title: Appropriate use of CT perfusion following aneurysmal subarachnoid hemorrhage: a Bayesian analysis approach.
abstract: OBJECTIVE
  In recent years CTP has been used as a complementary diagnostic tool in the evaluation of delayed cerebral ischemia and vasospasm. Our aim was to determine the test characteristics of CTP for detecting delayed cerebral ischemia and vasospasm in SAH, and then to apply Bayesian analysis to identify subgroups for its appropriate use.
  
  
  METHODS
  Our retrospective cohort comprised consecutive patients with SAH and CTP performed between days 6 and 8 following aneurysm rupture. Delayed cerebral ischemia was determined according to primary outcome measures of infarction and/or permanent neurologic deficits. Vasospasm was determined by using DSA. The test characteristics of CTP and its 95% CIs were calculated. Graphs of conditional probabilities were constructed by using Bayesian techniques. Local treatment thresholds (posttest probability of delayed cerebral ischemia needed to initiate induced hypertension, hypervolemia, and hemodilution or intra-arterial therapy) were determined via a survey of 6 independent neurologists.
  
  
  RESULTS
  Ninety-seven patients with SAH were included in the study; 39% (38/97) developed delayed cerebral ischemia. Qualitative CTP deficits were seen in 49% (48/97), occurring in 84% (32/38) with delayed cerebral ischemia and 27% (16/59) without. The sensitivity, specificity, and positive and negative predictive values (95% CI) for CTP were 0.84 (0.73-0.96), 0.73 (0.62-0.84), 0.67 (0.51-0.79), and 0.88 (0.74-0.94), respectively. A subgroup of 57 patients underwent DSA; 63% (36/57) developed vasospasm. Qualitative CTP deficits were seen in 70% (40/57), occurring in 97% (35/36) with vasospasm and 23% (5/21) without. The sensitivity, specificity, and positive and negative predictive values (95% CI) for CTP were 0.97 (0.92-1.0), 0.76 (0.58-0.94), 0.88 (0.72-0.95), and 0.94 (0.69-0.99), respectively. Treatment thresholds were determined as 30% for induced hypertension, hypervolemia, and hemodilution and 70% for intra-arterial therapy.
  
  
  CONCLUSIONS
  Positive CTP findings identify patients who should be carefully considered for induced hypertension, hypervolemia, and hemodilution and/or intra-arterial therapy while negative CTP findings are useful in guiding a no-treatment decision.
authors.affiliation: From the Departments of Radiology (R.P.K., A.G., H.D., C.E.J., A.J.T., J.C., P.C.S.).
authors.forename: R P
authors.initials: RP
authors.lastname: Killeen
authors.forename: A
authors.initials: A
authors.lastname: Gupta
authors.forename: H
authors.initials: H
authors.lastname: Delaney
authors.forename: C E
authors.initials: CE
authors.lastname: Johnson
authors.forename: A J
authors.initials: AJ
authors.lastname: Tsiouris
authors.forename: J
authors.initials: J
authors.lastname: Comunale
authors.forename: M E
authors.initials: ME
authors.lastname: Fink
authors.forename: H S
authors.initials: HS
authors.lastname: Mangat
authors.forename: A Z
authors.initials: AZ
authors.lastname: Segal
authors.forename: A I
authors.initials: AI
authors.lastname: Mushlin
authors.forename: P C
authors.initials: PC
authors.lastname: Sanelli
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001499:Bayes Theorem; D002533:Cerebral Angiography / Q000379:methods*; D002560:Cerebrovascular Circulation; D005260:Female; D006801:Humans; D002532:Intracranial Aneurysm / Q000000981:diagnostic imaging* / Q000503:physiopathology; D008297:Male; D008875:Middle Aged; D059906:Neuroimaging / Q000379:methods*; D012189:Retrospective Studies; D012680:Sensitivity and Specificity; D013345:Subarachnoid Hemorrhage / Q000000981:diagnostic imaging* / Q000503:physiopathology; D014057:Tomography, X-Ray Computed