Concerned about a SAH?  The thunderclap worst headache of your patient’s life?  Recent data suggests that a negative head CT within 6 hours of symptom onset in a neurologically intact patient doesn’t warrant an LP.

Perry et al:

  • Multicenter prospective cohort study
  • 240/3132 (7.7%) had SAH overall
  • SAH defined as: visualized on noncontrast head CT, xanthochromia on CSF, RBCs > 5 x 10^6/L in fourth CSF tube, aneurysm on CTA
  • All 121 patients with SAH identified by head CT

Backes et al:

  • Single center retrospective study in Netherlands of 250 patients
  • 137 patients had head CT within 6 hours of symptom onset out of which 69 patients had negative head CT and 1/69 had SAH from cervical AVM on LP

Block et al: 

  • Multicenter, retrospective study at 11 non-academic hospitals
  • 760 patients had head CT within 6 hours of symptom onset followed by an LP > 12 hours after headache onset
    • 52/760 had bilirubin on LP but no SAH on head CT
      • 1/52 patients with SAH and negative non contrast head CT had a perimesencephalic nonaneurysmal hemorrhage
        • no neurosurgical intervention and no rebleed at 26 month follow up
      • 51/52 patients with negative head CT and bilirubin on LP
        • 23: no CTA, MRA performed
        • 20: no aneurysm on CTA, MRA
        • 8: aneurysm on CTA, MRA
          • 3 aneurysms previously coiled and 5 non ruptured aneurysms

Perry et al 2011 Study, Backes et al 2012 study, Blok et al 2015 study all had 0 cases of death or negative outcomes in patients presenting with sudden onset of headache and a negative head CT within 6 hours of symptom onset of headache.


Perry JJ et al. Sensitivity of Computed Tomography Performed Within Six Hours of Onset of Headache for Diagnosis of Subarachnoid Haemorrhage: Prospective Cohort Study. BMJ 2011; 343: d4277. PMID: 21768192

Backes D et al. Time-Dependent Test Characteristics of Head Computed Tomography in Patients Suspected of Nontraumatic Subarachnoid Hemorrhage. Stroke 2012; 43(8): 2115 – 9. PMID: 22821609 

Blok KM et al. CT Within 6 Hours of Headache Onset to Rule Out Subarachnoid Hemorrhage in Non Academic Hospitals. Neurology 2015; 84(19): 1927 – 32. PMID: 25862794 

May 2024