About 20% of all strokes are hemorrhagic. Of these, about half involve rupture of either aneurysms (abnormal outpouchings of large arteries) which initially bleed into the subarachnoid space or of arteriovenous malformations which are often located within the brain and therefore tend to bleed into the brain itself.  Both of these pathologies are thought to be the consequence of developmental abnormalities and are characterized by thinned vascular walls.

Aneurysms commonly form at the branch points of large intracranial arteries. Sometimes aneurysms reveal themselves by compressing neighboring structures and producing neurologic symptoms.  In addition, aneurysms or, sometimes, arteriovenous malformations may bleed a little, producing sudden unexplained headache, seizure, or other neurological disturbance prior to a more massive rupture. Such warnings may make it possible to identify the problem and to initiate surgical intervention if it is indicated.

This patient had a rupture of a small artery that penetrates deep into the forebrain to supply the basal ganglia.  He rapidly lapsed into a coma and died within hours.  Can you see areas that are filled with blood?  Notice that blood fills the ventricles of the brain as well as its gray and white matter.

Here is an arteriogram taken shortly after the carotid artery was injected with a radioopaque dye.  Can you see a large aneurysm? This aneurysm was later successfully clipped.

This is the unfixed brain of a patient who collapsed and died shortly after rupture of an aneurysm.  There is blood on the surface of the brain, which is contained within the subarachnoid space. Notice how the blood follows the cortical sulci.