Ontogenetic aspects of traumatic brain edema--facts and suggestions

Pitfalls in the interpretation of pediatric head CTs: what the emergency radiologist needs to know

Pediatric radiology studies can be some of the most anxiety-inducing imaging examinations encountered in practice. This can be in part due to the wide range of normal anatomic appearances inherent to the pediatric population that create potential interpretive pitfalls for radiologists. The pediatric head is no exception; for instance, the inherent greater water content within the neonatal brain compared to older patients could easily be mistaken for cerebral edema, and anatomic variant calvarial sutures can be mistaken for skull fractures. This article reviews potential pitfalls emergency radiologists may encounter in practice when interpreting pediatric head CTs, including trauma, extra-axial fluid collections, intra-axial hemorrhage, and ventriculoperitoneal shunt complications.

Intracranial Densitometry-Augmented Machine Learning Enhances the Prognostic Value of Brain CT in Pediatric Patients With Traumatic Brain Injury: A Retrospective Pilot Study

Background: The inter- and intrarater variability of conventional computed tomography (CT) classification systems for evaluating the extent of ischemic-edematous insult following traumatic brain injury (TBI) may hinder the robustness of TBI prognostic models. Objective: This study aimed to employ fully automated quantitative densitometric CT parameters and a cutting-edge machine learning algorithm to construct a robust prognostic model for pediatric TBI. Methods: Fifty-eight pediatric patients with TBI who underwent brain CT were retrospectively analyzed. Intracranial densitometric information was derived from the supratentorial region as a distribution representing the proportion of Hounsfield units. Furthermore, a machine learning-based prognostic model based on gradient boosting (i.e., CatBoost) was constructed with leave-one-out cross-validation. At discharge, the outcome was assessed dichotomously with the Glasgow Outcome Scale (favorability: 1-3 vs. 4-5). In-hospital mortality, length of stay (>1 week), and need for surgery were further evaluated as alternative TBI outcome measures. Results: Densitometric parameters indicating reduced brain density due to subtle global ischemic changes were significantly different among the TBI outcome groups, except for need for surgery. The skewed intracranial densitometry of the unfavorable outcome became more distinguishable in the follow-up CT within 48 h. The prognostic model augmented by intracranial densitometric information achieved adequate AUCs for various outcome measures [favorability = 0.83 (95% CI: 0.72-0.94), in-hospital mortality = 0.91 (95% CI: 0.82-1.00), length of stay = 0.83 (95% CI: 0.72-0.94), and need for surgery = 0.71 (95% CI: 0.56-0.86)], and this model showed enhanced performance compared to the conventional CRASH-CT model. Conclusion: Densitometric parameters indicative of global ischemic changes during the acute phase of TBI are predictive of a worse outcome in pediatric patients. The robustness and predictive capacity of conventional TBI prognostic models might be significantly enhanced by incorporating densitometric parameters and machine learning techniques.

Diurnal variation of NMDA receptor expression in the rat cerebral cortex is associated with traumatic brain injury damage

OBJECTIVE

Data from our laboratory suggest that recovery from a traumatic brain injury depends on the time of day at which it occurred. In this study, we examined whether traumatic brain injury -induced damage is related to circadian variation in N-methyl-D-aspartate receptor expression in rat cortex.

RESULTS

We confirmed that traumatic brain injury recovery depended on the time of day at which the damage occurred. We also found that motor cortex N-methyl-D-aspartate receptor subunit NR1 expression exhibited diurnal variation in both control and traumatic brain injury-subjected rats. However, this rhythm is more pronounced in traumatic brain injury-subjected rats, with minimum expression in those injured during nighttime hours. These findings suggest that traumatic brain injury occurrence times should be considered in future clinical studies and when designing neuroprotective strategies for patients.

High sensitivity of spontaneous spike frequency to sodium leak current in a Lymnaea pacemaker neuron

The spontaneous rhythmic firing of action potentials in pacemaker neurons depends on the biophysical properties of voltage-gated ion channels and background leak currents. The background leak current includes a large K⁺ and a small Na⁺ component. We previously reported that a Na⁺ -leak current via U-type channels is required to generate spontaneous action potential firing in the identified respiratory pacemaker neuron, RPeD1, in the freshwater pond snail Lymnaea stagnalis. We further investigated the functional significance of the background Na⁺ current in rhythmic spiking of RPeD1 neurons. Whole-cell patch-clamp recording and computational modeling approaches were carried out in isolated RPeD1 neurons. The whole-cell current of the major ion channel components in RPeD1 neurons were characterized, and a conductance-based computational model of the rhythmic pacemaker activity was simulated with the experimental measurements. We found that the spiking rate is more sensitive to changes in the Na⁺ leak current as compared to the K⁺ leak current, suggesting a robust function of Na⁺ leak current in regulating spontaneous neuronal firing activity. Our study provides new insight into our current understanding of the role of Na⁺ leak current in intrinsic properties of pacemaker neurons.

Quantitative analysis of computed tomography images and early detection of cerebral edema for pediatric traumatic brain injury patients: retrospective study

BACKGROUND

The purpose of this study was to identify whether the distribution of Hounsfield Unit (HU) values across the intracranial area in computed tomography (CT) images can be used as an effective diagnostic tool for determining the severity of cerebral edema in pediatric traumatic brain injury (TBI) patients.

METHODS

CT images, medical records and radiology reports on 70 pediatric patients were collected. Based on radiology reports and the Marshall classification, the patients were grouped as mild edema patients (n=37) or severe edema patients (n=33). Automated quantitative analysis using unenhanced CT images was applied to eliminate artifacts and identify the difference in HU value distribution across the intracranial area between these groups.

RESULTS

The proportion of pixels with HU=17 to 24 was highly correlated with the existence of severe cerebral edema (P<0.01). This proportion was also able to differentiate patients who developed delayed cerebral edema from mild TBI patients. A significant difference between deceased patients and surviving patients in terms of the HU distribution came from the proportion of pixels with HU=19 to HU=23 (P<0.01).

CONCLUSIONS

The proportion of pixels with an HU value of 17 to 24 in the entire cerebral area of a non-enhanced CT image can be an effective basis for evaluating the severity of cerebral edema. Based on this result, we propose a novel approach for the early detection of severe cerebral edema.

Aquaporin-4 expression in cultured astrocytes after fluid percussion injury

The development of cytotoxic brain edema resulting in increased intracranial pressure is a major cause of death occurring in the early phase of traumatic brain injury (TBI). Such edema predominantly develops as a consequence of astrocyte swelling. We recently documented that fluid percussion injury (FPI) to cultured astrocytes causes cell swelling. Since aquaporin-4 (AQP4) has been strongly implicated in the development of brain edema/astrocyte swelling in various neurological conditions, this study examined the effect of in vitro trauma on AQP4 protein expression in cultured astrocytes. Exposure of astrocytes to FPI resulted in a significant upregulation of AQP4 protein in the plasma membrane due to neosynthesis, as cycloheximide blocked the trauma-induced AQP4 upregulation. Silencing the aqp4 gene by siRNA resulted in a significant reduction in trauma-induced astrocyte swelling, indicating a critical role of AQP4 in this process. We recently documented that oxidative/nitrative stress (ONS), the mitochondrial permeability transition (mPT), and activation of mitogen-activated protein kinases (MAPKs), contribute to trauma-induced astrocyte swelling in culture. We now show that inhibition of these factors reduces the upregulation of AQP4 following trauma. Since TBI has been shown to activate nuclear factor-kappa B (NF-κB), as well as the Na(+),K(+),Cl(-) co-transporter (NKCC), both of which are implicated in brain edema/astrocyte swelling in other conditions, we also examined the effect of BAY 11-7082 and bumetanide, inhibitors of NF-κB and NKCC, respectively, and found that these agents also significantly inhibited the trauma-induced AQP4 upregulation. Our findings show that in vitro trauma upregulates AQP4, and that ONS, MAPKs, mPT, NF-κB, and NKCC are involved in its upregulation.

THE ROLE OF INTRACELLULAR SODIUM (Na) IN THE REGULATION OF CALCIUM (Ca)-MEDIATED SIGNALING AND TOXICITY

It is known that activated N-methyl-D-aspartate receptors (NMDARs) are a major route of excessive calcium ion (Ca(2+)) entry in central neurons, which may activate degradative processes and thereby cause cell death. Therefore, NMDARs are now recognized to play a key role in the development of many diseases associated with injuries to the central nervous system (CNS). However, it remains a mystery how NMDAR activity is recruited in the cellular processes leading to excitotoxicity and how NMDAR activity can be controlled at a physiological level. The sodium ion (Na(+)) is the major cation in extracellular space. With its entry into the cell, Na(+) can act as a critical intracellular second messenger that regulates many cellular functions. Recent data have shown that intracellular Na(+) can be an important signaling factor underlying the up-regulation of NMDARs. While Ca(2+) influx during the activation of NMDARs down-regulates NMDAR activity, Na(+) influx provides an essential positive feedback mechanism to overcome Ca(2+)-induced inhibition and thereby potentiate both NMDAR activity and inward Ca(2+) flow. Extensive investigations have been conducted to clarify mechanisms underlying Ca(2+)-mediated signaling. This review focuses on the roles of Na(+) in the regulation of Ca(2+)-mediated NMDAR signaling and toxicity.

Traumatic brain injury in children--clinical implications

Traumatic brain injury (TBI) is the leading cause of death in childhood; however only very few studies focusing on the specific pathophysiology and treatment have been published to date. Head trauma is more likely in young children than in adults given the same deceleration of the body due to their large and heavy heads and weak cervical ligaments and muscles. Resulting brain injury is more severe due to their thin, pliable skulls and the yet unfused sutures. Accordingly, children below the age of 4 years have lower chances of a full recovery after severe TBI, although in general, neurologic recovery after severe brain injury in children is better than in adults. The time course of brain injury can be divided into two steps: primary and secondary injury. Primary brain injury exclusively results from the initial impact. In contrast, adverse physiologic conditions during recovery after head trauma may account for additional brain damage, which is then referred to as secondary brain injury. As primary brain injury can only be influenced by preventive measures, all therapeutic efforts during the post-injury period focus on the reduction of secondary injury to the traumatized brain. Several mechanisms have been identified to be involved in the development of post-traumatic secondary brain injury, which render the rationale for the key treatment strategies. Three evidence based measures are of critical importance to prevent or minimize secondary brain injury: (1) avoid hypoxemia, (2) avoid post-traumatic arterial hypotension, and (3) refer the traumatized child to an experienced trauma team at a center that provides the availability of special equipment, e.g. for surgical procedures and airway management, for this age group. For several other therapeutical means, e.g. hypothermia or specific surgical interventions, clinical evidence to date is insufficient to allow recommendation as rescue treatment for children at risk of severe neurological sequelae following TBI. This review discusses the clinical implication of pathophysiologic mechanisms of TBI in the developing brain according to the recent literature and current guidelines. It follows the clinical approach to a head injured child, that can be divided into three phases, i.e. initial assessment and stabilization, followed by first tier, and if necessary second tier therapeutic interventions to assure adequate oxygenation and perfusion of the brain.

Age-dependent differences in glutathione peroxidase activity after traumatic brain injury

Children younger than 4 years old have worse outcome after traumatic brain injury (TBI) compared to older children and adults. This increased susceptibility may in part be due to differences in the response to oxidative stress. We hypothesized that the immature brain does not have an adequate compensatory response to injury from oxidative stress. To begin to address this hypothesis, we first compared the general dimensions and water content in postnatal day 21 (P21) and adult murine brain in the naive state as well as after injury (edema). We examined glutathione peroxidase (GPx ) activity in cortical and subcortical regions in P21 and adult murine brain following a controlled cortical impact. Brain dimensions including areas of the mantle and hemispheres were similar in each of these groups. The thickness of the cortical mantle was significantly greater in the immature brain as compared to the mature brain (p = 0.01, respectively). Brain edema was assessed through changes in water content, and the response to oxidative challenge was identified by changes in GPx activity. The P21 brain was similar in vulnerability to posttraumatic brain edema when compared to adult. GPx activity in the adult brain was increased within 24 h post-injury in the cortex, thalamus and hippocampus (ANOVA, p < 0.05), whereas there was no compensatory increase in GPx activity in P21 brain, although baseline levels had reached adult levels developmentally. These findings support our hypothesis and illuminate the important role of oxidative stress after TBI in the immature brain that warrants further study.

Neuronal free Ca(2+)and BBB permeability and ultrastructure in head injury with secondary insult

OBJECTIVE

To study changes in free calcium (Ca(2+)), neuronal and blood-brain barrier (BBB) permeability and ultrastructure in brain after diffuse axonal injury (DAI) with secondary brain insults (SBIs).

METHOD

One hundred and twenty Sprague-Dawley (SD) rats were randomised into control, DAI alone and DAI with SBI groups which were sub-divided into 5 groups that were 0.5 h, 2 h, 12 h, 24 h, 48 h post trauma. The animal models of DAI and DAI with SBI have been described before (2). Fluorescence probe Fluo-3/Am was used to measure free Ca(2+)in neurons. Laser scan microscopy was used to detect fluorescence intensity. After the animals were anesthetized, Lanthanum nitrate liquid was used for intracardiac perfusion to assess BBB permeability. Under the transmission electron microscope, changes in cerebral ultrastructure and BBB permeability were observed.

RESULTS

The fluorescence intensity was weak in the control. The concentration of free Ca(2+)in neurons was obviously increased at 30 min after brain injury, reached a peak at 12 h-24 h (P< 0.01), and appeared to decrease at 48 h after injury. In the DAI alone group, BBB tight junction opening with particles of Lanthanum nitrate outside the vessels was found at 30 min after injury, and peaked at 24 h. In DAI with SBI, the changes in ultrastructure and BBB permeability were more severe than that in the DAI alone group at the same time interval. The shape of the fluorescence concentration curve was basically the same for both kinds of brain injury. The intensity of fluorescence in DAI with SBI was higher than that in the DAI alone group at the same time interval (P< 0.05).

CONCLUSION

In DAI alone and DAI with SBI, Ca(2+)overload and BBB permeability changes interact and both play important roles in the aggravation of brain damage.

Delayed cerebral edema and fatal coma after minor head trauma: role of the CACNA1A calcium channel subunit gene and relationship with familial hemiplegic migraine

Trivial head trauma may be complicated by severe, sometimes even fatal, cerebral edema and coma occurring after a lucid interval ("delayed cerebral edema"). Attacks of familial hemiplegic migraine (FHM) can be triggered by minor head trauma and are sometimes accompanied by coma. Mutations in the CACNA1A calcium channel subunit gene on chromosome 19 are associated with a wide spectrum of mutation-specific episodic and chronic neurological disorders, including FHM with or without coma. We investigated the role of the CACNA1A gene in three subjects with delayed cerebral edema. Two subjects originated from a family with extreme FHM, and one subject was the previously asymptomatic daughter of a sporadic patient with hemiplegic migraine attacks. In all three subjects with delayed severe edema, we found a C-to-T substitution resulting in the substitution of serine for lysine at codon 218 (S218L) in the CACNA1A gene. The mutation was absent in nonaffected family members and 152 control individuals. Haplotype analysis excluded a common founder for both families. Neuropathological examination in one subject showed Purkinje cell loss with relative preservation of granule cells and sparing of the dentate and inferior olivary nuclei. We conclude that the novel S218L mutation in the CACNA1A calcium channel subunit gene is involved in FHM and delayed fatal cerebral edema and coma after minor head trauma. This finding may have important implications for the understanding and treatment of this dramatic syndrome.