If aSAH is diagnosed, the next
step is to locate the aneurysm and visualise
its shape. This will help guide decisions about
how to treat the aneurysm. Cerebral digital
subtraction angiography is commonly used
for this purpose. CT angiography (CT head
with contrast medium to visualise the cerebral
arteries) is another option, but it is not clear
whether this scan is sensitive enough to identify
very small aneurysms of less than 3mm
(Connolly et al 2012).