We identified references for this Review by searches of PubMed between 1970 and December, 2013, and references from relevant articles. The search terms used were “aneurysm” and (“brain” or “cerebral” or intracranial”) and “unruptured”, and (“natural history” or “rupture” or “enlargement” or “risk factors” or “familial aneurysm” or “screening study” or “coiling” or “clipping”). There were no language restrictions. The final reference list was generated on the basis of relevance to the
ReviewUnruptured intracranial aneurysms: epidemiology, natural history, management options, and familial screening
Introduction
Intracranial saccular aneurysms are increasingly being detected in clinical practice as use of CT and MRI is becoming more common. Clinicians are often faced with a decision regarding optimum management, but there is substantial controversy, particularly regarding the treatment of small unruptured intracranial aneurysms. In this Review, we summarise the natural history of unruptured intracranial aneurysms and predictors of rupture; the risks of aneurysm coiling and clipping; the optimum management of unruptured intracranial aneurysms; and family screening recommendations in patients with an unruptured intracranial aneurysm.
Section snippets
Epidemiology
Intracranial saccular aneurysms, also known as berry aneurysms because of their shape, are common acquired lesions that occur in 1–2% of the population1, 2 and account for about 80–85% of non-traumatic subarachnoid haemorrhages.3 Findings from an analysis of 68 prevalence studies reporting data from 83 study populations showed an overall prevalence of intracranial saccular aneurysms of 3·2%.4 Findings from imaging studies in which arteriography and MRI were used suggest that the frequency of
Clinical issues
Intracranial aneurysms are increasingly found on cross-sectional imaging, including CT and MRI, done for reasons unrelated to the aneurysm. About 50% of aneurysms are found after subarachnoid haemorrhage,62 which has an incidence of 6–10 per 100 000 people per year, with higher rates in some parts of the world.4, 63, 64, 65 A possible aneurysm might be identified on cross-sectional imaging with CT or MRI, but typically MRA (figure 2) or CTA (figure 3) is necessary to clarify the presence and
Management
After an unruptured intracranial aneurysm is detected, several factors must be considered to identify the optimum approach to management. The risk of aneurysmal rupture without any intervention should be compared with the risks of endovascular treatment or surgical clipping. Many factors should be considered, including (1) aneurysmal factors such as location, size, morphology, whether there is a thrombus within the aneurysm, and presence of a daughter sac or multiple lobes; and (2) patient
Imaging follow-up in aneurysms treated conservatively
For aneurysms managed conservatively, repeat imaging at some intermittency to assess aneurysm growth is typically recommended. Early data suggested that the likelihood of growth for small aneurysms is low.70 More recent data suggested that even small aneurysms have a risk of growth. In one study using MRA,104 12 of 173 aneurysms less than 8 mm in diameter grew during a mean of 4 years of follow-up; size at initial detection was a key predictor of aneurysm growth. The overall frequency of
Issues in aneurysm management in patients with carotid disease
Because aneurysms frequently occur in the general population and are common in patients with cerebrovascular disease,109, 110, 111 a common clinical question is whether a patient with a known unruptured intracranial aneurysm who is found to have carotid stenosis can undergo treatment for the carotid occlusive disease. Data regarding rupture risk of such aneurysms are available from the North American Symptomatic Carotid Endarterectomy Trial,110 in which 3·1% of study patients had an unruptured
Conclusions and future directions
Although a wealth of data are available regarding the natural history and management of unruptured intracranial aneurysms, many issues and questions remain unanswered. The optimum management strategy for unruptured intracranial aneurysms, particularly small aneurysms, remains unclear. The available natural history data are useful, but well defined rupture risk data specific to aneurysm location and size are not available. Objective assessment of the risks of location-specific and size-specific
Search strategy and selection criteria
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