| Primary CT angiography (CTA) || |
Some have suggested use of CTA as the initial investigation . However, it does not lead to an improvement in the diagnostic yield of SAH over standard work up .
| Primary MR angiography (MRA) || |
Detection of acute SAH by MRA has a sensitivity of 94% within 4 days. Sensitivity may increase as time passes making this a useful tool for the investigation of patients with a delayed (>2 weeks) presentation .
| Lumbar puncture first || |
An LP first strategy has been postulated in patients with and no clinical evidence of raised intracranial pressure . However, CT first may point to SAH or another significant diagnosis without recourse to an invasive LP.