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Suguru Inao, Anthony Marmarou, Geoff D. Clarke, Bruce J. Andersen, Panos P. Fatouros and Harold F. Young

✓ Lactate dynamics in the brain, cerebrospinal fluid (CSF), and serum were studied in 20 chloralose-anesthetized cats following fluid-percussion trauma. Brain lactate and brain tissue pH were measured by hydrogen-1 and phophorus-31 magnetic resonance spectroscopy. The CSF, arterial, and cerebrovenous serum lactate levels as well as serum glucose concentration were quantified. In the six sham-operated control animals, brain, CSF, cerebrovenous, and arterial lactate levels as well as brain pH remained at normal values. In the five animals in the mild-trauma group (1.6 atm), brain and CSF lactate levels were moderately elevated, although the brain pH and serum lactate content remained at control values.

Severe trauma (3.1 atm) in nine cats produced an 82% increase in the brain lactate index and a reduction in brain tissue pH (7.02 ± 0.02 to 6.95 ± 0.02; mean ± standard error of the mean), indicating brain tissue acidosis caused by excessive lactate accumulation. Brain lactate levels reached a peak 1½ hours after severe trauma, then steadily decreased to normal levels by 8 hours posttrauma. Maximum increases of CSF and arterial lactate levels (from 1.4 ± 0.2 to 4.1 ± 0.4 and from 1.6 ± 0.2 to 4.1 to 0.6 mmol/liter, respectively) were observed 15 minutes after trauma, and the values decreased during the next 2 hours. The response was biphasic, with a secondary rise observed in both CSF and serum lactate levels during the remaining 4 hours of the experiment. The difference between the arterial and venous lactate levels (A-Vlact) gradually increased and reached a peak 2 hours postinjury (from −0.05 ± 0.10 to −0.41 ± 0.09 mmol/liter).

The results of this study show that the production of lactate in brain tissue, CSF, and blood increased in proportion to the severity of the injury. The observation that lactate levels in blood and CSF are maximum immediately following impact while brain lactate and A-Vlact are gradually increasing suggests that the brain-tissue production of lactate fails to account for the rapid appearance of lactate in CSF and blood. It is speculated that the initial elevation of CSF lactate values reflects the systemic response of trauma, and the secondary rise of CSF lactate levels following severe trauma is due to slow seepage of lactate produced by brain tissue into the CSF space. These studies are the first to describe the temporal profile of brain lactate production and eventual clearance by CSF and blood in fluid-percussion injury. The results emphasize the need for caution in interpreting elevated CSF lactate levels following head injury.

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Panos P. Fatouros and Anthony Marmarou

Object. The authors present a quantitative in vivo magnetic resonance (MR) imaging method and propose its use for the accurate assessment of brain water in humans.

Methods. With this technique, a pure T1-weighted image of a selected brain slice in a patient is generated, and the image is subsequently converted to a pure water image by means of an equation derived from a tissue relaxation model. The image intensity in the resulting water map directly yields absolute measures of water expressed in grams of water per gram of tissue at a given anatomical location. The method has been validated previously in a series of phantom experiments and in an infusion model of brain edema in cats. In this report, the authors evaluate the method by using samples of tissue harvested from patients who underwent surgery for brain tumor removal and apply the technique to a series of normal volunteers, providing average regional brain water content (fw) values for a range of tissues. Application of the method in pathological conditions such as head trauma, tumor, and hydrocephalus allows quantification of regional or global increases in fw that result from edema.

Conclusions. It is now possible to obtain accurate brain water measurements with the anatomical resolution of MR imaging. This permits monitoring of the development and resolution of edema in a variety of clinical circumstances, thus enhancing understanding of the underlying pathophysiological processes.

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Anthony Marmarou, Panos P. Fatouros, Pal Barzó, Gennarina Portella, Masaaki Yoshihara, Osamu Tsuji, Takuji Yamamoto, Fred Laine, Stefano Signoretti, John D. Ward, M. Ross Bullock and Harold F. Young

Object. The pathogenesis of traumatic brain swelling remains unclear. The generally held view is that brain swelling is caused primarily by vascular engorgement and that edema plays a relatively minor role in the swelling process. The goal of this study was to examine the roles of cerebral blood volume (CBV) and edema in traumatic brain swelling.

Methods. Both brain-tissue water and CBV were measured in 76 head-injured patients, and the relative contribution of edema and blood to total brain swelling was determined. Comparable measures of brain-tissue water were obtained in 30 healthy volunteers and CBV in seven volunteers. Brain edema was measured using magnetic resonance imaging, implementing a new technique for accurate measurement of total tissue water. Measurements of CBV in a subgroup of 31 head-injured patients were based on consecutive measures of cerebral blood flow (CBF) obtained using stable xenon and calculation of mean transit time by dynamic computerized tomography scanning after a rapid bolus injection of iodinated contrast material. The mean (± standard deviation) percentage of swelling due to water was 9.37 ± 8.7%, whereas that due to blood was −0.8 ± 1.32%.

Conclusions. The results of this study showed that brain edema is the major fluid component contributing to traumatic brain swelling. Moreover, CBV is reduced in proportion to CBF reduction following severe brain injury.

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Zhi-Jian Chen, George T. Gillies, William C. Broaddus, Sujit S. Prabhu, Helen Fillmore, Ryan M. Mitchell, Frank D. Corwin and Panos P. Fatouros

Object. The goal of this study was to validate a simple, inexpensive, and robust model system to be used as an in vitro surrogate for in vivo brain tissues in preclinical and exploratory studies of infusion-based intraparenchymal drug and cell delivery.

Methods. Agarose gels of varying concentrations and porcine brain were tested to determine the infusion characteristics of several different catheters at flow rates of 0.5 and 1 µl per minute by using bromophenol blue (BPB) dye (molecular weight [MW] ∼690) and gadodiamide (MW ∼573). Magnetic resonance (MR) imaging and videomicroscopy were used to measure the distribution of these infusates, with a simultaneous measurement of infusion pressures. In addition, the forces of catheter penetration and movement through gel and brain were measured.

Agarose gel at a 0.6% concentration closely resembles in vivo brain with respect to several critical physical characteristics. The ratio of distribution volume to infusion volume of agarose was 10 compared with 7.1 for brain. The infusion pressure of the gel demonstrated profiles similar in configuration and magnitude to those of the brain (plateau pressures 10–20 mm Hg). Gadodiamide infusion in agarose closely resembled that in the brain, as documented using T1-weighted MR imaging. Gadodiamide distribution in agarose gel was virtually identical to that of BPB dye, as documented by MR imaging and videomicroscopy. The force profile for insertion of a silastic catheter into agarose gel was similar in magnitude and configuration to the force profile for insertion into the brain. Careful insertion of the cannula using a stereotactic guide is critical to minimize irregularity and backflow of infusate distribution.

Conclusions. Agarose gel (0.6%) is a useful surrogate for in vivo brain in exploratory studies of convection-enhanced delivery.

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Anthony Marmarou, Stefano Signoretti, Panos P. Fatouros, Gina Portella, Gunes A. Aygok and M. Ross Bullock

Object

The edema associated with brain swelling after traumatic brain injury (TBI) has been thought to be vasogenic in origin, but the results of previous laboratory studies by the authors have shown that a cellular form of edema is mainly responsible for brain swelling after TBI. In this study the authors used magnetic resonance (MR) imaging techniques to identify the type of edema that occurs in patients with TBI.

Methods

Diffusion-weighted MR imaging was used to evaluate the apparent diffusion coefficient (ADC) in 44 patients with TBI (Glasgow Coma Scale Score < 8) and in eight healthy volunteers. Higher ADC values have been associated with vasogenic edema, and lower ADC values with a predominantly cellular form of edema. Regional measurements of ADC in patients with focal and diffuse injury were computed. The water content of brain tissue was also assessed in absolute terms by using MR imaging to measure the percentage of water per gram of tissue. Cerebral blood flow (CBF) was measured using stable Xe–computerized tomography (CT) studies to rule out ischemia as a cause of cellular edema.

The mean ADC value in the healthy volunteers was 0.82 ± 0.05 × 10−3 mm2/second. The ADC values in the patients with diffuse brain injury without swelling were close to the mean for the healthy volunteers. In contrast, the patients with brain swelling had increased brain water content and low ADC values (mean 0.74 ± 0.05 × 10−3 mm2/second). The ADC values correlated with CT classifications. In all patients with low ADC values, the CBF values were outside the range for ischemia.

Conclusions

The brain swelling observed in patients with TBI appears to be predominantly cellular, as signaled by low ADC values in brain tissue with high levels of water content.

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Stefano Signoretti, Anthony Marmarou, Gunes A. Aygok, Panos P. Fatouros, Gina Portella and Ross M. Bullock

Object

The goal of this study was to demonstrate the posttraumatic neurochemical damage in normal-appearing brain and to assess mitochondrial dysfunction by measuring N-acetylaspartate (NAA) levels in patients with severe head injuries, using proton (1H) magnetic resonance (MR) spectroscopy.

Methods

Semiquantitative analysis of NAA relative to creatine-containing compounds (Cr) and choline (Cho) was carried out from proton spectra obtained by means of chemical shift (CS) imaging and single-voxel (SV) methods in 25 patients with severe traumatic brain injuries (TBIs) (Glasgow Coma Scale scores ≤ 8) using a 1.5-tesla MR unit. Proton MR spectroscopy was also performed in 5 healthy volunteers (controls).

Results

The SV studies in patients with diffuse TBI showed partial reduction of NAA/Cho and NAA/Cr ratios within the first 10 days after injury (means ± standard deviations 1.59 ± 0.46 and 1.44 ± 0.21, respectively, in the patients compared with 2.08 ± 0.26 and 2.04 ± 0.31, respectively, in the controls; nonsignificant difference). The ratios gradually declined in all patients as time from injury increased (mean minimum values NAA/Cho 1.05 ± 0.44 and NAA/Cr 1.05 ± 0.30, p < 0.03 and p < 0.02, respectively). This reduction was greater in patients with less favorable outcomes. In patients with focal injuries, the periphery of the lesions revealed identical trends of NAA/Cho and NAA/Cr decrease. These reductions correlated with outcome at 6 months (p < 0.01). Assessment with multivoxel methods (CS imaging) demonstrated that, in diffuse injury, NAA levels declined uniformly throughout the brain. At 40 days postinjury, initially low NAA/Cho levels had recovered to near baseline in patients who had good outcomes, whereas no recovery was evident in patients with poor outcomes (p < 0.01).

Conclusions

Using 1H-MR spectroscopy, it is possible to detect the posttraumatic neurochemical damage of the injured brain when conventional neuroimaging techniques reveal no abnormality. Reduction of NAA levels is a dynamic process, evolving over time, decreasing and remaining low throughout the involved tissue in patients with poor outcomes. Recovery of NAA levels in patients with favorable outcomes suggests marginal mitochondrial impairment and possible resynthesis from vital neurons.