A model of focal cortical contusion in gerbils

A system of radiological criteria for grading and prognosticating temporal lobe contusions

INTRODUCTION

Temporal contusions are common in patients with head injuries and require close monitoring due to the propensity of these patients to deteriorate rapidly and fatally. This study attempts to introduce a radiological grading system for temporal lobe contusions and analyse its prognostic value so as to better identify patients at risk of deterioration.

METHODS

The study was conducted as a cross-sectional observational study from April 2011-March 2017 on 42 patients with temporal lobe contusion. Each patients was graded according to the proposed system from a minimum of four to a maximum of 13 and then further grouped in three grades - grade 1 (score = 4), grade 2 (score 5-7) and grade 3 (score > 7) - and their clinical course was closely observed.

RESULTS

The minimum and maximum scores observed were four and 11 respectively. The proposed grading system has statistically significant correlation to the Glasgow Coma Scale (p-value < 0.05). All patients in grade 1 (17) could be managed conservatively, while all those in grade 3 (five) needed immediate surgical intervention. Of 20 patients in grade 2, 11 had a score of 5-6 and did not require surgery, whereas nine patients had a score of seven and of these eight required delayed surgical intervention. This correlation was statistically significant (p-value < 0.05).

CONCLUSION

The proposed temporal lobe contusion grading system is a good radiological tool to predict the clinical course of patients and thereby identify patients at higher risk of delayed deterioration.

Neurogenic hypotension in patients with severe head injuries

OBJECTIVE

To examine the occurrence of hypotensive episodes in patients with severe traumatic brain injuries that are not of hypovolemic origin and to investigate possible neurogenic or iatrogenic causes of such episodes.

METHODS

We reviewed Traumatic Coma Data Bank (TCDB) records of the 248 patients with early hypotension. We attempted to eliminate episodes related to hemorrhagic hypovolemia by excluding patients with (1) extracranial injuries of Abbreviated Injury Scale scores > 3 (n = 99, 40%); (2) postresuscitation hematocrit levels < 35% (n = 76, 30.6%); (3) hematocrit levels decreasing to < 35% during the first 24 hours after injury (n = 47, 19%); and (4) patients with conflicting data (n = 5, 2%). This left 21 patients (8.5%) without discernible extracranial causes for their hypotension.

RESULTS

Of these 21 patients, 4 had no extracranial injuries and 4 had only a single injury with Abbreviated Injury Scale score = 1. Hypotensive episodes were not associated with terminal or unsalvageable status. Mortality was 43%. Of the multiple factors investigated, the only two that were strongly associated with these "unexplained" hypotensive episodes were the presence of a diffuse injury pattern on computed tomography (n = 15, 71%) and the early use of mannitol or furosemide (n = 16, 76%) (It was policy at TCDB centers that hypotensive patients not receive diuretics until they were resuscitated.)

CONCLUSIONS

(1) Some episodes of severe traumatic brain injury-related hypotension may be of neurogenic origin. (2) The risk/benefit ratio of early diuretic use in patients with severe traumatic brain injuries may be too high to support liberal use. These data strongly support the need for a study involving prospective collection of data describing the early blood pressure courses in such patients.

Expression of Cu,Zn-superoxide dismutase mRNA after cold and contusion injury in the rat brain

We analyzed the expression of Cu,Zn-superoxide dismutase (SOD) mRNA in both contusion and cold injury. Twenty-three rats were divided into 3 groups: a control group, a contusion group, and a cold injury group. Six hours after the injury, the rats were decapitated and the gray matter was resected from 3 portions: the core of the injured cortex, its periphery, and a distal portion on the non-lesion side. Based on the specific gravity of each sample, almost the same degree of edema developed in both injury groups. The mRNA expression in the cold injury group, however, significantly decreased in all portions. The extremely low temperature associated with cold injury is a possible cause of the decrease in Cu,Zn-SOD mRNA.

Brain water content, brain blood volume, blood chemistry, and pathology in a model of cerebral edema

STUDY OBJECTIVES

The objective was to correlate regional changes during brain water content with alterations in blood chemistry and cerebral pathology during hypo-osmotic edema.

PARTICIPANTS

Sprague-Dawley male adult rats were used in these studies.

DESIGN

Animals were block-randomized to receive either an intraperitoneal distilled water injection equivalent to 5% or 15% of their body weight or no injection (controls). Rats were sacrificed 15 or 60 minutes after water injection or at an equivalent time for controls.

INTERVENTIONS

No interventions were performed.

MEASUREMENTS AND MAIN RESULTS

Water content of cerebral cortical gray and white matter was calculated from measurements of tissue specific gravity. Blood plasma osmolality and sodium and potassium concentrations were determined at various times after water injection. An index of blood-brain barrier permeability was obtained by measuring brain red blood cell and plasma volumes. A qualitative assessment of edema was made from light and electron micrographs of the cerebral cortex. We found that water injection produced a dose-dependent decrease in plasma osmolality and sodium concentration within 15 minutes. Cortical water content was unchanged after this period. An influx of water into cerebral gray, and, less readily, into cerebral white matter occurred during the next 15 minutes. Whole blood specific gravity and brain blood content were unchanged and thus did not confound the measurement of cerebral water content. Hematocrit was increased 60 minutes after a 15% water injection. The blood-brain barrier remained intact throughout this period. Microscopy revealed astrocytic swelling with slight extracellular fluid accumulation 60 minutes after the water injection.

CONCLUSIONS

Homeostatic mechanisms in the cerebral cortex can maintain constant water content for at least 15 minutes during maintained intravascular hypo-osmolality. Fluid that subsequently moves into the tissue primarily enters an intracellular compartment. This model will be useful in investigating physiological mechanisms of brain water regulation and the pathogenesis of brain edema, a common clinical entity in emergency conditions.

Traumatic brain injury in the rat: effects on lipid metabolism, tissue magnesium, and water content

Tissue levels of free fatty acids (FFA), total phospholipid, cholesterol, thromboxane B2, water, Na+, K+, and Mg2+ were measured in rat brain after lateral fluid-percussion brain injury of moderate severity (2.0-2.2 atm). Brains of injured animals and sham-operated controls were frozen in situ with liquid N2 at 10 min, 4 h, and 24 h postinjury and removed. The left parietal cortex, which has been shown previously histologically to be the site of maximal injury, was dissected for analysis. Traumatic injury was associated with small increases in FFA levels at 10 min and 4 h and much larger increases at 24 h postinjury. Among the FFA, the largest increases were observed in stearate, arachidonate, and docosahexaenoate. Total phospholipid and cholesterol levels were decreased significantly at all experimental time points. Thromboxane levels were markedly elevated (30-fold) at 10 min posttrauma but substantially declined by 4 h and approached control values at 24 h. Total Mg2+ levels were significantly below control values at 4 h and 24 h posttrauma. No changes in water content were observed at any of these time points. Small decreases in tissue K+ occurred at 4 h; tissue Na+ levels were found to be slightly increased only at 24 h. These results are consistent with the hypothesis that changes in lipid metabolism and Mg2+ content of brain after injury may play a role in the pathophysiology of irreversible, posttraumatic tissue damage. In contrast, significant edema formation does not occur in this model and does not, therefore, appear to be a factor in the injury process.

Experimental intracerebral mass: time-related effects on local cerebral blood flow

Cerebral blood flow (CBF) was measured at different times during the first 150 minutes following an experimental space-occupying lesion produced with a 50-microliter microballoon in rats. Local CBF was measured with the carbon-14-labeled iodoantipyrine quantitative autoradiographic technique. A region of local ischemia developed around the mass, while the remote effects of the mass were minimal. The focal ischemic lesion enlarged with time, and simulated removal of the lesion within this design did not alleviate the ischemia.

Experimental intracerebral hemorrhage: effects of a temporary mass lesion

Late pathophysiological events after the production and subsequent removal of an intracerebral mass were investigated using a mechanical microballoon model to simulate intracerebral hemorrhage. Immediately following balloon inflation in the caudate nucleus of rats, there was a significant increase in intracranial pressure to 14 +/- 1 mm Hg (mean +/- standard error of the mean), accompanied by a reduction in cerebral blood flow (CBF) in the ipsilateral frontal cortex, as measured by the hydrogen-clearance technique. Carbon-14-iodoantipyrine autoradiography revealed a significant reduction in the CBF of the ipsilateral caudate nucleus 4 hours after balloon inflation: 31% of the caudate nucleus had a CBF of less than 20 ml X 100 gm-1 X min-1 compared to only 1% in the sham-treated control group (balloon insertion without inflation). The rats with an intracerebral mass exhibited a significant increase in the volume of ischemic damage in the ipsilateral caudate nucleus (17.1% of total volume) compared to only 1.7% in the sham-treated group; however, there was no evidence of cerebral edema. Ischemic damage and reduced CBF persisted for 4 hours after transient inflation of a microballoon in the caudate nucleus. This suggests that ischemic damage occurs at the time of formation of the lesion and is not prevented by its early removal.

A simple mechanical model using a piston to produce localized cerebral contusions in pigs

A simple mechanical model using a piston to produce localized cerebral contusions in pigs, is presented. The precision and reproducibility of the method are described by the biomechanical and pathological results. There are only pathological changes with haemorrhage and laceration close to the place of entry of the piston. The changes in the physiological parameters also indicate that the damage is focal. In this model, when kept intact, the dura mater offers considerable protection as no pathological changes in the brain are observed even when the energy at the time of the contusion is increased to twice the values which, when the dura is open, cause considerable damage.

Brain specific gravity and CT scan density measurements after human head injury

White matter specific gravity was measured using the microgravimetric method in 20 comatose patients with diffuse head injury who were undergoing intracranial pressure (ICP) monitoring, and in 19 patients with focal injuries who were undergoing evacuation of contusions or intracerebral hematomas. Computerized tomography (CT) density readings were obtained for each site of white matter sampling by locating the sampling site on the preoperative CT scan. A significant correlation was found between the specific gravity values and the CT density numbers (r = 0.775; p less than 0.001). Patients with focal injuries demonstrated reduced perifocal specific gravity, suggesting brain edema. The mean specific gravity in patients with diffuse injury was within the normal range. In 10 of 12 patients in whom the specific gravity was above the normal range, the CT density was also above the normal range. These data suggest that cerebral vascular engorgement is the cause of the high specific gravity. Six (60%) of this small subgroup of 10 patients also demonstrated a high ICP.

Acute responses to experimental blunt head trauma: topography of white matter edema

The location of edema and territory of extravasation of serum protein were examined in the white matter of cats with different forms of intracranial pathology following an impact-acceleration injury to the head. Edema was tested with an organic density gradient and Evans blue dye was used as a marker for breakdown of the blood-brain barrier. Animals with tissue hemorrhage (contusions) involving both cerebral cortex and white matter had a substantial, progressive accumulation of Evans blue-stained edema near tissue hemorrhage during the 6 h following trauma. In addition, this category of cats had a widespread, mild edema at 15 min after injury that was usually unaccompanied by Evans blue stain. Cats with cortical contusions had rather mild edema neighboring tissue hemorrhage; animals with subarachnoid hemorrhage in the absence of cerebral contusions had neither measurable edema nor (usually) visible Evans blue staining. We conclude that: acute traumatic cerebral edema varies considerably in presence, magnitude and territory with different forms of intracranial pathology; and mechanically induced edema can occur that is independent of spread of fluid from areas of tissue hemorrhage.

A rabbit model of intracerebral hematoma

The epiphenomena that seem to cause deterioration and death after spontaneous interacerebral hematoma (SICH) might best be studied in an animal model. Therefore, the principles for developing such a model and techniques to study these phenomena were evaluated. Animals will tolerate injection of 3%-5% of their brain volume with a high proportion of clots. Fluorescein can be used to study the blood-brain barrier, and gravimetry to study edema. Others have found that injection of a paraffin/oil mixture can be employed for a control model. Refinement of the fluorescein technique, development of a primate model, and directions for future research are suggested.

Acute responses to experimental blunt head trauma. Topography of cerebral cortical edema

Anesthetized cats subjected to impact followed by acceleration and rotation of the skull were sacrificed at 15 minutes or 6 hours after injury and were selected for study if unilateral cerebral contusion was present. Widespread areas of cerebral cortex were examined bilaterally for edema, using measurement of tissue density with an organic gradient, and for breakdown of the blood-brain barrier to plasma protein tagged with Evans blue dye. At both times tested, a halo of vasogenic edema (Evans blue stain plus decreased density) was present in the cortex surrounding areas of contusion. At 15 minutes after injury, animals with deep contusions also had a slight decrease in density without Evans blue staining, interpreted as cytotoxic edema, in some gyri neighboring the contusion. At 6 hours, cytotoxic edema was not evident, but some animals had vasogenic edema in the gyri adjoining the contusion. Most gyri contralateral to contused areas had neither Evans blue staining nor changes in tissue density. These findings suggest that, with the present head-injury model, acute changes in tissue density and vascular permeability occur in the cerebral cortex of hemispheres with contusion. These responses are related topographically to contusion sites, and change over the two times studied. The authors conclude that events in addition to spread of fluid from areas of contusion contribute to the edema of head injury, and that more than one form of edema can follow mechanical trauma to the brain.

Acute responses to blunt head trauma. Experimental model and gross pathology

This study of blunt craniocerebral trauma describes an experimental model that involves delivery of forceful blows to the resting movable skulls of anesthetized cats. Injuries inflicted by this method included skull fractures in 81% of cases, epidural hemorrhages in 50%, subdural hemorrhages in 80%, subarachnoid hemorrhages in 100%, and brain contusions in 84%. In the majority of instances the subdural and epidural hemorrhages were thin films of blood that did not compress or distort the subjacent brain. The distribution of cerebral contusions was restricted to the cerebral parenchyma beneath the locus of cranial impact except for contusions associated with skull fractures. This experimental model recapitulates clinically realistic human cranial trauma and produces pathological lesions suitable for investigation of the pathophysiology of blunt head trauma.