Chinese Small Intracranial Aneurysm Study (CSIAS)

1. Background: There is a lot of controversy regarding which aneurysms can be left untreated, or which aneurysms are needed to be treated with clipping or coiling. To date, no clinical trials have compared the safety and efficacy between conservative treatment and surgical clipping or endovascular coiling for small UIAs. 2. Study design: A multicenter prospective observation registry study. This study is undertaken to conform to the study protocol. Patients will be recruited between December 2016 and December 2018. Patients are eligible for the study if they meet the inclusion criteria and they are not eligible if any of the following exclusion criteria are met. 3. Procedures: All patients were interviewed by a multidisciplinary team that consisted of vascular neurosurgeons, interventional neuroradiologists and anesthetists. If patients meet all of the inclusion criteria: an unruptured aneurysms ≤5mm are enrolled and then followed up at 6 and12 months. Clinical observation, surgical clipping and endovascular coiling are the three treatment options for UIAs. In general, when an UIA is detected, it should be needed to quit smoking, to aggressively manage hypertension, and to control alcohol use. When an aggressive treatment is considered, treatment risks should be balanced against the risk of rupture.