What a Headache – Diagnostic Trends in SAH

June 7, 2024

Written by Doug Wallace

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This retrospective cohort study of Kaiser NorCal EDs found increasing use of CT cerebral angiography for spontaneous subarachnoid hemorrhage diagnosis to be associated with fewer lumbar punctures and higher detection of unruptured intracranial aneurysms, with no significant change in the miss rate for SAH or bacterial meningitis.

Sudden onset CTCA
Aneurysmal subarachnoid hemorrhage (SAH) accounts for a small amount of acute-onset headaches but carries serious risk of long term disability and death. The classic approach to SAH is noncontrast head CT followed by lumbar puncture (LP)  if there remains high clinical suspicion. Given non-aneurysmal spontaneous SAH has low associated morbidity and mortality, there has been an increasing trend of using CT cerebral angiography (CTCA) as a non-invasive alternative to LP. This is despite no direct evidence supporting this approach, though ACEP issued a 2019 recommendation for either use of CT + LP or CT + CTCA in assessing for aneurysmal SAH. In 2023 the American Heart and Stroke Associations made a strong recommendation favoring the classic approach of CT + LP, highlighting the ongoing contention surrounding this topic. Notably, LP is not without its own pitfalls nor controversy: see Point | Counterpoint – Do LP if Negative CT for SAH vs. Point | Counterpoint – No LP if Negative CT for SAH.

This retrospective cohort study assessed for changing trends in approach to SAH, the rate of unruptured intracranial aneurysm (UIA) diagnosis, as well the rate of missed diagnoses of SAH and bacterial meningitis with any change in approach.

7,557,395 encounters at 21 EDs between 2015 and 2021 were reviewed, and 72,881 patients with a chief complaint of headache underwent diagnostic testing for SAH. A six-fold increase in CTCA relative to LP was noted with a concomitant 33% increase in UIA diagnosis. The authors noted only 50 possible missed SAH cases (5% of all SAH cases), 6 of which were missed on CTCA. 21 cases of meningitis were potentially missed (18% of all meningitis cases). The proportion of missed diagnoses of either of these conditions did not increase during the study period despite changes in diagnostic approach.

How will this change my practice?
This is a controversial subject, and this article will not change my practice. My approach is all about pretest probability. High pretest probability (thunderclap headache, CNS depression, focal deficits, neck stiffness, syncope, exertional headache, etc…Ottawa Rule for SAH) and negative CT/CTCA equals need for LP in my practice. In general, I obtain CTCA with concern for SAH, understanding the limitations of the test (97%-98% sensitivity, with lower sensitivity for aneurysms <3 mm), followed by LP if an aneurysm is present or pretest probability is high enough despite negative imaging. Anecdotally, I have noted positive LPs for SAH in the setting of missed aneurysm on CTCA, though this is quite rare overall.

Source
Shifts in Diagnostic Testing for Headache in the Emergency Department, 2015 to 2021. JAMA Netw Open. 2024 Apr 1;7(4):e247373. doi: 10.1001/jamanetworkopen.2024.7373. PMID: 38639937; PMCID: PMC11031686.