Rinkel et al. concluded that the relative risk of symptomatic aneurysm rupture was 8.2 times greater than that of asymptomatic aneurysms. The overall rupture rate of unruptured intracranial aneurysms was 1.9 per 100 persons per year, and the associated risk factors were, in descending order, symptomatic aneurysms, aneurysms larger than 10 mm, location in the vertebrobasilar artery system, and female. The largest international multicenter study is currently being conducted by the ISUIA (International Study of Unruptured |ntracranialAneurysms Investigators).
The results of the phase I retrospective study showed that in patients with asymptomatic aneurysms without a history of subarachnoid hemorrhage (SAH), the annual rupture rate was 0.05% for aneurysms less than 10 mm in diameter, compared with 1% and more than 6% for those 10-25 mm and greater than 25 mm in diameter, respectively. In the phase II prospective study, 4,060 patients from more than 60 treatment centers in the United States, Canada, and Europe were observed for more than 7 years, including 1,692 patients in the untreated group, 1,917 patients in the microsurgery group, and 451 patients in the interventional group.
Patients in each group were further divided into two groups, namely the group of patients without a history of aneurysmal SAH and the group of patients with a history of aneurysmal SAH. The results showed that the 5-year cumulative rupture rates in the first group (no history of aneurysmal SAH) were 0% (3-7 mm diameter), 2.6% (7-12 mm), 14.5% (13-24 mm), and 40% (25 mm or more) for anterior circulation aneurysms and 2.5%, 14.5%, 18.4%, and 50% for posterior circulation aneurysms (including posterior communicating aneurysms), respectively, by size. For 7-12 mm aneurysms, the annual rupture rate is 0.5% for anterior circulation aneurysms and 2.9% for posterior circulation aneurysms.
According to weir, it is irresponsible to base treatment on the maximum diameter of the aneurysm alone. In the United States, more than 15,000 aneurysms with a maximum diameter <7 mln rupture each year, and most of these aneurysms are asymptomatic before rupture.
Britz: A retrospective study of 4619 patients with unruptured aneurysms found that survival rates were higher in patients with surgical clamping than in those without surgery, supporting early intervention for unruptured aneurysms.
Wiebers: 5-year morbidity and mortality study of 1692 patients with unruptured aneurysms without surgical treatment, 1917 with clamping surgery, and 451 with endovascular treatment: the natural morbidity and mortality of unruptured aneurysms were equal to or higher than those associated with damage from clamping surgery or endovascular surgery.
Krisht: concluded that the 10-year cumulative morbidity and mortality and severe disability rates for patients with unruptured aneurysms were not less than 7.5%, compared with 0.8% for those with surgical clamping and 3.4% for those with permanent disability, suggesting that surgical clamping may be preferable to no treatment if the patient’s life expectancy is not less than 10 years.
Vindlacheruvu: concluded that surgical treatment may benefit patients with unruptured aneurysms by prolonging life expectancy, except in patients with life expectancy shorter than 15 to 35 years or aged 45 to 70 years (depending on the size and location of the aneurysm) and anterior circulation unruptured aneurysms <7 mln in diameter.
For the management of unruptured aneurysms, the American Heart Association treatment guidelines are as follows.
① Small incidentally discovered intracavernous sinus aneurysms do not require treatment; large symptomatic intracavernous sinus aneurysms should be treated if age permits and if symptoms are severe or progressing.
② All intracranial symptomatic aneurysms should be considered for management; if they are emergencies, they should be treated urgently; for large and massive symptomatic aneurysms, the surgical risk is high and management should be centralized and individualized. ( Aneurysms with a history of SAH should be managed regardless of size, especially those located at the top of the basilar artery; the patient’s age, health status, and risk of treatment may affect the management of the aneurysm and should be closely monitored when treated conservatively. ( Asymptomatic aneurysms (<10 mm) without a history of SAH should be observed unless the patient is young, has a daughter aneurysm, or has other unique hemodynamic features that warrant consideration of treatment; a family history of SAH should also be considered for management Aneurysms larger than 10 mm should be managed based on consideration of age, health status, and risk of aneurysm rupture. For patients without SAH, the risk of bleeding from incidental small aneurysms is low, and close observation is advocated instead of treatment.
UIA without previous SAH
Wiebers: 130 patients were followed up for a mean of 8.3 years. 102 aneurysms < 10 mm in diameter did not rupture and 15 of 51 aneurysms ≥ 10 mm in diameter ruptured and bled during the follow-up period. 14 of them died and 1 survived after surgical clamping.
Locksley: A study of 165 patients with UIA found that 8 died between 3 months and 3 years after diagnosis and that all aneurysms were 7-10 mm in diameter, none of the UIAs under 7 mm in diameter ruptured and 3 of the 9 patients with 7-10 mm in diameter bled. In another study, 54 patients were followed up for a mean of 43.7 months, and aneurysm rupture was found in 8 of 39 patients with UIA.
Yasui: et al. followed 234 patients for a mean of 6.25 years, of whom 34 (14.5%) had bleeding, with an average annual rupture rate of 2.3%. In another study, 22 of 25 aneurysms with recent bleeding were < 9 mm in diameter at diagnosis, 16 of which were even < 5 mm in diameter, but were confirmed by angiography after rupture, 19 of which were enlarged, but 11 of which were still < 9 mm in diameter at the time of final rupture, including 5 of which were < 5 mm in diameter. This shows that even small UIAs should be treated promptly and followed up carefully.
UIA with SAH
The average annual rupture rate for the whole group was 1.4%. The mean time from detection to rupture was 9.6 years, and the cumulative rupture rate over 30 years was 32%. He concluded that the size of the aneurysm was the only relevant predictor of UIA rupture, but its predictive value was not certain.
Winn: 182 patients with previous SAH and multiple aneurysms were followed up for a mean of 7.7 years, 50 of whom underwent surgical treatment. He concluded that there was no clear correlation between the size of the aneurysm and the propensity to rupture and bleed, but that the rate of rebleeding was higher in those with diameters ≥10 mm. ISUIA concluded, after long-term follow-up of 722 patients with previous SAH, that the bleeding rate was 11 times higher in those with diameters <10 mm than in those without previous SAH of the same type (annual incidence 0.5%) and that the average annual rupture rate was 0.65% in those with diameters >10 mm. This study found that a factor predictive of UIA rupture was the location of the aneurysm at the tip of the basilar artery, where the risk of aneurysm rupture over a mean follow-up period of 7.5 years was 12% for UIAs <10 mm in diameter, compared with 3% for other sites. It is now believed that spontaneous SAH is most often caused by aneurysms of 7 to 10 mm, and this is used as a criterion to determine
In clinical screening for asymptomatic UIA, the benefits, risks, and consequences of bleeding should be weighed against the direct impact of the aneurysm on the patient and the risk of rupture and treatment. Using a mathematical model of aneurysms, it has been found that there is no theoretical value in screening for UIAs when all aneurysms are treated surgically and the complication rate is 5.1% and the annual rupture rate is 0.05%, whereas screening is warranted if the annual rupture rate exceeds 1%. Screening of the entire population for UIA is not necessary. Although smoking and alcohol consumption may increase the risk of SAH, they have not been found to increase the incidence of intracranial aneurysms, so screening for UIA in this group is also unnecessary.
Unruptured intracranial aneurysms – risk of spontaneous rupture and surgical intervention
For unruptured intracranial aneurysms without a history of SAH, the risk of rupture is very low at about 0.05% per year for aneurysms less than 10 mm in diameter, whereas for aneurysms of the same diameter with SAH, the risk of rupture is 11 times higher at about 0.5% per year, and for those without a history of SAH, the independent predictors of aneurysm rupture are aneurysm size and site; for those with SAH, the independent predictors are For those with SAH, the only independent predictor of aneurysm rupture was aneurysm size and site. The chance of aneurysm rupture was significantly lower in those without a history of SAH, and age was the only predictor of surgical outcome in the case of unruptured aneurysm repair. The study suggests that surgery for unruptured aneurysms up to 10 mm in diameter without a history of SAH seems unlikely to reduce disability and mortality.
The prevalence, site and size of asymptomatic cerebral aneurysms were compared in the presence or absence of a family history of aneurysm, history of aneurysmal SAH and by gender. The prevalence of asymptomatic cerebral aneurysm was 7.0% in all population groups, and 10.5% and 6.8% in those with and without a family history of aneurysm, respectively. Among those with a family history of aneurysm, the prevalence was 12.3% in women and 7.9% in men. The statistics showed a highly significant difference between the groups.
Among 115 relatives in 20 families, the prevalence of aneurysm was 33.9%, and the total prevalence of ruptured or asymptomatic aneurysm was 42.1% in 14 families with aneurysmal SAH, while it was only 17.9% in 6 families with asymptomatic aneurysm, and the prevalence of asymptomatic aneurysm was very low in the former. The study confirmed that the prevalence of cerebral aneurysms was higher in those with a family history of asymptomatic aneurysms, and the prevalence was higher in women than in men with a family history of aneurysms. Asymptomatic familial cerebral aneurysms are prone to rupture even when they are small at a young age, so it is important to check the size of the aneurysm regularly.
Epidemiological findings show that the incidence of cerebral aneurysms ranges from 0.2% to 8.9% of the population and can be asymptomatic for long periods of time. With the use of MRA, the chance of detecting unruptured cerebral aneurysms by chance has increased significantly. The risk of rupture of an unruptured cerebral aneurysm is 1 to 2 percent per year with a 50 percent mortality rate associated with each ruptured bleed. Obviously, once an intracranial aneurysm is detected, timely treatment is necessary. Surgery is currently one of the main treatment methods for cerebral aneurysms. The development of microsurgical techniques has significantly reduced the rate of surgical disability and mortality.
For small, asymptomatic unruptured aneurysms with no history of SAH, is conservative treatment the way to go?
Professor Weir argues against this, saying that approximately 15,000 SAHs in the United States each year result from aneurysms smaller than 7 mm, most of which are unruptured, solitary, asymptomatic, or even small before rupture. If this fraction of small ruptured aneurysms per year were added to the ISUIA trial, the rupture rate of small aneurysms would be as high as 7% to 14%. Many shortcomings of the ISUIA study were also analyzed:
(1) In the phase II study of ISUIA: the 5-year rupture rate of certain anterior circulation aneurysms (less than 7 mm) was 0, indicating that small aneurysms in these locations are safe, but in the clinical data of ruptured aneurysms, these locations accounted for 35% to 50% of aneurysms, including a high percentage of small aneurysms. In the pathological data, the rupture rate of aneurysms in these locations is also higher than that of unruptured aneurysms.
(ii) There is no physiological basis for separating posterior communicating aneurysms from anterior circulation aneurysms in the phase II study of ISUIA.
(iii) There was selection bias in the phase II study of ISUIA, with only 10.3% of anterior communicating and anterior cerebral aneurysms in phase II of ISUIA and a short follow-up period.
④Some of the results of the phase I studies of ISUIA were contradictory to those of phase II. People often consider the risk of surgery first, but for people with 37 years of life expectancy at age 40 or more than 20 years of life expectancy at age 60, the option of conservatively observing aneurysm enlargement to a dangerous volume is limited because some aneurysms have ruptured without enlargement, and enlargement is unforeseeable. Also, for small, asymptomatic aneurysms, the patient’s psychological factors should be considered, whether they can take the risk and whether this psychological stress will affect their quality of life.
Professor Weibers supports the view that the natural history of unruptured aneurysms is not known by studying patients with ruptured aneurysms. The findings from the ISUIA Phase I and II studies and other studies do not support interventions such as surgery or interventions because the data on the natural history of these unruptured aneurysms are very different compared to the rates of death and disability from interventions.
Johnston et al. concluded after a benefit evaluation that surgical or interventional treatment of small, asymptomatic, unruptured, non-SAH aneurysms may exacerbate clinical symptoms and is therefore neither effective nor valuable.
The results of the ISUIA phase I study showed that the annual rupture rate in patients with asymptomatic aneurysms without a history of SAH was 0.05% for those with diameters less than 10 mm, while the annual rupture rates were 1% for those with diameters between 10 and 25 mm and more than 6% for those with diameters greater than 25 mm. The results of the phase II prospective study were: the 5-year cumulative rupture rates of anterior circulation aneurysms in group 1 patients (without a history of aneurysmal SAH) were 0% (3-7 mm diameter), 2.6% (7-12 mm), 14.5% (13-24 mm), and 40% (25 mm or more), respectively, by size. Posterior circulation aneurysms (including posterior communicating aneurysms) were 2.5%, 14.5%, 18.4%, and 50%, respectively. For aneurysms of 7 to 12 mm in diameter, the annual rupture rate was 0.5% for anterior circulation aneurysms and 2.9% for posterior circulation aneurysms. The annual rupture rate for aneurysms less than 10 mm in phase I of this study was 0.05%, while the 5-year cumulative rupture rate for anterior circulation aneurysms of 3-7 mm in phase II, group 1 patients (without a history of aneurysmal SAH) was 0%, and such a benign course raises significant questions about interventional therapy.
There are no uniform criteria for whether to receive treatment for unruptured intracranial aneurysms. The size, location, lobularity, growth rate, multiplicity, and history of other ruptured aneurysms, as well as the patient’s age, gender, smoking history, family history of aneurysm, symptoms accompanying the aneurysm, and other underlying diseases should be taken into consideration (Zhao Jizong, Sun Jianjun). It is more controversial whether unruptured cerebral aneurysms should be treated surgically or not. For aneurysms with high risk of rupture, such as symptomatic unruptured aneurysms and aneurysms near the midline should be treated aggressively to avoid high morbidity and mortality and high disability caused by SAH; while for aneurysms that can accompany the patient smoothly for life, surgical treatment is not necessary to avoid the medically induced injury caused by surgery itself.
Since the 30-d mortality rate of aneurysmal SAH is 45% and approximately half of the survivors have irreversible brain damage, this raises the question for neurosurgeons as to how to treat this currently asymptomatic but potentially dangerous lesion. Prevention of hemorrhage is the most effective way to reduce mortality, so it is reasonable to consider UIAs for treatment prior to rupture. However, surgical treatment and embolization are not without risks. There is a debate whether patients with UIAs should be treated conservatively or with early surgical management. Therefore, a precise assessment and comparison of the risks of the various treatment options with the natural history of UIAs is needed, weighing the “risk-benefit ratio” before deciding how to proceed. In the management of UIAs, the “risk-benefit ratio” should be weighed. For surgeons trained in microvascular surgery, it is reasonable to keep the operative mortality rate below 1% and the disability rate below 7% for UIAs in the anterior circulation with a maximum diameter < 20 mm if the patient is in good health and < 65 years of age.
The management of UIAs includes the choice of treatment or observation. Factors favoring surgery include young patients with long expected survival, prior ruptured aneurysms, family history of aneurysm rupture, large aneurysms, symptomatic aneurysms, and aneurysm growth under observation. Factors favoring observational management include the elderly, short expected survival, coexisting disease status, and small asymptomatic aneurysms, and the experience, tendencies, and personal preferences of patients with UIAs influence treatment decisions and should also be considered. Based on available data, we have adopted the following principles for the management of UIAs. Symptomatic aneurysms: All symptomatic intradural aneurysms should be considered for treatment, and acute symptomatic aneurysms should be treated relatively urgently. Symptomatic large or massive aneurysms pose a high surgical risk and require an analysis of the individual patient and the risk of the aneurysm, as well as the experience of the surgical specialist. Small episodic intracavernous carotid aneurysms are usually not an indication for treatment.
For large symptomatic intracavernous sinus aneurysms, the treatment decision requires an individual analysis of the patient’s age, the severity and progression of symptoms, and the treatment of choice. Incidental aneurysms: Given the apparently low risk of bleeding from incidental small aneurysms (<10 mm) in patients without prior SAH, treatment is generally not recommended, but rather observation. However, younger patients in this group require special consideration for treatment. Similarly, small aneurysms reach a relative risk of treatment. Given the short survival expectancy and high treatment risk in older patients older than 65 years, observation of unruptured aneurysms in multiple aneurysms is favored in older patients with asymptomatic aneurysms: clamping or embolization of an unruptured aneurysm found immediately after surgical clamping or interventional embolization of a ruptured aneurysm. If the unruptured aneurysm cannot be treated at the same time because the surgical access cannot be reached, the patient's condition is poor, or the aneurysm neck is too wide for GDC embolization, etc., the patient should be treated according to the principle of incidental aneurysm after recovery.
In general, endovascular treatment was preferred in this group, especially for patients with large aneurysms in symptomatic aneurysms and patients with severe risk in multiple aneurysms, while patients selected for the surgical group were in relatively good clinical condition and not difficult to operate. The final result of endovascular treatment was 92.9%, which was still slightly higher than the excellent rate of surgical treatment. Although not statistically significant, this suggests that neurointerventional treatment should be considered for patients with a 10 mm size, subcyst formation and other rare kinetic features, a positive family history of aneurysm or aneurysmal SAH. In those patients managed conservatively, periodic follow-up imaging should be considered, and treatment should be considered once changes in aneurysm size or structure are observed. Aneurysms located at the apex of the basilar artery have a relatively high risk of bleeding, and treatment decisions must take into account the patient’s age, the presence of
Treatment decisions must take into account the patient’s age, the presence of medical and neurological conditions, and the associated treatment risks. If the decision is made to observe, periodic CT (MRA) or selective angiographic reassessment should be considered to observe changes in aneurysm size, however, technical considerations need to be taken into account to improve the reliability of the measurements. If the maximum diameter of the aneurysm is >5 mm, if the aneurysm is enlarging during observation, if the aneurysm is located in the anterior circulation, if the patient is young (<65 years of age) and in good health, surgery should be performed very often; otherwise, a more conservative approach can be taken unless the patient insists on surgical treatment. Asymptomatic aneurysms ≥10 mm in diameter should generally be considered for treatment.