This week: Headaches and ruling out subarachnoid hemorrhages. Meat and potatoes content, but definitely important points to highlight here.
Article: Marcolini, E., & Hine, J. (2019). Approach to the Diagnosis and Management of Subarachnoid Hemorrhage. Western Journal of Emergency Medicine: Integrating Emergency Care with Population Health, 20(2). http://dx.doi.org/10.5811/westjem.2019.1.37352
What: This is a nice review article in WEJM that covers some of latest evidence in the evaluation and management of subarachnoid bleeds. I want to draw attention to the diagnostic side of the issue. Specifically, when to scan, when to tap, and when to scan again.
SGEM has covered the utility of Lumbar Puncture after CT: http://thesgem.com/2015/11/sgem134-listen-to-what-the-british-doctors-say-about-lps-post-ct-for-sah/
EMRAP had a Free Open-Access segment on the topic: https://www.emrap.org/episode/emrap2020may/subarachnoid
Why: SAH is a high-mortality diagnosis with a missed diagnosis carrying a 20% mortality in the first 2 hours and 40% within a week. These days, many departments have relatively modern CT scanners that can take thin cuts of the brain. In light of this, there’s some strong evidence that a non-contrast CT scan within 6 hours of headache onset is very sensitive (97-99%) for detecting intracranial hemorrhage. ACEP’s 2019 Clinical Policy gives it a Level B recommendation.(1) But what about after 6 hrs? Sensitivity of a non-contrast CT for intracranial hemorrhage then drops to ~85%
Traditional teaching tells us to follow-up with a lumbar puncture if the CT scan is negative. But others may be tempted by the option of a CTA Brain scan to simply rule out the presence of aneurysm.
So according to the evidence, what’s the Golden Path here? CT/LP? CT/CTA? There isn’t one.
While the AHA/ASA guidelines support a CT/LP approach, Sayer et al showed a Number Needed to Treat (or Tap) of 250 to find one case of aneurysm.(2) Other studies have put the NNT at 700 or higher. A lumbar puncture also carries various risks, including Post-LP headache, injury, and infection. On the other hand, some papers have estimated a high sensitivity for CTA scans for detecting aneurysms, but CT angiography will miss aneurysms < 4 mm in size. Unfortunately, even small aneurysms can have devastating consequences, so that limitation is notable. If we have a very pre-test probability for SAH, an LP should be considered even in the setting of a non-diagnostic CTA. If an aneurysm is detected on CTA, then an LP should be considered to help determine if the aneurysm is actually bleeding and causing the patient’s presentation. In this light, we may accidentally attribute an incidental aneurysm as the cause of a headache and push a patient down a road of unnecessary invasive testing.
So ultimately any approach involves a bit of discussion. You need to talk with your patients about the risks/benefits and use a shared-decision making approach. If you can reach a consensus with your hospital’s Neurosurgery Department about a best approach, then you could also breath a little easier. But this is a nuanced and difficult topic that remains under debate. And this discussion doesn’t take into account the various alternative diagnosis that lumbar punctures may help diagnose (infection and IIH for example).
Written by Jorge Aceves, MD
Chief Resident, Emergency Medicine, Cook County Health
Twitter: @joaceve91