The Evaluation of Occult Subarachnoid Hemorrhage: Why Are We Still Doing LPs? Is CTA A Better Alternative?

Author: Justin Bright, MD (EM Senior Staff Physician, Henry Ford Hospital, Detroit, MI) / Editor: Alex Koyfman, MD

Full disclosure: this isn’t going to be a practice-changing article based on multiple prior research studies. Instead, I want to discuss something we all deal with in our daily practice. I want to share with you what I found, and what I think about it. I hope this will generate some real discussion about where we are, what we do, and whether or not there’s a way to do it better.

It’s 4pm on a Wednesday. As per usual, the chart rack is full, and you’re trying to stay positive and keep up morale of the entire team. You pick up your next chart, and as you read the chief complaint, your heart sinks into your belly. The complaint is, “severe headache,” and you’re already trying to figure out how you’re going to fit an LP into your busy patient load.

Headaches are experienced in all types of ways by our patients. Many are benign – but we are in the catastrophe business. How do we know if the headache is actually a brain mass? Or what if it’s a raging intracranial hemorrhage? And if it is a brain bleed, what kind will it be? If we have a suspicion of subarachnoid hemorrhage (SAH), did our mouse click for “head CT (non-contrast)” just commit us and our patient to a lumbar puncture?

Before we dive into that question, I think it’s important to backtrack a bit and understand just what it is we’re looking for, and why CT/LP are married together in our evaluation of subarachnoid hemorrhage. A SAH is most commonly due to an aneurysmal leak or rupture at some point along the Circle of Willis. Based on reported incidence, a non-traumatic SAH occurs in 10% of headache presentations.¹ Reported sensitivity for non-contrast CT to detect aneurysmal subarachnoid hemorrhage is reported between 90-95%^2,3. To put it into context, if you take 100 known subarachnoid hemorrhages, the initial screening non-contrast head CT would have identified 90-95 of them – or nearly all of them. In addition, I think it’s a safe assumption that the patients that are critically ill or have neurologic deficits are likely to have clear cut larger bleeds very evident on CT. If your CT shows a bleed, it is quite common for CTA of the head to be the next step – sometimes by automatic radiology protocol while the patient is still lying on the CT table. The purpose of the CTA is to identify an aneurysmal source of the bleeding.

This discussion is not about those patients. It’s about the patients with a negative non-contrast CT that answers “yes” to the question, “is this, without a doubt, the absolute worst headache in the history of your lifetime?” Traditionally, this patient buys themselves a lumbar puncture. Once you have opened up the door to an LP, it’s a difficult one to close. There are many issues that need to be considered. Is your patient willing to undergo the procedure? If not, what is your true level of suspicion versus doing the LP because you know you’re supposed to? How much time are you willing to spend discussing the importance of the procedure with your patient? If your patient consents, are they feeling well enough to be positioned properly for a successful LP? Does their body habitus allow for a successful LP? What do you do if you’re unsuccessful? Do you call it a day with a now incomplete work-up? Do you involve IR and get it done under fluoroscopy? Do you know how to use ultrasound as an adjunct? Did enough time lapse to accurately determine presence of xanthrochromia? Do you even have the time to dedicate to getting an LP done in an emergency department blowing up all around you?

I just can’t help thinking, isn’t there a better way? Deep down, I think CTA of the head after a negative non-contrast CT might be better. The problem is, there is relatively little research on it. Most research on CTA in SAH is focused on comparing CTA to traditional angiography to determine location of an aneurysm in a patient with an already identified bleed. There is enough research to suggest that the two are virtually equivalent in accuracy, and that CTA is easier, faster, and less risky for the patient⁴. As such, CTA has replaced angiography as the diagnostic test to find the source of bleeding.

I see the following benefits for CTA of the head after a negative non-contrast study. The CTA will identify aneurysms. A negative non-contrast CT and subsequently negative CTA can rule out SAH with post-test probability approaching 99%⁵. It is fast. It is easy for the physician to order it and get other things done while the study is being done. It is non-invasive for the patient. It’s difficult to have an incomplete or failed study. There are no doubt drawbacks to CTA, namely that it’s a double radiation exposure, and the usual concerns regarding IV contrast dye. Furthermore, while the limited studies out there demonstrate that CTA is very good at identifying an aneurysm, the question becomes, what if the study identifies a non-bleeding aneurysm in a patient presenting with a headache? Is that aneurysm the cause? Is it an incidental finding? What subsequent testing, procedures, and even surgeries might the patient be subjected to as a result of this incidental finding? The converse of this argument is that LP will never identify the non-bleeding aneurysm in the first place. In defense of LP, it may identify other sources of headache, such as meningitis or increased intracranial pressure that a CTA will not.

So what does it all mean? What I have gathered in my search for answers is that there are definitely emergency physicians currently using CTA to evaluate headache patients in lieu of lumbar puncture. I personally believe that CTA is likely to give me the answer I’m looking for – is there an aneurysm, and if so, is it bleeding? However, the research on the subject is far too limited for a change of practice to occur at this time. In addition, the ACEP Clinical Policy on Headache guidelines still recommends lumbar puncture after a negative non-contrast head CT⁶. The policy doesn’t even discuss the use of CTA in the manner I have discussed here. As such, if you ever find yourself in medicolegal trouble in a headache case, use of CTA over LP would not be supported by your own governing body. But… I do think CTA is the future. I think there will be a time – probably sooner than we realize – when there is a transition to CTA instead. Someone among us will design a study that shows it’s a superior approach to the headache patient.

References / Further Reading:
1. Singer, Olgilvy, and Rordorf. “Aneurysmal Subarachnoid Hemorrhage: Epidemiology, risk factors, and pathogenesis.” UpToDate. Published September 2013; Accessed December 1, 2014. http://www.uptodate.com/contents/aneurysmal-subarachnoid-hemorrhage-epidemiology-risk-factors-and-pathogenesis
2. Perry JJ, et al. Sensitivity of computed tomography performed within six hours of onset of headache for diagnosis of subarachnoid haemorrhage: prospective cohort study.
SOBMJ. 2011; 343:d4277.
3. van der Wee N, et al. Detection of subarachnoid haemorrhage on early CT: is lumbar puncture still needed after a negative scan?. Neurosurg Psychiatry. 1995;58(3):357.
4. Villablanca JP, et al. Three-dimensional helical computerized tomography angiography in the diagnosis, characterization, and management of middle cerebral artery aneurysms: comparison with conventional angiography and intraoperative findings. J Neurosurg. 2002;97(6):1322.
5. McCormack RF, Hutson A. Can computed tomography angiography of the brain replace lumbar puncture in the evaluation of acute-onset headache after a negative noncontrast cranial computed tomography scan? Emerg Med. 2010 Apr;17(4):444-51.
6. Edlow, et al. Clinical Policy: Critical Issues in the Evaluation and Management
of Adult Patients Presenting to the Emergency Department With Acute Headache. Annals of Emergency Medicine. 2008 October; 52(4) 407-418.
7. Sen. “CT Angiography for detection of Subarachnoid Haemorrhage.” Best Bets. Published May 2008; Accessed December 1, 2014. http://bestbets.org/bets/bet.php?id=859
8. http://www.ncbi.nlm.nih.gov/pubmed/23067018