title: Natural History of Unruptured Intracranial Aneurysms : A Retrospective Single Center Analysis.
abstract: OBJECTIVE
  We conducted a retrospective cohort study to elucidate the natural course of unruptured intracranial aneurysms (UIAs) at a single institution.
  
  
  METHODS
  Data from patients diagnosed with UIA from March 2000 to May 2008 at our hospital were subjected to a retrospective analysis. The cumulative and annual aneurysm rupture rates were calculated. Additionally, risk factors associated with aneurysmal rupture were identified.
  
  
  RESULTS
  A total of 1339 aneurysms in 1006 patients met the inclusion criteria. During the follow-up period, 685 aneurysms were treated before rupture via either an open surgical or endovascular procedure. Six hundred fifty-four UIAs were identified and not repaired during the follow-up period. The mean UIA size was 4.5±3.2 mm, and 86.5% of the total UIAs had a largest dimension <7 mm. Among these UIAs, 18 ruptured at a median of 1.6 years (range : 27 days to 9.8 years) after day 0. The annual rupture risk during a 9-year follow-up was 1.00%. A multivariate Cox proportional hazards analysis revealed that the aneurysm size and a history of subarachnoid hemorrhage (SAH) were statistically significant risk factors for rupture. For an aneurysms smaller than 7 mm in the absence of a history of SAH, the annual rupture risk was 0.79%.
  
  
  CONCLUSIONS
  In our study, the annual rupture risk for UIAs smaller than 7 mm in the absence of a history of SAH was higher than that of Western populations but similar to that of the Japanese population.
authors.affiliation: Department of Neurosurgery, Seoul National University Bundang Hospital, Seongnam, Korea.
authors.forename: Hyoung Soo
authors.initials: HS
authors.lastname: Byoun
authors.affiliation: Department of Neurosurgery, Seoul National University Bundang Hospital, Seongnam, Korea.
authors.forename: Won
authors.initials: W
authors.lastname: Huh
authors.affiliation: Department of Neurosurgery, Seoul National University Bundang Hospital, Seongnam, Korea.
authors.forename: Chang Wan
authors.initials: CW
authors.lastname: Oh
authors.affiliation: Department of Neurosurgery, Seoul National University Bundang Hospital, Seongnam, Korea.
authors.forename: Jae Seung
authors.initials: JS
authors.lastname: Bang
authors.affiliation: Department of Neurosurgery, Seoul National University Bundang Hospital, Seongnam, Korea.
authors.forename: Gyojun
authors.initials: G
authors.lastname: Hwang
authors.affiliation: Department of Neurosurgery, Seoul National University Bundang Hospital, Seongnam, Korea.
authors.forename: O-Ki
authors.initials: OK
authors.lastname: Kwon
keywords: Intracranial aneurysms; Natural history; Risk factors; Rupture rate