Wartime traumatic cerebral vasospasm: recent review of combat casualties

Practical pearls for management of cranial injury in the developing world

Traumatic brain injury (TBI) remains a leading cause of morbidity and mortality, with approximately 69 million individuals affected globally each year, particularly in low- and middle-income countries (LMICs) where neurosurgical resources are limited. The neurocognitive consequences of TBI range from life-threatening conditions to more subtle impairments such as cognitive deficits, impulsivity, and behavioral changes, significantly impacting patients' reintegration into society. LMICs bear about 70% of the global trauma burden, with causes of TBI differing from high-income countries (HICs). The lack of equitable neurosurgical care in LMICs exacerbates these challenges. Improving TBI care in LMICs requires targeted resource allocation, neurotrauma registries, increased education, and multidisciplinary approaches within trauma centers. Reports from successful neurotrauma initiatives in low-resource settings provide valuable insights into safe, adaptable strategies for managing TBI when "gold standard" protocols are unfeasible. This review discusses common TBI scenarios in LMICs, highlighting key epidemiological factors, diagnostic challenges, and surgical techniques applicable to resource-limited settings. Specific cases, including epidural hematoma, subdural hematoma, subarachnoid hemorrhage, and cerebrospinal fluid leaks, are explored to provide actionable insights for improving neurosurgical outcomes in LMICs.

Temporal Alterations in Cerebrovascular Glycocalyx and Cerebral Blood Flow after Exposure to a High-Intensity Blast in Rats

The glycocalyx is a proteoglycan-glycoprotein structure lining the luminal surface of the vascular endothelium and is susceptible to damage due to blast overpressure (BOP) exposure. The glycocalyx is essential in maintaining the structural and functional integrity of the vasculature and regulation of cerebral blood flow (CBF). Assessment of alterations in the density of the glycocalyx; its components (heparan sulphate proteoglycan (HSPG/syndecan-2), heparan sulphate (HS), and chondroitin sulphate (CS)); CBF; and the effect of hypercapnia on CBF was conducted at 2-3 h, 1, 3, 14, and 28 days after a high-intensity (18.9 PSI/131 kPa peak pressure, 10.95 ms duration, and 70.26 PSI·ms/484.42 kPa·ms impulse) BOP exposure in rats. A significant reduction in the density of the glycocalyx was observed 2-3 h, 1-, and 3 days after the blast exposure. The glycocalyx recovered by 28 days after exposure and was associated with an increase in HS (14 and 28 days) and in HSPG/syndecan-2 and CS (28 days) in the frontal cortex. In separate experiments, we observed significant decreases in CBF and a diminished response to hypercapnia at all time points with some recovery at 3 days. Given the role of the glycocalyx in regulating physiological function of the cerebral vasculature, damage to the glycocalyx after BOP exposure may result in the onset of pathogenesis and progression of cerebrovascular dysfunction leading to neuropathology.

Design of a simplified cranial substitute with a modal behavior close to that of a human skull

Individuals exposed to the propagation of shock waves generated by the detonation of explosive charges may suffer Traumatic Brain Injury. The mechanism of cranial deflection is one of many hypotheses that could explain the observed brain damage. To investigate this physical phenomenon in a reproducible manner, a new simplified cranial substitute was designed with a mechanical response close to that of a human skull when subjected to this type of loading. As a first step, a Finite Element Model was employed to dimension the new substitute. The objective was indeed to obtain a vibratory behavior close to that of a dry human skull over a wide range of frequencies up to 10 kHz. As a second step, the Finite Element Model was used together with Experimental Modal Analyses to identify the vibration modes of the substitute. A shaker excited the structure via a metal rod, while a laser vibrometer recorded the induced vibrations at defined measurement points. The results showed that despite differences in material properties and geometry, the newly developed substitute has 10/13 natural frequencies in common with those of dry human skulls. When filled with a simulant of cerebral matter, it could therefore be used in future studies as an approximation to assess the mechanical response of a simplified skull substitute to a blast threat.

Twenty Years of Blast-Induced Neurotrauma: Current State of Knowledge

Blast-induced neurotrauma (BINT) is an important injury paradigm of neurotrauma research. This short communication summarizes the current knowledge of BINT. We divide the BINT research into several broad categories-blast wave generation in laboratory, biomechanics, pathology, behavioral outcomes, repetitive blast in animal models, and clinical and neuroimaging investigations in humans. Publications from 2000 to 2023 in each subdomain were considered. The analysis of the literature has brought out salient aspects. Primary blast waves can be simulated reasonably in a laboratory using carefully designed shock tubes. Various biomechanics-based theories of BINT have been proposed; each of these theories may contribute to BINT by generating a unique biomechanical signature. The injury thresholds for BINT are in the nascent stages. Thresholds for rodents are reasonably established, but such thresholds (guided by primary blast data) are unavailable in humans. Single blast exposure animal studies suggest dose-dependent neuronal pathologies predominantly initiated by blood-brain barrier permeability and oxidative stress. The pathologies were typically reversible, with dose-dependent recovery times. Behavioral changes in animals include anxiety, auditory and recognition memory deficits, and fear conditioning. The repetitive blast exposure manifests similar pathologies in animals, however, at lower blast overpressures. White matter irregularities and cortical volume and thickness alterations have been observed in neuroimaging investigations of military personnel exposed to blast. Behavioral changes in human cohorts include sleep disorders, poor motor skills, cognitive dysfunction, depression, and anxiety. Overall, this article provides a concise synopsis of current understanding, consensus, controversies, and potential future directions.

Interventional Treatment of Symptomatic Vasospasm in the Setting of Traumatic Brain Injury: A Systematic Review of Reported Cases

Traumatic subarachnoid hemorrhage (tSAH) is frequently comorbid with traumatic brain injury (TBI) and may induce secondary injury through vascular changes such as vasospasm and subsequent delayed cerebral ischemia (DCI). While aneurysmal SAH is well studied regarding vasospasm and DCI, less is known regarding tSAH and the prevalence of vasospasm and DCI, the consequences of vasospasm in this setting, when treatment is indicated, and which management strategies should be implemented. In this article, a systematic review of the literature that was conducted for cases of symptomatic vasospasm in patients with TBI is reported, association with tSAH is reported, risk factors for vasospasm and DCI are summarized, and commonalities in diagnosis and management are discussed. Clinical characteristics and treatment outcomes of 38 cases across 20 studies were identified in which patients with TBI with vasospasm underwent medical or endovascular management. Of the patients with data available for each category, the average age was 48.7 ± 20.3 years (n = 31), the Glasgow Coma Scale score at presentation was 10.6 ± 4.5 (n = 35), and 100% had tSAH (n = 29). Symptomatic vasospasm indicative of DCI was diagnosed on average at postinjury day 8.4 ± 3.0 days (n = 30). Of the patients, 56.6% (n = 30) had a new ischemic change associated with vasospasm confirming DCI. Treatment strategies are discussed, with 11 of 12 endovascularly treated and 19 of 26 medically treated patients surviving to discharge. tSAH is associated with vasospasm and DCI in moderate and severe TBI, and patients with clinical and radiographic evidence of symptomatic vasospasm and subsequent DCI may benefit from endovascular or medical management strategies.

Shear shock wave injury in vivo: High frame-rate ultrasound observation and histological assessment

Using high frame-rate ultrasound and ¡1μm sensitive motion tracking we previously showed that shear waves at the surface of ex vivo and in situ brains develop into shear shock waves deep inside the brain, with destructive local accelerations. However post-mortem tissue cannot develop injuries and has different viscoelastodynamic behavior from in vivo tissue. Here we present the ultrasonic measurement of the high-rate shear shock biomechanics in the in vivo porcine brain, and histological assessment of the resulting axonal pathology. A new biomechanical model of brain injury was developed consisting of a perforated mylar surface attached to the brain and vibrated using an electromechanical shaker. Using a custom sequence with 8 interleaved wide beam emissions, brain imaging and motion tracking were performed at 2900 images/s. Shear shock waves were observed for the first time in vivo wherein the shock acceleration was measured to be 2.6 times larger than the surface acceleration ( 95g vs. 36g). Histopathology showed axonal damage in the impacted side of the brain from the brain surface, accompanied by a local shock-front acceleration of >70g. This shows that axonal injury occurs deep in the brain even though the shear excitation was at the brain surface, and the acceleration measurements support the hypothesis that shear shock waves are responsible for deep traumatic brain injuries.

Deferoxamine reduces endothelial ferroptosis and protects cerebrovascular function after experimental traumatic brain injury

Cerebrovascular dysfunction resulting from traumatic brain injury (TBI) significantly contributes to poor patient outcomes. Recent studies revealed the involvement of iron metabolism in neuronal survival, yet its effect on vasculature remains unclear. This study aims to explore the impact of endothelial ferroptosis on cerebrovascular function in TBI. A Controlled Cortical Impact (CCI) model was established in mice, resulting in a significant increase in iron-related proteins such as TfR1, FPN1, and FTH, as well as oxidative stress biomarker 4HNE. This was accompanied by a decline in expression of the ferroptosis inhibitor GPX4. Moreover, Perls' staining and nonhemin iron content assay showed iron overload in brain microvascular endothelial cells (BMECs) and the ipsilateral cortex. Immunofluorescence staining revealed more FTH-positive cerebral endothelial cells, consistent with impaired perfusion vessel density and cerebral blood flow. As a specific iron chelator, deferoxamine (DFO) treatment inhibited such ferroptotic proteins expression and the accumulation of lipid-reactive oxygen species following CCI, enhancing glutathione peroxidase (GPx) activity. DFO treatment significantly reduced iron deposition in BMECs and brain tissue, and increased density of the cerebral capillaries as well. Consequently, DFO treatment led to improvements in cerebral blood flow (as measured by laser speckle imaging) and behavioral performance (as measured by the neurological severity scores, rotarod test, and Morris water maze test). Taken together, our results indicated that TBI induces remarkable iron disorder and endothelial ferroptosis, and DFO treatment may help maintain iron homeostasis and protect vascular function. This may provide a novel therapeutic strategy to prevent cerebrovascular dysfunction following TBI.

The Neurovascular Unit as a Locus of Injury in Low-Level Blast-Induced Neurotrauma

Blast-induced neurotrauma has received much attention over the past decade. Vascular injury occurs early following blast exposure. Indeed, in animal models that approximate human mild traumatic brain injury or subclinical blast exposure, vascular pathology can occur in the presence of a normal neuropil, suggesting that the vasculature is particularly vulnerable. Brain endothelial cells and their supporting glial and neuronal elements constitute a neurovascular unit (NVU). Blast injury disrupts gliovascular and neurovascular connections in addition to damaging endothelial cells, basal laminae, smooth muscle cells, and pericytes as well as causing extracellular matrix reorganization. Perivascular pathology becomes associated with phospho-tau accumulation and chronic perivascular inflammation. Disruption of the NVU should impact activity-dependent regulation of cerebral blood flow, blood-brain barrier permeability, and glymphatic flow. Here, we review work in an animal model of low-level blast injury that we have been studying for over a decade. We review work supporting the NVU as a locus of low-level blast injury. We integrate our findings with those from other laboratories studying similar models that collectively suggest that damage to astrocytes and other perivascular cells as well as chronic immune activation play a role in the persistent neurobehavioral changes that follow blast injury.

Effects of Low-Level Blast on Neurovascular Health and Cerebral Blood Flow: Current Findings and Future Opportunities in Neuroimaging

Low-level blast (LLB) exposure can lead to alterations in neurological health, cerebral vasculature, and cerebral blood flow (CBF). The development of cognitive issues and behavioral abnormalities after LLB, or subconcussive blast exposure, is insidious due to the lack of acute symptoms. One major hallmark of LLB exposure is the initiation of neurovascular damage followed by the development of neurovascular dysfunction. Preclinical studies of LLB exposure demonstrate impairment to cerebral vasculature and the blood-brain barrier (BBB) at both early and long-term stages following LLB. Neuroimaging techniques, such as arterial spin labeling (ASL) using magnetic resonance imaging (MRI), have been utilized in clinical investigations to understand brain perfusion and CBF changes in response to cumulative LLB exposure. In this review, we summarize neuroimaging techniques that can further our understanding of the underlying mechanisms of blast-related neurotrauma, specifically after LLB. Neuroimaging related to cerebrovascular function can contribute to improved diagnostic and therapeutic strategies for LLB. As these same imaging modalities can capture the effects of LLB exposure in animal models, neuroimaging can serve as a gap-bridging diagnostic tool that permits a more extensive exploration of potential relationships between blast-induced changes in CBF and neurovascular health. Future research directions are suggested, including investigating chronic LLB effects on cerebral perfusion, exploring mechanisms of dysautoregulation after LLB, and measuring cerebrovascular reactivity (CVR) in preclinical LLB models.

Post-Traumatic Cerebral Infarction: A Narrative Review of Pathophysiology, Diagnosis, and Treatment

Traumatic brain injury (TBI) is a common diagnosis requiring acute hospitalization. Long-term, TBI is a significant source of health and socioeconomic impact in the United States and globally. The goal of clinicians who manage TBI is to prevent secondary brain injury. In this population, post-traumatic cerebral infarction (PTCI) acutely after TBI is an important but under-recognized complication that is associated with negative functional outcomes. In this comprehensive review, we describe the incidence and pathophysiology of PTCI. We then discuss the diagnostic and treatment approaches for the most common etiologies of isolated PTCI, including brain herniation syndromes, cervical artery dissection, venous thrombosis, and post-traumatic vasospasm. In addition to these mechanisms, hypercoagulability and microcirculatory failure can also exacerbate ischemia. We aim to highlight the importance of this condition and future clinical research needs with the goal of improving patient outcomes after TBI.

Low-intensity open-field blast exposure effects on neurovascular unit ultrastructure in mice

Mild traumatic brain injury (mTBI) induced by low-intensity blast (LIB) is a serious health problem affecting military service members and veterans. Our previous reports using a single open-field LIB mouse model showed the absence of gross microscopic damage or necrosis in the brain, while transmission electron microscopy (TEM) identified ultrastructural abnormalities of myelin sheaths, mitochondria, and synapses. The neurovascular unit (NVU), an anatomical and functional system with multiple components, is vital for the regulation of cerebral blood flow and cellular interactions. In this study, we delineated ultrastructural abnormalities affecting the NVU in mice with LIB exposure quantitatively and qualitatively. Luminal constrictive irregularities were identified at 7 days post-injury (DPI) followed by dilation at 30 DPI along with degeneration of pericytes. Quantitative proteomic analysis identified significantly altered vasomotor-related proteins at 24 h post-injury. Endothelial cell, basement membrane and astrocyte end-foot swellings, as well as vacuole formations, occurred in LIB-exposed mice, indicating cellular edema. Structural abnormalities of tight junctions and astrocyte end-foot detachment from basement membranes were also noted. These ultrastructural findings demonstrate that LIB induces multiple-component NVU damage. Prevention of NVU damage may aid in identifying therapeutic targets to mitigate the effects of primary brain blast injury.

Particular Surgical Technique for Transorbital-Penetrating Craniocerebral Injury Inflicted by a Screwdriver: Technical Case Report

Surgical techniques for non-missile penetrating brain injuries (PBI) are challenging because they require good preoperative planning. Generally, extraction is performed ipsilaterally at the entry site. In certain cases, the extraction can be performed contralaterally through the inner end of the foreign body; however, this requires special consideration. We present a case report of a patient who had a stab wound on the head via a screwdriver and underwent surgery, during which extraction was performed contralaterally through the inner end of the screwdriver without inducing any neurological deficit. Careful preoperative planning and surgical technique modification are required to minimize morbidity and mortality in patients with PBIs.

Outcomes following therapeutic intervention of post-traumatic vasospasm: A systematic review and meta-analysis

BACKGROUND

Vasospasm occurrence following traumatic brain injury may impact neurologic and functional recovery of patients, yet treatment of post-traumatic vasospasm (PTV) has not been well documented. This systematic review and meta-analysis aims to assess the current evidence regarding favorable outcome as measured by Glasgow Outcome Scale (GOS) scores following treatment of PTV.

METHODS

A systematic review of PubMed, Ovid MEDLINE, and Ovid EMBASE was conducted following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. Included manuscripts were methodically scrutinized for quality; occurrence of PTV; rate of favorable outcome following each treatment modality; and follow-up duration. Treatments evaluated were calcium channel blockers (CCBs), endovascular intervention, and dopamine-induced hypertension. Outcomes were compared via the random-effects analysis.

RESULTS

Fourteen studies with 1885 PTV patients were quantitatively analyzed: 982 patients who received tailored therapeutic intervention and 903 patients who did not receive tailored therapy. For patients undergoing treatment, the rate of favorable outcome was 57.3 % (500/872 patients; 95 % CI 54.1 - 60.6 %) following administration of CCBs, 94.1 % (16/17 patients; 95 % CI 82.9 - 100.0 %) following endovascular intervention, and 54.8 % (51/93 patients; 95 % CI 44.7 - 65.0 %) following dopamine-induced hypertension. Of note, the endovascular group had the highest rate of favorable outcome but was also the smallest sample size (n = 17). Patients who received tailored therapeutic intervention for PTV had a higher rate of favorable outcome than patients who did not receive tailored therapy: 57.7 % (567/982 patients; 95 % CI 54.1 - 60.8 %) versus 52.0 % (470/903 patients; 95 % CI 48.8 - 55.3 %), respectively.

CONCLUSIONS

The available data suggests that tailored therapeutic intervention of PTV results in a favorable outcome. While endovascular intervention of PTV had the highest rate of favorable outcome, both CCB administration and dopamine-induced hypertension had similar lower rates of favorable outcome.

Neuroendovascular Surgery Applications in Craniocervical Trauma

Cerebrovascular injuries resulting from blunt or penetrating trauma to the head and neck often lead to local hemorrhage and stroke. These injuries present with a wide range of manifestations, including carotid or vertebral artery dissection, pseudoaneurysm, occlusion, transection, arteriovenous fistula, carotid-cavernous fistula, epistaxis, venous sinus thrombosis, and subdural hematoma. A selective review of the literature from 1989 to 2023 was conducted to explore various neuroendovascular surgical techniques for craniocervical trauma. A PubMed search was performed using these terms: endovascular, trauma, dissection, blunt cerebrovascular injury, pseudoaneurysm, occlusion, transection, vasospasm, carotid-cavernous fistula, arteriovenous fistula, epistaxis, cerebral venous sinus thrombosis, subdural hematoma, and middle meningeal artery embolization. An increasing array of neuroendovascular procedures are currently available to treat these traumatic injuries. Coils, liquid embolics (onyx or n-butyl cyanoacrylate), and polyvinyl alcohol particles can be used to embolize lesions, while stents, mechanical thrombectomy employing stent-retrievers or aspiration catheters, and balloon occlusion tests and super selective angiography offer additional treatment options based on the specific case. Neuroendovascular techniques prove valuable when surgical options are limited, although comparative data with surgical techniques in trauma cases is limited. Further research is needed to assess the efficacy and outcomes associated with these interventions.

Double Blast Wave Primary Effect on Synaptic, Glymphatic, Myelin, Neuronal and Neurovascular Markers

Explosive blasts are associated with neurological consequences as a result of blast waves impact on the brain. Yet, the neuropathologic and molecular consequences due to blast waves vs. blunt-TBI are not fully understood. An explosive-driven blast-generating system was used to reproduce blast wave exposure and examine pathological and molecular changes generated by primary wave effects of blast exposure. We assessed if pre- and post-synaptic (synaptophysin, PSD-95, spinophilin, GAP-43), neuronal (NF-L), glymphatic (LYVE1, podoplanin), myelin (MBP), neurovascular (AQP4, S100β, PDGF) and genomic (DNA polymerase-β, RNA polymerase II) markers could be altered across different brain regions of double blast vs. sham animals. Twelve male rats exposed to two consecutive blasts were compared to 12 control/sham rats. Western blot, ELISA, and immunofluorescence analyses were performed across the frontal cortex, hippocampus, cerebellum, and brainstem. The results showed altered levels of AQP4, S100β, DNA-polymerase-β, PDGF, synaptophysin and PSD-95 in double blast vs. sham animals in most of the examined regions. These data indicate that blast-generated changes are preferentially associated with neurovascular, glymphatic, and DNA repair markers, especially in the brainstem. Moreover, these changes were not accompanied by behavioral changes and corroborate the hypothesis for which an asymptomatic altered status is caused by repeated blast exposures.

A combat casualty relevant dismounted complex blast injury model in swine

BACKGROUND

Improvised explosive devices have resulted in a unique polytrauma injury pattern termed dismounted complex blast injury (DCBI), which is frequent in the modern military theater. Dismounted complex blast injury is characterized by extremity amputations, junctional vascular injury, and blast traumatic brain injury (bTBI). We developed a combat casualty relevant DCBI swine model, which combines hemorrhagic shock (HS) and tissue injury (TI) with a bTBI, to study interventions in this unique and devastating military injury pattern.

METHODS

A 50-kg male Yorkshire swine were randomized to the DCBI or SHAM group (instrumentation only). Those in the DCBI group were subjected to HS, TI, and bTBI. The blast injury was applied using a 55-psi shock tube wave. Tissue injury was created with bilateral open femur fractures. Hemorrhagic shock was induced by bleeding from femoral arteries to target pressure. A resuscitation protocol modified from the Tactical Combat Casualty Care guidelines simulated battlefield resuscitation for 240 minutes.

RESULTS

Eight swine underwent the DCBI model and five were allocated to the SHAM group. In the DCBI model the mean base excess achieved at the end of the HS shock was -8.57 ± 5.13 mmol·L -1 . A significant coagulopathy was detected in the DCBI model as measured by prothrombin time (15.8 seconds DCBI vs. 12.86 seconds SHAM; p = 0.02) and thromboelastography maximum amplitude (68.5 mm DCBI vs. 78.3 mm in SHAM; p = 0.0003). For the DCBI models, intracranial pressure (ICP) increased by a mean of 13 mm Hg, reaching a final ICP of 24 ± 7.7 mm Hg.

CONCLUSION

We created a reproducible large animal model to study the combined effects of severe HS, TI, and bTBI on coagulation and ICP in the setting of DCBI, with significant translational applications for the care of military warfighters. Within the 4-hour observational period, the swine developed a consistent coagulopathy with a concurrent brain injury evidenced by increasing ICP.

Zone 1 REBOA in a combat DCBI swine model does not worsen brain injury

BACKGROUND

Zone 1 resuscitative endovascular balloon occlusion of the aorta has been recommended for refractory shock after a dismounted complex blast injury for the austere combat scenario. While resuscitative endovascular balloon occlusion of the aorta should enhance coronary perfusion, there is a potential risk of secondary brain injury due to loss of cerebral autoregulation. We developed a combat casualty relevant dismounted complex blast injury swine model to evaluate the effects of resuscitative endovascular balloon occlusion of the aorta zone I on intracranial pressure and cerebral edema. We hypothesized that zone 1 aortic occlusion with resuscitative endovascular balloon occlusion of the aorta would increase mean arterial pressure transmitted in excessive intracranial pressure, thereby worsening brain injury.

METHODS

50 kg male Yorkshire swine were subjected to a combination dismounted complex blast injury model consisting of blast traumatic brain injury (50 psi, ARA Mobile Shock Laboratory), tissue injury (bilateral femur fractures), and hemorrhagic shock (controlled bleeding to a base deficit goal of 10 mEq/L). During the shock phase, pigs were randomized to no aortic occlusion (n = 8) or to 30 minutes of zone 1 resuscitative endovascular balloon occlusion of the aorta (zone 1 aortic occlusion group, n = 6). After shock, pigs in both groups received a modified Tactical Combat Casualty Care-based resuscitation and were monitored for an additional 240 minutes until euthanasia/death for a total of 6 hours. Intracranial pressure was monitored throughout, and brains were harvested for water content. Linear mixed models for repeated measures were used to compare mean arterial pressure and intracranial pressure between zone 1 aortic occlusion and no aortic occlusion groups.

RESULTS

After dismounted complex blast injury, the zone 1 group had a significantly higher mean arterial pressure during hemorrhagic shock compared to the control group (41.2 mm Hg vs 16.7 mm Hg, P = .002). During balloon occlusion, intracranial pressure was not significantly elevated in the zone 1 aortic occlusion group vs control, but intracranial pressure was significantly lower in the zone 1 group at the end of the observation period. In addition, the zone 1 aortic occlusion group did not have increased brain water content (zone 1 aortic occlusion: 3.95 ± 0.1g vs no aortic occlusion: 3.95 ± 0.3 g, P = .87). Troponin levels significantly increased in the no aortic occlusion group but did not in the zone 1 aortic occlusion group.

CONCLUSION

Zone 1 aortic occlusion using resuscitative endovascular balloon occlusion of the aorta in a large animal dismounted complex blast injury model improved proximal mean arterial pressure while not significantly increasing intracranial pressure during balloon inflation. Observation up to 240 minutes postresuscitation did not show clinical signs of worsening brain injury or cardiac injury. These data suggest that in a dismounted complex blast injury swine model, resuscitative endovascular balloon occlusion of the aorta in zone 1 may provide neuro- and cardioprotection in the setting of blast traumatic brain injury. However, longer monitoring periods may be needed to confirm that the neuroprotection is lasting.

Rationale and Methods for Updated Guidelines for the Management of Penetrating Traumatic Brain Injury

Penetrating traumatic brain injury (pTBI) affects civilian and military populations resulting in significant morbidity, mortality, and healthcare costs. No up-to-date and evidence-based guidelines exist to assist modern medical and surgical management of these complex injuries. A preliminary literature search revealed a need for updated guidelines, supported by the Brain Trauma Foundation. Methodologists experienced in TBI guidelines were recruited to support project development alongside two cochairs and a diverse steering committee. An expert multi-disciplinary workgroup was established and vetted to inform key clinical questions, to perform an evidence review and the development of recommendations relevant to pTBI. The methodological approach for the project was finalized. The development of up-to-date evidence- and consensus-based clinical care guidelines and algorithms for pTBI will provide critical guidance to care providers in the pre-hospital and emergent, medical, and surgical settings.

Vasospasm Surveillance by a Simplified Transcranial Doppler Protocol in Traumatic Brain Injury

OBJECTIVE

To detect post-traumatic vasospasm in patients with traumatic brain injury (TBI), we implemented a simplified transcranial Doppler (TCD) surveillance protocol in a neurointensive care setting. In this study, we evaluate the yield of this protocol.

METHODS

Adult patients with TBI admitted to the neurointensive care unit were examined with TCD by 2 intensive care nurses trained in TCD examinations. Flow velocities of the middle cerebral arteries were recorded. TCD suspected vasospasm was defined as the mean flow velocity >120 cm/s, and when detected, the protocol recommended a supplementary computed tomography angiography. The rate of detection of TCD suspected vasospasm and the subsequent rate of radiological diagnosis of vasospasm were recorded. In multivariate logistic regression analysis, we evaluated age, initial Glasgow Coma Scale, craniotomy, and decompressive craniectomy as potential predictors of developing increased TCD velocity.

RESULTS

A total of 84 patients with TBI with a median initial Glasgow Coma Scale score of 6 were examined by TCD. TCD suspected vasospasm was found in the middle cerebral arteries of 18% of examined patients. Two-thirds of patients with TCD suspected vasospasm were investigated with a subsequent computed tomography angiography, and 80% of these patients received a radiological diagnosis of vasospasm. In logistic regression analysis, decompressive craniectomy was significantly associated with increased risk of developing TCD suspected vasospasm (odds ratio: 11.57, 95% confidence interval: 2.59-51.73, P = 0.001).

CONCLUSIONS

The implementation of a simplified TCD surveillance protocol in a neurointensive care setting yielded an 18% detection rate of TCD suspected vasospasm. In our cohort of patients with TBI, decompressive craniectomy was associated with increased risk of developing TCD suspected vasospasm.

Blast-related traumatic brain injury: Report of a severe case and review of the literature

Background:

Traumatic brain injury (TBI) is a well-known brain dysfunction commonly encountered in activities such as military combat or collision sports. The etiopathology can vary depending on the context and bomb explosions are becoming increasingly common in war zones, urban terrorist attacks, and civilian criminal feuds. Blast-related TBI may cause the full severity range of neurotrauma, from a mild concussion to severe, penetrating injury. Recent classifications of the pathophysiological mechanisms comprise five factors that reflect the gravity of the experienced trauma and suggest to the clinician different pathways of injury and consequent pathology caused by the explosion.

Case Description:

In the present report, the authors describe a case of 26 years old presenting with blast-related severe TBI caused by the detonation of an explosive in an amusement arcade. Surgical decompression to control intracranial pressure and systemic antibiotic treatment to manage and prevent wound infections were the main options available in a civilian hospital.

Conclusion:

While numerous studies examined the burden of blast-related brain injuries on service members, few papers have tackled this problem in a civilian setting, where hospitals are not sufficiently equipped, and physicians lack the necessary training. The present case demonstrates the urgent need for evidence-based diagnostic and therapeutic protocols in civilian hospitals that would improve the outcome of such patients.

A Novel Gating Mechanism of Aquaporin-4 Water Channel Mediated by Blast Shockwaves for Brain Edema

As the principal water channel in the brain, aquaporin-4 (AQP4) plays a vital role in brain edema, but its role in blast brain edema is unclear. On the basis of molecular simulations, we reveal the atomically detailed picture of AQP4 in response to blast shockwaves. The results show that the shockwave alone closes the AQP4 channel; however, shock-induced bubble collapse opens it. The jet from bubble collapse forcefully increases the distance between helices and the tilt angles of six helices relative to the membrane vertical direction in a very short time. The average channel size increases about 2.6 times, and the water flux rate is nearly 20 times higher than for normal states. It is responsible for abnormal water transport and a potential cause of acute blast brain edema. Additionally, the open AQP4 channel quickly returns to its normal state, which is in turn helpful for edema absorption. Thus, a novel gating mechanism for AQP4 related to the secondary structure change has been provided, which is different from the previous residue-mediated gating mechanism.

Cerebral vascular strains in dynamic head impact using an upgraded model with brain material property heterogeneity

Cerebral vascular injury (CVI) is a frequent consequence of traumatic brain injury but has often been neglected. Substantial experimental work exists on vascular material properties and failure/subfailure thresholds. However, little is known about vascular in vivo loading conditions in dynamic head impact, which is necessary to investigate the risk, severity, and extent of CVI. In this study, we resort to the Worcester Head Injury Model (WHIM) V2.1 for investigation. The model embeds the cerebral vasculature network and is further upgraded to incorporate brain material property heterogeneity based on magnetic resonance elastography. The brain material property is calibrated to match with the previously validated anisotropic V1.0 version in terms of whole-brain strains against six experimental datasets of a wide range of blunt impact conditions. The upgraded WHIM is finally used to simulate five representative real-world head impacts drawn from contact sports and automotive crashes. We find that peak strains in veins are considerably higher than those in arteries and that peak circumferential strains are also higher than peak axial strains. For a typical concussive head impact, cerebral vascular axial strains reach the lowest reported yield strain of ∼7-8%. For severe automotive impacts, axial strains could reach ∼20%, which is on the order of the lowest reported ultimate failure strain of ∼24%. These results suggest in vivo mechanical loading conditions of the cerebral vasculature (excluding bridging veins not assessed here) due to rapid head rotation are at the lower end of failure/subfailure thresholds established from ex vivo experiments. This study provides some first insight into the risk, severity, and extent of CVI in real-world head impacts.

Localizing Clinical Patterns of Blast Traumatic Brain Injury Through Computational Modeling and Simulation

Blast traumatic brain injury is ubiquitous in modern military conflict with significant morbidity and mortality. Yet the mechanism by which blast overpressure waves cause specific intracranial injury in humans remains unclear. Reviewing of both the clinical experience of neurointensivists and neurosurgeons who treated service members exposed to blast have revealed a pattern of injury to cerebral blood vessels, manifested as subarachnoid hemorrhage, pseudoaneurysm, and early diffuse cerebral edema. Additionally, a seminal neuropathologic case series of victims of blast traumatic brain injury (TBI) showed unique astroglial scarring patterns at the following tissue interfaces: subpial glial plate, perivascular, periventricular, and cerebral gray-white interface. The uniting feature of both the clinical and neuropathologic findings in blast TBI is the co-location of injury to material interfaces, be it solid-fluid or solid-solid interface. This motivates the hypothesis that blast TBI is an injury at the intracranial mechanical interfaces. In order to investigate the intracranial interface dynamics, we performed a novel set of computational simulations using a model human head simplified but containing models of gyri, sulci, cerebrospinal fluid (CSF), ventricles, and vasculature with high spatial resolution of the mechanical interfaces. Simulations were performed within a hybrid Eulerian—Lagrangian simulation suite (CTH coupled via Zapotec to Sierra Mechanics). Because of the large computational meshes, simulations required high performance computing resources. Twenty simulations were performed across multiple exposure scenarios—overpressures of 150, 250, and 500 kPa with 1 ms overpressure durations—for multiple blast exposures (front blast, side blast, and wall blast) across large variations in material model parameters (brain shear properties, skull elastic moduli). All simulations predict fluid cavitation within CSF (where intracerebral vasculature reside) with cavitation occurring deep and diffusely into cerebral sulci. These cavitation events are adjacent to high interface strain rates at the subpial glial plate. Larger overpressure simulations (250 and 500kPa) demonstrated intraventricular cavitation—also associated with adjacent high periventricular strain rates. Additionally, models of embedded intraparenchymal vascular structures—with diameters as small as 0.6 mm—predicted intravascular cavitation with adjacent high perivascular strain rates. The co-location of local maxima of strain rates near several of the regions that appear to be preferentially damaged in blast TBI (vascular structures, subpial glial plate, perivascular regions, and periventricular regions) suggest that intracranial interface dynamics may be important in understanding how blast overpressures leads to intracranial injury.

Blast-induced temporal alterations in blood-brain barrier properties in a rodent model

The consequences of blast-induced traumatic brain injury (bTBI) on the blood–brain barrier (BBB) and components of the neurovascular unit are an area of active research. In this study we assessed the time course of BBB integrity in anesthetized rats exposed to a single blast overpressure of 130 kPa (18.9 PSI). BBB permeability was measured in vivo via intravital microscopy by imaging extravasation of fluorescently labeled tracers (40 kDa and 70 kDa molecular weight) through the pial microvasculature into brain parenchyma at 2–3 h, 1, 3, 14, or 28 days after the blast exposure. BBB structural changes were assessed by immunostaining and molecular assays. At 2–3 h and 1 day after blast exposure, significant increases in the extravasation of the 40 kDa but not the 70 kDa tracers were observed, along with differential reductions in the expression of tight junction proteins (occludin, claudin-5, zona occluden-1) and increase in the levels of the astrocytic water channel protein, AQP-4, and matrix metalloprotease, MMP-9. Nearly all of these measures were normalized by day 3 and maintained up to 28 days post exposure. These data demonstrate that blast-induced changes in BBB permeability are closely coupled to structural and functional components of the BBB.

Biaxial softening of isolated cerebral arteries following axial overstretch

Arteries play a critical role in carrying essential nutrients and oxygen throughout the brain; however, vessels can become damaged in traumatic brain injury (TBI), putting neural tissue at risk. Even in the absence of hemorrhage, large deformations can disrupt both the physiological and mechanical behavior of the cerebral vessels. Our group recently reported the effect of vessel overstretch on axial mechanics; however, that work did not address possible changes in circumferential mechanics that are critical to the regulation of blood flow. In order to address this in the present work, ovine middle cerebral arteries were isolated and overstretched axially to 10, 20, or 40% beyond the in vivo configuration. Results showed a statistically significant decrease in circumferential stiffness and strain energy, as well as an increase in vessel diameter following 40% overstretch (p < 0.05). These passive changes would lead to a decrease in vascular resistance and likely play a role in previous reports of cellular dysfunction. We anticipate that our findings will both increase understanding of vessel softening phenomena and also promote improved modeling of cerebrovascular mechanics following head trauma.

An Endovascular Surgery Experience in Far-Forward Military Healthcare-A Case Series

SUMMARY

INTRODUCTION

The advancement of interventional neuroradiology has drastically altered the treatment of stroke and trauma patients. These advancements in first-world hospitals, however, have rarely reached far forward military hospitals due to limitations in expertise and equipment. In an established role III military hospital though, these life-saving procedures can become an important tool in trauma care.

MATERIALS AND METHODS

We report a retrospective series of far-forward endovascular cases performed by 2 deployed dual-trained neurosurgeons at the role III hospital in Kandahar, Afghanistan during 2013 and 2017 as part of Operations Resolute Support and Enduring Freedom.

RESULTS

A total of 15 patients were identified with ages ranging from 5 to 42 years old. Cases included 13 diagnostic cerebral angiograms, 2 extremity angiograms and interventions, 1 aortogram and pelvic angiogram, 1 bilateral embolization of internal iliac arteries, 1 lingual artery embolization, 1 administration of intra-arterial thrombolytic, and 2 mechanical thrombectomies for acute ischemic stroke. There were no complications from the procedures. Both embolizations resulted in hemorrhage control, and 1 of 2 stroke interventions resulted in the improvement of the NIH stroke scale.

CONCLUSIONS

Interventional neuroradiology can fill an important role in military far forward care as these providers can treat both traumatic and atraumatic cerebral and extracranial vascular injuries. In addition, knowledge and skill with vascular access and general interventional radiology principles can be used to aid in other lifesaving interventions. As interventional equipment becomes more available and portable, this relatively young specialty can alter the treatment for servicemen and women who are injured downrange.

Unrepaired decompressive craniectomy worsens motor performance in a rat traumatic brain injury model

Decompressive craniectomy (DC) is often required to manage rising intracranial pressure after traumatic brain injury (TBI). Syndrome of the trephine (SoT) is a reversible neurologic condition that often occurs following DC as a result of the unrepaired skull. The purpose of the present study is to characterize neurological impairment following TBI in rats with an unrepaired craniectomy versus rats with a closed cranium. Long Evans male rats received a controlled cortical impact (CCI) over the caudal forelimb area (CFA) of the motor cortex. Immediately after CCI, rats received either a hemi-craniectomy (TBI Open Skull Group) or an immediate acrylic cranioplasty restoring cranial anatomy (TBI Closed Skull Group). Motor performance was assessed on a skilled reaching task on post-CCI weeks 1—4, 8, 12, and 16. Three weeks after the CCI injury, the TBI Closed Skull Group demonstrated improved motor performance compared to TBI Open Skull Group. The TBI Closed Skull Group continued to perform better than the TBI Open Skull Group throughout weeks 4, 8, 12 and 16. The protracted recovery of CFA motor performance demonstrated in rats with unrepaired skulls following TBI suggests this model may be beneficial for testing new therapeutic approaches to prevent SoT.

Periventricular White Matter Alterations From Explosive Blast in a Large Animal Model: Mild Traumatic Brain Injury or "Subconcussive" Injury?

The neuropathology of mild traumatic brain injury in humans resulting from exposure to explosive blast is poorly understood as this condition is rarely fatal. A large animal model may better reflect the injury patterns in humans. We investigated the effect of explosive blasts on the constrained head minimizing the effects of whole head motion. Anesthetized Yucatan minipigs, with body and head restrained, were placed in a 3-walled test structure and exposed to 1, 2, or 3 explosive blast shock waves of the same intensity. Axonal injury was studied 3 weeks to 8 months postblast using β-amyloid precursor protein immunohistochemistry. Injury was confined to the periventricular white matter as early as 3-5 weeks after exposure to a single blast. The pattern was also present at 8 months postblast. Animals exposed to 2 and 3 blasts had more axonal injury than those exposed to a single blast. Although such increases in axonal injury may relate to the longer postblast survival time, it may also be due to the increased number of blast exposures. It is possible that the injury observed is due to a condition akin to mild traumatic brain injury or subconcussive injury in humans, and that periventricular injury may have neuropsychiatric implications.

Prehospital Detection of Life-Threatening Intracranial Pathology: An Unmet Need for Severe TBI in Austere, Rural, and Remote Areas

Severe traumatic brain injury (TBI) is a leading cause of death and disability worldwide, especially in low- and middle-income countries, and in austere, rural, and remote settings. The purpose of this Perspective is to challenge the notion that accurate and actionable diagnosis of the most severe brain injuries should be limited to physicians and other highly-trained specialists located at hospitals. Further, we aim to demonstrate that the great opportunity to improve severe TBI care is in the prehospital setting. Here, we discuss potential applications of prehospital diagnostics, including ultrasound and near-infrared spectroscopy (NIRS) for detection of life-threatening subdural and epidural hemorrhage, as well as monitoring of cerebral hemodynamics following severe TBI. Ultrasound-based methods for assessment of cerebrovascular hemodynamics, vasospasm, and intracranial pressure have substantial promise, but have been mainly used in hospital settings; substantial development will be required for prehospital optimization. Compared to ultrasound, NIRS is better suited to assess certain aspects of intracranial pathology and has a smaller form factor. Thus, NIRS is potentially closer to becoming a reliable method for non-invasive intracranial assessment and cerebral monitoring in the prehospital setting. While one current continuous wave NIRS-based device has been FDA-approved for detection of subdural and epidural hemorrhage, NIRS methods using frequency domain technology have greater potential to improve diagnosis and monitoring in the prehospital setting. In addition to better technology, advances in large animal models, provider training, and implementation science represent opportunities to accelerate progress in prehospital care for severe TBI in austere, rural, and remote areas.

Sex as a Biological Variable in Preclinical Modeling of Blast-Related Traumatic Brain Injury

Approaches to furthering our understanding of the bioeffects, behavioral changes, and treatment options following exposure to blast are a worldwide priority. Of particular need is a more concerted effort to employ animal models to determine possible sex differences, which have been reported in the clinical literature. In this review, clinical and preclinical reports concerning blast injury effects are summarized in relation to sex as a biological variable (SABV). The review outlines approaches that explore the pertinent role of sex chromosomes and gonadal steroids for delineating sex as a biological independent variable. Next, underlying biological factors that need exploration for blast effects in light of SABV are outlined, including pituitary, autonomic, vascular, and inflammation factors that all have evidence as having important SABV relevance. A major second consideration for the study of SABV and preclinical blast effects is the notable lack of consistent model design—a wide range of devices have been employed with questionable relevance to real-life scenarios—as well as poor standardization for reporting of blast parameters. Hence, the review also provides current views regarding optimal design of shock tubes for approaching the problem of primary blast effects and sex differences and outlines a plan for the regularization of reporting. Standardization and clear description of blast parameters will provide greater comparability across models, as well as unify consensus for important sex difference bioeffects.

Bibliometric Analysis of the Top 100 Most Cited Articles on Cerebral Vasospasm

OBJECTIVE

Bibliometric analysis reflects the scientific recognition and influential performance of a published article within its field. Our aim is to identify and analyze the top 100 most-cited articles on cerebral vasospasm.

METHODS

A title-specific search was carried out using the Scopus database. The top 100 cited articles including the keywords "Cerebral Vasospasm" AND "Vasospasm" were retrieved and stratified in a descending order: title, authors, institution, publishing journal, country of origin, year of publication, and topic of each article were studied.

RESULTS

The top 100 articles have an accumulative citation count of 20,972, with 209 average citations per article. Publication dates ranged from 1968 to 2012, with the most productive years between 1998 and 2005. Clinical studies are the most frequent category, followed by pathophysiology. The list includes 7 clinical trials, which received accumulative citations of 1525. The top cited article had received 2109 citations, with 52.7 citations per year. The top 100 articles were published across 14 countries, with most originating from the United States. The lead research institution was the University of Alberta. The most used journal was Journal of Neurosurgery.

CONCLUSIONS

Bibliometric analysis has garnered major interest in recent years. It shows the publication trends, knowledge evolution, and evidence-based practice throughout the years. The collection of highly cited articles may assist physicians in gaining a better understanding of the nature of cerebral vasospasm and optimize their clinical practice.

The Silver Lining: Advances in the Surgical Management of Brain Trauma Attributable to War

Within the text we elaborate on the relationship between war and medicine, particularly as it pertains to neurosurgery and the management of brain trauma, and emphasize neurosurgical advancements in the treatment of brain trauma gleaned from U.S.-involved conflicts of the 21st century.

Treatment of traumatic intracranial aneurysm: Experiences at a single center

OBJECTIVE

To report the treatment and outcome of traumatic intracranial aneurysm (TICA) cases at the Southwest Hospital, Army Medical University in China.

PATIENTS AND METHODS

All patients diagnosed with TICA at our institution from January 1, 1977, to October 31, 2018, and meeting the inclusion/exclusion criteria were included in the study. Cases were reported separately for those diagnosed before 1998 and those after 1998.

RESULTS

A total of 25 patients were included in the study. Ten were diagnosed with TICA prior to 1998. Seven of these 10 patients were treated surgically with parent artery sacrificed, including aneurysmectomy, trapping, and bypass. The mean Glasgow Outcome Scale (GOS) score for the 7 patients with surgical treatment was 3.1. Three of the 10 patients died of severe complications, including intracranial infection, delayed bleeding, and deadly injury. After 1998, 15 patients were diagnosed with TICA. Thirteen presented with head trauma and two with iatrogenic TICA following ventricle drainage or sphenoid ridge meningioma resection. Thirteen were treated with endovascular treatment, including coil alone, glue, coil-associated glue, stent alone, stent-assisted coil embolization, one with clipping, and one with conservative treatment. The 13 patients with endovascular treatment achieved a mean GOS score of 4.5. Among the 13 patients, one died from intracranial infection, one suffered recurrence, and one had intraoperative rupture.

CONCLUSION

Although the treatment of TICA has traditionally been surgical, endovascular treatment with different techniques, such as endovascular patch, provides a valuable alternative. Currently, the flow diverter is a popular embolization device and may represent another valid treatment option for TICA.

Ocular changes in traumatic brain injury: A review

Traumatic brain injury is represented by a penetrating or non-penetrating head injury, which causes disruption in the normal functioning of the brain. Traumatic brain injury has been an ardently debated topic of discussion due to its prevalence in media centric persons such as military personnel and athletes. Current assessments for traumatic brain injury have looked at vestibulo-ocular and vascular parameters to aid in diagnosis. Innovations in non-invasive ophthalmic imaging have allowed for the visualization of specific tissue structure/function relationships in a variety of ophthalmic and neurodegenerative diseases. As the eye and brain share significant embryological and physiological pathways, ocular imaging modalities may provide a novel and impactful tool in advancing assessment of traumatic brain injury. Herein, we examined the available literature and data on visual fields, mean retinal nerve fiber layer thickness, retinal ganglion cell layer thickness, and cerebral blood flow following traumatic brain injury. This review of published individual and population-based studies was performed in order to explore the feasibility and importance of considering ocular imaging biomarkers following traumatic brain injury.

Exposure to Blast Overpressure Impairs Cerebral Microvascular Responses and Alters Vascular and Astrocytic Structure

Exposure to blast overpressure may result in cerebrovascular impairment, including cerebral vasospasm. The mechanisms contributing to this vascular response are unclear. The aim of this study was to evaluate the relationship between blast and functional alterations of the cerebral microcirculation and to investigate potential underlying changes in vascular microstructure. Cerebrovascular responses were assessed in sham- and blast-exposed male rats at multiple time points from 2 h through 28 days after a single 130-kPa (18.9-psi) exposure. Pial microcirculation was assessed through a cranial window created in the parietal bone of anesthetized rats. Pial arteriolar reactivity was evaluated in vivo using hypercapnia, barium chloride, and serotonin. We found that exposure to blast leads to impairment of arteriolar reactivity >24 h after blast exposure, suggesting delayed injury mechanisms that are not simply attributed to direct mechanical deformation. Observed vascular impairment included a reduction in hypercapnia-induced vasodilation, increase in barium-induced constriction, and reversal of the serotonin effect from constriction to dilation. A reduction in vascular smooth muscle contractile proteins consistent with vascular wall proliferation was observed, as well as delayed reduction in nitric oxide synthase and increase in endothelin-1 B receptors, mainly in astrocytes. Collectively, the data show that exposure to blast results in delayed and prolonged alterations in cerebrovascular reactivity that are associated with changes in the microarchitecture of the vessel wall and astrocytes. These changes may contribute to long-term pathologies involving dysfunction of the neurovascular unit, including cerebral vasospasm.

The TRPC6 inhibitor, larixyl acetate, is effective in protecting against traumatic brain injury-induced systemic endothelial dysfunction

BACKGROUND

The incidence of traumatic brain injuries (TBIs) is on the rise in the USA. Concussions, or mild TBIs without skull fracture, account for about 75% of all TBIs. Mild TBIs (mTBIs) lead to memory and cognitive deficits, headaches, intraocular pressure rises, axonal degeneration, neuroinflammation, and an array of cerebrovascular dysfunctions, including increased vascular permeability and decreased cerebral blood flow. It has been recently reported that besides vascular dysfunction in the cerebral circulation, mTBI may also cause a significant impairment of endothelial function in the systemic circulation, at least within mesenteric microvessels. In this study, we investigated whether mTBI affects endothelial function in aortas and determined the contribution of transient receptor potential canonical (TRPC) channels to modulating mTBI-associated endothelial dysfunction.

METHODS

We used a model of closed-head mTBI in C57BL/6, 129S, 129S-C57BL/6-F2 mice, and 129S-TRPC1 and 129S-C57BL/6-TRPC6 knockout mice to determine the effect of mTBI on endothelial function in mouse aortas employing ex vivo isometric tension measurements. Aortic tissue was also analyzed using immunofluorescence and qRT-PCR for TRPC6 expression following mTBI.

RESULTS

We show that in various strains of mice, mTBI induces a pronounced and long-lasting endothelial dysfunction in the aorta. Ablation of TRPC6 protects mice from mTBI-associated aortic endothelial dysfunction, while TRPC1 ablation does not impact brain injury-induced endothelial impairment in the aorta. Consistent with a role of TRPC6 activation following mTBI, we observed improved endothelial function in wild type control mice subjected to mTBI following 7-day in vivo treatment with larixyl acetate, an inhibitor of TRPC6 channels. Conversely, in vitro treatment with the pro-inflammatory endotoxin lipopolysaccharide, which activates endothelial TRPC6 in a Toll-like receptor type 4 (TLR4)-dependent manner, worsened aortic endothelial dysfunction in wild type mice. Lipopolysaccharide treatment in vitro failed to elicit endothelial dysfunction in TRPC6 knockout mice. No change in endothelial TRPC6 expression was observed 7 days following TBI.

CONCLUSIONS

These data suggest that TRPC6 activation may be critical for inducing endothelial dysfunction following closed-head mTBI and that pharmacological inhibition of the channel may be a feasible therapeutic strategy for preventing mTBI-associated systemic endothelial dysfunction.

Low-level blast exposure disrupts gliovascular and neurovascular connections and induces a chronic vascular pathology in rat brain

Much concern exists over the role of blast-induced traumatic brain injury (TBI) in the chronic cognitive and mental health problems that develop in veterans and active duty military personnel. The brain vasculature is particularly sensitive to blast injury. The aim of this study was to characterize the evolving molecular and histologic alterations in the neurovascular unit induced by three repetitive low-energy blast exposures (3 × 74.5 kPa) in a rat model mimicking human mild TBI or subclinical blast exposure. High-resolution two-dimensional differential gel electrophoresis (2D-DIGE) and matrix-assisted laser desorption/ionization (MALDI) mass spectrometry of purified brain vascular fractions from blast-exposed animals 6 weeks post-exposure showed decreased levels of vascular-associated glial fibrillary acidic protein (GFAP) and several neuronal intermediate filament proteins (α-internexin and the low, middle, and high molecular weight neurofilament subunits). Loss of these proteins suggested that blast exposure disrupts gliovascular and neurovascular interactions. Electron microscopy confirmed blast-induced effects on perivascular astrocytes including swelling and degeneration of astrocytic endfeet in the brain cortical vasculature. Because the astrocyte is a major sensor of neuronal activity and regulator of cerebral blood flow, structural disruption of gliovascular integrity within the neurovascular unit should impair cerebral autoregulation. Disrupted neurovascular connections to pial and parenchymal blood vessels might also affect brain circulation. Blast exposures also induced structural and functional alterations in the arterial smooth muscle layer. Interestingly, by 8 months after blast exposure, GFAP and neuronal intermediate filament expression had recovered to control levels in isolated brain vascular fractions. However, despite this recovery, a widespread vascular pathology was still apparent at 10 months after blast exposure histologically and on micro-computed tomography scanning. Thus, low-level blast exposure disrupts gliovascular and neurovascular connections while inducing a chronic vascular pathology.

Military-related risk factors for dementia

INTRODUCTION

In recent years, there has been growing discussion to better understand the pathophysiological mechanisms of traumatic brain injury and post-traumatic stress disorder and how they may be linked to an increased risk of neurodegenerative diseases including Alzheimer's disease in veterans.

METHODS

Building on that discussion, and subsequent to a special issue of Alzheimer's & Dementia published in June 2014, which focused on military risk factors, the Alzheimer's Association convened a continued discussion of the scientific community on December 1, 2016.

RESULTS

During this meeting, participants presented and evaluated progress made since 2012 and identified outstanding knowledge gaps regarding factors that may impact veterans' risk for later life dementia.

DISCUSSION

The following is a summary of the invited presentations and moderated discussions of both the review of scientific understanding and identification of gaps to inform further investigations.

In situ Study Unravels Bio-Nanomechanical Behavior in a Magnetic Bacterial Nano-cellulose (MBNC) Hydrogel for Neuro-Endovascular Reconstruction

Surgical clipping and endovascular coiling are well recognized as conventional treatments of Penetrating Brain Injury aneurysms. These clinical approaches show partial success, but often result in thrombus formation and the rupture of aneurysm near arterial walls. The authors address these challenging brain traumas with a unique combination of a highly biocompatible biopolymer hydrogel rendered magnetic in a flexible and resilient membrane coating integrated to a scaffold stent platform at the aneurysm neck orifice, which enhances the revascularization modality. This work focuses on the in situ diagnosis of nano-mechanical behavior of bacterial nanocellulose (BNC) membranes in an aqueous environment used as tissue reconstruction substrates for cerebral aneurysmal neck defects. Nano-mechanical evaluation, performed using instrumented nano-indentation, shows with very low normal loads between 0.01 to 0.5 mN, in the presence of deionized water. Mechanical testing and characterization reveals that the nano-scale response of BNC behaves similar to blood vessel walls with a very low Young´s modulus, E (0.0025 to 0.04 GPa), and an evident creep effect (26.01 ± 3.85 nm s^-1 ). These results confirm a novel multi-functional membrane using BNC and rendered magnetic with local adhesion of iron-oxide magnetic nanoparticles.

Low Glasgow Coma Score in Traumatic Intracranial Hemorrhage Predicts Development of Cerebral Vasospasm

BACKGROUND

The exact mechanism, incidence, and risk factors for cerebral vasospasm after traumatic intracranial hemorrhage (ICH) continue to be poorly characterized. The incidence of post-traumatic vasospasm (PTV) varies depending on the detection modality.

OBJECTIVE

We aimed to shed light on the predictors, associations, and true incidence of cerebral vasospasm after traumatic ICH using digital subtraction angiography (DSA) as the gold standard.

METHODS

We examined a prospectively maintained database of traumatic brain injury (TBI) patients to identify patients with ICH secondary to TBI enrolled between 2002 and 2015 at our trauma center. Patients with TBI-associated ICH and evidence of elevated velocities on transcranial Doppler and computed tomography angiograms, confirmed with DSA were included. The diagnostic cerebral angiograms were evaluated by 2 blinded neurointerventionalists for cerebral vasospasm. Statistical analyses were conducted to determine predictors of PTV.

RESULTS

Twenty patients with ICH secondary to TBI and evidence of vasospasm underwent DSAs. Seven patients (7/20; 35%) with traumatic ICH developed cerebral vasospasm and of those, 1 developed delayed cerebral ischemia (1/7; 14%). Of these 7 patients, 6 presented with subarachnoid hemorrhage (6/7; 85%). Vasospasm was substantially more common in patients with a Glasgow Coma Scale <9 (P = 0.017) than in all other groups.

CONCLUSIONS

PTV as demonstrated by DCA may be more common than previously reported. Patients who exhibit PTV were more likely to have a Glasgow Coma Scale <9. This subgroup of patients may benefit from more systematic screening for the development of PTV, and earlier monitoring for signs of delayed cerebral ischemia.

Selective Vulnerability of the Foramen Magnum in a Rat Blast Traumatic Brain Injury Model

Primary blast traumatic brain injury (bTBI) accounts for a significant proportion of wartime trauma. Previous studies have demonstrated direct brain injury by blast waves, but the effect of the location of the blast epicenter on the skull with regard to brain injury remains poorly characterized. In order to investigate the role of the blast epicenter location, we modified a previously established rodent model of cranium-only bTBI to evaluate two specific blast foci: a rostrally focused blast centered on bregma (B-bTBI), which excluded the foramen magnum region, and a caudally focused blast centered on the occipital crest, which included the foramen magnum region (FM-bTBI). At all blast overpressures studied (668-1880 kPa), rats subjected to FM-bTBI demonstrated strikingly higher mortality, increased durations of both apnea and hypoxia, and increased severity of convexity subdural hematomas, than rats subjected to B-bTBI. Together, these data suggest a unique role for the foramen magnum region in mortality and brain injury following blast exposure, and emphasize the importance of the choice of blast focus location in experimental models of bTBI.

Modeling the Long-Term Consequences of Repeated Blast-Induced Mild Traumatic Brain Injuries

Repeated mild traumatic brain injury (rmTBI) caused by playing collision sports or by exposure to blasts during military operations can lead to late onset, chronic diseases such as chronic traumatic encephalopathy (CTE), a progressive neurodegenerative condition that manifests in increasingly severe neuropsychiatric abnormalities years after the last injury. Currently, because of the heterogeneity of the clinical presentation, confirmation of a CTE diagnosis requires post-mortem examination of the brain. The hallmarks of CTE are abnormal accumulation of phosphorylated tau protein, TDP-43 immunoreactive neuronal cytoplasmic inclusions, and astroglial abnormalities, but the pathomechanism leading to these terminal findings remains unknown. Animal modeling can play an important role in the identification of CTE pathomechanisms, the development of early stage diagnostic and prognostic biomarkers, and pharmacological interventions. Modeling the long-term consequences of blast rmTBI in animals is especially challenging because of the complexities of blast physics and animal-to-human scaling issues. This review summarizes current knowledge about the pathobiologies of CTE and rmbTBI and discusses problems as well as potential solutions related to high-fidelity modeling of rmbTBI and determining its long-term consequences.

Material Properties of Rat Middle Cerebral Arteries at High Strain Rates

Traumatic brain injury (TBI), resulting from either impact- or nonimpact blast-related mechanisms, is a devastating cause of death and disability. The cerebral blood vessels, which provide critical support for brain tissue in both health and disease, are commonly injured in TBI. However, little is known about how vessels respond to traumatic loading, particularly at rates relevant to blast. To better understand vessel responses to trauma, the objective of this project was to characterize the high-rate response of passive cerebral arteries. Rat middle cerebral arteries (MCAs) were isolated and subjected to high-rate deformation in the axial direction. Vessels were perfused at physiological pressures and stretched to failure at strain rates ranging from approximately 100 to 1300 s−1. Although both in vivo stiffness and failure stress increased significantly with strain rate, failure stretch did not depend on rate.

Ultrastructural brain abnormalities and associated behavioral changes in mice after low-intensity blast exposure

Explosive blast-induced mild traumatic brain injury (mTBI), a "signature wound" of recent military conflicts, commonly affects service members. While past blast injury studies have provided insights into TBI with moderate- to high-intensity explosions, the impact of primary low-intensity blast (LIB)-mediated pathobiology on neurological deficits requires further investigation. Our prior considerations of blast physics predicted ultrastructural injuries at nanoscale levels. Here, we provide quantitative data using a primary LIB injury murine model exposed to open field detonation of 350 g of high-energy explosive C4. We quantified ultrastructural and behavioral changes up to 30 days post blast injury (DPI). The use of an open-field experimental blast generated a primary blast wave with a peak overpressure of 6.76 PSI (46.6 kPa) at a 3-m distance from the center of the explosion, a positive phase duration of approximate 3.0 milliseconds (ms), a maximal impulse of 8.7 PSI × ms and a sharp rising time of 9 × 10^-3 ms, with no apparent impact/acceleration in exposed animals. Neuropathologically, myelinated axonal damage was observed in blast-exposed groups at 7 DPI. Using transmission electron microscopy, we observed and quantified myelin sheath defects and mitochondrial abnormalities at 7 and 30 DPI. Inverse correlations between blast intensities and neurobehavioral outcomes including motor activities, anxiety levels, nesting behavior, spatial learning and memory occurred. These observations uncover unique ultrastructural brain abnormalities and associated behavioral changes due to primary blast injury and provide key insights into its pathogenesis and potential treatment.