title: Assessment of image-derived risk factors for natural course of unruptured cerebral aneurysms.
abstract: OBJECTIVE
  The goal of this prospective longitudinal study was to test whether image-derived metrics can differentiate unruptured aneurysms that will become unstable (grow and/or rupture) from those that will remain stable.
  
  
  METHODS
  One hundred seventy-eight patients harboring 198 unruptured cerebral aneurysms for whom clinical observation and follow-up with imaging surveillance was recommended at 4 clinical centers were prospectively recruited into this study. Imaging data (predominantly CT angiography) at initial presentation was recorded. Computational geometry was used to estimate numerous metrics of aneurysm morphology that described the size and shape of the aneurysm. The nonlinear, finite element method was used to estimate uniform pressure-induced peak wall tension. Computational fluid dynamics was used to estimate blood flow metrics. The median follow-up period was 645 days. Longitudinal outcome data on these aneurysm patients-whether their aneurysms grew or ruptured (the unstable group) or remained unchanged (the stable group)-was documented based on follow-up at 4 years after the beginning of recruitment.
  
  
  RESULTS
  Twenty aneurysms (10.1%) grew, but none ruptured. One hundred forty-nine aneurysms (75.3%) remained stable and 29 (14.6%) were lost to follow-up. None of the metrics-including aneurysm size, nonsphericity index, peak wall tension, and low shear stress area-differentiated the stable from unstable groups with statistical significance.
  
  
  CONCLUSIONS
  The findings in this highly selected group do not support the hypothesis that image-derived metrics can predict aneurysm growth in patients who have been selected for observation and imaging surveillance. If aneurysm shape is a significant determinant of invasive versus expectant management, selection bias is a key limitation of this study.
authors.affiliation: Department of Biomedical Engineering, University of Iowa;
authors.forename: Manasi
authors.initials: M
authors.lastname: Ramachandran
authors.affiliation: Department of Biomedical Engineering, University of Iowa;
authors.forename: Rohini
authors.initials: R
authors.lastname: Retarekar
authors.affiliation: Department of Biomedical Engineering, University of Iowa;
authors.forename: Madhavan L
authors.initials: ML
authors.lastname: Raghavan
authors.affiliation: Department of Biomedical Engineering, University of Iowa;
authors.forename: Benjamin
authors.initials: B
authors.lastname: Berkowitz
authors.affiliation: Department of Biomedical Engineering, University of Iowa;
authors.forename: Benjamin
authors.initials: B
authors.lastname: Dickerhoff
authors.affiliation: Department of Biomedical Engineering, University of Iowa;
authors.forename: Tatiana
authors.initials: T
authors.lastname: Correa
authors.affiliation: Department of Biomedical Engineering, University of Iowa;
authors.forename: Steve
authors.initials: S
authors.lastname: Lin
authors.affiliation: Department of Neurosurgery, University of Iowa Hospitals and Clinics; and.
authors.forename: Kevin
authors.initials: K
authors.lastname: Johnson
authors.affiliation: Department of Neurosurgery, University of Iowa Hospitals and Clinics; and.
authors.forename: David
authors.initials: D
authors.lastname: Hasan
authors.affiliation: Department of Surgery, Division of Neurosurgery, Beth Israel Deaconess Medical Center; and.
authors.forename: Christopher
authors.initials: C
authors.lastname: Ogilvy
authors.affiliation: Department of Neurosurgery, Jefferson University Hospital, Philadelphia;
authors.forename: Robert
authors.initials: R
authors.lastname: Rosenwasser
authors.affiliation: Department of Epidemiology, University of Iowa, Iowa City, Iowa;
authors.forename: James
authors.initials: J
authors.lastname: Torner
authors.affiliation: Department of Neurosurgery, Penn State University, Hershey; and.
authors.forename: Einar
authors.initials: E
authors.lastname: Bogason
authors.affiliation: Department of Neurosurgery, Massachusetts General Hospital, Boston, Massachusetts;
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Stapleton
authors.affiliation: Department of Neurosurgery, Penn State University, Hershey; and.|Department of Engineering Science and Mechanics, Pennsylvania State University, State College, Pennsylvania.
authors.forename: Robert E
authors.initials: RE
authors.lastname: Harbaugh
mesh_terms: D017542:Aneurysm, Ruptured / Q000453:epidemiology / Q000209:etiology; D002533:Cerebral Angiography; D018450:Disease Progression; D005260:Female; D020342:Finite Element Analysis; D005500:Follow-Up Studies; D006801:Humans; D007091:Image Processing, Computer-Assisted; D002532:Intracranial Aneurysm / Q000473:pathology*; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D017711:Nonlinear Dynamics; D011379:Prognosis; D011446:Prospective Studies; D012307:Risk Factors; D015983:Selection Bias; D014057:Tomography, X-Ray Computed; D016896:Treatment Outcome
keywords: CE = contrast enhanced; CTA = CT angiography; Dmax = maximum diameter; LSA = low shear area; MRA = MR angiography; NSI = nonsphericity index; PWT = peak wall tension; TOF = time of flight; aneurysm; aneurysm growth; quantified aneurysm shape; subarachnoid hemorrhage; vascular disorders