Lacerating and penetrating wounds of the brain are most commonly due to fractures of the skull. Injuries to the brain by fragments of bone may occur in the presence of an intact scalp. Lacerations of the corpus callosum or septum pellucidum may occur due to blunt trauma to the head without any fractures of the skull (Figure 6.9). This latter phenomenon appears to be more common in younger individuals, who have more elastic bone. Lacerations of the brain may show little and even no bleeding around them. This
is apparently due to vasospasm of arteries, which can maintain a bloodless field for as long as one hour.9
With severe hyperextension of the head, such as occurs in motor vehicle accidents when individuals are thrown forward, their faces impacting the windshield or visor region, and their bodies continuing forward, there may be injury to the brain stem. This injury can range from tears and hemorrhages in the pyramids at the junction of the medulla oblongata and pons to avulsion of the brain stem at the pontomedullary junction (Figure 6.10).18 These injuries are commonly associated with fractures of the base of the skull and fractures of the upper cervical vertebrae. Subarachnoid hemorrhage is usually present over the brain stem.
In contrast to adults, impact trauma in infants (5 months or younger) does not produce cortical contusions, but rather, grossly visible lacerations in the cerebral white matter and microscopic lacerations of the outermost layer of the cortex, which run parallel to the surface of the brain.11 The lacerations of the cerebral white matter occasionally extend through the cortex or wall of the ventricles or both. They are most often present in the orbital and temporal lobes and in the first and second frontal convolutions. Minimal bleeding is present in the lacerations and sometimes in the adjacent white matter. The earliest cellular reaction is seen at 36 h and is obvious by 72 h. Unlike contusions in the adult brain, the location and distribution of the white matter lacerations cannot be used to indicate whether the injuries were from a fall or a blow.
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