title: A mathematical model of utility for single screening of asymptomatic unruptured intracranial aneurysms at the age of 50 years.
abstract: BACKGROUND
  Although rupture of intracranial aneurysms carries high mortality and morbidity rates, the clinical and financial benefit of screening certain high-risk groups is uncertain. We designed a mathematical model to interrogate the clinical benefit and cost-effectiveness of screening.
  
  
  METHODS
  A decision tree analysis model was used to calculate the outcome and cost of two scenarios applied to the same population: one-off screening for intracranial aneurysms versus not screening. Each scenario had an associated gain or loss of Quality Adjusted Life Years (QALY) and cost; the difference between the two scenarios was calculated. The variable inputs were the aneurysm prevalence and risk of rupture after 5 years. Sensitivity analyses were performed to determine the effects of altering various factors on outcomes.
  
  
  RESULTS
  Screening of the asymptomatic general population results in a QALY loss, equating to a negative clinical impact. The threshold 5-year risk of rupture at which screening resulted in a gain in QALYs was 13 %. This held true for any prevalence between 1 and 25 %. Risk of rupture had a greater impact on outcome than prevalence. Halving the risk of intervention (either surgery or coiling) reduced the threshold 5-year risk of rupture at which screening results in gain of QALYs to 6 %. The age of screening also had important effects on outcome.
  
  
  CONCLUSIONS
  The QALY benefit and cost-effectiveness of screening are most sensitive to the 5-year risk of rupture. Screening is beneficial only in populations with a high risk of rupture; this should be the focus of future research.
authors.affiliation: Division of Neurosurgery, Addenbrooke's Hospital & University of Cambridge, Hills Road, Cambridge, CB2 0QQ, UK. lml34@doctors.org.uk
authors.forename: Lucia M
authors.initials: LM
authors.lastname: Li
authors.forename: Diederik O
authors.initials: DO
authors.lastname: Bulters
authors.forename: Ramez W
authors.initials: RW
authors.lastname: Kirollos
mesh_terms: D017542:Aneurysm, Ruptured / Q000175:diagnosis / Q000191:economics; D003362:Cost-Benefit Analysis; D003663:Decision Trees; D004739:England; D005260:Female; D006801:Humans; D002532:Intracranial Aneurysm / Q000175:diagnosis* / Q000191:economics; D008297:Male; D008403:Mass Screening / Q000191:economics / Q000706:statistics & numerical data*; D008875:Middle Aged; D008962:Models, Theoretical; D019057:Quality-Adjusted Life Years; D018570:Risk Assessment