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Deshmukh, A.S.; Priola, S.M.; Katsanos, A.H.; Scalia, G.; Costa Alves, A.; Srivastava, A.; Hawkes, C. Intracranial Aneurysms. Encyclopedia. Available online: https://encyclopedia.pub/entry/53858 (accessed on 18 June 2024).
Deshmukh AS, Priola SM, Katsanos AH, Scalia G, Costa Alves A, Srivastava A, et al. Intracranial Aneurysms. Encyclopedia. Available at: https://encyclopedia.pub/entry/53858. Accessed June 18, 2024.
Deshmukh, Aviraj S., Stefano M. Priola, Aris H. Katsanos, Gianluca Scalia, Aderaldo Costa Alves, Abhilekh Srivastava, Christine Hawkes. "Intracranial Aneurysms" Encyclopedia, https://encyclopedia.pub/entry/53858 (accessed June 18, 2024).
Deshmukh, A.S., Priola, S.M., Katsanos, A.H., Scalia, G., Costa Alves, A., Srivastava, A., & Hawkes, C. (2024, January 16). Intracranial Aneurysms. In Encyclopedia. https://encyclopedia.pub/entry/53858
Deshmukh, Aviraj S., et al. "Intracranial Aneurysms." Encyclopedia. Web. 16 January, 2024.
Intracranial Aneurysms
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Intracranial aneurysms represent a major global health burden. Rupture of an intracranial aneurysm is a catastrophic event. Without access to treatment, the fatality rate is 50% in the first 30 days. Over the last three decades, treatment approaches for intracranial aneurysms have changed dramatically. There have been improvements in the medical management of aneurysmal subarachnoid haemorrhage, and there has been an evolution of treatment strategies. Endovascular therapy is now the mainstay of the treatment of ruptured intracranial aneurysms based on robust randomised controlled trial data. 

endovascular coiling surgical clipping unruptured intracranial aneurysm

1. Introduction

Intracranial aneurysms (IA) are focal pathological dilatations of the cerebral arteries. While typically asymptomatic, the rupture of an IA leading to SAH is responsible for 5% of all strokes [1]. IA account for 80–85% of non-traumatic subarachnoid haemorrhage (SAH), but can also lead to intraparenchymal or subdural haemorrhage [1]. The average incidence of aneurysmal bleeding is approximately 9 per 100,000 person-years with the highest rates reported in Japanese and Finnish populations [2]. Though the annual incidence rates of ruptured IA are relatively stable, unruptured intracranial aneurysms (UIA), are increasingly detected in clinical practice, due to the widespread availability of advanced cross-sectional neuroimaging. The prevalence of IA is variable and depends on the evaluation methods used but IA are estimated to be found in 2–3.2% of the general population with a male to female ratio of 1:2 [3].
Aneurysmal subarachnoid haemorrhage is a catastrophic event with very high morbidity and mortality. About 15% of patients with ruptured IA could not even reach a hospital and there is a 50% thirty-day mortality in the remaining survivors [4]. Compared to other subtypes of stroke, patients affected due to SAH tend to be younger, which results in a greater loss of productive life [5]. Rebleeding is the most imminent danger; which drastically decreases the chances of a good outcome. The risk of rebleeding is at its maximum in the initial 24 h, during which the risk ranges from 4.1% to 17.3% [6]. Therefore, early diagnosis and aneurysm occlusion is a priority. Nowadays, many centres tend to operate within the first 24 h of onset via an endovascular or open surgical modality. On the other hand, unruptured aneurysms, with an annual risk of rupture 0.49–1.8%, represent a challenge in terms of conservative management versus aggressive intervention [7]. Further, selecting an appropriate treatment strategy is a complex decision, which varies according to patient and aneurysm-related factors.

2. Aneurysm Pathophysiology

The cerebrovascular system is inherently susceptible to aneurysm formation, although the aetiology of these abnormalities may be diverse. The important ones include the absence of an external elastic lamina, paucity of supportive perivascular tissues, and attenuated tunica media in the intracranial arterial system [8]. The distribution of cerebral aneurysms around the bifurcations or branch location points towards hemodynamic factors and/or wall shear stress as a principal determinant for aneurysm formation, growth and rupture (Figure 1). Incidence of IA is high in females, smokers, hypertensives, and a few geographical regions. Apart from this, multiple familial conditions are associated with a high incidence of IA, such as autosomal dominant inherited polycystic kidney disease, Marfan syndrome, fibromuscular dysplasia (FMD), alpha1-antitrypsin deficiency, etc. (Table 1). The list is exhaustive and illustrative of the fact that multiple genetic, hemodynamic and environmental factors act together in the formation and growth of IA [8].
Figure 1. Schematic diagram of a bifurcation aneurysm. (A) Bifurcation aneurysm. (B) Ruptured bifurcation aneurysm. (C) Surgical clipping of bifurcation aneurysm.
Table 1. Risk factors for aneurysm formation.

3. Aneurysm Classification

IA can be classified using several schemes (Table 2). Clinically, they can be classified on the basis of rupture status: ruptured or unruptured. According to morphology, aneurysms are classified into saccular and non-saccular types. Non-saccular IA are further classified into fusiform, dolichoectatic, and dissecting aneurysms. According to location in the intracranial circulation, aneurysms are divided into anterior (90%) and posterior circulation (10%) aneurysms. IA are also classified by size into small (<10 mm), large (10–25 mm), and giant (>25 mm) categories. Aneurysm angioarchitecture is important for planning suitability for endovascular management and can thus be classified according to neck size and relationship with the dome. Apart from serving a descriptive purpose, these classification systems also help in predicting prognosis, plan management, and appropriate treatment strategies. For example, despite advances in knowledge about aneurysm pathophysiology and technology, aneurysms with a large size (>10 mm), wide neck, unfavourable dome-to-neck ratio (<2), posterior circulation location and fusiform configuration remain therapeutic challenges with >20% faring poorly despite the best endovascular or surgical treatment [9][10]. Researchers' review is focussed on the management of the saccular aneurysm, which is the single largest group of IA (Figure 1A).

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