Subcortical White Matter Metabolic Changes Remote from Focal Hemorrhagic Lesions Suggest Diffuse Injury after Human Traumatic Brain Injury

OBJECTIVE:We used positron emission tomographic studies to prospectively examine the relationship between glucose and oxidative metabolism in the subcortical white matter (WM) acutely after traumatic brain injury (TBI). The objective was to determine the nature, extent, and degree of metabolic abnormalities in subcortical brain regions remote from hemorrhagic lesions. METHODS:Sixteen normal volunteers and 10 TBI patients (Glasgow Coma Scale score, 4–10; age, 17–64 yr; 6 with focal and 4 with diffuse injury) were studied. Each subject underwent dynamic positron emission tomographic studies using [15O]CO, 15O2, [15O]H2O, and fluorodeoxyglucose plus a magnetic resonance imaging scan acutely after TBI. Parametric images of the metabolic rate of oxygen and metabolic rate of glucose were generated, and a molar oxygen-to-glucose utilization ratio was calculated. Data from gray matter and WM remote from hemorrhagic lesions, plus whole brain, were analyzed. RESULTS:There was a significant reduction in the subcortical WM oxygen-to-glucose utilization ratio after TBI compared with normal values (3.99 ± 0.77 versus 5.37 ± 1.00; P < 0.01), whereas the mean cortical gray matter and whole-brain values remained unchanged. WM metabolic changes, which were diffuse throughout the hemispheres, were characterized by a reduction in the metabolic rate of oxygen without a concomitant drop in the metabolic rate of glucose. CONCLUSION:The extent and degree of subcortical WM metabolic abnormalities after moderate and severe TBI suggest that diffuse WM injury is a general phenomenon after such injuries. This pervasive finding may indicate that the concept of focal traumatic injury, although valid from a computed tomographic imaging standpoint, may be misleading when considering metabolic derangements associated with TBI.