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.