Practice Rational Imaging

Investigating suspected subarachnoid haemorrhage in adults

BMJ 2011; 342 doi: (Published 06 May 2011) Cite this as: BMJ 2011;342:d2644
  1. S C Brown, neuroradiology fellow1,
  2. S Brew, consultant neuroradiologist1,
  3. J Madigan, consultant neuroradiologist2
  1. 1Radiology Department, National Hospital for Neurology and Neurosurgery, London WC1N 3BG, UK
  2. 2Neuroradiology Department, St George’s Hospital, London SW17 0QT
  1. Correspondence to: S Brown satsuki{at}
  • Accepted 21 March 2011

The authors discuss how to decide which imaging methods to use for investigating suspected subarachnoid haemorrhage in adults

Learning points

  • Most non-traumatic subarachnoid haemorrhage is caused by rupture of an intracranial aneurysm

  • Computed tomography is very sensitive in detecting acute subarachnoid haemorrhage but should not be relied on as the sole diagnostic investigation

  • Lumbar puncture should be done at least 12 hours, after the onset of symptoms

  • Computed tomography angiography is sensitive in detecting intracranial aneurysms, but catheter angiography is still the optimal investigation and may still be necessary

  • Magnetic resonance imaging may be more sensitive than computed tomography in detecting subacute haemorrhage and is good for delayed presentations

A 52 year old man presented to the emergency department with nausea and vomiting after sudden onset of headache two days previously that had radiated to his cervical spine. He had associated dizziness and had fallen twice. He had no medical history of note, but he smoked. On examination, he had blood pressure 160/88 mm Hg, Glasgow coma score 15, normal reactive pupils, and no other signs or focal neurology. Blood tests showed a mild neutrophilia and mildly raised C reactive protein and cholesterol concentration. His clotting and all other tests were normal.

What should be the next investigation?

The cause of headache needs to be established. In this case the history of sudden onset of headache raises the suspicion of intracranial haemorrhage. Alternative intracranial disease should still be considered because more benign conditions can also give a similar history. In less obvious presentations, as many as 50% of haemorrhages may be misdiagnosed, with failure to obtain the correct imaging accounting for 73% of these cases.1

Most (80-85%) primary subarachnoid haemorrhages are caused by ruptured saccular aneurysms. If these are untreated there is a 20-40% chance of rebleeding in the first three to four weeks,2 3 with …

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