The detection and management of unruptured intracranial aneurysms

The incidence of subarachnoid haemorrhage (SAH) is 6-8 per 100 000 person y ears, peaking in the sixth decade. SAH, mostly due to rupture of an intracr anial aneurysm, accounts for a quarter of cerebrovascular deaths. Aneurysms increase in frequency with age beyond the third decade, are 1.6 times more common in women and are associated with a number of genetic conditions. Pr ospective autopsy and angiographic studies indicate that between 3.6 and 6% of the population harbour an intracranial aneurysm. Studies have found an increased rate of SAH in first degree relatives of SAH patients (relative r isk 3.7-6.6). In affected families, the most frequent relationship between sufferers is sibling to sibling. The rupture rate: of asymptomatic aneurysm s was thought to be 1-2% per annum, but the recent International Study of U nruptured Intracranial Aneurysms found that the rupture rate of small aneur ysms was only 0.05% per annum in patients with no prior SAH, and 0.5% per a nnum for large (>10 mm diameter) aneurysms and for all aneurysms in patient s with previous SAH. Non-invasive tests such as magnetic resonance angiogra phy (MRA), computed tomographic angiography (CTA) and transcranial Doppler (TCD) have been advocated as alternatives to intra-arterial digital subtrac tion angiography to screen for aneurysms. Although all are promising techni ques, the quality of data testing their accuracy is limited. Overall report ed sensitivity for CTA and MRA (TCD is poorer) was 76-98% and specificity w as 85-100%,but many subjects had an aneurysm or recent SAH, which could ove restimate accuracy. CTA and MRA are much poorer methods for the detection o f aneurysms <5 mm diameter, which account for up to one-third of unruptured aneurysms. Elective surgical clipping of asymptomatic aneurysms has a morb idity of 10.9% and mortality of 3.8%. Treatment of aneurysms by Guglielmi c oils, for which there is less long-term follow-up available, has a 4% morbi dity and 1% mortality, but only achieves complete aneurysm occlusion in 52- 78% of cases. There has been interest in screening for aneurysms, but the i ndication for, and cost effectiveness of screening are unclear because aneu rysm prevalence varies, rupture rate is low, non-invasive imaging tests are not yet accurate enough to exclude small aneurysms and the morbidity and m ortality for elective surgical treatment of unruptured aneurysms is high. T here may be a limited role for investigation of high risk subgroups. Ideall y, screening in such subgroups should be tested in a randomized trial. The avoidance of risk factors for aneurysms such as smoking, hypertension and h ypercholesterolaemia should be part of the management of at-risk subjects.