Does that young, well appearing patient with the “worst headache of their life” really need that lumbar puncture (LP)? It’s an issue that’s constantly weighing over physicians’ heads when evaluating a patient with headache in the emergency department. The thought of potentially missing a sentinel bleed from an aneurysm or AVM is something that keeps us up at night. Few studies have directly asked the question – is it sufficient to perform a CT angiography (CTA) of the head without a lumbar puncture in the evaluation of subarachnoid hemorrhage?
In 2010 there was a mathematical analysis performed which showed that CT/CTA is almost as effective as CT/LP in identifying subarachnoid hemorrhage, although no prospective randomized trials have been performed due to the sheer number of patients required to obtain sufficient power.
Then in 2011 BMJ released an important article suggesting that CT within 6 hours of symptoms onset is nearly 100% sensitive for the presence of SAH. A more recent article confirmed similar findings in a nonacademic setting with staff radiologists.
It is important to note, however, that not all spontaneous subarachnoid hemorrhages are due to aneurysmal bleeding. Nonaneurysmal bleeding occurs in 15% of diagnosed subarachnoid hemorrhages. Causes of these include paramesencephalic hemorrhage (10%), arterial dissection, cerebral arteriovenous malformation, dural arteriovenous fistulas, vascular lesions around the spinal cord, among other rare conditions. The larger of the group, paramesencephalic hemorrhage, has a good prognosis with little risk of rebleeding and mortality. The question therefore remained whether or not pathologies unable to be detected by CTA are clinically relevant.
In 2014 a paper was published assessing the outcomes of patients who had > 5 RBCs on their LP after initial negative CT and subsequent negative CT angiography. The study successfully followed 181 patients meeting these inclusion criteria for 53 months. None of the patients had a subsequent bleed or new lesion found on further imaging, although one patient was eventually diagnosed with vasculitis when they returned 2 weeks later with an intraparenchymal hemorrhage and hemiparesis. As such, data suggests that seeking out the subarachnoid hemorrhage that does not have an etiology identifiable by angiography may be unnecessary when it comes to clinical outcomes.
For now, the current ACEP Clinical Policy (from 2008) states that patients arriving with an acute-onset severe headache with a negative head CT require lumbar puncture to rule out subarachnoid hemorrhage. With more data supporting the utilization of CTA instead of performing an LP.
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