Final answer:
Subarachnoid hemorrhage is bleeding into the subarachnoid space, detectable by CT scanning or lumbar puncture, that can cause significant brain damage by increasing intracranial pressure.
Step-by-step explanation:
The subarachnoid space is an area between the arachnoid membrane and the pia mater surrounding the brain and spinal cord, containing the cerebrospinal fluid (CSF). Subarachnoid hemorrhage (SAH) is a type of stroke caused by bleeding into this space, leading to a range of neurological complications. When a SAH occurs, blood mixes with the CSF in the subarachnoid space, which can be detected by a CT scan or a lumbar puncture testing CSF for blood components. This bleeding can increase intracranial pressure, causing damage to the brain tissues and potentially disrupting cerebral blood flow. The median aperture is a connection from the fourth ventricle to the subarachnoid space allowing CSF to circulate, and in the context of SAH, it could potentially be involved in the distribution of the hemorrhage.