Quantification of brain edema and hemorrhage by MRI after experimental traumatic brain injury in rabbits predicts subsequent functional outcome

Comparing Imaging Biomarkers of Cerebral Edema after TBI in Young Adult Male and Female Rats

Traumatic brain injury (TBI) is one of the leading causes of death and disability worldwide. Cerebral edema following TBI is known to play a critical role in injury severity and prognosis. In the current study we used multimodal magnetic resonance imaging (MRI) to assess cerebral edema 24 hours after unilateral contusive TBI in male and female rats. We then directly quantified brain water content in the same subjectsex vivo.We found that both males and females had similarly elevated T₂ values after TBI compared with sham controls. Apparent diffusion coefficient (ADC) was more variable than T₂ and did not show significant injury effects in males or females. Brain water was elevated in male TBI rats compared with sham controls, but there was no difference between female TBI and sham groups. Notably, MRI biomarkers of edema were more closely correlated with brain water in male rats; female rats did not show any relationship between brain water and T₂ or ADC. These observations raise questions about the interpretation of radiological findings traditionally interpreted as edema in female TBI patients. A better understanding of sex differences and similarities in the pathophysiology of post-traumatic edema is needed to help improve patient management and the development of effective treatment strategies for men and women.

Dynamic features of brain edema in rat models of traumatic brain injury

We explored the dynamic features of brain edema after traumatic brain injury (TBI) using healthy adult male Wistar rats. After inducing moderate brain injuries in the rats, we divided them randomly among seven groups on the basis of the time elapsed between TBI and examination: 1, 6, 12, 24, 48, 72, and 168 h. All rats were scanned using diffusion-weighted imaging (DWI) to observe tissue changes in the contusion penumbra (CP) after TBI. Immunoglobulin G expression was also detected. At 1 h after TBI, there was an annular light-colored region in the CP where the intercellular space was enlarged, suggesting vasogenic edema. At 6 h, the cells expanded, their nuclei shrank, and the cytoplasm was replaced by vacuoles, indicating intracellular edema. Vasogenic edema and intracellular edema increased 12 h after TBI, but decreased 24 h after TBI, with vasogenic edema increasing 48 h after TBI. By 72 h after TBI, intracellular edema dominated until resolution of all edema by 168 h after TBI. DWI indicated that the relative apparent diffusion coefficient increased markedly at 1 h after TBI, but was reduced at 6 and 12 h after TBI. At 48 h, relative apparent diffusion coefficient increased gradually and then declined at 72 h. In rats, TBI-related changes include dynamic variations in intracellular and vasogenic edema severity. Routine MRI and DWI examinations do not distinguish between the center of trauma and CP; however, the apparent diffusion coefficient diagram can portray variations in CP edema type and degree at different time-points following TBI.

Early stage of diffusional kurtosis imaging and dynamic contrast-enhanced magnetic resonance imaging correlated with long-term neurocognitive function after experimental traumatic brain injury

Development of a reliable biomarker for prognostic monitoring of cognitive impairment after traumatic brain injury (TBI) is of great importance. The aim of the study was to explore the value of early diffusional kurtosis imaging (DKI) and dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) in evaluation of chronic cognitive function after TBI. MRI was performed on TBI and control rats at 7 days post-injury. MRI parameters were measured in bilateral cortex, hippocampus, thalamus and corpus callosum (CC). All the rats underwent Morris water maze (MWM) at 6 months after injury. Immunohistochemistry (IHC) analysis of neuron [NeuN], astroglia [GFAP], microglia [Iba-1], and myelin [MBP] was performed after the MWM test. Our study revealed that, TBI group showed higher volume transfer coefficient (K^trans) value in ipsilateral cortex (P < 0.0001) and no detectable changes in other regions-of-interest (ROIs), compared with control group. DKI showed higher MK in all ipsilateral ROIs (P < 0.05), higher MD in ipsilateral cortex, hippocampus and CC (P < 0.05 for all) in TBI group. TBI group had worse performance in MWM test at 6 months post-injury(P < 0.05). IHC analysis showed lower NeuN, and higher GFAP and Iba-1 in all ipsilateral ROIs (P < 0.05) in TBI rats. NeuN, and GFAP and Iba-1 correlated significantly with MK value in ipsilateral regions of cortex. The MK value of ipsilateral cortex and CC and K^trans value of ipsilateral cortex also correlated significantly with time in the target quadrant. Therefore, our study indicated that early DKI and DCE-MRI could be used to assess the microstructural changes associated with long-term cognitive outcome following TBI.

Traumatic hemorrhagic brain injury: impact of location and resorption on cognitive outcome

OBJECTIVE

Hemorrhagic contusions are often the most visible lesions following traumatic brain injury. However, the incidence, location, and natural history of traumatic parenchymal hemorrhage and its impact on neurological outcome have been understudied. The authors sought to examine the location and longitudinal evolution of traumatic parenchymal hemorrhage and its association with cognitive outcome.

METHODS

Sixteen patients with hemorrhagic contusions due to acceleration-deceleration injuries underwent MRI in the acute (mean 6.3 days postinjury) and chronic (mean 192.9 days postinjury) phases. ImageJ was used to generate GRE and FLAIR volumes. To account for the effect of head-size variability across individuals, the authors calculated each patient's total brain tissue volume using SIENAX. GRE and FLAIR volumes were normalized to the total brain tissue volume, and values for absolute and percent lesion volume and total brain volume change were generated. Spearman's rank correlations were computed to determine associations between neuroimaging and 6-month postinjury neuropsychological testing of attention (Symbol Digit Modalities Test [SDMT], oral [O] and written [W] versions), memory (Selective Reminding Test, total learning and delayed recall), and executive function (Trail Making Test Part B [TMT-B]).

RESULTS

The patients' mean age was 31.4 ± 14.0 years and their mean Glasgow Coma Scale score at admission was 7.9 ± 2.8. Lesions were predominantly localized to the frontal (11 lesions) and temporal (9 lesions) lobes. The average percent reductions in GRE and FLAIR volumes were 44.2% ± 46.1% and 80.5% ± 26.3%, respectively. While total brain and frontal lesion volumes did not correlate with brain atrophy, larger temporal lobe GRE and FLAIR volumes were associated with larger volumes of atrophy (GRE: acute, −0.87, p < 0.01, chronic, −0.78, p < 0.01; FLAIR: acute, −0.81, p < 0.01, chronic, −0.88, p < 0.01). Total percent volume change of GRE lesions correlated with TMT-B (0.53, p < 0.05) and SDMT-O (0.62, p < 0.05) scores. Frontal lobe lesion volume did not correlate with neuropsychological outcome. However, robust relationships were seen in the temporal lobe, with larger acute temporal lobe GRE volumes were associated with worse scores on both oral and written versions of the SDMT (SDMT-W, −0.85, p < 0.01; SDMT-O, −0.73, p < 0.05). Larger absolute change in temporal GRE volume was strongly associated with worse SDMT scores (SDMT-W, 0.88, p < 0.01; SDMT-O, 0.75, p < 0.05). The same relationships were also seen between temporal FLAIR lesion volumes and neuropsychological outcome.

CONCLUSIONS

Traumatic parenchymal hemorrhages are largely clustered in the frontal and temporal lobes, and significant residual blood products are present at 6 months postinjury, a potential source of ongoing secondary brain injury. Neuropsychological outcome is closely tied to lesion volume size, particularly in the temporal lobe, where larger GRE and FLAIR volumes are associated with more brain atrophy and worse SDMT scores. Interestingly, larger volumes of hemorrhage resorption were associated with worse SDMT and TMT-B scores, suggesting that the initial tissue damage had a lasting impact on attention and executive function.

Treatment of Edema Associated With Intracerebral Hemorrhage

OPINION STATEMENT

Cerebral edema (i.e., "brain swelling") is a common complication following intracerebral hemorrhage (ICH) and is associated with worse clinical outcomes. Perihematomal edema (PHE) accumulates during the first 72 h after hemorrhage, and during this period, patients are at risk of clinical deterioration due to the resulting tissue shifts and brain herniation. First-line medical therapies for patients symptomatic of PHE include osmotic agents, such as mannitol in low- or high-dose bolus form, or boluses of hypertonic saline (HTS) at varied concentrations with or without subsequent continuous infusion. Decompressive craniectomy may be required for symptomatic edema refractory to osmotherapy. Other strategies that reduce PHE such as hypothermia and minimally invasive surgery have shown promise in pilot studies and are currently being evaluated in larger clinical trials. Ongoing basic, translational, and clinical research seek to better elucidate the pathophysiology of PHE to identify novel strategies to prevent edema formation as a next major advance in the treatment of ICH.

A Review of the Effectiveness of Neuroimaging Modalities for the Detection of Traumatic Brain Injury

The incidence of traumatic brain injury (TBI) in the United States was 3.5 million cases in 2009, according to the Centers for Disease Control and Prevention. It is a contributing factor in 30.5% of injury-related deaths among civilians. Additionally, since 2000, more than 260,000 service members were diagnosed with TBI, with the vast majority classified as mild or concussive (76%). The objective assessment of TBI via imaging is a critical research gap, both in the military and civilian communities. In 2011, the Department of Defense (DoD) prepared a congressional report summarizing the effectiveness of seven neuroimaging modalities (computed tomography [CT], magnetic resonance imaging [MRI], transcranial Doppler [TCD], positron emission tomography, single photon emission computed tomography, electrophysiologic techniques [magnetoencephalography and electroencephalography], and functional near-infrared spectroscopy) to assess the spectrum of TBI from concussion to coma. For this report, neuroimaging experts identified the most relevant peer-reviewed publications and assessed the quality of the literature for each of these imaging technique in the clinical and research settings. Although CT, MRI, and TCD were determined to be the most useful modalities in the clinical setting, no single imaging modality proved sufficient for all patients due to the heterogeneity of TBI. All imaging modalities reviewed demonstrated the potential to emerge as part of future clinical care. This paper describes and updates the results of the DoD report and also expands on the use of angiography in patients with TBI.

Multimodal MR imaging of acute and subacute experimental traumatic brain injury: Time course and correlation with cerebral energy metabolites

BACKGROUND

Traumatic brain injury (TBI) is one of the leading causes of death and permanent disability world-wide. The predominant cause of death after TBI is brain edema which can be quantified by non-invasive diffusion-weighted magnetic resonance imaging (DWI).

PURPOSE

To provide a better understanding of the early onset, time course, spatial development, and type of brain edema after TBI and to correlate MRI data and the cerebral energy state reflected by the metabolite adenosine triphosphate (ATP).

MATERIAL AND METHODS

The spontaneous development of lateral fluid percussion-induced TBI was investigated in the acute (6 h), subacute (48 h), and chronic (7 days) phase in rats by MRI of quantitative T2 and apparent diffusion coefficient (ADC) mapping as well as perfusion was combined with ATP-specific bioluminescence imaging and histology.

RESULTS

An induced TBI led to moderate to mild brain damages, reflected by transient, pronounced development of vasogenic edema and perfusion reduction. Heterogeneous ADC patterns indicated a parallel, but mixed expression of vasogenic and cytotoxic edema. Cortical ATP levels were reduced in the acute and subacute phase by 13% and 27%, respectively, but were completely normalized at 7 days after injury.

CONCLUSION

The partial ATP reduction was interpreted to be partially caused by a loss of neurons in parallel with transient dilution of the regional ATP concentration by pronounced vasogenic edema. The normalization of energy metabolism after 7 days was likely due to infiltrating glia and not to recovery. The MRI combined with metabolite measurement further improves the understanding and evaluation of brain damages after TBI.

Quantitative evaluation of hyperbaric oxygen efficacy in experimental traumatic brain injury: an MRI study

To use DCE-magnetic resonance imaging (MRI) and diffusion-weighted imaging to evaluate the hyperbaric oxygen efficacy (HBO) in experimental traumatic brain injury (TBI). Forty-two rabbits were randomly divided into four groups: TBI, TBI + HBO, sham group, sham + HBO. The TBI + HBO and sham + HBO received a total of 10 HBO treatments within 7 days following TBI, and MRI was performed within a month after TBI. Functional assessments were performed pre-TBI, and at 1 and 30 days. In focal lesion area, K(trans) in TBI + HBO group was lower than TBI group at both acute and subacute phase (p < 0.05). ADC was higher in TBI + HBO group than TBI group at acute phase (p < 0.01), but lower at subacute phase (p < 0.05). In perifocal area, K(trans) were lower in TBI + HBO group than TBI group at acute phase (p < 0.01) after TBI. ADC was lower in the TBI + HBO group than in the TBI group at both acute and subacute phase (p < 0.01).The VCS was higher in TBI + HBO group than TBI group at 30 days (p < 0.05). HBO could improve the impaired BBB and cytotoxic edema after TBI and promote the recovery of neurofunction.