Trauma

10.1055/b-0034-102659

Trauma

A few definitions are in order to introduce the topic of brain trauma. A cortical contusion is simply a bruise of the brain′s surface. The inferofrontal and anteroinferior temporal portions of these two lobes of the brain are particularly vulnerable ( Fig. 1.47 ). The term “coup” is used to reference an injury that lies directly beneath the area of impact. The term “contrecoup” is used for an injury that occurs remote from the site of impact, along a direct line but opposite to this site, caused by acceleration effects. Imaging of acute head injury is the province of CT. Acute intracranial hemorrhage and bone fractures are well seen and evaluated ( Fig. 1.48 ).

**Fig. 1.47** Contusion, parenchymal. High velocity contusion injuries are illustrated in two different patients, showing characteristic areas of the brain involved. In the first, there is a large hemorrhagic contusion, with the area of hemorrhage surrounded by low density (edema), overlying the right petrous apex. Also noted is a small acute epidural hematoma on the left. In the second patient, low-density regions are noted in the low frontal lobes bilaterally, corresponding to nonhemorrhagic parenchymal contusions.

**Fig. 1.48** Skull fracture. A nondisplaced left parietal skull fracture (*asterisk*) is seen on this axial CT image reconstructed with a bone algorithm. It is anterior to the lambdoid suture. The insert, a magnification of a portion of the image immediately superior to that displayed, reveals two small foci of pneumocephalus (*arrows*), an important clue to the radiologist to search for a nearby skull fracture in the setting of trauma. Note also the extracranial soft tissue swelling adjacent to the fracture.

Parenchymal Injury

Diffuse axonal injury (DAI) and cortical contusion are the two most common findings in the setting of trauma with a closed head injury. Subcortical gray matter injury also occurs, but much less frequently. DAI occurs due to shear-strain forces with rapid deceleration. There are three common locations (given in order from the most to the least common, which also parallels the degree of severity of the injury from least to most): the gray–white matter junction, the corpus callosum (splenium), and the brainstem ( Fig. 1.49 ). CT is often normal in this setting.

**Fig. 1.49** Diffuse axonal injury. Edema (high signal intensity) and petechial hemorrhage (low signal intensity) are seen on T2-weighted scans at the gray–white matter junction of the frontal lobe in this patient who was involved in a high velocity auto accident. The GRE scan better visualizes the T2* effect due to this hemorrhage (deoxyhemoglobin). The FLAIR scan at the level of the splenium of the corpus callosum reveals edema therein (*black arrow*), a less frequent and more clinically significant injury. The GRE scan of the brainstem reveals hemorrhage (*white arrow*) within the cerebral peduncles, the least common area of involvement of the three illustrated, and the most severe clinically.

Injuries at the gray–white matter junction will be seen as multiple small foci of abnormal high signal intensity on FLAIR scans. Most commonly these involve the frontal lobe. If the lesions are hemorrhagic, they will be well seen in the acute time frame on T2*-weighted gradient echo scans, due to the presence of deoxyhemoglobin. Susceptibility weighted imaging offers a further improvement in sensitivity to T2* effects, and in cases with hemorrhage will demonstrate more extensive injury. The second most common injury seen in DAI is a shear injury of the corpus callosum, with the majority involving the splenium. This injury and the subsequently described injury of the brainstem are usually not seen in isolation but with extensive shear injury at the gray–white matter junction. In the brainstem, lesions are seen most often in the pons and the dorsolateral midbrain. Lesions in the brainstem carry a very poor prognosis, often with a fatal outcome.

In patients evaluated months to years following severe head trauma, the residual from DAI involving injury at the gray–white matter junction can be visualized, with high signal intensity on FLAIR due to gliosis and low signal intensity on T2*-weighted images due to the presence of hemosiderin. Encephalomalacia, with both gliosis and cystic changes, will be seen in areas of prior contusion. In severe injury, there may be resultant generalized cerebral atrophy.

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