A cerebral hemorrhage is an intra-axial hemorrhage; that is, it occurs within the brain tissue rather than outside of it. The other category of intracranial hemorrhage is extra-axial hemorrhage, such as epidural, subdural, and subarachnoid hematomas, which all occur within the skull but outside of the brain tissue. There are two main kinds of intra-axial hemorrhages: intraparenchymal hemorrhage and intraventricular hemorrhages. As with other types of hemorrhages within the skull, intraparenchymal bleeds are a serious medical emergency because they can increase intracranial pressure. The mortality rate for intraparenchymal bleeds is over 40%.
Intracerebral bleeds are the second most common cause of stroke, accounting for 30–60% of hospital admissions for stroke. High blood pressure raises the risk of spontaneous intracerebral hemorrhage by two to six times. More common in adults than in children, intraparenchymal bleeds due to trauma are usually due to penetrating head trauma, but can also be due to depressed skull fractures, acceleration-deceleration trauma, rupture of an aneurysm or arteriovenous malformation (AVM), and bleeding within a tumor. A very small proportion is due to cerebral venous sinus thrombosis.
Intraparenchymal hemorrhage can be recognized on CT scans because blood appears brighter than other tissue and is separated from the inner table of the skull by brain tissue. The tissue surrounding a bleed is often less dense than the rest of the brain due to edema, and therefore shows up lighter on the CT scan.
For spontaneous ICH seen on CT scan, the death rate (mortality) is 34–50% by 30 days after the insult.