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Intra-axial hemorrhages are potentially deadly because they can increase intracranial pressure and crush delicate brain tissue or reduce its blood supply, causing ischemia. 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 hemmorrages: intraparenchymal hemorrhage and intraventricular hemorrhages.
It is particularly common in infants, especially premature infants or those of very low birth weight (Annibale and Hill, 2003). Most intraventricular hemorrhages occur in the first 72 hours after birth (Annibale and Hill, 2003).
Intraventricular hemorrhage is rare in adults (Mayfrank et al., 1997) and requires a great deal of force to cause. Thus the hemorrhage usually does not occur without an extensive associated damage, and so the outcome is rarely good (Dawodu, 2004; Vinas and Pilistis, 2004). Brain contusions and subarachnoid hemorrhages are commonly associated with IVH (LeRoux et al., 1992). The bleeding can involve the middle communicating artery or the posterior communicating artery. In both adults and infants, IVH can cause dangerous increases in intracranial pressure, damage to the brain tissue, and hydrocephalus (Mayfrank et al., 1997; Annibale and Hill, 2003).
Intraparenchymal hemorrhage, or intracerebral hemorrhage, another type of intra-axial bleeding, can be caused by brain trauma, or it can occur spontaneously in hemorrhagic stroke. 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% (Sanders and McKenna, 2001).
More common in adults than in children, intraparenchymal bleeds are usually due to penetrating trauma, but can also be due to depressed skull fractures, acceleration-deceleration trauma (McCaffrey, 2001; Orlando Regional Healthcare, 2004; Shepherd, 2004), rupture of an aneurysm or arteriovenous malformation (AVM), and bleeding within a tumor.
The risk of death from an intraparenchymal bleed is especially high when the injury occurs in the brain stem (Sanders and McKenna, 2001). Intraparenchymal bleeds within the medulla are almost always fatal, because they cause damage to cranial nerve X, the vagus nerve, which plays an important role in blood circulation and breathing (McCaffrey, 2001). This kind of hemorrhage can also occur in the cortex or subcortical areas, usually in the frontal or temporal lobes when due to head injury, and sometimes in the cerebellum (McCaffrey, 2001; Graham and Gennareli, 2000).
Patients with intraparenchymal bleeds have symptoms that correspond to the functions controlled by the area of the brain that is damaged by the bleed (Vinas and Pilistis, 2004). Other symptoms include those that indicate a rise in intracranial pressure due to a large mass putting pressure on the brain (Vinas and Pilistis, 2004).
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.
Intracerebral hematomas that occur slowly over the course of hours or days are called delayed intracerebral hematomas. These can occur in brain contusions or in areas in which no abnormality was found in CT scans (Vinas and Pilistis, 2004). These patients appear normal after trauma and then suddenly their condition deteriorates (Vinas and Pilistis, 2004).
An intracerebral hemorrhage continuous with subdural hemorrhage is called a burst lobe.
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