A subarachnoid haemorrhage (SAH) occurs when there is bleeding around the brain into the subarachnoid space. This is a space between two of the protective layers which surround the brain. These are the pia mater, which covers the brain directly, and the arachnoid mater, which is separated from the pia mater by a space filled with fluid. This fluid, the cerebrospinal fluid, is there to cushion and protect the brain from injury.
This is a companion discussion topic for the original article at https://patient.info/brain-nerves/subarachnoid-haemorrhage-leaflet