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CT Angiography for detection of Subarachnoid Haemorrhage

Three Part Question

In [patients with clinical suspicion of subarachnoid haemorrhage and a normal plain CT] is [CT Angiography better than lumbar puncture] in [improving the detection of SAH]?

Clinical Scenario

A 41 year old man comes to the emergency department complaining of sudden onset of excruciating headache with photophobia and episodes of vomiting.He is afebrile and has a blood pressure of 180/110mmHg. You are worried he may have a subarachnoid haemorrhage and arrange an urgent CT scan.The radiologist kindly agrees to it and reports no haemorrhage seen on a non-contrast CT head scan. He is still symptomatic and gets admitted for a lumber puncture. You have heard about Computed Tomographic Angiography (CTA) as a primary diagnostic study for SAHs and wonder if this should have been the first step and if he should still go onto have a CTA instead of an LP?

Search Strategy

MEDLINE, EMBASE, CINAHL, Database of Abstracts of Reviews of Effects, ACP Journal Club and Cochrane Database of Systematic Reviews via OVID interface 01/08
SAH {Including Related Terms}.OR exp Subarachnoid Hemorrhage/ OR subarachnoid subarachnoid ] AND [exp Angiography/ or exp Tomography, X-Ray Computed/ or exp Cerebral Angiography/ or CT ] LIMIT to (english language and humans and "diagnosis (sensitivity)"

Search Outcome

795 papers were found in total, 2 of which was relevant.

Relevant Paper(s)

Author, date and country Patient group Study type (level of evidence) Outcomes Key results Study Weaknesses
Carstairs, S; Tanen, D; Duncan, T; et al
131 patients with symptoms suggestive of SAH presenting to one hospital over a two year period. Patients were excluded if there was a history of allergic reaction to contrast or iodine, there was a history of reactive lung disease or there was evidence of renal insufficiency. 106 out of 131 patients completed the study.All patients had a plain CT scan of the brain followed by CT angiography. Patients with a negative CT then underwent lumbar puncture. If the CT or LP was positive the CTA result was made available to the receiving neurosurgeon. Otherwise the CTA was reported within 24h. All non-contrast CTs and CTAs were then reread in a blinded fashion by a neurosurgeon and 2 neuroradiologists 3-24 months after the patients initial presentation. Patients followed up for 1y.Patients with SAH on non-contrast CT1 patient, CTA also positiveNot clear how long after the onset of pain the LP was performed. Xanthochromia was screened visually rather than using spectophotometry. Small numbers of positive patients.
Patients with negative CT but positive LP2 patients, both had positive CTA
Patients with negative CT and negative LP but positive CTA2 patients had aneurysms, 1 patient had normal DS angiogram
Nijjar S. Patel B. McGinn G. West M.
2007 Oct.
243 patients with spontaneous SAH confirmed by CT or LP presenting to 1 institution between January 2000 and June 2005.Retrospective review of data of 243 patients with spontaneous SAH confirmed by CT or LP went on to have CTAs. 201 had an +ve CTA showing acutely ruptured aneurysm. 42 remaining had further imaging i.e Cather Angiogram, MRI/MRA or DSA. Of these 33 were thought to have perimesencephalic haemorrhages, 6 had AV malformation and 1 had a PCA aneurysm. For a subgroup of 171 patients who had Neurosurgery, CTA correctly detected the ruptured aneurysm 170 patients.Detection of acutely ruptured aneurysm201/243 had a positive CTA scan for an acutely ruptured aneurysmThe study wasn't powered.The surgeons weren't blinded to the preoperative CTA findings. The study really only looks at the efficacy of CTA as a diagnostic tool for picking up acutely ruptured anuerysms as the cause of SAH as CTA looks at vascular anatomy.
Detection of acutely ruptured aneurysm when comparing preoperative CTA findings with intraoperative findings170/171 CTA correctly detected the ruptured aneurysm


DSA (Digital Subtraction Angiography) is considered the gold standard for diagnosis and analysis of intracranial aneurysm. However it is invasive, time consuming, costly, requires specialist expertise and has an overall complication rate of 1%.CT scans are an extremely useful investigation in patients with suspected SAH. However, it is possible to fail to identify small haemorrhages that are obscured by artifact or bone and the process does depend on the expertise of the radiologist. Lumbar puncture for a negative non-contrast head CT is mandatory to rule out subarachnoid haemorrhage in patients with a clinical suspicion of the same. The procedure is time-consuming, unpleasant for patients, can be technically difficult and is not without risks of complication. CT Angiography is rapidly being used worldwide as a primary diagnostic tool for SAH because of its quick, easy, non-invasive nature. Besides the information regarding the vascular anatomy needed for those patients who subsequently require Neurosurgery. Studies looking at pick up rate for CTA in detecting ruptured aneurysms, which is the commonest cause of operable SAHs, show promising results. Thus CT Angiography may be used to improve the diagnostic power of CT and reduce or remove the need for lumbar puncture. But the problem of performing CTAs is that incidental aneurysms that exist in around 2% of the population maybe picked up. However, in the clinical setting of a patient presenting with and lone, acute, severe headache, this might be relevant and a systematic review by Rinkel et al (1998) has suggests that aneurysms found during investigation of symptomatic patients have a relative risk of rupture of 8.3 compared with patients who have aneurysms found as an incidental finding.

Clinical Bottom Line

Only 2 small studies were found comparing CT angiography with non-contrast CT and lumbar puncture for diagnosis of a subarachnoid haemorrhage. Although the results of these studies are encouraging the management of suspected SAH cannot be altered on the basis of so few patients. It remains an interesting area for further research.

Level of Evidence

Level 3 - Small numbers of small studies or great heterogeneity or very different population.


  1. Carstairs, S; Tanen, D; Duncan, T; et al Computed Tomographic Angiography for the Evaluation of Aneurysmal Subarachnoid Hemorrhage Academic Emergency Medicine 2006; 13: 486-492
  2. Rinkel, G; Djibuti, M; Algra, A; van Gijn, J Prevalence and risk of rupture of intracranial aneurysms: a systematic review Stroke 1998; 29: 251-6
  3. Nijjar S. Patel B. McGinn G. West M. Computed tomographic angiography as the primary diagnostic study in spontaneous subarachnoid hemorrhage. Journal of Neuroimaging. 17(4):295-9, 2007 Oct.