Any brain hemorrhage can potentially be life-threatening. The location and severity of a hemorrhage are two important factors dictating survival and complications. To understand the types of brain hemorrhages and their consequences, one must understand some basic ideas about the brain and its vasculature.
The brain requires a constant blood supply to sustain life. A lack of blood flow into the brain tissue, and consequently oxygen, can result in an infarct (cerebral infarct is also known as a stroke), an area of dead tissue. A number of blood vessels of varying sizes feed the brain, keeping both it and the body it controls alive. Because of the brain’s important role, it is protected within the cranium, a confining cavity of limited space. As long as the brain does not swell or the cavity accumulate additional fluid, the brain is cushioned and safe within this space.
The brain tissue is surrounded by thin tissue. Meninges are the membranes of the central nervous system, including those of the brain. These layers of tissue separate the brain tissue from the skull bone. The space between the inner membrane and the brain where cerebrospinal fluid circulates is the subarachnoid space. The outer membrane is called the dura mater. Anything between the dura mater and bone is epidural; between the dura mater and inner membranes is subdural.
When a blood vessel feeding the brain and its tissues ruptures, it hemorrhages (leaks) into the surrounding tissue. The four types of brain hemorrhage are divided based on the affected tissue: intracerebal (inside the brain), subarachnoid (between the brain and meninges), subdural (between the meninges), and epidural (between the dura mater and skull).
Intracerebral hemorrhages are usually caused by hypertension, which wears away and damages susceptible blood vessels in various tissues, including the brain, over time. This pathology includes aneurysms. This type of bleeding accounts for 8-13% of all strokes (Medscape). The blood may displace the brain parenchyma, causing increased pressure within the brain, in addition to an infarct and potentially extend bleeding into the ventricles. More than 20,000 people die from intracerebral hemorrhages each year in the U.S.
Subarachnoid hemorrhages are usually caused by aneurysms (80% of all cases), particularly berry aneurysms (also known as intracerebral saccular aneurysms). This bleeding accounts for 6-8% of all strokes (Medscape). The blood accumulation (hematoma) can increase pressure in the brain cavity, resulting in seizures and motor loss. Most people do not survive this form of hemorrhage past 1 month.
A subdural hemorrhage causes a subdural hematoma, an accumulation of blood between the membranes around the brain. This type of bleed is usually caused by a head injury (traumatic hemorrhage) that breaks or stretches the veins on the brain surface. The bleeding occurs quickly, compressing the brain tissue. The pressure within the cranium is sometimes reduced by drilling a hole in the skull drain the hematoma, or removing a portion of the bone (craniotomy) until the pressure subsides. Brain herniation of the brain stem through the bottom of the skull is a possible fatal complication.
An epidural hemorrhage causes an epidural hematoma and typically occurs when a skull fracture damages an underlying blood vessel. These bleeds do not always increase the pressure in the brain, but if left untreated they can lead to more serious complications. This is the least common type of brain hemorrhage.