But if an aneurysm grows, the wall becomes weaker. Aneurysms frequently cause no symptoms, but when they enlarge can produce headache, double vision, loss of vision, facial numbness, enlarged pupil size or drooping eyelid. Aneurysms can be surgically repaired, depending on their location. Hemorrhage causes 17 percent of strokes. Ten percent of these are intracerebral, and seven percent are subarachnoid.
Brains cells begin dying within a few minutes of a stroke's onset.
Called the ischemic cascade, this process is a series of chemical mechanisms which includes release of excitatory amino acid neurotransmitters, particularly glutamate. This triggers an increase in concentration of calcium within cells. This results in activation of messengers and genes that set in motion a series of events that results in cell death, as well as a spreading of the process to adjacent cells. The ischemic cascade kills brain cells quickly in the stroke's core area and endangers cells more slowly in a larger surrounding area of brain tissue for which blood supply is compromised but not completely cut off. Prompt medical treatment may save brain cells in this surrounding area, called the penumbra.