Microangiographic changes following cerebral contusion in rats

A perfusion procedure for imaging of the mouse cerebral vasculature by X-ray micro-CT

BACKGROUND

Micro-CT is a novel X-ray imaging modality which can provide 3D high resolution images of the vascular network filled with contrast agent. The cerebrovascular system is a complex anatomical structure that can be imaged with contrast enhanced micro-CT. However, the morphology of the cerebrovasculature and many circulatory anastomosis in the brain result in high variations in the extent of contrast agent filling in the blood vessels and as a result, the vasculature of different subjects appear differently in the acquired images. Specifically, the posterior circulation is not consistently perfused with the contrast agent in many brain specimens and thus, many major vessels that perfuse blood to the midbrain and hindbrain are not visible in the micro-CT images acquired from these samples.

NEW METHOD

In this paper, we present a modified surgical procedure of cerebral vasculature perfusion through the left ventricle with Microfil contrast agent, in order to achieve a more uniform perfusion of blood vessels throughout the brain and as a result, more consistent images of the cerebrovasculature. Our method consists of filling the posterior cerebral circulation with contrast agent, followed by the perfusion of the whole cerebrovasculature.

RESULTS

Our histological results show that over 90% of the vessels in the entire brain, including the cerebellum, were filled with contrast agent.

COMPARISON WITH EXISTING METHOD

Our results show that the new technique of sample perfusion decreases the variability of the posterior circulation in the cerebellum in micro-CT images by 6.9%.

CONCLUSIONS

This new technique of sample preparation improves the quality of cerebrovascular images.

Traumatic cerebral contusion: pathobiology and critical aspects

Traumatic brain injury is a major cause of mortality in developed countries. Cerebral parenchymal injury is evidenced by a significant percentage of patients. The most important structural lesion of the brain is the cerebral contusion, which is a complex and dynamic area, a result of the primary lesion and which is associated with ischemic and inflammatory phenomena that need to be known by the neurosurgeon. We present a review of the most important aspects of brain contusion.

Opposed effects of hypertonic saline on contusions and noncontused brain tissue in patients with severe traumatic brain injury

OBJECTIVE

The aim of this study was to quantify the effect of hypertonic saline solution on contused and noncontused brain tissue in patients with traumatic brain injury. We hypothesize that hypertonic saline would increase the volume of brain contusion while decreasing the volume of noncontused hemispheric areas.

DESIGN

Prospective observational study.

SETTING

Neurosciences critical care unit of a university hospital.

PATIENTS

Fourteen traumatic brain injury patients with increased intracranial pressure.

INTERVENTIONS

A computed tomography scan was performed before and after a 20-min infusion of 40 mL of 20% saline.

MEASUREMENTS AND MAIN RESULTS

The volume, weight, and specific gravity of contused and noncontused hemispheric areas were assessed from computed tomography DICOM images by using a custom-designed software (BrainView). Physiologic variables and natremia were measured before and after infusion. Hypertonic saline significantly increased natremia from 143 +/- 5 to 146 +/- 5 mmol/L and decreased intracranial pressure from 23 +/- 3 to 17 +/- 5 mm Hg. The volume of the noncontused hemispheric areas decreased by 13 +/- 8 mL whereas the specific gravity increased by 0.029 +/- 0.027%. The volume of contused hemispheric tissue increased by 5 +/- 5 mL without any con-comitant change in density. There was a wide interindividual variability in the response of the noncontused hemispheric tissue with changes in specific gravity varying between -0.0124% and 0.0998%.

CONCLUSIONS

Three days after traumatic brain injury, the blood- brain barrier remains semipermeable in noncontused areas but not in contusions. Further studies are needed to tailor the use of hypertonic saline in patients with traumatic brain injury according to the volume of contusions assessed on computed tomography.

Acute Subdural Hematoma: New Model Delineation and Effects of Coagulation Inhibitors

OBJECTIVE

To develop a highly reproducible rat model and behavioral tests for acute subdural hematoma (ASDH) and to investigate the role of intravascular coagulation and thrombin in the pathogenesis of brain injury in this model.

METHODS

A new method was implemented to inject 200 microl of autologous blood subdurally in rats. Immunohistochemistry was used to investigate intravascular fibrin deposition and thrombin levels in the cortex underlying the ASDH. Effectiveness of systemic heparin, argatroban, or ginkgolide B treatment was determined by histological lesion volume, number of occluded microvessels, and neurological deficits. Neurological deficits were monitored for 7 days after ASDH by use of forelimb placing, forelimb use asymmetry, and corner turn tests.

RESULTS

Consistent brain damage and sensorimotor deficits were observed in all animals with ASDH. Histological analysis demonstrated occluded microvessels and enlarged perivascular spaces in the underlying cortex starting 1 hour after hematoma induction. Fibrin and thrombin immunoreactivity were increased in the lesioned cortical parenchyma at 4 and 24 hours. However, no intravascular fibrin deposition was detected. Heparin induced hemorrhagic transformation in the cortical lesion and did not attenuate microvessel occlusion. Argatroban and ginkgolide B did not induce hemorrhage but failed to improve microvessel occlusion, lesion volume, and neurological deficits.

CONCLUSION

Intravascular coagulation and thrombin are not the major mediators of brain damage after ASDH. The model and behavioral tests presented in this study can be used to investigate other putative mechanisms of injury and to test future therapeutic interventions in ASDH.

Association between intravascular microthrombosis and cerebral ischemia in traumatic brain injury

OBJECTIVE

To determine the association between traumatic cerebral ischemia and intravascular thrombosis, a common finding after traumatic brain injury (TBI).

METHODS

We reviewed samples of the frontal cortex and hippocampus from individuals who had sustained a fatal TBI. Sections stained with hematoxylin and eosin were reviewed and rated for severity of selective neuronal necrosis (SNN). Because intravascular fibrin microthrombi may lyse within a few days of TBI, we restricted our analysis to patients who had died within 48 hours of injury. Medical records in all cases were reviewed to rule out severe or prolonged hypotension or hypoxemia. Eleven patients with severe or global SNN were compared with 11 patients in whom SNN was mild or absent. Slides adjacent to the hematoxylin and eosin sections were stained with an immunofluorescent antibody to antithrombin III and were reviewed for intravascular microthrombosis. The number of microthrombi on each slide was counted by an investigator blinded to the hematoxylin and eosin findings, and density of intravascular microthrombi was calculated.

RESULTS

Intravascular microthrombi were noted in every section, excluding control (non-TBI) brain tissue. However, the density of microthrombi varied with the degree of SNN. We found a highly significant difference in the mean density of microthrombi between patients with severe SNN (7.74 +/- 3.7/cm(2)) and those with little or no SNN (2.58 +/- 1.0/cm(2)). Furthermore, a good correlation was noted between the location of intravascular microthrombi and that of SNN.

CONCLUSION

These data support a strong link between intravascular microthrombosis and neuronal death after brain trauma in humans and may have important implications for new therapeutic approaches.

Intravascular coagulation: a major secondary insult in nonfatal traumatic brain injury

OBJECT

The goal of this study was to determine the frequency with which cerebral intravascular coagulation (IC) complicates traumatic brain injury (TBI). The authors also investigated the incidence of IC in relation to varying mechanisms, time courses, and severities of TBI and in different species.

METHODS

Tissue was sampled from surgical specimens of human cerebral contusions, from rats with lateral fluid-percussion injuries, and from pigs with head rotational acceleration injuries. Immunohistochemical fluorescent staining for antithrombin III was performed to detect cerebral intravascular microthrombi. Abundant IC was found in all specimens, and microthrombi had formed in arterioles and venules of all sizes, ranging from 10 to 600 microm. Although it was more pronounced in focal lesions and more severe injuries, considerable IC was also observed in mild and diffuse injuries. The authors found a strong association between the severity of coagulopathy and the density of IC.

CONCLUSIONS

These results strongly support the contention that IC is a universal response to TBI and an important secondary cerebral insult.

Quantitative analysis of microvascular alterations in traumatic brain injury by endothelial barrier antigen immunohistochemistry

Endothelial barrier antigen (EBA) is a protein triplet located in the plasma membrane of microvascular endothelium and selectively expressed in the normal nervous system. In this study, microvascular alterations following traumatic brain injury were studied using EBA immunohistochemistry. Anesthetized, physiologically regulated, normothermic Sprague-Dawley rats received moderate (1.5-2.0 atm) parieto-occipital parasagittal fluid-percussion traumatic brain injury (TBI). Control rats were subjected to similar anesthesia and physiological monitoring. Seven days after operative procedures, brains were perfusion-fixed, and coronal sections were reacted for EBA immunohistochemistry using a monoclonal antibody to rat EBA. Selected sections were reacted for isolectin B4 histochemistry. Computerized image analysis was used to compute numbers of EBA-immunopositive vascular profiles and mean vascular profile areas. In control brains, virtually all brain microvessels were clearly and positively immunostained, and antibody binding was specific for blood vessels. In rats with TBI, EBA immunoreactivity was greatly reduced in the zone of cortical contusion. Within the core contusion, fractional areas occupied by vascular profiles were markedly reduced (on average, by 57%), vascular profile counts were diminished, and lectin histochemistry revealed a robust inflammatory response with abundant macrophages. Taken together, these findings were thought to indicate frank microvascular destruction. At adjacent peri-contusional sites, the intensity of EBA immunostaining was also diminished; and vascular profile counts were reduced at adjacent cortical sites and homologous contralateral sites. The latter findings were interpreted as sublethal microvascular alterations possibly related to cerebral edema. The present results confirm that EBA is a specific immunohistochemical marker of normal central nervous system microvessels; that it is suitable for use in formaldehyde-fixed material; and that it is useful in quantitatively assessing microvascular alterations observed at contusional, peri-contusional and more remote sites following traumatic brain injury.