Does a Normal Head CT Within 6 Hours of Onset of Headache Rule Out SAH?

Background: The traditional standard workup for ruling out subarachnoid hemorrhage (SAH) has been a non-contrast head CT and, if negative, a lumbar puncture. The thought behind this is that the sensitivity of head CT to rule out SAH is not 100% and declines over time and missing a SAH is potentially devastating. There has been a series of studies published in the past few years looking at the value of a negative head CT scan performed within 6 hours of headache onset in ruling out SAH. I have heard many say that if they have a negative Head CT at 6 hours or less in a neurologically intact patient they would not perform a lumbar puncture.

What Trials are we Reviewing?

1. 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
2. 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
3. Blok KM et al. CT Within 6 Hours of Headache Onset to Rule Out Subarachnoid Hemorrhage in NonAcademic Hospitals. Neurology 2015; 84(19): 1927 – 32. PMID: 25862794

What Does the #FOAMed Twitterati Say?

Perry et al 2011 Study [1]

• Multicenter Prospective Cohort Study
• SAH Defined as any of the Following:
  • SAH on Unenhanced Head CT
  • Visible Xanthochromia in CSF
  • RBCs >5 x 10⁶/L in Final Tube of CSF
  • Aneurysm Identified on Cerebral Angiography
• 240/3132 patients or 7.7% had SAH Overall

• 953 Patients Had a Head CT Performed ≤6 Hours After Onset of Headache:
  • All 121 patients with SAH were identified by Head CT
• 2179 Patients Had a Head CT performed >6 Hours After Onset:
  • 119 patients got LPs after a negative Head CT
  • 17/119 patients had positive LPs, but negative Head CT
    • 6 had neurosurgical intervention (Ventricular drain, aneurysm coiling or clipping)
    • 10 No cause for bleeding found
    • 1 Case secondary to a brain tumor
• CAVEATS: Not all patients got an LP
• BOTTOM LINE: 0 Cases of death or negative outcome at 3 months if head CT negative and performed within 6 hours of symptom onset of headache.

Backes et al 2012 [2]

• Single Center Retrospective Study in the Netherlands of 250 patients

• 137 Patients Had a Head CT Performed ≤6 Hours After Onset of Headache:
  • 69 Patients had negative Head CT
    • 1/69 had SAH from cervical AVM on LP
• 113 Patients Had a Head CT performed >6 Hours After Onset:
  • 76 Patients had negative Head CT
    • 5/76 had SAH
      • 4 Aneurysmal SAH
      • 1 Thoracic AVM
• CAVEATS: All patients got LPs and Head CTs read by Neuroradiologists
• BOTTOM LINE: 0 cases of death or negative outcomes in patients presenting with sudden onset headache and a negative head CT performed within 6 hours or less of symptom onset of headache.

Blok et al 2015 [3]

• Multicenter, Retrospective Study at 11 Non-Academic Hospitals
• 760 patients were included in the analysis and underwent head CT within 6 hours after onset of acute headache followed by an LP >12 hours after headache onset
• 52/760 (6.8%) patients found to have 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
  • Benign clinical course with no neurosurgical intervention or rebleed at 26 month follow up
  • NPV: 99.9%
  • Other 51 patients with negative head CT and bilirubin on LP:
    • 23 Did not have CTA, MRA or DSA performed based on “clinical grounds”
    • 20 had no aneurysm on CTA, MRA, or DSA
    • 8 had an aneurysm on CTA, MRA or DSA
      • 3 aneurysms were previously coiled
      • Other 5 aneurysms were deemed non-ruptured aneurysms
• BOTTOM LINE: 0 cases of death or negative outcomes in patients presenting with sudden onset of headache and a negative head CT performed within 6 hours or less of symptom onset of headache

Discussion:

• Between the three studies reviewed ZERO cases of aneurysmal SAH were missed if a patient had a head CT performed within 6 hours of headache onset, a normal mental status, and no focal neurologic deficits.
• Multiple cases of perimesencephalic bleeding were missed and undiagnosed, but none of the patients had a poor outcome (i.e. death). It turns out that 1 in 20 patients can actually have an aneurysmal perimencephalic bleed.
• Doing LPs is not a benign procedure. It can be uncomfortable; can have complications such as post LP headaches, subdural hematomas, or even cerebral venous sinus thrombosis. LPs can also cause false positive results leading to more down stream testing.
• So in a patient with a negative head CT within 6 hours the chances of having an aneurysmal SAH is <1%. Adding an LP is a balance between catching the rare SAH vs the complications of the lumbar puncture as well as the complications of false positive tests (i.e. additional downstream testing, surgical intervention etc).
• In the Blok trial, there are a lot of assumptions made with the group of patients who had + bilirubin on LP especially the group found to have an aneurysm. In the study the authors stated that aneurysm rupture was unlikely because of the following:
  • Trace of bilirubin, but no RBCs in CSF
  • Pituitary Apoplexy was diagnosed with CT and MRI
  • Marginally elevated bilirubin excess, but proof of absence of bilirubin with regular spectrophotometry and RBC count in CSF of 5×10⁶/L
  • CSF Leiden method suggested presence of bilirubin, but inspection of the absorption spa turn proved absence of bilirubin
  • RBC count in CSF <100×10⁶/L
  • Marginally elevated bilirubin excess, but proof of absence of bilirubin with regular spectrophotometry
• There was a 4th study performed by Sayer et al [4] looking at the rate of SAH diagnosis via an LP after a negative non-contrast head CT, which they defined as spectrophotometric detection of bilirubin, not by CSF RBC count or xanthochromia. There were 2,248 patients who met inclusion criteria with only 92 (4.8%) of LPs being positive. All patients with a positive LP underwent CTA or MRA with only 8 aneurysms and one carotid cavernous fistula diagnosed.  In other words 9/2248 (0.47%) of all patients receiving LPs after negative head CT were found to have a vascular abnormality. There was however no data provided on the timing to CT or LP in this study.
• Finally, not all headaches are SAH only. Certainly other life threatening etiologies exist such as meningitis/encephalitis and an LP is the gold standard test in making this diagnosis.

Clinical Take Home Point: In patients with a history consistent with SAH, normal mental status, no focal neurologic deficits, and a negative head CT performed within 6 hours, a shared decision strategy should be used as this is not a 100% sensitive strategy, but should also be balanced with the risk of complications such as post LP headache and false positive testing.

References:

1. 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
2. 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
3. Blok KM et al. CT Within 6 Hours of Headache Onset to Rule Out Subarachnoid Hemorrhage in NonAcademic Hospitals. Neurology 2015; 84(19): 1927 – 32. PMID: 25862794 
4. Sayer, D et al. An Observational Study of 2,248 Patients Presenting With Headache, Suggestive of Subarachnoid Hemorrhage, Who Received Lumbar Punctures Following Normal Computed Tomography of the Head. Journal of Academic Emergency Medicine. 2015 Nov; 22(11):1267-73. PMID: 26480290
5. Dubosh NM et al. Sensitivity of Early Brain Computed Tomography to Exclude Aneurysmal Subarachnoid Hemorrhage: A Systematic Review and Meta-Analysis. Stroke 2016 [epub ahead of print] PMID: 26797666

For More Thoughts on This Topic Checkout:

• Rob Orman on ERCast: The Subarachnoid Enigma
• Chris Gray at St. Emlyn’s Blog: Lets Talk About Subarachnoid Hemorrhage
• Ken Milne at The SGEM: SGEM #48 – Thunderstruck (Subarachnoid Hemorrhage)
• Ken Milne at The SGEM: SGEM #134 – Listen, to What the British Doctors Say About LPs Post CT for SAH
• Ken Milne at The SGEM: SGEM #140 – CT Scans to Rule Out Subarachnoid Hemorrhages in a Non-Academic Setting
• Ryan Radecki at EMLit of Note: Is the 6-Hour CT for SAH Debate Over?

Post Peer Reviewed By: Anand Swaminathan (Twitter: @EMSwami)