General reviewUnruptured intracranial aneurysms: An updated review of current concepts for risk factors, detection and management
Introduction
An intracranial aneurysm is an acquired focal outpouching (typically either saccular or fusiform) of a cerebral artery wall [1]. Its most feared complication is rupture, causing blood to erupt into the subarachnoid space with potentially fatal and frequently disabling outcomes [2], [3]. The consequences of an aneurysmal subarachnoid hemorrhage (aSAH) are devastating, with at least a quarter of such patients not surviving the rupture or its immediate complications, while leaving roughly half the survivors with permanent disabling neurological deficits [4].
With the greater availability of technical improvements and the ever-widening indications for noninvasive vascular neuroimaging [5], unruptured intracranial aneurysms (UIAs) are increasingly being discovered incidentally and an steadily growing number of patients are being referred to or seeking counseling from specialized centers regarding opportunities for screening (for example, for fear of occult UIAs after a relative has suffered an aSAH) [6]. However, UIAs represent a challenging situation to manage for several reasons:
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while the vast majority of UIAs never rupture [7], [8], [9], the consequences of such an event are severe and represent a major healthcare problem [4], [10];
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the natural history of UIAs is still not entirely understood and there is no accurate way to discriminate UIAs likely to rupture from those that will not [11], [12];
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the currently available treatments for repairing UIAs are invasive and associated with non-trivial morbidity, a risk particularly relevant in previously asymptomatic patients [13];
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the popular belief that an UIA is an imminent and ever-present peril has important psychosocial effects in patients with identified but untreated UIAs [14], [15].
Therefore, screening might, in some cases, not achieve its ultimate goal of improving quality years of life.
As a consequence, when offering screening for UIAs or advising for interventional vs. conservative management in patients with UIAs, physicians face a complex situation where no option is risk-free.
The optimal management and counseling should therefore focus on tailoring each encounter to the patient's specific level of risk and psychoaffective status, based on the available (albeit incomplete) evidence.
The American Heart Association (AHA)/American Stroke Association (ASA) issued guidelines for the management of UIAs in 2015 [16]. The present review does not intend to provide further guidelines, but aims to address the latest evidence on the epidemiology, natural history, risk factors, clinical and imaging presentations, treatment and follow-up of UIAs.
Section snippets
Epidemiology
The reported prevalence of UIAs varies by assessment modality [magnetic resonance imaging (MRI), computed tomography (CT), conventional angiography, autopsy] and subpopulation sampling, but remains rather consistently between 2% and 6% [17], [18], [19], [20].
The largest epidemiological study to date, published in 2011 [18], aggregated the results of 68 studies in a meta-analysis of 94,912 patients with 1450 UIAs. In their report, the investigators estimated the prevalence of UIAs in a
Screening
Screening policies for UIAs have been evaluated by cost-effectiveness or value-based approaches [68] in which the estimated financial burden of implementing screening was weighed against morbidity–mortality risks, and the direct and indirect financial consequences, of discovering a UIA. In studies evaluating the quality-adjusted life years in various settings, value-based screening policies had characteristics that seemed favorable only in populations at high risk (those with higher UIA
Clinical imaging presentations
An important cause of UIA discovery is an aSAH due to another IA [27]. In the absence of hemorrhage, UIAs are commonly asymptomatic and may only be discovered during workups of various unrelated or non-specific conditions, including headaches in particular [73].
Treatment
Treatment of UIAs aims to exclude its lumen from the circulating intracranial vessels to prevent bleeding. This can be achieved by external (surgical) clipping of the aneurysm at its neck or by packing the lumen of the aneurysm with metal coils (and/or diverting blood flow by placing a stent to block aneurysm inflow) [93].
Follow-up
The overarching goal of UIA follow-up is to prevent rupture by detecting factors that may portend high risk (such as aneurysm growth or morphological evolution), or detecting recurrence or the evolution of aneurysm remnants after treatment. Follow-up in rare instances may also detect de novo (newly formed) aneurysms.
However, no study has explored the optimal follow-up interval after discovering an UIA or which modality should be preferred for such purposes. Most of the available work indicates
Conclusion
UIAs represent a complex clinical situation. However, despite tremendous progress in the field, many questions have yet to be answered before it becomes possible to optimally advise, treat and follow these patients.
Disclosure of interest
The authors declare that they have no competing interest.
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