Basic Overview
A primary traumatic brain injury is a direct injury, the initial brain trauma or mechanical force that injures the brain, causing direct primary damage. Within the brain, neurons, glial cells, and blood vessels may be crushed.
A secondary traumatic brain injury is the range of consequences or complications that can occur as a result of the primary TBI, and can occur any time between minutes to days after the injury. This involves effects that may occur from cerebral edema, cerebral vasospasm, hemorrhage, hematoma, infection, and ischemia. During a primary injury, lacerations or compression of brain tissue may occur from a piece of broken bone, a foreign object, or a rupture or compression of cerebral blood vessels. Even though the skull protects the brain, an abnormal force on the head may cause the brain to rotate or move within the skull, potentially damaging the brain tissue. A shearing injury may occur as the lobes of the brain move against each other.
Any damage or trauma to the brain causes loss of function, depending on the area of the brain that was injured and its function. Bleeding and damaged cells in the injured area cause inflammation and ischemia, increased intracranial pressure (ICP), vasospasm, loss of function. As the inflammation and bleeding decrease, some neurons may begin to heal and regain function. Necrosis (cell and tissue death) occurs, and is replaced by the build up of scar tissue. Secondary injury occurs from the additional effects of the primary injury. Ruptured blood vessels cause blood to collect, forming a hematoma. Hematomas may occur instantly, or up to days after the injury. Bleeding increases pressure on the nearby tissue and generally increases ICP. A solid mass occurs when blood partially coagulates. Blood cells undergo hemolysis (breakdown) when blood accumulates slowly. When cells breakdown, osmotic pressure increases and draws more water, which increases the size and pressure of the cell mass, therefore increasing ICP. If the cell mass is left untreated, a herniation may occur. Bleeding in the brain may also cause a vasospasm, which increases ischemia, and also damages neurons. Infection, hypoxia, and anoxia may also occur, increasing ischemia in the brain. |
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