EXERCISE 12-5. HEAD TRAUMA
12-12. In Case 12-12, what is the diagnosis (Figure 12-29 A, B)?
A. Subdural hematoma
B. Cerebral contusion
C. Epidural hematoma
E. Subdural hygroma
12-13. In Case 12-13, what is the main radiologic finding (Figure 12-30)?
A. Subdural hematoma
B. Epidural hematoma
C. Duret hemorrhage
D. Cerebral contusions
E. Shearing injuries
12-1. In this case, a predominantly high-density, extra-axial, hemorrhagic collection (black arrows) is pro-ducing mass effect on the right frontal lobe on an unenhanced head CT scan (Figure 12-29 A). Mass effect results in marked distortion of the underly-ing cortex and leftward subfalcine herniation (white arrow) (Figure 12-29 A). A linear nonde-pressed fracture is present along the anterior aspect of the right parietal bone (black arrow) (Figure 12-29 B). The biconvex appearance of this lesion is typical of an epidural hematoma, which is the acute finding in this case (C is the correct answer to Question 12-12).
12-13. In this case, there are multiple areas of increased at-tenuation within the frontal lobes, especially on the left (arrows) (Figure 12-30). These areas correspond to multiple hemorrhagic contusions involving the brain parenchyma (D is the correct answer to Ques-tion 12-13).
Intracranial abnormalities in head trauma can be classi-fied as either primary or secondary. Primary lesions occur at the moment of injury and include skull fractures, extracerebral hemorrhage (eg, epidural or subdural hematomas, subarachnoid hemorrhage), and intracere-bral hemorrhage (eg, brain contusion, brainstem injury, diffuse axonal injury).
The secondary effects of head trauma are actually com-plications of the primary intracranial injury. Elevated in-tracranial pressure and cerebral herniation are responsible for most of the secondary effects of head trauma, which in many cases may be more devastating to the patients than the initial injury.
Epidural hematoma is usually associated with skull fractures that lacerate the middle meningeal artery or a dural sinus. Up to one-half of patients with epidural hematomas have a lucid in-terval after the head trauma occurs. On CT, epidural hematomas usually appear as biconvex, high-attenuation, extra-axial masses. Most are located in the temporoparietal area. Underlying skull fractures are common. Intracranial brain herniation may also be a prominent feature in this con-dition. One important imaging feature in epidural hematomas is that they do not cross skull sutures, but may cross the midline.
Subdural hematoma, on the other hand, is usually a cres-cent-shaped extra-axial collection that may cross suture lines, but is confined by the dural reflections (Figure 12-31). These lesions are more lethal than are epidural hematomas; the subdural hematoma mortality rate is over 50%. CT can usually, but not always, distinguish between epidural hematomas and subdural hematomas. Subdural hematomas are a commonly identified abnormality in the abused child (nonaccidental trauma). CT scans are obtained to detect thepresence of subdural hematomas (Figure 12-32). A brain MRI, however, can more sensitively delineate small extra-axial hematomas, subdural hematomas of varying ages, and coexisting cortical contusions or shearing injuries. A shear-ing injury (or diffuse axonal injury) is associated with an overall poor prognosis and is recognized as small petechial hemorrhages at the gray-white junction and in the corpus callosum. Interhemispheric (para- and intrafalcial) sub-dural hematomas may arise from tearing of bridging veins along the falx cerebri in shaking injuries and are nearly pathognomic for nonaccidental trauma. Retinal hemor-rhages may be present and are also suspicious, especially if bilateral. In addition, cerebral ischemia/infarction and mul-tiple, complex, unexplained skull fractures may be associ-ated findings.
Cerebral contusions (Case 12-13) are the second most common form of brain parenchymal injury in primary head trauma (diffuse axonal injury is the most common parenchy-mal injury). Cerebral contusions can be thought of as brain bruises. They result either from the brain striking a bony ridge inside the skull during rapid acceleration/deceleration, as occurs in a motor vehicle accident, or from a depressed skull fracture. These lesions tend to occur in particular anatomic locations, especially the undersurfaces and poles of the frontal and temporal lobes (Figure 12-33). CT scans show areas of low attenuation (edema) and hemorrhage at the site of injury. Delayed hemorrhage, 1 to 2 days after a head injury, is common with contusions.