Although the lumbar puncture is a cool procedure, and very satisfying when it goes as planned, it is time-consuming, possibly painful to the patient, requires discussion/consent that can take a fair amount of time, and requires CSF fluid analysis which can also take a lot of time. It also requires skill (and occasionally luck), which some have more than others. What this all boils down to is most emergency physicians hoping that there is a better, easier test than an LP when we are ruling-out subarachnoid hemorrhage (SAH) in our headache patients.
When I was a resident, I remember distinctly that there were widely varying practices among attendings. Some were fine with just getting a plain CT and stopping the work-up there; some wanted CT/CTA; others wanted the traditional CT followed by LP. I was given variable explanations for these practices, and was left wondering: who was right?
If you really want to listen to some good lectures about SAH in general and have this question (and many others) answered thoroughly, you owe it to yourself to listen to SMARTEM’s podcasts entitled “Subarachnoid Hemorrhage: A Rational Approach” from Dec 18, 2010 (1h 53min) and the newer “SAH: A Picture is Worth a Thousand LPs” from Nov 7, 2012 (2h 11min). If these seem too long for you, you can hop over to ERCast’s podcast entitled “The Subarachnoid Enigma” from May 8, 2015 (19 min).
Here’s the spoiler alert: CTA cannot replace LP. To be specific, we are talking about patients with a normal plain CT and a normal neurological examination. The problem with CTA is that it is very good at finding aneurysms > 3mm. Great, right? No! Because the issues are:
1. The CTA will NOT tell you if that aneurysm has bled at any point in time
2. Roughly 2.5% of people in this country have aneurysms, so it may be a completely incidental finding.
So who cares if you find an aneurysm incidentally, haven’t you still done the patient a huge favor? Not necessarily…You have now basically assured the patient that they will get an angiography (the real, invasive kind) and possibly a neurosurgical intervention. These are not benign procedures and have significant complications and fairly high complication rates.
So you need to do the LP. Still don’t believe me? Check out these resources:
-Life in the Fastlane has a nice general summary of headache assessment/management in the ED
Life in the Fastlane link
-There is a wonderful article in Academic Emergency Medicine called “What are the Unintended Consequences of Changing the Diagnostic Paradigm for Subarachnoid Hemorrhage After Brain Computed Tomography to Computed Tomographic Angiography in Place of Lumbar Puncture”. You can view the article in it’s entirety with this link: CTA in Place of LP article
I really encourage you to take a look at these things so that you can have an active discussion with your attendings while working-up these patients and so that you are knowledgeable about this very important topic.
Please share any questions/comments you may have!