Aneurysmal clipping has been the standard method for treatment. However, with the technological Sirolimus advances in devices, endovascular treatment has been used with increasing frequency. The selection of a treatment method for an unruptured intracranial aneurysm should be individualized based on patient’s factors, aneurysmal factors, and facility and performance of centers. In 2013, Greving et al. presented the PHASES score for prediction of risk of rupture of intracranial aneurysms [52]. The scoring system was developed from a pooled analysis of individual patient data from 8382 participants in six prospective cohort studies. Predictors included age, hypertension, history of SAH,

aneurysm size, aneurysm location, and geographical region, and were independently associated with the rupture risk of an intracranial aneurysm. According to the PHASES score, a high PHASES score corresponds to a great 5-year risk of aneurysm rupture (Table 1). It is not yet complete, but this study is the first proposal to reliably predict the long-term risk of aneurysm rupture and a risk prediction chart could serve as a valuable aid for treatment of an UIA. Table 1 PHASES Aneurysm Risk Score General principles Aneurysm size was an important predictor of rupture risk and could be considered preferentially in determining whether to treat. In ISUIA (International Study of

UIAs) published in 2003, calculating the total risk of rupture for patients demonstrates that for aneurysms 7 to 12

mm, 13 to 24 mm, and greater than 25 mm in diameter, the yearly rupture rates are 1.2, 3.1, and 8.6%, respectively [53]. Small, single incidental aneurysms less than 5 mm in diameter should be managed conservatively. However, treatment of a small aneurysm would be considered a relative rupture risk according to risk factors like location, history of SAH, symptomatic intracranial aneurysm, family history of aneurysm, and aneurysm with a multilobule or bleb. SUAVe (Small Unruptured Aneurysm Verification), published in 2010, was a prospective study to assess the annual risk of rupture of UIAs less than 5 mm in diameter [54]. In SUAVe, the overall annual risk rate of rupture was demonstrated to be 0.54%/year (single unruptured aneurysms: 0.34%/year, multiple unruptured Carfilzomib aneurysms: 0.95%/year). And patients <50 years of age (P=0.046; hazard ratio, 5.23; 95% CI,1.03 to 26.52), aneurysm diameter of ≥4.0 mm (P=0.023; hazard ratio, 5.86; 95% CI, 1.27 to 26.95), hypertension (P=0.023; hazard ratio, 7.93; 95% CI, 1.33 to 47.42), and aneurysm multiplicity (P=0.0048; hazard ratio, 4.87; 95% CI, 1.62 to 14.65) were found to be significant predictive factors for rupture of small aneurysms. Results of this study showed that the rupture risk of a small cerebral aneurysm in Japan was higher compared with that of ISUIA. And, in UCAS (Unruptured Cerebral Aneurysm Study of Japan), reported in 2011, the overall rate of rupture of cerebral aneurysms was 0.