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

Written by Salim Rezaie REBEL EM Medical Category: Neurology

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?

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 NonAcademic Hospitals. Neurology 2015; 84(19): 1927 – 32. PMID: 25862794

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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 10 6 /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

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

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 5×10 6 /L CSF Leiden method suggested presence of bilirubin, but inspection of the absorption spa turn proved absence of bilirubin RBC count in CSF <100×10 6 /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:

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 NonAcademic Hospitals. Neurology 2015; 84(19): 1927 – 32. PMID: 25862794 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 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

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