Impact injuries can produce contusions and lacerations of the brain. Contusions are the most frequently encountered traumatic lesion of the brain. Contusions involve the crests of the gyri, but can extend into the white matter as wedge-
shaped lesions.9 Contusions are more severe when associated with skull fractures and are less severe in brains with diffuse axonal injury.1 Cortical contusions consist of areas of hemorrhage and necrosis that originate at the moment of impact. Occasionally, hemorrhage may be present without necrosis or necrosis with little or no hemorrhage.9 The contusion hemorrhages are located at or near the crest of a gyrus. They are usually multiple in number, streak-like, and densely arranged (Figure 6.6) though occasionally solitary. If the hemorrhage is close to the surface of the cortex, there may be overlying focal subarachnoid hemorrhage. If death is not immediate, the bleeding will continue. The amount of bleeding depends on the type (small artery, capillary, vein) and caliber of the vessel injured as well as if there is any adjacent necrosis. If necrosis is present, the contusions develop a wedge-shaped appearance with the base of the wedge at the crest and the point toward the white matter. If there is profuse bleeding, the areas of hemorrhage may expand into the white matter or subarachnoid space, essentially forming an area of intracerebral hemorrhage.
Contusion necrosis, just as contusion hemorrhage, tends to be in the cortex, at the crest of the gyri, sparing the cortex of the sulci.9 The area of necrosis is wedge shaped, with the base of the wedge at the cortical crest. The area of necrosis is usually delineated by accompanying hemorrhage, though the exact extent of the necrosis may not become clear for 10-12 h. If the necrosis is purely ischemic, without hemorrhage, the lesion becomes visible grossly 10-12 h after the injury as an area of swollen gelantinous parenchyma.9,10 Microscopically, it becomes visible at 3-5 h. Over time, contusions are reabsorbed with resultant golden-brown areas of gliosis.
Contusions are most often found in the frontal and temporal lobes of the brain. Less commonly, contusions are present on the lateral and ventral surfaces of the cerebral hemispheres. Contusions are not usually seen in infants. Rather, one sees lacerations involving the white matter, most commonly in the frontal and temporal lobes.9,11 Contusions may be absent in severe open fractures of the skull, with massive lacerations or even evisceration of the brain. Thus, in jumps and falls from great heights, massive lacerations of the brain are often unaccompanied by contusions.
1. Coup contusions. These occur at the site of impact and are due to the inbending bone snapping back (rebounding), inflicting tensile force injuries to the brain.12 Coup contusions are less common than the second type of contusion.
2. Contrecoup contusions occur in the brain at locations directly opposite to the point of impact (Figure 6.7).They are tensile force
Figure 6.7 Contrecoup contusions of temporal poles due to fall on back of head.
injuries due to the brain rebounding backward from the skull following impact.12 They are seen most commonly in the frontal poles, orbital gyri and temporal lobes. Contrecoup contusions are classically associated with falls. As their name indicates (contre being French for opposite), they develop opposite to the point of impact. Thus, an individual falling on the left side of the back of his head will have contrecoup contusions of the right frontal and temporal lobes. A fall onto the top of the head would result in contusions of the ventral surface of the cerebral hemispheres. Contrecoup contusions are virtually never seen in the occipital lobes, in spite of the frequent occurrence of individuals' falling on their faces. While usually, one has only contrecoup injuries following a fall, and no coup injuries, on occasion, an individual might have both coup and contrecoup contusions (Figure 6.8). When this occurs, the contrecoup contusions will always be much more extensive and severe than the coup contusions.
With blows to the head, if contusions are produced, they should be only coup contusions. Occasionally, however, the coup contusions are accompanied by contrecoup contusions. In these instances, the contrecoup contusions will be less extensive and less severe than the coup contusions. The usual teaching is that, with blows to the head, if there are no coup contusions, there are no contrecoup contusions. This may not be completely correct. The authors have seen rare cases in which individuals have been struck on the head and there were small contrecoup contusions, but no coup contusions. There is always the possibility in these cases that, after such individuals were struck, they collapsed, striking their heads and incurring a contrecoup contusion from the fall.
Figure 6.7 Contrecoup contusions of temporal poles due to fall on back of head.
3. Fracture contusions are associated with fractures of the skull. They do not necessarily bear any relation to the point of impact, as the fracture line can be some distance from this point.
4. Intermediary coup contusions are hemorrhagic contusions in the deep structures of the brain, for example, the white matter, basal ganglia, corpus callosum, brain stem, and along the line of impact — that is, between the location of the coup and contrecoup points. They are said to be seen only in falls.9 Intermediary contusions should not be mistaken for gliding contusions.
5. Gliding contusions are focal hemorrhages located in the cortex and underlying white matter of the dorsal surfaces of the cerebral hemispheres, principally in the frontal region. They are seen in falls and motor vehicle accidents.9,13 They are independent of the site and direction of impact and are often found in association with diffuse axonal injury.13
6. Herniation contusions are caused by impaction of the medial portion of the temporal lobes against the edge of the tentorium, or the cere-bellar tonsils against the foramen magnum. These are also independent of the site and direction of impact.
The most important fact to remember about contusions is the relation of coup and contrecoup contusions to falls and blows. A fall on the head will produce contrecoup contusions opposite the point of impact and no or very minor coup contusions at the point of impact. A blow to the head results in coup contusions and no or minor contrecoup contusions.
Intracerebral hematomas are discrete collections of blood within the cerebral parenchyma that are not in contact with the surface of the brain.14 They are principally located in the white matter of the fronto-temporal lobes and are caused by impact. They are said to differ from hemorrhagic intermediary coup contusions in that they are well demarcated, homogeneous collections of blood, in contrast to contusions that are blood and contused cerebral parenchyma. In the authors' opinion, this distinction is artifactual, and may just reflect a longer survival time by the intracerebral hematomas with continued bleeding. One of the most interesting aspects of intracerebral hematomas is that they can appear hours to days after the injury.1517 There have been numerous cases where a computerized tomography (CT) scan on admission has shown no intracerebral hematomas, but subsequent CT scans, taken several hours to several days after admission, revealed some. In some instances, their development has been followed by successive CT scans. Primary intracerebral hemorrhages involving the basal ganglia are found in approximately 10% of fatal head injuries. They are caused by deceleration/acceleration forces and are commonly found in association with diffuse axonal injury and gliding contusions.14 In 90% of the cases, the cause of the injury was either a motor vehicle accident or a fall. In the study by Adams et al. 43 of 63 patients had small (less than 20 mm) hematomas.13
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