Fast track — ArticlesPrevalence of unruptured intracranial aneurysms, with emphasis on sex, age, comorbidity, country, and time period: a systematic review and meta-analysis
Introduction
Rupture of an intracranial aneurysm causes subarachnoid haemorrhage. Because such haemorrhage mostly affects relatively young people (ie, younger than 65 years) and has a high case fatality and morbidity, it is an important subtype of stroke.1 The proportion of years of potential life lost from subarachnoid haemorrhage is similar to that of ischaemic stroke and intracerebral haemorrhage,2 and a recent calculation found a total economic burden of £510 million annually for subarachnoid haemorrhage in the UK.3
The incidence of subarachnoid haemorrhage is higher in Finland and Japan than in other regions, increases with age, and is higher in women.4 These regional, sex, and age differences and the slight decline in the incidence of subarachnoid haemorrhage between 1950 and 20054 might result from differences in the prevalence of aneurysms, differences in the risk of rupture, or both.
In 1998, we published a systematic review on the prevalence of unruptured intracranial aneurysms (UIAs).5 Since then, non-invasive techniques for imaging of intracranial vessels have become increasingly available and used, which has coincided with an increase in incidental detection of aneurysms6 and the publication of many new studies on the prevalence of UIAs. We aimed to incorporate the new data into the existing pooled data to provide more accurate estimates on the prevalence of UIAs in healthy populations and in groups of people undergoing brain imaging for a specific reason. We also aimed to increase the knowledge of prevalence in sex, age, and comorbidity subgroups, and to study regional differences and time trends in the extended dataset.
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Search strategy and selection criteria
Our search methods were similar to those in our previous review.5 We did a PubMed and Embase search to retrieve all studies on the prevalence of UIAs published before March, 2011. In brief, we used the keywords “aneurysm(s) AND (cerebral OR brain OR intracranial OR berry OR basilar OR saccular OR communicating) AND (unruptured OR incidental OR prevalence OR risk)” (see webappendix p 1). We also checked the Web of Science for articles citing our previous review and searched the personal database
Results
68 studies met our predefined inclusion criteria (table 1 and figure 1),9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76 19 studies from our previous review5 and 49 new studies. We included four case-control studies (of which one was an autopsy study),26, 58, 61, 74 63
Discussion
In our analysis, the prevalence of UIAs was influenced by the presence of polycystic disease, a positive family history, age, and sex, but not by region. The prevalence was significantly higher in patients aged 30 years or older compared with those who were younger than 30 years. Women had a higher prevalence of UIAs than men, mainly attributable to an excess in women older than 50 years. Patients with ADPKD and patients with a positive family history of intracranial aneurysm or subarachnoid
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