Head injuries are classified by three aspects such as missile and nonmissile injury, primary and secondary brain damage, or focal and diffuse damage of brain. Emphasis, in the past, has tended to be placed on primary or immediate impact damage, and secondary damage or complications of the original injury. Recently there is a trend for clinicians and pathologists to classify brain damages as focal or diffuse. It is import-ant, however, to declare the cause or the manner of death because of the various clinical course of patients with head trauma and confused findings of injuries by long hospitalization in the developed intensive care unit or sustained brain death. Examiners must be a expert to identify the secondary changes after primary brain damage.
The primary injuries of brain are concussion, contusion, diffuse axonal injuries, multiple small hemorrhages in the brain(diffuse vascular injury of brain), and unusually tear in the brain stem(at the pontomedullary junction) cranial nerves, pituitary stalk, and vessels. The secondary damage are intracranial hematoma by disruption of vessels, cerebral edema and brain swelling, brain damage secondary to raised intracranial pressure, ischemic brain damage, infection, and fat embolism.
All of these primary or secondary damages of brain have time-sequential macroscopic and histologic changes and they may be a diffuse or focal changes. The diffuse changes are usually brain edema or swelling, increased intracranial pressure, and the midline shifting or herniation of the brain with various type. These changes make the other complicated brain damages such as herniation contusion, discreted petechial hemorrhage, and/or hypoxic damages. The focal changes are, in early stages after trauma, destruction of tissue, inflammatory reaction by neutrophils and macrophages, hemorrhage. As the time is lapsed, proliferation of capillaries and fibroblasts make localized scar or fluid-filled cyst. Various degree of gliosis are noted at the periphery of the lesion. To identify these time-sequential changes which are focal or diffuse, proper fixation of total brain, multiple dissection, and special stains are necessary.
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