Population Covered By The Guidance
This pathway provides guidance on the imaging of adult patients with acute severe headache.
Lead Researcher: Abhishta Bhandari
Experts & Contributors: Marc Agzarian, Kevin Chu, Richard Geraghty, Bronwyn Peirce, Con Phatouros
Date reviewed: August 2023
Date Published: June 2025
Subarachnoid Haemorrhage
Subarachnoid Haemorrhage
Left Posterior Communicating Cerebral Artery Aneurysm
Ruptured Berry Aneurysm
Subarachnoid Haemorrhage
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CT is the initial investigation of choice in the assessment of severe sudden onset headache, i.e. Thunderclap Headache.
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SAH may present as three patterns. Diffuse haemorrhage where the blood is centred around suprasellar or central basal cisterns extending into the periphery, centred around the perimesencephalic or low basal cisterns (known as idiopathic mesencephalic haemorrhage) and the third being on the cerebral convexities.
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There are other causes of SAH such as intimal dissection, Posterior Reversible Encephalopathy Syndrome, however intradural aneurysms are the most common.
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A normal CT may rule-out SAH when performed within 6 hours of ictus on 3rd generation CT scanners, and imaging interpreted ideally by a neuroradiologist.
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Lumbar Puncture is required after a negative CT if performed 6 or more hours after headache onset.
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Lumbar Puncture should be performed 12 hours after the onset of symptoms.
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CT Angiography (CTA) may be used in the investigation of cerebral aneurysms. If available digital subtraction angiography is gold standard in the exclusion of cerebral vascular abnormalities. A single-phase mixed CTA/CTV may be beneficial to give an idea of arterial and venous latency.
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Treatment of aneurysms can be achieved through interventional radiology or neurosurgery (clipping).
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CTA may reveal an alternative cause of Thunderclap Headache such as reversible vasoconstriction syndrome (RVCS), cervicocranial dissection or AVM bleed.
References are graded from Level I to V according to the Oxford Centre for Evidence-Based Medicine, Levels of Evidence.Download the document
References
- Edlow JA, Panagos PD, Godwin SA, Thomas TL, Decker WW. 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;52(4):407-36. (Review article).
- Perry JJ, Stiell IG, Sivilotti ML, Bullard MJ, Emond M, Symington C, et al. Sensitivity of computed tomography performed within six hours of onset of headache for diagnosis of subarachnoid haemorrhage: prospective cohort study. BMJ (Clinical research ed). 2011;343:d4277. (Level II Evidence).
- Sayer D, Bloom B, Fernando K, Jones S, Benton S, Dev S, 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. Academic Emergency Medicine. 2015;22(11):1267-73 (Level II evidence).
- Blok KM, Rinkel GJE, Majoie C, Hendrikse J, Braaksma M, Tijssen CC, et al. CT within 6 hours of headache onset to rule out subarachnoid hemorrhage in nonacademic hospitals. Neurology. 2015;84(19):1927-32 (Level III evidence).
- Mark DG, Kene MV, Udaltsova N, Vinson DR, Ballard DW. Sensitivity of a Clinical Decision Rule and Early Computed Tomography in Aneurysmal Subarachnoid Hemorrhage. West J Emerg Med. 2015;16(5):671-6 (Level II evidence).
- Dubosh NM, Bellolio MF, Rabinstein AA, Edlow JA. Sensitivity of early brain computed tomography to exclude aneurysmal subarachnoid hemorrhage: a systematic review and meta-analysis. Stroke; a journal of cerebral circulation. 2016;47(3):750-5 (Level I evidence).
- April MD, Keim SM, Koyfman A, Meurer WJ, Schmitzberger F, Long B. IS A LUMBAR PUNCTURE REQUIRED TO RULE OUT ATRAUMATIC SUBARACHNOID HEMORRHAGE IN EMERGENCY DEPARTMENT PATIENTS WITH HEADACHE AND NORMAL BRAIN COMPUTED TOMOGRAPHY MORE THAN SIX HOURS AFTER SYMPTOM ONSET? Journal of Emergency Medicine. 2021;61(1):97-104 (Review Article).
- Perry JJ, Sivilotti ML, Émond M, Hohl CM, Khan M, Lesiuk H, et al. Prospective implementation of the Ottawa subarachnoid hemorrhage rule and 6-hour computed tomography rule. Stroke; a journal of cerebral circulation. 2020;51(2):424-30 (Level II evidence).
- Khatri GD, Sarikaya B, Cross NM, Medverd JR. The role of imaging in the management of non-traumatic subarachnoid hemorrhage: a practical review. Emergency Radiology. 2021;28(4):797-808. (Review article).
- Backes D, Rinkel GJ, Kemperman H, Linn FH, Vergouwen MD. Time-dependent test characteristics of head computed tomography in patients suspected of nontraumatic subarachnoid hemorrhage. Stroke; a journal of cerebral circulation. 2012;43(8):2115-9. (Level III evidence).
- Philipp LR, McCracken DJ, McCracken CE, Halani SH, Lovasik BP, Salehani AA, et al. Comparison Between CTA and Digital Subtraction Angiography in the Diagnosis of Ruptured Aneurysms. Neurosurgery. 2017;80(5):769-77 (Level II evidence).
- Lu L, Zhang LJ, Poon CS, Wu SY, Zhou CS, Luo S, et al. Digital subtraction CT angiography for detection of intracranial aneurysms: comparison with three-dimensional digital subtraction angiography. Radiology. 2012;262(2):605-12. (Level II Evidence).
- Guo W, He X-Y, Li X-F, Qian D-X, Yan J-Q, Bu D-L, et al. Meta-analysis of diagnostic significance of sixty-four-row multi-section computed tomography angiography and three-dimensional digital subtraction angiography in patients with cerebral artery aneurysm. Journal of the neurological sciences. 2014;346(1):197-203 (Level I evidence).
- 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? Acad Emerg Med. 2010;17(4):444-51 (Review Article).
- Mayberg MR, Batjer HH, Dacey R, Diringer M, Haley EC, Heros RC, et al. Guidelines for the management of aneurysmal subarachnoid hemorrhage. A statement for healthcare professionals from a special writing group of the Stroke Council, American Heart Association. Stroke; a journal of cerebral circulation. 1994;25(11):2315-28. (Review article).
- White PM, Wardlaw JM, Easton V. Can noninvasive imaging accurately depict intracranial aneurysms? A systematic review. Radiology. 2000;217(2):361-70. (Level II Evidence).
- Cieściński J, Serafin Z, Strześniewski P, Lasek W, Beuth W. DSA volumetric 3D reconstructions of intracranial aneurysms: A pictorial essay. Pol J Radiol. 2012;77(2):47-53 (Review article).
- Dalyai R, Chalouhi N, Theofanis T, Jabbour PM, Dumont AS, Gonzalez LF, et al. Subarachnoid hemorrhage with negative initial catheter angiography: a review of 254 cases evaluating patient clinical outcome and efficacy of short- and long-term repeat angiography. Neurosurgery. 2013;72(4):646-52; discussion 51-2. (Level II Evidence).
- Lindgren A, Vergouwen MDI, van der Schaaf I, Algra A, Wermer M, Clarke MJ, et al. Endovascular coiling versus neurosurgical clipping for people with aneurysmal subarachnoid haemorrhage. Cochrane Database of Systematic Reviews. 2018(8):(Level I evidence).
- Connolly Jr ES, Rabinstein AA, Carhuapoma JR, Derdeyn CP, Dion J, Higashida RT, et al. Guidelines for the management of aneurysmal subarachnoid hemorrhage: a guideline for healthcare professionals from the American Heart Association/American Stroke Association. Stroke; a journal of cerebral circulation. 2012;43(6):1711-37. (Review article).
- National guidelines for analysis of cerebrospinal fluid for bilirubin in suspected subarachnoid haemorrhage. Ann Clin Biochem. 2003;40(Pt 5):481-8 (Guideline).
- Chu K, Hann A, Greenslade J, Williams J, Brown A. Spectrophotometry or Visual Inspection to Most Reliably Detect Xanthochromia in Subarachnoid Hemorrhage: Systematic Review. Annals of emergency medicine. 2014;64(3):256-64 (Level II evidence).
- Chu KH, Bishop RO, Brown AF. Spectrophotometry, not visual inspection for the detection of xanthochromia in suspected subarachnoid haemorrhage: A debate. Emerg Med Australas. 2015;27(3):267-72 (Review article).
- Cody R, Mohsenifard M, Yip G, Aldridge E, Bridge F, Datta M, et al. Worth the risk? Contemporary indications, yield and complications of lumbar punctures in a metropolitan Australian health service. Internal Medicine Journal. 2023;53(8):1332-8. (Level III evidence).
- Lummel N, Schoepf V, Burke M, Brueckmann H, Linn J. 3D fluid-attenuated inversion recovery imaging: reduced CSF artifacts and enhanced sensitivity and specificity for subarachnoid hemorrhage. AJNR Am J Neuroradiol. 2011;32(11):2054-60 (Level III evidence).
- Naganawa S. The Technical and Clinical Features of 3D-FLAIR in Neuroimaging. Magn Reson Med Sci. 2015;14(2):93-106 (Review article).
- Chen X, Liu Y, Tong H, Dong Y, Ma D, Xu L, et al. Meta-analysis of computed tomography angiography versus magnetic resonance angiography for intracranial aneurysm. Medicine (Baltimore). 2018;97(20):e10771 (Level I evidence).
- Cornelissen BM, Leemans EL, Slump CH, Marquering HA, Majoie CB, van den Berg R. Vessel wall enhancement of intracranial aneurysms: fact or artifact? Neurosurgical Focus. 2019;47(1):E18 (Review article).
- Edjlali M, Gentric J-C, Régent-Rodriguez C, Trystram D, Hassen WB, Lion S, et al. Does aneurysmal wall enhancement on vessel wall MRI help to distinguish stable from unstable intracranial aneurysms? Stroke; a journal of cerebral circulation. 2014;45(12):3704-6 (Level II evidence).
Pathway User Guide
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The relative radiation level (RRL) of each imaging investigation is displayed in the pop up box.
| SYMBOL | RRL | EFFECTIVE DOSE RANGE |
|---|---|---|
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None | 0 |
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Minimal | < 1 millisieverts |
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Low | 1-5 mSv |
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Medium | 5-10 mSv |
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High | >10 mSv |
Disclaimer
Status Of Recommendations Each pathway is designed to assist clinicians in situations when faced with a large array of possible diagnostic tests and examinations. However, it is recognised that diagnostic practice may differ from a particular pathway depending on local availability of equipment and expertise, as well as the experience of individual clinicians. Therefore each pathway is neither a rigid set of rules, nor a substitute for clinical assessment, and individual patient circumstances should always be considered.
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Computed Tomography (CT)/Computed Tomography Angiography (CTA)
Initial investigation of choice for those who present with thunderclap headache. CTA can be used for the detection of aneurysms greater than 3-5mm depending on CT technology. A mixed phase CTA/CTV can also be beneficial. It can also be used to rule out differentials such as reversible vasoconstriction syndrome, cervicocranial dissection thus is recommended to be performed at the same time as CT.
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Initial imaging modality of choice for investigation of thunderclap headache.
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The diagnostic test accuracy of CT depends on the timing as red blood cells in the CSF degrade over time.
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In a large multi-centre prospective cohort study, 953 patients who were neurologically intact and imaged within 6 hours of headache onset CT (“six hour rule”) had a sensitivity of 100 percent and specificity of 100 percent. Overall for 3132 patients enrolled the sensitivity of CT for SAH was 92.9 percent and specificity 100 percent. Following this study there have been isolated reports of false negative SAH with one study involving 2248 patients demonstrating that one patient that had a SAH despite normal CT scan within 6 hours . Another study reporting on 760 patients demonstrated a NPV of 99.99% with one false negative SAH. Mark et al. reported that 20% of aneurysmal subarachnoid haemorrhages were missed in their case-control study of 55 patients . Nonetheless a 2016 systematic review of 8907 patients demonstrated a sensitivity of 98.7% and specificity of 99.9% in detecting SAH in 6 hours . Given the discomfort and risks associated with LP, there may be benefit from a shared decision approach between the patient and the clinician regarding foregoing a LP if the CT is negative and within 6 hours.
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The Ottawa subarachnoid rule can be used to identify those that are high/low risk of haemorrhage if clinical gestalt is insufficient.
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This rule states imaging is indicated in those that meet the following criteria: Age ≥40, neck pain/stiffness, witnessed LOC, onset with exertion, instantly peaking/thunderclap headache, limited neck flexion. Inclusion criteria: alert, adult with severe non-traumatic headache reaching maximal intensity in an hour. Exclusion criteria: new neurological deficits, prior history of aneurysm, subarachnoid haematoma, brain tumour or history of recurrent headaches (≥3 episodes in ≥6 months)
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The Ottawa subarachnoid haemorrhage rule has also been shown to be similar to the 6 hour rule in a large prospective study.
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CT provides an estimate of the extent of the haemorrhage and allows recognition of midline shift and hydrocephalus.
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Limitations:
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Loss of sensitivity with increasing time between onset of headache and neuroimaging.
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Possible false negative results for blood with a haematocrit of less than 30%
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Given the broad differentials for thunderclap headache it is recommended to perform a CTA at the same time as the CT.
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CTA has largely replaced the need for bedside LP or image guided LP in uncertain cases.
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CTA is a non-invasive imaging modality for demonstrating vascular anatomy, with greater than 90% sensitivity for depiction of cerebral aneurysms greater than 5mm in size.
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CTA should be from aortic arch to vertex with high contrast flow rates as reasonably achievable.
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In a 2012 study on digital subtraction CTA had a sensitivity of 97.8 percent and specificity of 88.7 percent for the detection of intracranial aneurysms when compared against 3D DSA. A single centre retrospective cohort study of 643 patients found that CTA has low sensitivity (55.7%) for aneurysms <5mm, however they did not report on the CT quality . Newer technology such as 64 multi-section CT scanners are more beneficial.
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May pick up differential diagnosis of thunderclap headache such as those caused by reversible vasoconstriction syndrome (RVCS). Signs of RVCS on CTA include narrowing of vessels (string and beads appearance) however may be evident only until 7 days post ictus. May demonstrate cervicocranial dissection or arteriovenous malformations.
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It has been suggested that CT followed by CTA can replace CT/LP thus can be used in situations where LP is not able to be done or patient preference is to not perform the LP.
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Limitations of CTA:
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Limited evaluation of collateral pathways and cerebral vasculature imaging over time
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Inferior spatial resolution compared to DSA
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Does not offer therapeutic opportunity.
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Can find incidental aneurysms in 2% of the population, thus it will be unknown if these cases are the bleeding aneurysm or incidental.
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Increased radiation dose
Digital Subtraction Angiography (DSA)
Gold standard for the detection of ruptured intracranial aneurysms and depicting the cerebral vascular anatomy.
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Digital Subtraction Angiography is a fluoroscopic technique whereby contrast is injected into a blood vessel. A pre-contrast and post-contrast image are taken and once “subtraction” between the two is performed the contrast filled vessel remains in the image.
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It is considered 'gold standard' for the detection of ruptured intracranial aneurysms and depicting cerebral vascular anatomy.
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Highly sensitive for detection of small aneurysms, small arteriovenous malformations and dural vascular malformations.
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3D “CT like” acquisitions can be performed to increase the sensitivity for the detection of subtle aneurysms (such as “blood blister” aneurysms).
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SAH is found to have no vascular origin with initial catheter angiography in approximately 15 percent of cases.
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Advantages:
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Offers the opportunity for treatment of aneurysms commonly through coiling, stents, flow diverters and balloons.
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Better outcomes with endovascular coiling compared to neurosurgical clipping.
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Disadvantages:
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Invasive procedure with associated complications
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Not readily available in the ED setting
Magnetic Resonance Imaging (MRI)
Can be used when CTA is contraindicated. 3D T2 FLAIR sequences can detect subarachnoid blood.
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MRI can be used to detect small amounts of subarachnoid blood using a 3D T2 FLAIR sequence. This is because small amounts of subarachnoid blood can cause non-suppression of the CSF, resulting in hyperintense blood visualised in the subarachnoid space. This is more sensitive than traditional T2* sequences that image blood products.
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MRI technique must include susceptibility sequences for blood products. A repeat MRI/MRA is indicated in 6-8 weeks to rule out progressive vasculitis.
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MRA has a similar high specificity and sensitivity for intracranial aneurysms thus may be a viable alternative to CTA in cases where this is contraindicated.
Emerging literature demonstrates that vessel wall enhancement may be a means of detecting impending aneurysmal rupture, and can be used in situations where it is uncertain which aneurysms has ruptured.