Tapan Mehta, MBBS, MPH
Since the 1980s, the epidemiology of cerebrovascular diseases has changed significantly. Primary, secondary and tertiary prevention interventions have advanced with technology, and they are sufficient enough to change the epidemiologic outlook of cerebrovascular diseases. In addition to the advances in medical and surgical interventions, awareness for controlling the vascular risk factors has also increased, including a significant decrease in prevalence of smoking. Understanding epidemiology of intracranial aneurysm has become even more important in today’s era given more and more treatment options are becoming available, which are effective and safe.
Korja et. al present an interesting and novel epidemiologic trend in Finnish population suggesting a decrease in size of ruptured intracranial aneurysms over the past two decades.
The study included 2660 patients from January 1989 to December 2008. The diagnosis of SAH is based on lumbar punctures and computed tomographic scans. Two-dimensional computed tomographic angiography reformats or digital subtraction angiography images were used for aneurysm size measurement. All patients with age 18 years or above with unruptured intracranial aneurysms treated with either endovascular or surgical approach were also identified.
Anterior circulation ruptured intracranial aneurysms accounted for 91%, and the 4 most common locations accounted for 84% of all 2660 patients (middle cerebral artery 33%, anterior communicating artery 32%, posterior communicating artery 14%, pericallosal artery 5%). Sizes of All Ruptured Intracranial Aneurysms by sex, age (dichotomized at 50 years), and 4-Year Admission Groups are described in Table 1. Endovascularly or surgically treated asymptomatic unruptured intracranial aneurysms in adults (≥18 Years) without a history of subarachnoid hemorrhage are described in Table 2. In people <50 years, the average annual mean size of RIAs decreased 16% in women and 13% in men (decreasing linear trend; P=0.001). RIA sizes did not change in 50-year-old or older patients, whereas the proportion of posterior circulation RIAs almost tripled to 13% with a linear relationship (P<0.001).
The limitations — including measurement bias with conventional versus CT angiography, inability to include people dying of aneurysmal subarachnoid hemorrhage before reaching the hospital, external validity of the study findings and lack of information on causative factors — are important to consider.
An increase in prevalence of unruptured intracranial aneurysm is attributed to incidental findings with increase in prevalence of head imaging. A majority of the aneurysms sizing above 7mm and some even smaller than that with high risk features are offered treatment in the past two decades to prevent future rupture. The trend of increase in treatment rates of unruptured intracranial aneurysms is disproportionate to the rate of increase in population size (especially in developed countries). Naturally, unruptured larger aneurysms are more likely to be symptomatic and also more frequently treated compared to smaller ones. These changes of treatment trends could be an important factor determining average size of ruptured intracranial aneurysms presenting to hospitals. Further investigations on persistence of these findings in the last decade with external validation would have a significant impact on how we manage unruptured intracranial aneurysms in the future.