title: Can computed tomography angiography of the brain replace lumbar puncture in the evaluation of acute-onset headache after a negative noncontrast cranial computed tomography scan?
abstract: OBJECTIVE
  The primary goal of evaluation for acute-onset headache is to exclude aneurysmal subarachnoid hemorrhage (SAH). Noncontrast cranial computed tomography (CT), followed by lumbar puncture (LP) if the CT is negative, is the current standard of care. Computed tomography angiography (CTA) of the brain has become more available and more sensitive for the detection of cerebral aneurysms. This study addresses the role of CT/CTA versus CT/LP in the diagnostic workup of acute-onset headache.
  
  
  METHODS
  This article reviews the recent literature for the prevalence of SAH in emergency department (ED) headache patients, the sensitivity of CT for diagnosing acute SAH, and the sensitivity and specificity of CTA for cerebral aneurysms. An equivalence study comparing CT/LP and CT/CTA would require 3,000 + subjects. As an alternative, the authors constructed a mathematical probability model to determine the posttest probability of excluding aneurysmal or arterial venous malformation (AVM) SAH with a CT/CTA strategy.
  
  
  RESULTS
  SAH prevalence in ED headache patients was conservatively estimated at 15%. Representative studies reported CT sensitivity for SAH to be 91% (95% confidence interval [CI] = 82% to 97%) and sensitivity of CTA for aneurysm to be 97.9% (95% CI = 88.9% to 99.9%). Based on these data, the posttest probability of excluding aneurysmal SAH after a negative CT/CTA was 99.43% (95% CI = 98.86% to 99.81%).
  
  
  CONCLUSIONS
  CT followed by CTA can exclude SAH with a greater than 99% posttest probability. In ED patients complaining of acute-onset headache without significant SAH risk factors, CT/CTA may offer a less invasive and more specific diagnostic paradigm. If one chooses to offer LP after CT/CTA, informed consent for LP should put the pretest risk of a missed aneurysmal SAH at less than 1%.
authors.affiliation: Department of Emergency Medicine, University at Buffalo School of Medicine and Biomedical Sciences, Buffalo, NY, USA. rmccormack@kaleidahealth.org
authors.forename: Robert F
authors.initials: RF
authors.lastname: McCormack
authors.forename: Alan
authors.initials: A
authors.lastname: Hutson
mesh_terms: D000208:Acute Disease; D015901:Angiography, Digital Subtraction; D002533:Cerebral Angiography / Q000379:methods*; D003287:Contrast Media; D004635:Emergency Medicine / Q000592:standards / Q000639:trends; D004636:Emergency Service, Hospital; D005188:False Negative Reactions; D005260:Female; D006261:Headache / Q000175:diagnosis / Q000209:etiology; D006801:Humans; D007091:Image Processing, Computer-Assisted; D002532:Intracranial Aneurysm / Q000175:diagnosis / Q000000981:diagnostic imaging*; D008297:Male; D010147:Pain Measurement; D018570:Risk Assessment; D012680:Sensitivity and Specificity; D012720:Severity of Illness Index; D013129:Spinal Puncture / Q000379:methods; D013345:Subarachnoid Hemorrhage / Q000175:diagnosis / Q000000981:diagnostic imaging*; D014057:Tomography, X-Ray Computed / Q000379:methods*
chemical_list: D003287:Contrast Media