NEUROIMAGING
Computerized tomography (CT) scans are typically obtained early after significant TBI. This relatively rapid imaging study is helpful in evaluating whether there is a condition that requires prompt neurosurgical evaluation and intervention (38-41).
Specifically, it is helpful in detecting extra-axial hemorrhage, fractures, acute hydrocephalus, or parenchymal hemorrhages that are relatively large. However, the presence of a skull fracture is not indicative of intracranial pathology (39).Magnetic resonance imaging (MRI) is more sensitive for the detection of intraparenchymal lesions than CT scan, but takes longer than CT and often cannot be done early post-injury due to the child's medical instability and need for supportive interventions. It is advisable, however, to obtain MRI when the child's condition allows it. Different MRI techniques can be used to evaluate for specific abnormalities (41). For example, susceptibility-weighted imaging was shown to identify a greater number of lesions than other techniques in one study comparing outcome from pediatric TBI and imaging findings. In this study, children were grouped according to normal, mild impairment, and poor outcome and different imaging modalities were compared. CT did not demonstrate a difference between groups for lesion count or volume. Susceptibility-weighted, fluid-attenuated inversion recovery (FLAIR), and T2-weighted MRI all demonstrated significant difference between the normal versus mild impairment and mild versus poor outcome groups for both volume and number of lesions. They also reported that normal CT scans were seen in 40% of the poor outcome group (38). Others have also reported association between the volume of lesion and severity of injury (42).
Other authors have compared neuropsychological outcomes and imaging findings longer term after injury. One study of 14 children aged 10 to 18 years 6 to 12 months after mild to moderate TBI and a matched comparison group used diffusion tensor imaging (DTI) to evaluate white matter. Authors reported that the groups had no difference in overall intelligence, but did demonstrate differences in processing speed, working memory, executive function, and behavioral problems.
Also, the TBI group had lower fractional anisotropy (FA) in three white matter regions: inferior frontal, superior frontal, and supracallosal. FA in the frontal and supracallosal regions correlated with executive function. Supracallosal FA also correlated with motor speed and behavior problems (43). Another group reported DTI findings in an acutely injured child with normal CT imaging. DTI demonstrated temporary marked increase in anisotropy in large areas of the cortical and subcortical right hemisphere at 18 hours after injury. At 135 hours post-injury, subtle changes in anisotropy were present (44).Late after injury, several different imaging findings can be used to assess global change in the brain. These include cerebral diffusivity, corpus callosum volume, and volumes of brain and ventricles. Increased diffusivity is thought to be related to an increase in the extracellular space. In young children who experience TBI, late cerebral atrophy or decreased total brain volume could be related to tissue loss due to the injury itself or impaired brain growth. In typically developing individuals, white matter is reported to increase by 12.4% from age 4-22 (17). One study of children and adolescents at least 6 years after TBI found a correlation between corpus callosum volume and processing speed and Visuospatial abilities. Ventricular volume did not correlate as well with results of neuropsychological testing. Corpus callosum is reported to continue to increase in size in typically developing individuals into early adulthood (45). It is imperative to evaluate scans over time to see the full extent of damage (40).