ABSTRACT
The arachnoid mater is the middle of the three meninges that surround the brain and spinal cord. It is attached to the dura (the outermost layer), but is separated from the innermost pia mater by the subarachnoid space, which contains cerebrospinal fluid (CSF). A subarachnoid haemorrhage (SAH) is defined as bleeding into this subarachnoid space. SAH is classified into traumatic or non-traumatic. Causes of non-traumatic SAH are rupture of intracranial aneurysm, accounting for 85% of spontaneous bleeds, and ten per cent of cases are non-aneurysmal and no cause is found. The most important determinant of outcome following SAH is the neurological condition at the time of admission. In contrast to subarachnoid haemorrhage, an intracerebral haemorrhage is caused by bleeding into the brain tissue itself. Non-traumatic cases may be caused by systemic hypertension, damaged blood vessels or congenital abnormalities, such as an arteriovenous malformation (AVM).
