Around 2-5% of patients presenting to the Emergency Department will be there because of a headache.(1) Most of these are benign, but it’s not uncommon to be faced with a patient with the worst headache of their life. Until now, it has been recommended that all patients with a clinical suspicion of sub-arachnoid haemorrhage and a negative CT head be referred for a lumbar puncture at 12 hours after the onset of headache.(2) Is it time for a change? Can we send some of these patients home? Can we avoid referring them for what can be an unpleasant procedure?
Let’s talk about subarachnoid haemorrhage (SAH).
What is it? Is it bad?
Well, it’s pretty much what it says, a bleed into the subarachnoid space. Of all of your headache patients, around 1-3% will have a SAH.(3) Roughly 85% are caused by a ruptured saccular (berry) aneurysm, 10% by perimesencephalic bleed (benign), and the rest by arteriovenous malformation and other rare causes.(4) SAH carries a poor prognosis, at the worst, 25% will die within 24 hours, and a further 25% within 1 month. Of those who survive, up to 50% will have some form of disability. Without intervention, there is a 3% yearly rebleed rate.(1)
The typical headache is described as a sudden onset headache, like a blow to the back of the head, or a “thunderclap” headache, and whilst this should certainly ring alarm bells for SAH, patients can present differently. Most neurologists agree though, that in the context of a headache, to include SAH as a differential, its onset to peak must be within minutes, and it must last for longer than one hour.(1) Symptoms can last for weeks, and whilst adverse features such as nausea, vomiting, neurology, seizures, neck pain and stiffness, confusion, and decreased conscious level are uncommon, the absence of these does not immediately rule out SAH.
Okay, so we know it’s bad. What can we do to minimise our chances of missing one of these?
What’s the evidence?
In November 2015, a Best BET(5) was published in the Emergency Medicine Journal, which looked at whether a scan within 6 hours of headache is sensitive enough to rule out subarachnoid without need for further investigation. A previous BET(6) had looked at CT in general to rule out SAH, however since then 4 studies have looked at early scanning with good results. The conclusion of the BET is that a scan within 6 hours is sensitive enough to rule out SAH in patients presenting without adverse features, on a third generation scanner with thin slices, if reported by an experienced radiologist.
Just before publication of the BET, a further study by Sayer et al.(6) was published, which looked at 2,248 patients who underwent lumbar puncture after a negative CT head. They found 92 positive and 299 inconclusive results but only 9 vascular abnormalities. This means an NNT (number needed to tap) of 250 and a lot of false negative lumbar punctures. Relating to our initial 6 hour CT, only 1 of these false negative scans occured within 6 hours. Whilst this was not the focus of the paper, it reinforces the idea of early CT to rule out SAH.
The Sayer paper has been reviewed well across the blogosphere, and you can read a great appraisal at SGEM, where Kirsty Challen also produced this brilliant #paperinapic to illustrate the results in an easy to understand format.
So, your patient presented with a headache, it came on over a few minutes and has lasted longer than an hour but less than six. They have no adverse features, but you are worried about SAH, and you want a CT scan that will help you to make a decision. How are you going to go about this?
CT scanning and SAH
Firstly, find out what generation scanner you have. Our 2 scanners here in Virchester are both 3rd generation, and from talking to our friendly radiographers it is likely that if you’re in the UK, your scanners are too. Indeed, all 16+ slice scanners recommended by the Department of Health Centre for Evidence-based Purchasing are 3rd generation.(7) Therefore, this shouldn’t be a stumbling block, but do check.
Next, talk to your radiologists. In order to give patients the correct information to make a decision on management, the scan must be thin slice, and must be reported by a radiologist experienced in reporting CT heads. This means that the radiologist must prescribe a thin slice protocol for the scan, and ensure someone experienced reports it, with specific focus on looking for a subarachnoid haemorrhage. You must make sure you include this information on the request form and when you speak to them.
It would be sensible for your clinical director to liaise with the radiology clinical director to ensure all parties are clear on the process, as this will make the pathway run more smoothly. Of course, the difficulty will be the 3am scan…
Okay, your scan comes back clear, no impression of subarachnoid haemorrhage. Now to talk to the patient about what you have found. At this point you should have already mentioned that you are looking to exclude SAH, as they need to know what the CT scan is for.
Having undertaken a history, examination, and a CT head, the patient should know that you’re worried about a subarachnoid haemorrhage. They will likely be relieved by the scan being normal, and based on your clinical judgement, and results of the assessment, maybe you will be too.
If, based on these results, and your assessment of the patient, you do not have a high concern for subarachnoid haemorrhage, some of the evidence above may be helpful to inform the patient that:
- No investigation is 100% accurate.
- Based on the assessment done it is very likely this is a benign problem but there is a small risk that this is something serious, and things could get worse.
- The next investigation we could do is a lumbar puncture, though they would need to be admitted to hospital, and there are risks to doing this procedure as well.
- However, research suggests that for patients like them, we would need perform a lumbar puncture on 250 patients to get one positive result, and some others of these 250 patients would get a false positive, leading to further tests which may be unnecessary and carry further risks.
- The patient could return at any time if they were concerned or their symptoms changed.
This may enable a joint decision to be made for conservative management at home.
This is a potential concept to reduce the number of invasive procedures based on the current evidence which shows that a large number of these may be unnecessary, and could possibly lead to further harm both from these procedures and further investigations undertaken in the case of false positive results. Further research is looking into decision tools which could be used to stratify patients into low- and high-risk groups and may help us to do this even better.
In patients presenting with lone headache, with clinical suspicion of subarachnoid haemorrhage but no adverse features, a CT head is sufficient to rule this out, if performed within 6 hours of onset on a thin-slice, 3rd generation CT and reported by an experienced radiologist.
For patients who do not meet the above criteria, or those presenting after 6 hours, an urgent CT head should be requested, and if negative, current evidence suggests these patients could also be discharged.
If there is a high clinical concern for subarachnoid haemorrhage despite negative imaging (for example in patients with previous SAH), the patient should be referred for further investigation.
Patients who are discharged should be given advice to return if they develop adverse features such as neurology or decreased conscious level, or are concerned about new or evolving symptoms.
Of course, if they have a positive scan, urgent neurosurgical opinion should be sought and local guidelines followed regarding management.
A hot topic at the moment, and one that I’m sure will produce much more research in the coming months. Hopefully this gives some food for thought, and I know many people are doing this already. It would be great to read your comments, but I’ll leave the last word to the indomitable Ian Stiell:
— Ian Stiell (@EMO_Daddy) November 7, 2015
- Davenport R, Acute Headache in the Emergency Department. J Neurol Neurosurg Psychiatry 2002;72:ii33-ii37
- GEMNet Guidelines on lone acute severe headache
- Goldstein JN, Camargo CA, Pelletier AJ , et al. Headache in United States Emergency Departments, work up and frequency of pathological diagnoses. Cephalagia 2006;26:684–690.
- Radiopaedia article on SAH
- Gray C & Foëx BA, Does a normal CT scan within 6h rule out subarachnoid haemorrhage? Emerg Med J 2015;32:898-899 – also here
- Carley S & Wallmann P, Does a normal CT scan rule out a subarachnoid haemorrhage? Emerg Med J 2001;18:271-273 updated in 2008 here
- Sayer D, Bloom B et al. An Observational Study of 2,248 Patients Presenting With Headache, Suggestive of Subarachnoid Hemorrhage, Who Received Lumbar Punctures Following Normal Computed Tomography of the Head. Acad Emerg Med 2015;22:1267-73
- Centre for Evidence-based Purchasing website
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