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Headache Diagnostic Pathway

Rob Orman, MD and Cameron Berg, MD FAAEM

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Lisa Chavez, RN and Kathy Garvin, RN

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EM:RAP 2017 February Written Summary 971 KB - PDF

Cam Berg takes on the acute headache workup.

Headache Diagnostic Pathway

Rob Orman MD and Cam Berg MD


Take Home Points

     90% of subarachnoid hemorrhages are from aneurysms. These have high morbidity and mortality.

     CT performed within 6 hours of headache onset is nearly 100% sensitive and 100% specific for subarachnoid hemorrhage.

     The Ottawa Subarachnoid Hemorrhage rule may be used to risk stratify patients.

     The risk of subarachnoid hemorrhage with a negative CT within 6 hours is approximately 1/1000.

     Lumbar puncture has a high rate of false positive results.


      About 90% of subarachnoid hemorrhages are from aneurysms. These are the ones we want to detect because they have high morbidity and mortality. The other 10% are perimesencephalic bleeds that aren’t as dangerous and may not be consequential if missed.

      The accelerated diagnostic protocol is predicated on the Perry article. 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 Jul 18;343:d4277.PMC3138338

     CT performed within 6 hours on non-traumatic headache patients was nearly 100% sensitive and 100% specific for the diagnosis of subarachnoid hemorrhage. The time limit of 6 hours is important due to the changes blood undergoes with time. Acute blood on CT is bright. Resolving blood gradually becomes isodense which may be difficult to see in the subarachnoid space.

     The CT scanners used in this study were not very advanced. The radiologists were not specialized in neuroradiology.

      The patient enters the ADP after presenting with a headache concerning for subarachnoid hemorrhage. Patients are entered into the pathway based on clinician gestalt.

     The Ottawa Subarachnoid Hemorrhage rule is used to risk stratify patients. The absence of any of these findings essentially rules out subarachnoid hemorrhage. This rule has been prospectively validated at multiple sites.

      Age > 39.

      Neck pain, stiffness or limited flexion.

      Witnessed loss of consciousness.

      Exertional onset.


      Perry, JJ et al. Clinical decision rules to rule out subarachnoid hemorrhage for acute headache. JAMA. 2013 Sep 25;310(12):1248-55.PMID: 24065011

     If the Ottawa decision rule is negative, no further work-up is performed. However, if there is something about the patient that makes you think they are higher risk than the average patient, you might still want to pursue an LP.

     If the Ottawa decision rule is positive, the patient receives a noncontrast head CT.

      Carpenter, CR et al. Spontaneous subarachnoid hemorrhage: a systematic review and meta-analysis describing diagnostic accuracy of history, physical examination, imaging, and lumbar puncture with an exploration of test thresholds. Acad Emerg Med. 2016 Sep;23(9):963-1003.PMID: 27306497

     This article advised CT within 6 hours was extremely good at ruling out subarachnoid hemorrhage. They recommend LP be performed after CT only in patients with a pre-CT probability of greater than 20% for subarachnoid hemorrhage.

     In comparison, the subset of patients included in the Perry article had a pre-CT probability of subarachnoid hemorrhage of 7.7%. 20% would be a very high risk group.

      If the CT is positive, the patient rules in. If the symptom onset was under 6 hours and the CT is negative, the patient is ruled out.

      There is a small risk of subarachnoid hemorrhage with negative CT under 6 hours (1/1000). Should you discuss this with patient? Berg says, “Based on the results on your tests today, it appears extremely unlikely you are suffering from a bleeding aneurysm. To the best our knowledge, the possibility is about 1 in 1000 or less. To be 100% certain the next thing we would do is a more invasive test like a spinal tap. At this point, I would not recommend the test but I would be happy to perform it if you remain worried.”

      Lumbar puncture has a very high incidence of false positive results. About 15% of emergency lumbar punctures have red blood cells due to trauma. If you combine this feature with a low prevalence of actual disease, you get a likelihood ratio of a true positive of a lumbar puncture after negative CT within 6 hours is 1 in 200. It is a false positive 99.5% of the time.

      CT performs differently after 6 hours. Instead of being close to 100% sensitive, it is more like 90%. This is not high enough. If the patient has a concerning story with symptoms greater than 6 hours from onset, they would receive a CT head followed by lumbar puncture.

      What is a positive lumbar puncture? The ideal is either xanthochromia defined by colorimetric analysis or greater than 2000 red cells in the tube with the lowest number of cells.

      Why not just do a CT angiogram? Between 2-5% of the population have an incidental aneurysm. However, there is no evidence of benefit of detection or intervention when patients are asymptomatic. A few small ED trials have looked at this. The data is not promising. It is costly, involves a large amount of radiation and there is no evidence it benefits our patient.

      What do you do if the lumbar puncture is positive? Now you do the CT angiogram. The majority of lumbar punctures are false positives. You want a confirmatory test to show there is an aneurysm that could be bleeding.

      Since Berg started the ADP, they have decreased lumbar puncture utilization by 30%. They have decreased the length of stay in headache work-ups by about an hour. They are all on the same page. The radiologists, neurosurgery and consultants are in agreement.

      If you are going to create an ADP, make sure your consultants are all on board and agree with the plan. It is ok if your gestalt tells you to deviate from the protocol. That is why we practice and train.




Image of Headache ADPHeadache ADP

David W. -

I think there's a misleading statement in here at 10:06 minutes. The guest expert states "the possibility is approximately 1:1000 or less" regarding the risk of a SAH with a negative 6hr CT. I think he is conflating the sensitivity with the negative predictive value.

I think he is getting this 1:1000 number from the sensitivity of the CT, which he thinks is probably 99.9%, just shy of Perry's estimate of 100%. However, this means the chance of getting a negative CT in a patient whom we KNOW to have a SAH is 1:1000, which, of course, is not a helpful number. To explain to the patient, you really care about the negative predictive value. If we assume the 6hr CT has a 99.9% sensitivity, and, for arguments sake, 99.9% specificity (again, just shy of Perry's 100%) then the negative predictive value - which is the patient's chance of having a SAH with a negative CT head - is in fact about 1:125,000. The risk our expert is quoting to the patient is inflated by a factor of 100! (This estimate uses a prevalence of 7.7%).

David W. -

Correction: real risk is 1 in 12500. Which is lower than the risk quoted by the expert by a factor of 12.

Yulia S., Dr -

A question for Cam Berg - do you wait 12 hr to perform LP in your ADP?
What's your thoughts on spectrophotometry for exclusion of xantochromia?
Thank you.


David H., M.D. (@BritFltDoc) -

Dr Berg,
Thank again for your segment. I think though the discussion about the next test, after a neg CT scan for acute thunderclap headache with an onset greater than 6 hours, needs to expand beyond that of SAH. While this is the subject of the ADP, for the true sudden in onset, maximal in onset, unusual headache, SAH is not the only DDx. When neck pain is added in to the symptom complex, arterial vessel dissection is also a worthy differential diagnosis. So I think the consideration of CT angiography is worthwhile, as you assess for both aneurysm and dissection with one test. As you mentioned, an LP is far from a perfect test, with problematic false positives, leading to the CTA anyway. And while serious complications are rare, post LP headache, requiring return ED visits and procedures are not uncommon. I think there are many factors to consider when deciding the next test after neg CT: is there another DDx you are considering, patient body habitus and likelihood of non traumatic tap, use of anti-platelet agents, and patient preference to an invasive procedure versus extra radiation and risk of incidental aneurysm. Thanks, David

Roee S. -

Question for Dr. Berg- I am a second year EM resident in Jerusalem, Israel, and am interested in implementing your ADPs as a teaching tool for medical students rotating in the ED and new interns. I was hoping that you could share the ADPs that you have implemented with me.
Thank you!

Rob O -

Hi Roee, I am sending you all of the ADPs right now. Enjoy!
-Rob O

Paul B. -

I am curious about your thoughts on the use of the Ottawa SAH rule and investigation rate. In the 2013 derivation paper by Perry et al. they show that implementation of the original rule (from the 2010 BMJ article) would have led to an investigation rate of 74%, however the modified rule (the one you are advocating using) had an investigation rate of 85%. The investigation rate in the study was 84% (without implementation of the rule). Additionally, in 2015 Bellolio et al. attempted to externally validate the modified rule via a retrospective chart review published in the American Journal of Emergency Medicine. I think there are a number of problems with the study, however, in the patients the rule was applied to it appeared to dramatically increase the rate of work up (and none were missed by standard work up).

Taken in aggregate it seems to me this rule does not decrease investigation rate from standard practice.
In the original 2010 BMJ derivation article the authors write "Such rules should be highly sensitive and reliable while also reducing the number of patients requiring investigation to rule out subarachnoid hemorrhage." It seems the rule has achieved the former, but failed at the latter. Given this, it seems to me that using this as an entry way to the diagnostic pathway will increase (or at least not decrease) CT utilization from standard care. It seems to me that in both the 2010 BMJ article and the 2013 JAMA article all patients with SAH received a CT scan with out using the rule, so I am uncertain the benefit of adding this over standard care.

I appreciate your thoughts!

Paul B. -

Additionally, you mention that after implementing this pathway you have reduced LP rates by 30%. I am curious what your before/after CT rate is this is most applicable to the Ottawa SAH rule.

Jeffrey F. -

Why not perform the CTA first for patients that present outside of 6 hours and then perform the lumbar puncture only after an aneurysm is found to get a better idea if the aneurysm is incidental or not? If maybe 15 % of LP's are going to be false positive, then these patients will get a CTA anyways and will be exposed to the harm of both LP and CTA. Unless the incidence of clinically insignificant aneurysms would result in us doing more LPS could CTA first be a reasonable approach for HA outside 6 hours?

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