Annual medical expenditures covered by the NHIS for SAH was 120 billion Korean Won (KRW) in 2010, which had gradually increased by an annual growth rate of 7.74%, reaching 272 billion KRW in 2021.9 At the exchange rate of December 2022, it is approximately 215 million USD. Even so, this cost is limited to what is covered by the insurance, and the amount of non-insured treatment is not included. Moreover, SAH results in death and severe disability in > 50% of all patients. Considering not only the loss of the patient's labor force, but also the family's labor force sacrificed for the patient's care, the socio-economic loss due to SAH becomes even greater. Considering the high cost of SAH, there have been few researches regarding the epidemiology of IA. Although a few studies reported the prevalence of IAs as 2.8–7.0%, the study populations were limited to single institutes or provinces.5–7 This is because, in most countries, there are no databases on the state of medical use at the national level. Using the national database of the Republic of Korea, the incidence and risk factors of IA were reported.1 The estimated age-sex standardized incidence of IA was 52.2 per 100,000 person-year.
Unlike other critical diseases that are costly, SAH can be prevented if we can find IAs before rupture, because most spontaneous cases of SAH are caused by rupture of IA. However, considering together the estimated incidence and prevalence calculated from the participants who had undergone neurovascular imaging, most IA patients have been undiagnosed because they did not undergo appropriate examinations.1, 5–7 In fact, from 2008 to 2016, the number of national incident cases of unruptured IA had increased by 336.7%. The annual growth rate approached to 30%. Meanwhile, in the same time window, the number of SAH patients did not decrease, but rather increased by 2.4%.10 The rates of detection and treatment for unruptured IA seemed to be the tip of the iceberg to reduce the number of SAH. This also supports the idea that most IA patients are undiagnosed.
The guidelines for screening IA are as follows: 1) patients with two family members or more with IA or SAH should be offered aneurysmal screening by CTA or MRA. The risk factors that predict a particularly high risk of aneurysm occurrence in such families include history of hypertension, smoking, and female sex; and 2) patients with a history of autosomal dominant polycystic kidney disease (ADPKD), particularly those with a familial history of IA, should be offered to undergo screening by CTA or MRA, and it is reasonable to offer CTA or MRA to patients with coarctation of the aorta or microcephalic osteodysplastic primordial dwarfism.3 According to the familial history of IA, IA detection among first-degree relatives of those with sporadic SAH was approximately 4% (95% CI, 2.6–5.8), with a somewhat higher risk among siblings than among children of those affected.11,12 According to a meta-analysis of unruptured IA, the adjusted prevalence ratio was 3.4 (95% CI, 1.9–5.9).13 However, considering the nationwide proportion of IA, populations with a familial history of IA are rare.10 Similarly, the reason ADPKD was included in the screening guideline is that it shows a high prevalence rate as compared to the general population. Among ADPKD patients, the prevalence of IA was estimated to be up to 13.4%.14 A previous meta-analysis reported that the prevalence ratio of ADPKD was 6.9 (95% CI, 3.5–14.0).13 However, the estimated prevalence of ADPKD, which is the most common hereditary kidney disease in Korea, was approximately 1/10,000.15 Moreover, only 0.3% of patients with unruptured IA had a history of polycystic kidney disease.16 Therefore, this criterion can cover only a few number of the population. Moreover, the abovementioned meta-analysis included only approximately 600 patients with unruptured IA for the adjusted analysis.
Thus, a strategy to identify participants at a high risk of developing IA among the general populations is needed, because neurovascular imaging is very expensive to carry out for the whole population, and there is always a risk of potential side effects due to the use of contrast agent. In a previous work, we proposed a risk assessment algorithm for IA using a machine learning method that utilized national healthcare examination data.4 The risk of IA was evaluated in quintile risk groups, and the highest risk group showed a 49.9 times higher risk of IA than the lowest risk group. The odds ratio of the highest risk group over the entire population was 4.7 (95% CI, 3.7–5.9). However, the limitation of the validation analysis in the previous work is that, due to the nature of the NHIS data, the analysis results include both those who underwent and those who did not undergo neurovascular examinations. To overcome these limitations and prove the algorithms value in actual clinical settings, it is important to validate the predictive power of the algorithm among participants who have performed neurovascular examinations for screening purposes.
In this study, we showed that the standardized prevalence of IA was 6.44% (95% CI, 5.24–7.90) in the highest risk group, which showed an odds ratio of 38.5 compared with 0.18% (95% CI, 0.05–0.69) in the lowest risk group. Moreover, the dose-response relation was also found to be statistically significant. The standardized odds ratio of the highest risk group over the entire participants was 3.0 (95% CI, 2.2–4.0). Although the adjusted odds of IA in the highest risk group was slightly lower than the items included in current guideline, the extent of coverage is much wider, because this risk assessment algorithm had been trained using data obtained from a national healthcare examination database of patients aged > 20 years without any restrictions in terms of medical and familial histories.
There are several limitations to our study. First, this study was designed as a retrospective validation; thus, we needed to consider potential biases. To overcome the population characteristics of those who visited CNUHH, a direct standardization was applied using data from a national database. As a result, age and sex distributions were statistically adjusted. Second, the diagnostic test performed was CTA. Although catheter angiography remains the gold standard for identifying IA, CTA shows comparable sensitivity and specificity along with MRA.17 Moreover, considering the high procedure-related risk of catheter angiography, it is not suitable for use for screening purposes. In this study, two radiology specialists cross-read the CTA to enhance the diagnostic accuracy.
In conclusion, we showed the clinical efficacy and validity of a prediction algorithm for risk estimation of IA using real-world data. Many IA cases with a high risk of rupture can be detected and treated before disaster using this strategy. In addition, as the occurrence of fatal SAH is decreased, it can contribute to minimizing the economic and social losses caused by this disease.