The increase in the number of neuroimaging exams provided an increase in the diagnosis of incidental intracranial aneurysms. Aneurysms are acquired lesions consisting of fragile dilatations that occur in bifurcations of the main arteries of the cerebrovascular system, commonly occurring between 40 and 60 years of age.
It is considered a complex disease, in which idiopathic, genetic and environmental factors (such as smoking and high blood pressure) play a role in the pathophysiology.
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The prevalence of aneurysms is estimated at 3%, while the annual incidence of subarachnoid hemorrhage – its main complication – is around 0.006 and 0.01%. Therefore, it is estimated that only 1 unruptured aneurysm will rupture for every 300 to 500 individuals with an aneurysm annually. Thus, it is important to clinically identify which subgroup of patients has a higher risk of aneurysmal rupture.
There is a dilemma regarding the management of an unruptured aneurysm. If, on the one hand, the decision of a conservative treatment of the unruptured aneurysm carries the risk of future serious complications such as its rupture; on the other hand, the surgical treatment of this aneurysm also presents complications such as thromboembolism or rupture. Therefore, it is important to analyze aspects of this disease in order to verify the best treatment route: conservative versus surgical.
Risk of UIA rupture
The main risk of the presence of an unruptured intracranial aneurysm is the risk of rupture. In 2014, the PHASES study was published, which has the analysis with the largest sample and with the highest level of evidence about the risk of aneurysmal rupture.
Currently, the PHASES score is intended to estimate the risk of aneurysmal rupture by evaluating 6 independent predictors: (1) population, (2) arterial hypertension, (3) age, (4) aneurysm size, (5) previous history of SAH by another aneurysm and (6) location of the aneurysm.
As one of the variables of the PHASES score, the size of the aneurysm is correlated with the risk of rupture. In this context, scores that estimate the growth of the aneurysm are important – since the growth and alteration of the morphology of the aneurysm are instability markers that can make it prone to rupture. Some authors consider an increase of 1 mm in aneurysms ≤ 5 mm significant and 2 mm in those with a size > 5 mm.
The ELAPSS score used to predict the growth of an aneurysm at 3 and 5 years is available based on factors such as (1) previous SAH, (2) location, (3) age, (4) population, and (5) patient size. aneurysm.
It is important to note that the PHASES score should only be used as a guide, since several other risk factors related to aneurysmal rupture were not included.
Observational studies have shown an association of factors such as smoking and alcohol consumption with a higher incidence of SAH. However, it is still uncertain whether the risk of aneurysmal rupture decreases in patients with unruptured aneurysm after normalization of blood pressure and cessation of smoking and alcohol consumption.
In addition, individuals with a history of unruptured familial intracranial aneurysms have a 17-fold increased risk of rupture compared to rupture rates of similar aneurysms without a family history in an international UIA study. It is worth mentioning that, despite the increased risk of rupture in familial intracranial aneurysms, there is no clarification on specific genes that may be related to the increased risk.
Management of unruptured aneurysms
Clinical management of unruptured intracranial aneurysm is related to smoking cessation, as well as blood pressure control. The American Heart Association recommends maintaining a systolic blood pressure < 140mmHg.
There is a phase 3 clinical trial currently underway, known as the PROTECT-U trial, which investigates the possibility of aspirin and systolic blood pressure control (< 120mmHg) as possible interventional agents to reduce the risk of aneurysm growth and rupture.
The decision on surgical intervention for an unruptured aneurysm should ideally be made by a neurovascular team that analyzes several variables such as: risk of aneurysmal rupture, risk of surgical/endovascular treatment, treatment durability and individual factors (age, comorbidities , lifestyle, personal desires).
The UIATS score makes it possible to help this decision process (conservative versus surgical treatment) by evaluating factors related to the patient, the aneurysm and the risk factors related to the treatment. A difference of ≥ 3 points makes it possible to recommend one treatment over the other, while a difference of up to 2 points does not allow a definition of this recommendation.
It should be noted that this score is also a guide, as it may be inappropriate to recommend treatment of all anterior communicant aneurysms without considering the age or size of the aneurysm, as well as all aneurysms ≥ 7 mm for elderly smokers over 80 years of age.
Among the surgical treatments, there is the possibility of endovascular or neurosurgical therapy. The International Subarachnoid Haemorrhage Trial demonstrated better coiling outcomes compared to microsurgical clipping in ruptured aneurysms. The evidence from this study, however, may not be applicable to unruptured aneurysms.
Neuroimaging follow-up of unruptured aneurysms
Neuroimaging follow-up, either CT or MR angiography, is recommended to access potential growth of this unruptured aneurysm when managed conservatively. The American Heart Association suggests follow-up between 6-12 months and annual or bi-annual neuroimaging (level of evidence IIb).
Screening: who has a nomination?
The prevalence of unruptured aneurysm in individuals with a history of aneurysm in 1 family member is around 4% – marginally above the general population – screening is not recommended. Currently, guidelines recommend screening for individuals with a history of at least 2 first-generation family members with a history of unruptured aneurysm or SAH, where the aneurysm prevalence is estimated to be around 8-10% in those over 30 years of age.
In addition, there are certain diseases that predispose to the formation of intracranial aneurysms, such as: autosomal dominant polycystic kidney disease, coarctation of the aorta, type 4 Ehlers-Danlos syndrome, Marfan syndrome, fibromuscular dysplasia, hereditary hemorrhagic telangiectasia, among others. In these risk groups, screening is generally recommended for autosomal dominant polycystic kidney disease and aortic coarctation.
▪ Unruptured aneurysms affect around 3% of the population and, in general, most do not rupture.
▪ The main risk factors for aneurysmal rupture are: size, location and growth of the aneurysm, as well as smoking and high blood pressure.
▪ In small aneurysms, the risk of endovascular/neurosurgical treatment is often greater than the risk of rupture of that aneurysm.
▪ In aneurysms larger than 5mm in a young population, surgical treatment may be considered, especially if there is an irregular, large aneurysm with a family history.
▪ Screening for unruptured aneurysms is indicated for (1) individuals with a history of at least 2 first-generation family members with a history of unruptured aneurysm or SAH or (2) individuals with autosomal dominant polycystic kidney disease.
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