independently associated with IAR after adjusting for other confounding factors, regardless of drinking habits (Table 6). Therefore, the effect of AFS on aneurysmal rupture may be independent of drinking behavior. One possible explanation is that ALDH2 may have other effects on blood vessels in addition to its effects on alcohol metabolism. ALDH2 is expressed in multiple organs, such as the liver, kidney, and myocardium (41, 42), and has the potential to influence hormonal and lipid metabolism systems due to its polymorphisms. Several studies have shown that ALDH2 is associated with nitric oxide production in the vascular endothelium (43, 44), which may lead to endothelial apoptosis and oxidative stress (36). These effects may promote structural remodeling and fragility in aneurysm walls that eventually result in rupture (45, 46). In addition, Yang et al. (11) found that ALDH2 deficiency reduces the risk of aortic aneurysm and dissection in mice and humans via microRNA-mediated phenotypic switching of aortic vascular wall cells. However, the relevance of this mechanism in intracranial aneurysms has not been investigated.

In our study, 86.9% of RIAs were located at a bifurcation. In the multivariate model, bifurcation location was independently associated with increased odds of rupture (OR, 4.9). At an arterial bifurcation, the arterial wall is constantly in a weakened state because of high hemodynamic pressure and high blood flow, which explains the higher risk of rupture at these locations (47). In addition, aneurysm size ≥ 7 mm was also independently associated with rupture (OR, 2.17), which is consistent with previous reports (8, 48). However, Aoki (49) reported that SR, not aneurysm size, predicts rupture in UIAs. The increased risk of rupture with increasing SR is attributed to the presence of more dangerous hemodynamic features in aneurysms with higher SR (50). Our study also found that both SR and irregular shape are independently associated with rupture.

Interestingly, history of ischemic stroke was associated with lower odds of aneurysmal rupture. Statins and antiplatelet agents are commonly used for prevention of stroke in patients with hyperlipidemia and those with a previous ischemic stroke. Several recent studies have emphasized the potential protective effect of these agents for aneurysmal rupture (51–56). Potential mechanisms include anti-inflammatory effects, stimulation of extracellular matrix production, and chemotactic migration of mesenchymal progenitor cells to stabilize aneurysm walls (57, 58).

To the best of our knowledge, the relationship between AFS and intracranial aneurysm rupture has not been investigated in other populations. However, there is considerable subjectivity in AFS data obtained via questionnaires alone. Several studies have shown the presence of the alcohol dehydrogenase 2*2 allele in East Asians, which encodes a hyperactive form of alcohol dehydrogenase 2 that presents with AFS because acetaldehyde accumulates faster than ALDH2 can metabolize it (59); however, this polymorphism is found in a very low percentage of the population (17). Although we found an association between AFS and intracranial aneurysm rupture, single nucleotide sequencing would be required to determine the responsible gene and polymorphism.

This study has several other limitations. First, it was retrospective and conducted in a single center, so bias may have been introduced. Moreover, our data did not include amount of alcohol consumed, which almost certainly influences the association between AFS and aneurysmal rupture. Second, the alcohol flushing questionnaire used did not evaluate alcohol-related symptoms other than flushing, nor did it assess AFS severity. This lack of discrimination could potentially overestimate the accuracy of identifying ALDH2 gene mutations. Questionnaires may be more sensitive in detecting alcohol-related symptoms such as sleepiness, nausea, headache, and throbbing, according to several studies (60, 61). Finally, the characteristics of an aneurysm, such as AR, size, and SR, may be subject to change following rupture, which could have introduced bias in previous research.