endovascular occlusion with detachable platinum coils has become an established treatment for managing patients who have ruptured intracranial aneurysms ( 1 - 3 ) . although numerous studies regarding endovascular or surgical treatment for ruptured intracranial aneurysms have been reported in the literature , there are only two randomized , prospective studies comparing endovascular coiling and surgical clipping to date ( 4 - 6 ) . the results of the first , prospective randomized trial from finland compared endovascular and surgical treatment of ruptured intracranial aneurysms was published in 1999 and 2000 ( 4 , 5 ) . the study included 109 patients with acute ( < 72 hours ) aneurysmal subarachnoid hemorrhage who were suitable for both endovascular coiling and surgical clipping . aneurysms were considered suitable for both coiling and clipping if : 1 ) the neck of the aneurysm was smaller than the fundus ; 2 ) it was not a fusiform aneurysm ; 3 ) the neck of the aneurysm and relationship to the parent vessel was distinguishable ; and 4 ) the diameter of the aneurysm was bigger than the smallest coil , or 2 mm , resulting in approximately half of the patients with aneurysmal subarachnoid hemorrhage suitable for randomization . as an immediate postembolization angiographic result , posterior circulation aneurysms showed more complete occlusion with coiling than with surgery ( p = 0.045 ) , whereas anterior circulation ( anterior cerebral artery , anterior communicating aneurysm , and pericallosal artery ) aneurysms showed the better angiographic outcome with surgical clipping than with endovascular coiling ( p = 0.005 ) . the procedure - related mortality rate was 2% in the endovascular group and 4% in the surgical group . at 12 months , the clinical outcome did not significantly differ between two groups , as 79% of endovascular versus 75% of surgical patients had good or moderate recovery on glasgow outcome scale ( p = 0.3 ) . as 12-month angiographic results , 76.9% of the endovascular group showed total obliteration of the aneurysm , whereas 86.0% of the surgical group showed total obliteration , which was not statistically significant . the authors concluded that the clinical outcome at 3 and 12 months was comparable after endovascular and surgical treatment of ruptured intracranial aneurysms . isat was a randomized , multicenter trial compared surgical clipping with endovascular coiling in patients with ruptured intracranial aneurysms ( 6 - 8 ) . between 1994 and 2002 , 2143 patients were enrolled in the study from 43 neurosurgical centers , most in the united kingdom and europe . the primary objective of the isat was to determine whether there was a reduction in the proportion of patients who were dead or dependent ( defined as modified rankin scale , mrs 3 - 6 ) at 1 year by following a coiling strategy compared with a clipping strategy . recruitment of patients was stopped after an interim analysis showed a benefit of endovascular treatment on the primary outcome at 1 year . the complete 1-year data from isat was published in the lancet in 2005 ( 7 ) . two - hundred - fifty of 1,063 ( 23.5% ) patients allocated to endovascular coiling were dead or dependent at 1 year , compared with 326 of 1,055 ( 30.9% ) patients allocated to surgical clipping : an absolute risk reduction of 7.4% ( 95% ci 3.6% to 11.2% , p = 0.0019 ) . the early survival advantage in the coiled group was maintained for up to 7 years and was statistically significant ( log rank p = 0.03).the risk of epilepsy was substantially lower with endovascular coiling than with clipping : relative risk 0.52 ( 95% ci 0.37 to 0.74 ) . there was no significant difference in the frequency of rebleeding between the groups ( log rank p = 0.22 ) . the rebleeding risk after 1 year in the coiled group is approximately 0.2% per patient year with follow - up from 1 to 8 years with a mean of 4 years . isat concluded that endovascular coiling of ruptured intracranial aneurysms , when a patient is in good clinical grade and the aneurysm anatomy is suitable for endovascular treatment , is more likely than neurosurgical treatment to lead to independent survival at l year . since the 1-year results of isat study were released , treatment of patients with a ruptured intracranial aneurysm has changed significantly over the past decade . in many centers , coiling has become the mainstay of treatment of ruptured intracranial aneurysms when both coiling and clipping are considered suitable . the long - term follow - up results of isat were published in the lancet neurology in 2009 ( 8) . at 5 years six - hundred - twenty - six of 755 ( 83% ) patients treated by endovascular coiling were independent at 1 year , compared with 584 of 713 ( 82% ) patients treated by surgical clipping . however , the risk of death was still significantly lower in the coiling group than in the clipping group ( relative risk 0.77 , 95% ci 0.61 - 0.98 ; p = 0.03 ) . at 5 years , 112 of 1,046 ( 11% ) patients in the coiling group have died , compared with 144 of 1,041 ( 14% ) patients in the clipping group ( log rank , p = 0.03 ) . the annual risk of the treated aneurysm rebleeding is higher in the patients treated by the coiling than in those treated by the clipping : 10 rebleeding occurred in the coiling group and 3 in the clipping group . however , the risk remains low and is at a similar level to the risk of further subarachnoid hemorrhage ( sah ) from another source , either a pre - existing aneurysm or a newly formed aneurysm . the main finding of the study is that rates of independence become essentially equivalent at 5 years , whereas mortality rates still favor the patients treated by endovascular coiling . the major contribution to the achievement of equivalent long - term functional outcomes might be the continuing improvement in the neurological function of less severely disabled patients in the clipping group between year 2 and year 5 . , isat has demonstrated that endovascular coiling of ruptured intracranial aneurysms has benefits over surgical clipping in those patients suitable for either treatment , but this difference decreases over time ( 9 ) . with the significant advances in the imaging techniques and widespread use of noninvasive intracranial imaging studies such as ct or mr angiography , the incidental detection of unruptured intracranial aneurysm ( uia ) has increased greatly . the management of patients with uias becomes an important public health issue , but still remains a controversial topic . there has been no published randomized , controlled trial with regard to compare natural history and coiling or clipping , or clipping and coiling for the management of patients with uias , but one such trial is currently ongoing . international study of unruptured intracranial aneurysms ( isuia ) is the largest natural history study of uia ( 10,11 ) . a prospective cohort study from isuia showed that the 5-year cumulative rupture risk of uias smaller than 7 mm in the anterior circulation with no history of sah to be 0% and that with a history of sah 1.5% ( 11 ) . aneurysms at posterior circulations ( basilar tip and the posterior communicating artery ) , aneurysms larger than 10 mm , and aneurysms that are found in patients who had bled from a prior aneurysm were found to have higher risks ( about 0.5% per year ) . table 2 shows the 5-year cumulative rupture rates of uia among patients in the unopearated prospective cohort of isuia . isuia data provided the first , international prospective data set , but there have been many criticisms of the isuia study , especially with regard to patient selection bias . detailed discussion about these criticisms is out of range for this review and is well described elsewhere . it is generally believed that the risk of rupture for a uia is approximately 1% per year for lesions 7 - 10 mm in diameter observational study published in 2009 , ishibashi et al . reported that the annual rupture rate for 529 uias was 1.4% during mean follow - up period of 905.3 days ( 14 ) . in their study , a previous history of sah ( the hazard ratio 7.3 ; 95% ci , 2.5 to 21.2 ) , posterior circulation aneurysm ( the hazard ratio 2.9 ; 95% ci , 1.1 to 8) , and large size were significant independent predictors for aneurysm rupture . the hazard ratio in the large sized ( > 10 mm ) and giant ( > 25 mm ) aneurysm were 12.3 and 50 compared with that for small sized ( < 5 mm ) uias . more recently , a prospective multi - center , observational study to determine the optimal management for small uias has been published by japanese group ( 15 ) . in that study , 448 uias < 5 mm in size the annual rupture rate for small uias smaller than 5 mm is quite low : 0.54% overall , 0.34% for single aneurysms , and 0.95% for multiple aneurysms . patient < 50 years of age , aneurysm diameter of > 4 mm , hypertension , and aneurysm multiplicity were found to be significant predictive factors for rupture of small uias . other reported risk factors for rupture of uias in the literature include cigarette smoking and female sex . a recently published systematic review and meta - analysis found an overall risk of poor outcomes ( mrs 3 - 6 ) is in the range of 4 - 5% after endovascular coiling in patients with uia ( 16 ) . recurrence rate is high : 24.4% of the patients followed up for 0.4 - 3.2 years . the annual risk of bleeding per patient - year after endovascular coiling was 0.2% , but the lack of systematic follow - up , short observation periods , and missing data hampered the assessment of clinical efficacy of endovascular coiling ( 16 ) . a rct is ongoing to answer the question whether active treatment can improve the outcome of patients with uia as compared with observation . team trial ( trial on endovascular aneurysm management ) is an international , randomized , multicenter , controlled trial comparing endovascular treatment versus conservative management of uias ( 17 ) . primary endpoint is mortality and morbidity ( mrs 3 - 6 ) from intracranial hemorrhage or treatment . secondary endpoints include incidence of hemorrhagic events , morbidity related to endovascular coiling , morphological results , overall clinical outcome and quality of life . the study will be conducted in 60 international centers and will enroll 2,002 patients equally divided between the two groups . the duration of the study is 14 years , the first three years being for patient recruitment plus a minimum of 10 years of follow - up . preventive treatment with coiling or clipping in patients with uia can be justified when the benefits outweigh the risks of such treatments , with strong evidence supported by valid data . currently , in the absence of randomized controlled studies , any proposed treatment algorithms for uias remain invalid ( 16 , 17 ) . in conclusions , short - term results of isat study showed that endovascular coiling of ruptured intracranial aneurysms , when a patient is in good clinical grade and the aneurysm anatomy is suitable for endovascular treatment , is more likely than neurosurgical treatment to lead to independent survival at l year . long - term follow - up results of isat study showed that rates of independence become essentially equivalent at 5 years , whereas mortality rates still favor the patients treated by endovascular coiling . thus , isat study has demonstrated that endovascular coiling of ruptured intracranial aneurysms has benefits over surgical clipping in those patients suitable for either treatment , but this difference decreases over time . because rct comparing conservative management with surgical clipping and with endovascular coiling have not been performed to date for unruptured intracranial aneurysms , a rct is ongoing to answer the question whether active treatment can improve the outcome of patients with uia as compared with observation .
endovascular coiling has become the primary treatment modality for the treatment of intracranial ruptured aneurysms in many centers . 
 a multicenter randomized controlled trial ( rct ) , isat study , has demonstrated that endovascular coiling of ruptured intracranial aneurysms has benefits over surgical clipping in those patients suitable for either treatment . because rct comparing conservative management with surgical clipping and with endovascular coiling have not been performed to date for unruptured intracranial aneurysms , the best management for unruptured 
 aneurysm remains unclear . 
 a rct is ongoing to answer the question whether active treatment can improve the outcome of patients with unruptured intracranial aneurysms as compared with observation .