Concussive brain injury from explosive blast

Abstract

ObjectiveExplosive blast mild traumatic brain injury (mTBI) is associated with a variety of symptoms including memory impairment and posttraumatic stress disorder (PTSD). Explosive shock waves can cause hippocampal injury in a large animal model. We recently reported a method for detecting brain injury in soldiers with explosive blast mTBI using magnetic resonance spectroscopic imaging (MRSI). This method is applied in the study of veterans exposed to blast.MethodsThe hippocampus of 25 veterans with explosive blast mTBI, 20 controls, and 12 subjects with PTSD but without exposure to explosive blast were studied using MRSI at 7 Tesla. Psychiatric and cognitive assessments were administered to characterize the neuropsychiatric deficits and compare with findings from MRSI.ResultsSignificant reductions in the ratio of N-acetyl aspartate to choline (NAA/Ch) and N-acetyl aspartate to creatine (NAA/Cr) (P < 0.05) were found in the anterior portions of the hippocampus with explosive blast mTBI in comparison to control subjects and were more pronounced in the right hippocampus, which was 15% smaller in volume (P < 0.05). Decreased NAA/Ch and NAA/Cr were not influenced by comorbidities – PTSD, depression, or anxiety. Subjects with PTSD without blast had lesser injury, which tended to be in the posterior hippocampus. Explosive blast mTBI subjects had a reduction in visual memory compared to PTSD without blast.InterpretationThe region of the hippocampus injured differentiates explosive blast mTBI from PTSD. MRSI is quite sensitive in detecting and localizing regions of neuronal injury from explosive blast associated with memory impairment.

Neuronal and glial changes in the brain resulting from explosive blast in an experimental model

“…This finding corresponds to similar findings in the blast-exposed human brain based on MRSI [6]. Additionally, we observed significant astrocyte activation comparable to that observed in other studies of both explosive blast and closed head traumatic brain injury [8, 17].…”

“…A MRSI study on warfighters exposed to explosive blast in the battle field several months to years prior to imaging, and exhibiting symptoms of mTBI showed significant decreases in the ratios of NAA/Choline and NAA/Creatine in the hippocampus, providing evidence of neuronal loss in the hippocampus [6, 11]. The greater neuronal loss resulting from multiple exposures also has some support in human studies [6]. …”

“…Metabolite ratio reductions in the right hippocampus were more extensive than in the left. Hippocampal volume measurements revealed that the right hippocampus was about 20% smaller than the left [6]. These findings suggest neuronal injury in the hippocampus.…”

“…These findings suggest neuronal injury in the hippocampus. The changes were independent of co-morbidities such as PTSD and depression [6, 11, 12] but associated with reductions in visual memory [6]. These findings suggest neuronal injury in the hippocampus.…”

Primary blast injury causes cognitive impairments and hippocampal circuit alterations

“…In human blast TBI, several recent studies report alterations in hippocampal volume, differences in slow wave generation measured with magnetoelectroencephalography, and biochemical changes detected with magnetic resonance spectroscopy within regions that include the hippocampus (de Lanerolle et al, 2014; Huang et al, 2014). Preclinical rodent studies show blast exposure will cause alterations in hippocampal microstructure, increases in different forms of phosphorylated Tau, reductions in axonal conduction velocity, and LTP deficits in the hippocampal circuitry after injury (Budde et al, 2013; Effgen et al, 2015; Goldstein et al, 2012; Huber et al, 2013; Vogel et al, 2015; Yin et al, 2014).…”