Chinese Small Intracranial Aneurysm Study (CSIAS)

Intracranial aneurysms are common in the general population. The overall prevalence of unruptured intracranial aneurysms (UIAs) is estimated of 2.3-3.2% in the population without specific risk factors for SAH. As noninvasive imaging modalities are more commonly used than before, UIAs are increasingly being detected. Most patients with small aneurysms (less than 5mm) are incidentally found in clinical practice. Some studies indicate that the majority of patients with UIAs, particularly with small aneurysms (\<7mm), have a low risk of rupture, and others have found that small ruptured aneurysms have a high proportion in patients with SAH. Therefore, there is a lot of controversy regarding which small aneurysms can be left untreated, or which aneurysms are needed to be treated with clipping or coiling. The prevalence varies widely among different detection methods, race/ethnicity or patients with other inherited diseases. Although a wealth of data is available for the natural history of UIAs, the true natural history remains unknown because case selection bias occur in almost all studies. However, data on Chinese UIA is unknown. Using the MR angiography (MRA) to detect aneurysms, the prevalence is 7% of selected adult population in China. Therefore, small UIAs are very common and are increasingly being detected in clinical practice. Conservative treatment, surgical clipping and endovascular coiling are the three treatment options for UIAs. The optimal treatment remains controversial, particularly for small aneurysms (less than 7mm). To date, no clinical trials have compared the safety and efficacy between conservative treatment and surgical clipping or endovascular coiling for UIAs. It may be impossible to conduct the randomized controlled study considering aneurysm ruptured as a devastating event. However, surgical clipping or endovascular treatment itself carries a risk of immediate morbidity or mortality. Therefore, a substantial variability widely exists in treatm