Magnetic resonance spectroscopy in traumatic brain injury

Transient alterations of creatine, creatine phosphate, N-acetylaspartate and high-energy phosphates after mild traumatic brain injury in the rat

In this study, the concentrations of creatine (Cr), creatine phosphate (CrP), N-acetylaspartate (NAA), ATP, ADP and phosphatidylcholine (PC) were measured at different time intervals after mild traumatic brain injury (mTBI) in whole brain homogenates of rats. Anaesthetized animals underwent to the closed-head impact acceleration "weight-drop" model (450 g delivered from 1 m height = mild traumatic brain injury) and were killed at 2, 6, 24, 48 and 120 h after the insult (n = 6 for each time point). Sham-operated rats (n = 6) were used as controls. Compounds of interest were synchronously measured by HPLC in organic solvent deproteinized whole brain homogenates. A reversible decrease of all metabolites but PC was observed, with minimal values recorded at 24 h post-injury (minimum of CrP = 48 h after impact). In particular, Cr and NAA showed a decrease of 44.5 and 29.5%, respectively, at this time point. When measuring NAA in relation to other metabolites, as it is commonly carried out in "in vivo" (1)H-magnetic resonance spectroscopy ((1)H-MRS), an increase in the NAA/Cr ratio and a decrease in the NAA/PC ratio was observed. Besides confirming a transient alteration of NAA homeostasis and ATP imbalance, our results clearly show significant changes in the cerebral concentration of Cr and CrP after mTBI. This suggests a careful use of the NAA/Cr ratio to measure NAA by (1)H-MRS in conditions of altered cerebral energy metabolism. Viceversa, the NAA/PC ratio appears to be a better indicator of actual NAA levels during energy metabolism impairment. Furthermore, our data suggest that, under pathological conditions affecting the brain energetic, the Cr-CrP system is not a suitable tool to buffer possible ATP depletion in the brain, thus supporting the growing indications for alternative roles of cerebral Cr.

Evaluation of delayed neuronal and axonal damage secondary to moderate and severe traumatic brain injury using quantitative MR imaging techniques

BACKGROUND AND PURPOSE

Traumatic brain injury (TBI) is a classic model of monophasic neuronal and axonal injury, in which tissue damage mainly occurs at the moment of trauma. There is some evidence of delayed progression of the neuronal and axonal loss. Our purpose was to test the hypothesis that quantitative MR imaging techniques can estimate the biologic changes secondary to delayed neuronal and axonal loss after TBI.

MATERIALS AND METHODS

Nine patients (age, 11-28 years; 5 male) who sustained a moderate or severe TBI were evaluated at a mean of 3.1 years after trauma. We applied the following techniques: bicaudate (BCR) and bifrontal (BFR) ventricle-to-brain ratios; T2 relaxometry; magnetization transfer ratio (MTR); apparent diffusion coefficient (ADC); and proton spectroscopy, by using an N-acetylaspartate/creatine (NAA/Cr) ratio measured in normal-appearing white matter (NAWM) and the corpus callosum (CC). The results were compared with those of a control group.

RESULTS

BCR and BFR mean values were significantly increased (P < or = .05) in patients due to secondary subcortical atrophy; increased T2 relaxation time was observed in the NAWM and CC, reflecting an increase in water concentration secondary to axonal loss. Increased ADC mean values and reduced MTR mean values were found in the NAWM and CC, showing damage in the myelinated axonal fibers; and decreased NAA/Cr ratio mean values were found in the CC, indicating axonal loss.

CONCLUSIONS

These quantitative MR imaging techniques could noninvasively demonstrate the neuronal and axonal damage in the NAWM and CC of human brains, secondary to moderate or severe TBI.

Early and sustained alterations in cerebral metabolism after traumatic brain injury in immature rats

Although studies have shown alterations in cerebral metabolism after traumatic brain injury (TBI), clinical data in the developing brain is limited. We hypothesized that post-traumatic metabolic changes occur early (<24 h) and persist for up to 1 week. Immature rats underwent TBI to the left parietal cortex. Brains were removed at 4 h, 24 h, and 7 days after injury, and separated into ipsilateral (injured) and contralateral (control) hemispheres. Proton nuclear magnetic resonance (NMR) spectra were obtained, and spectra were analyzed for N-acetyl-aspartate (NAA), lactate (Lac), creatine (Cr), choline, and alanine, with metabolite ratios determined (NAA/Cr, Lac/Cr). There were no metabolic differences at any time in sham controls between cerebral hemispheres. At 4 and 24 h, there was an increase in Lac/Cr, reflecting increased glycolysis and/or decreased oxidative metabolism. At 24 h and 7 days, there was a decrease in NAA/Cr, indicating loss of neuronal integrity. The NAA/Lac ratio was decreased ( approximately 15-20%) at all times (4 h, 24 h, 7 days) in the injured hemisphere of TBI rats. In conclusion, metabolic derangements begin early (<24 h) after TBI in the immature rat and are sustained for up to 7 days. Evaluation of early metabolic alterations after TBI could identify novel targets for neuroprotection in the developing brain.

TEMPORAL WINDOW OF METABOLIC BRAIN VULNERABILITY TO CONCUSSION

OBJECTIVE

In the present study, the occurrence of the temporal window of brain vulnerability was evaluated in concussed athletes by measuring N-acetylaspartate (NAA) using proton magnetic resonance (1H-MR) spectroscopy.

METHODS

Thirteen nonprofessional athletes who had a sport-related concussive head injury were examined for NAA determination by means of 1H-MR spectroscopy at 3, 15, and 30 days postinjury. All athletes but three suspended their physical activity. Those who continued their training had a second concussive event and underwent further examination at 45 days from the initial injury. The single case of one professional boxer, who was studied before the match and 4, 7, 15, and 30 days after a knockout, is also presented. Before each magnetic resonance examination, patients were asked for symptoms of mild traumatic brain injury, including physical, cognitive, emotional, and sleep disturbances. Data for 1H-MR spectroscopy recorded in five normal, age-matched, control volunteers, who were previously screened to exclude previous head injuries, were used for comparison. Semiquantitative analysis of NAA relative to creatine (Cr)- and choline (Cho)-containing compounds was performed from proton spectra obtained with a 3-T magnetic resonance system.

RESULTS

Regarding the values of the NAA-to-Cr ratio (2.21 ± 0.11) recorded in control patients, singly concussed athletes, at 3 days after the concussion, showed a decrease of 18.5% (1.80 ± 0.04; P &lt; 0.001). Only a modest 3% recovery was observed at 15 days (1.88 ± 0.1; P &lt; 0.001); at 30 days postinjury, the NAA-to-Cr ratio was 2.15 ± 0.1, revealing full metabolic recovery with values not significantly different from those of control patients. These patients declared complete resolution of symptoms at the time of the 3-day study. The three patients who had a second concussive injury before the 15-day study showed an identical decrease of the NAA-to-Cr ratio at 3 days (1.78 ± 0.08); however, at 15 days after the second injury, a further diminution of the NAA-to-Cr ratio occurred (1.72 ± 0.07; P &lt; 0.05 with respect to singly concussed athletes). At 30 days, the NAA-to-Cr ratio was 1.82 ± 0.1, and at 45 days postinjury, the NAA-to-Cr ratio showed complete recovery (2.07 ± 0.1; not significant with respect to control patients). This group of patients declared a complete resolution of symptoms at the time of the 30-day study.

CONCLUSION

Results of this pilot study carried out in a cohort of singly and doubly concussed athletes, examined by 1H-MR spectroscopy for their NAA cerebral content at different time points after concussive events, demonstrate that also in humans, concussion opens a temporal window of brain metabolic imbalance, the closure of which does not coincide with resolution of clinical symptoms. The recovery of brain metabolism is not linearly related to time. A second concussive event prolonged the time of NAA normalization by 15 days. Although needing confirmation in a larger group of patients, these results show that NAA measurement by 1H-MR spectroscopy is a valid tool in assessing the full cerebral metabolic recovery after concussion, thereby suggesting its use in helping to decide when to allow athletes to return to play after a mild traumatic brain injury.

Clinical review: Prognostic value of magnetic resonance imaging in acute brain injury and coma

Progress in management of critically ill neurological patients has led to improved survival rates. However, severe residual neurological impairment, such as persistent coma, occurs in some survivors. This raises concerns about whether it is ethically appropriate to apply aggressive care routinely, which is also associated with burdensome long-term management costs. Adapting the management approach based on long-term neurological prognosis represents a major challenge to intensive care. Magnetic resonance imaging (MRI) can show brain lesions that are not visible by computed tomography, including early cytotoxic oedema after ischaemic stroke, diffuse axonal injury after traumatic brain injury and cortical laminar necrosis after cardiac arrest. Thus, MRI increases the accuracy of neurological diagnosis in critically ill patients. In addition, there is some evidence that MRI may have potential in terms of predicting outcome. Following a brief description of the sequences used, this review focuses on the prognostic value of MRI in patients with traumatic brain injury, anoxic/hypoxic encephalopathy and stroke. Finally, the roles played by the main anatomical structures involved in arousal and awareness are discussed and avenues for future research suggested.

Characterizing 'mild' in traumatic brain injury with proton MR spectroscopy in the thalamus: Initial findings

OBJECTIVE

Although most mild traumatic brain injury (mTBI) patients suffer any of several post-concussion symptoms suggestive of thalamic involvement, they rarely present with any MRI-visible pathology. The aim here, therefore, is to characterize their thalamic metabolite levels with proton MR spectroscopy (1H-MRS) compared with healthy controls.

METHODS

T1-weighted MRI and multi-voxel 1H-MRS were acquired at 3 Tesla from 20 mTBI (Glasgow Coma Scale score of 15-13) patients, 19-59 years old, 0-7 years post-injury; and from 17 age and gender matched healthy controls. Mixed model regression was used to compare patients and controls with respect to the mean absolute N-acetylaspartate (NAA), choline (Cho) and creatine (Cr) levels within each thalamus.

RESULTS

The mTBI-induced thalamic metabolite concentration changes were under +/- 13.0% for NAA, +/- 13.5% for Cr and +/- 18.8% for Cho relative to their corresponding concentrations in the controls: NAA: 10.08 +/- 0.30 (mean +/- standard error), Cr: 5.62 +/- 0.18 and Cho: 2.08 +/- 0.09 mM. These limits represent the minimal detectable differences between the two cohorts.

CONCLUSION

The change in metabolic levels in the thalamus of patients who sustained clinically defined mTBI could be an instrumental characteristic of 'mildness'. 1H-MRS could, therefore, serve as an objective laboratory indicator for differentiating 'mild' from more severe categories of head-trauma, regardless of the presence or lack of current clinical symptoms.

Examining lactate in severe TBI using proton magnetic resonance spectroscopy

PRIMARY OBJECTIVE

Clinical management of acute traumatic brain injury (TBI) has emphasized identification of secondary mechanisms of pathophysiology. An important objective in this study is to use proton magnetic resonance spectroscopy (pMRS) to examine early metabolic disturbance due to TBI.

RESEARCH DESIGN

The current design is a case study with repeated measures.

METHOD AND PROCEDURE

Proton magnetic resonance imaging was used to examine neurometabolism in this case of very severe brain trauma at 9 and 23 days post-injury. MRI was performed on a clinical 1.5 Tesla scanner.

MAIN OUTCOMES AND RESULTS

These data also reveal that pMRS methods can detect lactate elevations in an adult surviving severe head trauma and are sensitive to changes in basic neurometabolism during the first month of recovery.

CONCLUSIONS

The current case study demonstrates the sensitivity of pMRS in detecting metabolic alterations during the acute recovery period. The case study reveals that lactate elevations may be apparent for weeks after severe neurotrauma. Further work in this area should endeavour to determine the ideal time periods for pMRS examination in severe TBI as well as the ideal locations of data acquisition (e.g. adjacent or distal to lesion sites).

Structural and functional neuroimaging in mild-to-moderate head injury

Head injury is a major cause of disability and death in adults. Significant developments in imaging techniques have contributed to the knowledge of the pathophysiology of head injury. Although extensive research is available on severe head injury, less is known about mild-to-moderate head injury despite the fact that most patients sustain this type of injury. In this review, we focus on structural and functional imaging techniques in patients with mild-to-moderate head injury. We discuss CT and MRI, including different MRI sequences, single photon emission computed tomography, perfusion-weighted MRI, perfusion CT, PET, magnetic resonance spectroscopy, functional MRI and magnetic encephalography. We outline the advantages and limitations of these various techniques in the contexts of the initial assessment and identification of brain abnormalities and the prediction of outcome.

Imaging after brain injury

Head injury remains an important cause of death and disability in young adults. This review will discuss the role of structural imaging using computed tomography (CT) and magnetic resonance imaging (MRI) and physiological imaging using CT perfusion, 131Xe CT, MRI and spectroscopy (MRS), single photon emission computed tomography, and positron emission tomography (PET) in the assessment, management, and prediction of outcome after head injury. CT allows rapid assessment of brain pathology which ensures patients who require urgent surgical intervention receive appropriate care. Although MRI provides greater spatial resolution, particularly within the posterior fossa and deep white matter, a complete assessment of the burden of injury requires imaging of cerebral physiology. Physiological imaging techniques can only provide 'snap shots' of physiology within the injured brain, but they can be repeated, and such data can be used to assess the impact of therapeutic interventions. Perfusion imaging based on CT techniques (xenon CT and CT perfusion) can be implemented easily in most hospital centres, and provide quantitative perfusion data in addition to structural images. PET imaging provides unparalleled insights into cerebral physiology and pathophysiology, but is not widely available and is primarily a research tool. MR technology continues to develop and is becoming generally available. Using a complex variety of sequences, MR can provide data concerning both structural and physiological derangements. Future developments with such imaging techniques should improve understanding of the pathophysiology of brain injury and provide data that should improve management and prediction of functional outcome.

Acute metabolic brain changes following traumatic brain injury and their relevance to clinical severity and outcome

BACKGROUND

Conventional MRI can provide critical information for care of patients with traumatic brain injury (TBI), but MRI abnormalities rarely correlate to clinical severity and outcome. Previous magnetic resonance spectroscopy studies have reported clinically relevant brain metabolic changes in patients with TBI. However, these changes were often assessed a few to several days after the trauma, with a consequent variation of the metabolic pattern due to temporal changes.

METHODS

Proton magnetic resonance spectroscopic imaging (1H-MRSI) examinations were performed in 10 patients with TBI 48-72 h after the trauma, to obtain early measurements of central brain levels of N-acetylaspartate (NAA), choline (Cho), creatine (Cr) and lactate (La). Metabolite values were expressed as ratios to (1) a metabolic pattern, given by the sum of the resonance intensities of all metabolites detected in the same voxel and (2) intravoxel Cr.

RESULTS

NAA ratios were found to be significantly lower in patients with TBI than in normal controls. In contrast, Cho ratios were significantly higher in patients with TBI than in normal controls. Increased La levels were found in 5 of 10 patients with TBI. Both NAA and La values correlated closely with those of the Glasgow Coma Scale at presentation (r = 0.73 and -0.62, respectively; p<0.01 for both) and the Glasgow Outcome Scale at 3 months (r = -0.79 and 0.79, respectively; p<0.01 for both).

CONCLUSION

Spectroscopic measures of neuro-axonal damage occurring soon after a brain trauma are clinically relevant. Significant increases in cerebral La level also may be detected when 1H-MRSI is performed early after the trauma and, at this stage, can represent a reliable index of injury severity and disease outcome in patients with TBI.

N-Acetylaspartate in the CNS: from neurodiagnostics to neurobiology

The brain is unique among organs in many respects, including its mechanisms of lipid synthesis and energy production. The nervous system-specific metabolite N-acetylaspartate (NAA), which is synthesized from aspartate and acetyl-coenzyme A in neurons, appears to be a key link in these distinct biochemical features of CNS metabolism. During early postnatal central nervous system (CNS) development, the expression of lipogenic enzymes in oligodendrocytes, including the NAA-degrading enzyme aspartoacylase (ASPA), is increased along with increased NAA production in neurons. NAA is transported from neurons to the cytoplasm of oligodendrocytes, where ASPA cleaves the acetate moiety for use in fatty acid and steroid synthesis. The fatty acids and steroids produced then go on to be used as building blocks for myelin lipid synthesis. Mutations in the gene for ASPA result in the fatal leukodystrophy Canavan disease, for which there is currently no effective treatment. Once postnatal myelination is completed, NAA may continue to be involved in myelin lipid turnover in adults, but it also appears to adopt other roles, including a bioenergetic role in neuronal mitochondria. NAA and ATP metabolism appear to be linked indirectly, whereby acetylation of aspartate may facilitate its removal from neuronal mitochondria, thus favoring conversion of glutamate to alpha ketoglutarate which can enter the tricarboxylic acid cycle for energy production. In its role as a mechanism for enhancing mitochondrial energy production from glutamate, NAA is in a key position to act as a magnetic resonance spectroscopy marker for neuronal health, viability and number. Evidence suggests that NAA is a direct precursor for the enzymatic synthesis of the neuron specific dipeptide N-acetylaspartylglutamate, the most concentrated neuropeptide in the human brain. Other proposed roles for NAA include neuronal osmoregulation and axon-glial signaling. We propose that NAA may also be involved in brain nitrogen balance. Further research will be required to more fully understand the biochemical functions served by NAA in CNS development and activity, and additional functions are likely to be discovered.

Minor traumatic brain injury in sports: a review in order to prevent neurological sequelae

Minor traumatic brain injury (mTBI) is caused by inertial effects, which induce sudden rotation and acceleration forces to and within the brain. At less severe levels of injury, for example in mTBI, there is probably only transient disturbance of ionic homeostasis with short-term, temporary disturbance of brain function. With increased levels of severity, however, studies in animal models of TBI and in humans have demonstrated focal intra-axonal alterations within the subaxolemmal, neurofilament and microtubular cytoskeletal network together with impairment of axoplasmic transport. These changes have, until very recently, been thought to lead to progressive axonal swelling, axonal detachment or even cell death over a period of hours or days, the so-called process of "secondary axotomy". However, recent evidence has suggested that there may be two discrete pathologies that may develop in injured nerve fibers. In the TBI scenario, disturbances of ionic homeostasis, acute metabolic changes and alterations in cerebral blood flow compromise the ability of neurons to function and render cells of the brain increasingly vulnerable to the development of pathology. In ice hockey, current return-to-play guidelines do not take into account these new findings appropriately, for example allow returning to play in the same game. It has recently been hypothesized that the processes summarized above may predispose brain cells to assume a vulnerable state for an unknown period after mild injury (mTBI). Therefore, we recommend that any confused player with or without amnesia should be taken off the ice and not be permitted to play again for at least 72h.

The Role of Quantitative Neuroimaging Indices in the Differentiation of Ischemia From Demyelination: An Analytical Study With Case Presentation

BACKGROUND AND PURPOSE

Differentiation of acute and subacute ischemic stroke lesions from acute demyelinating lesions of multiple sclerosis (MS) may not be possible on conventional magnetic resonance imaging (MRI). Both lesion types enhance on T1 with gadolinium (Gd) contrast and both are hyperintense on diffusion-weighted imaging (DWI). This study is an analysis of two quantitative MR indices: (1) calculated apparent diffusion coefficients (ADCs) and (2) T2 relaxation times (T2R) as means toward differentiating acute ischemic lesions from acute demyelinating lesions. Chronic ischemic and demyelinating lesions were evaluated for comparison as well.

METHODS

The MRI of nine patients with both acute and chronic ischemic lesions and six patients with both acute and chronic demyelinating lesions were analyzed for ADC and T2Rs. The indices were measured by manually placing regions of interest (ROIs) at the anatomic center of the acute lesion. Acute ischemic lesions were chosen by their hyperintensity on DWI and hypointensity on ADC mapping. Acute demyelinating lesions were selected by peripheral contrast enhancement after the administration of Gd. Computation of the ADC involved the diffusion coefficient on a region by region basis as follows: D = -(b(0)/b(1000))ln(S(b1000)/S(b0)), where S(b1000) is the signal intensity on DWI and S(b0) is the signal intensity on T2 with diffusion sensitivities of b(0) and b(1000), respectively. Computation of the T2R was made as follows: T2R = (TE(T2)--TE(PD))/(ln SI(PD)--ln SI(T2)), where TE is the echo time of the different pulse sequences, SI is signal intensity on the different echo sequences, and PD represents proton density sequence.

RESULTS

Twenty-nine acute ischemia, 27 acute demyelination, 28 chronic ischemia, and 43 chronic demyelination image sets were analyzed. The differences between ADC(acute infarct) (0.760) versus ADC(acute plaque) (1.106) were significant (p < 0.02). The differences between T2R(acute infarct) (235.5) versus T2R(acute plaque) (170.5) were also significant (p < 0.02).

CONCLUSIONS

ADC in combination with T2R is a useful tool to differentiate acute ischemic from acute demyelinating lesions. The use of these neuroimaging indices along with magnetic resonance spectroscopy metabolite ratios is then demonstrated in elucidating the pathophysiological mechanism for a case of delayed posttraumatic bilateral internuclear ophthalmoplegia.

Prospective longitudinal proton magnetic resonance spectroscopic imaging in adult traumatic brain injury

PURPOSE

To investigate whether longitudinal magnetic resonance proton spectroscopic imaging (MRSI) demonstrates regional metabolite abnormalities after traumatic brain injury (TBI) that predict long-term neurologic outcome.

MATERIALS AND METHODS

Two-dimensional-MRSI (point resolved spectroscopy sequence [PRESS]; TR/TE = 3000/144 msec; 10 mm) was acquired prospectively in 42 adults with severe TBI through the level of the corpus callosum 7 +/- 4 days after injury. Measurements were repeated in 31 patients six to 12 months after injury. Regional and pooled (all regions combined) mean ratios were compared with control values and then used to predict long-term (six- to -12-month) neurologic outcome (good vs. poor) using a logistic regression model.

RESULTS

Initial pooled mean N-acetylaspartate (NAA) ratios were lower (P < 0.01) and choline (Cho)/creatine (Cr) ratios higher (P < 0.01) in all TBI patients compared to controls. Ratios from the corpus callosum region were affected most and predicted long-term dichotomized outcome with 83% accuracy. When repeated at six to 12 months after injury, pooled mean NAA/Cr remained lower (P = 0.03) and Cho/Cr remained higher (P = 0.01) in patients with poor outcomes.

CONCLUSION

The NAA/Cr ratio from the corpus callosum was most useful for outcome prediction. Chronic alterations of metabolite ratios are likely due to neuronal loss and glial proliferation long after injury.

Imaging of cerebral blood flow and metabolism

PURPOSE OF REVIEW

To review the techniques for imaging cerebral blood flow and metabolism following injury to the brain.

RECENT FINDINGS

Xenon enhanced computerized tomography (Xenon CT), CT perfusion and single photon emission CT provide measurements of cerebral perfusion, while positron emission tomography (PET), and magnetic resonance imaging and spectroscopy (MRI and MRS) are able to assess both perfusion and cerebral metabolism. Xenon CT and CT perfusion are readily available and have proved useful in a variety of causes of brain injury. PET is an extremely useful research tool for defining cerebral physiology, but is limited in its availability. Despite the continuing development of MRI and MRS imaging, the scanning environment remains hostile for critically ill patients, and further research is required before the techniques become generally available.

SUMMARY

Imaging of cerebral blood flow and metabolism has been shown to be useful following a variety of causes of brain injury, as it can help to define the cause and extent of injury, identify appropriate treatments and predict outcome. Imaging based on CT techniques (Xenon CT and CT perfusion) can be implemented easily in most hospital centres, and are able to provide quantitative perfusion data in addition to structural images.

[Neuroradiological investigations in mild brain injuries: state of the art and practical recommendations]

OBJECTIVES

To clarify the contribution of each technique of neuroradiological and nuclear medicine investigations after mild brain injuries. To analyze the pathophysiological mechanisms of the lesions. To update indications for imaging techniques in the short or long term management. To define the practical recommendations.

METHOD

The international databases were consulted for each neuroradiological technique; the most valuable articles were retained for study (PubMed, ).

RESULTS AND DISCUSSION

Standard skull X-rays are obsolete. Craniofacial (bony windows) and brain CT-scan (parenchymal windows) is the most efficient diagnosis tool in the acute phase because of its accessibility. Brain MRI is less accessible in the emergency setting but is feasible in some centers. It is the best choice in the first weeks following mild brain injury but may be normal. Taking into account the limitations of morphological imaging, functional imaging techniques (SPECT, fMRI, PET-scan) are necessary as they may show axonal damage or brain atrophy. There is however the problem of availability. SPECT is the most accessible. Spectro-MRI is promising. In spite of progress in neuroradiological investigation methods, the neuropsychological evaluation and multi-disciplinary treatment of these patients by a skilled team remains of utmost importance.

Early morphologic and spectroscopic magnetic resonance in severe traumatic brain injuries can detect "invisible brain stem damage" and predict "vegetative states"

A precise evaluation of the brain damage in the first days of severe traumatic brain injured (TBI) patients is still uncertain despite numerous available cerebral evaluation methods and imaging. In 5-10% of severe TBI patients, clinicians remain concerned with prolonged coma and long-term marked cognitive impairment unexplained by normal morphological T2 star, flair, and diffusion magnetic resonance imaging (MRI). For this reason, we prospectively assessed the potential value of magnetic resonance spectroscopy (MRS) of the brain stem to evaluate the functionality of the consciousness areas. Forty consecutive patients with severe TBI were included. Single voxel proton MRS of the brain stem and morphological MRI of the whole brain were performed at day 17.5 +/- 6.4. Disability Rating Scale and Glasgow Outcome Scale (GOS) were evaluated at 18 months posttrauma. MRS appeared to be a reliable tool in the exploration of brainstem metabolism in TBI. Three different spectra were observed (normal, cholinergic reaction, or neuronal damage) allowing an evaluation of functional damage. MRS disturbances were not correlated with anatomical MRI lesions suggesting that the two techniques are strongly complementarity. In two GOS 2 vegetative patients with normal morphological MRI, MRS detected severe functional damage of the brainstem (NAA/Cr < 1.50) that was described as "invisible brain stem damage." MRI and MRS taken separately could not distinguish patients GOS 3 (n = 7) from GOS 1-2 (n = 11) and GOS 4-5 (n = 20). However, a principal component analysis of combined MRI and MRS data enabled a clear-cut separation between GOS 1-2, GOS 3, and GOS 4-5 patients with no overlap between groups. This study showed that combined MRI and MRS provide a reliable evaluation of patients presenting in deep coma, specially when there are insufficient MRI lesions of the consciousness pathways to explain their status. In the first few days post-trauma metabolic (brainstem spectroscopy) and morphological (T2 star and Flair) MRI studies can predict the long-term neurological outcome, especially the persistent vegetative states and minimally conscious state.

Functional MRI evidence for disparate developmental processes underlying intelligence in boys and girls

Previous research has shown evidence for sex differences in the neuroanatomical bases for intelligence in adults. Possible differences in the neuroanatomical correlates of intelligence and their developmental trajectories between boys and girls were investigated using functional MRI (fMRI). A large cohort of over 300 children, ages 5-18, performed the semantic processing task of silent verb generation. Regions were found in the left hemisphere exhibiting positive correlations of blood-oxygenation-level-dependent (BOLD) activation with IQ, including the middle temporal gyrus, prefrontal cortex (Broca's area), medial frontal gyrus, precuneus, and cingulate gyrus, while the superior temporal gyrus in the right hemisphere displayed a negative correlation of BOLD activation with IQ. Significant sex-X-IQ and sex-X-IQ-X-age interaction effects were also seen in the left middle temporal gyrus and left inferior frontal gyrus. Using a data-driven analysis procedure, a sex-X-IQ-X-age interaction was also demonstrated in the functional connectivity between regions in the left hemisphere, parameterized as a weighted sum of pairwise covariances between fMRI time courses. While young girls (<13 years) exhibited no correlation of connectivity with intelligence, older girls (>13 years) demonstrated a positive association of functional connectivity with intelligence. Boys, however, demonstrated the opposite developmental trajectory, from a positive association of connectivity with intelligence in young boys (ages <9 years), to a negative association in older boys (ages >13 years). Our results provide evidence for disparate neuroanatomical trajectories underlying intelligence in boys and girls.

Utilidad de la PET con FDG en la valoración del paciente con traumatismo craneoencefálico severo crónico

INTRODUCTION

To describe the changes in cerebral glucose metabolism after a severe traumatic brain injury (TBI), at the beginning of the rehabilitation, to analyze its diagnostic agreement with morphologic neuroimaging technologies (MR/CT) and to correlate the neuroimaging findings with the intensity of the TBI and the functional ability for daily activities.

MATERIAL AND METHODS

Prospective study of 55 patients who had sustained a severe TBI (GCS < or = 8) by means of 18F-FDG PET and MR/CT. The agreement between anatomical and functional neuroimagen studies was measured. Correlation between cerebral injury severity in neuroimaging, clinical functional evaluation assessed with Barthel-M Index and GCS were tested.

RESULTS

100 % of patients showed changes in cerebral metabolism, being the thalamus the area more frequently affected. 60 % of patients showed injuries in MR/CT, more frequently in frontal areas. The agreement for the diagnosis of pathology between morphologic and functional neuroimagen was very low. The TBI severity showed significant statistical correlation with the degree of cerebral metabolism and the level of disability.

CONCLUSIONS

18F-FDG PET allows to know the cerebral glucose metabolism at the beginning of the rehabilitation, being correlated with the TBI severity and the level of patient's disability for daily activities. 18F-FDG PET diagnoses major number of injuries that traditional neuroimaging and demonstrates a high thalamic vulnerability, with injuries in up to 76 % of patients with severe TBI.

Extracellular N-acetylaspartate depletion in traumatic brain injury

N-Acetylaspartate (NAA) is almost exclusively localized in neurons in the adult brain and is present in high concentration in the CNS. It can be measured by proton magnetic resonance spectroscopy and is seen as a marker of neuronal damage and death. NMR spectroscopy and animal models have shown NAA depletion to occur in various types of chronic and acute brain injury. We investigated 19 patients with traumatic brain injury (TBI). Microdialysis was utilized to recover NAA, lactate, pyruvate, glycerol and glutamate, at 12-h intervals. These markers were correlated with survival and a 6-month Glasgow Outcome Score. Eleven patients died and eight survived. A linear mixed model analysis showed a significant effect of outcome and of the interaction between time of injury and outcome on NAA levels (p = 0.009 and p = 0.004, respectively). Overall, extracellular NAA was 34% lower in non-survivors. A significant non-recoverable fall was observed in this group from day 4 onwards, with a concomitant rise in lactate-pyruvate ratio and glycerol. These results suggest that mitochondrial dysfunction is a significant contributor to poor outcome following TBI and propose extracellular NAA as a potential marker for monitoring interventions aimed at preserving mitochondrial function.

Bench to bedside: evidence for brain injury after concussion--looking beyond the computed tomography scan

The emergency management of cerebral concussion typically centers on the decision to perform a head computed tomography (CT) scan, which only rarely detects hemorrhagic lesions requiring neurosurgery. The absence of hemorrhage on CT scan often is equated with a lack of brain injury. However, observational studies revealing poor long-term cognitive outcome after concussion suggest that brain injury may be present despite a normal CT scan. To explore this idea further, the authors reviewed the evidence for objective neurologic injury in humans after concussion, with particular emphasis on those with a normal brain CT. This evidence comes from studies involving brain tissue pathology, CT scanning, magnetic resonance image (MRI) scanning, serum biomarkers, formal cognitive and balance tests, functional MRI, positron emission tomography, and single-photon emission computed tomography scanning. Each section is accompanied by technical information to help the reader understand what these tests are, not to endorse their use clinically. The authors discuss the strengths and weaknesses of the evidence in each case. These reports make a compelling case for the existence of concussion as a clinically relevant disease with demonstrable neurologic pathology. Areas for future emergency medicine research are suggested.

Magnetic Resonance Spectroscopy

Magnetic resonance spectroscopy (MRS) complements magnetic resonance imaging (MRI) as a non-invasive means for the characterization of tissue. While MRI uses the signal from hydrogen protons to form anatomic images, proton MRS uses this information to determine the concentration of brain metabolites such as N-acetyl aspartate (NAA), choline (Cho), creatine (Cr) and lactate in the tissue examined. The most widely used clinical application of MRS has been in the evaluation of central nervous system disorders.MRS has its limitations and is not always specific but, with good technique and in combination with clinical information and conventional MRI, can be very helpful in diagnosing certain entities. For example, a specific pattern of metabolites can be seen in disorders such as Canavan's disease, creatine deficiency, and untreated bacterial brain abscess. MRS may also be helpful in the differentiation of high grade from low grade brain tumors, and perhaps in separating recurrent brain neoplasm from radiation injury.

Update of neuropathology and neurological recovery after traumatic brain injury

This review focuses on the potential for traumatic brain injury to evoke both focal and diffuse changes within the brain parenchyma, while considering the cellular constituents involved and the subcellular perturbations that contribute to their dysfunction. New insight is provided on the pathobiology of traumatically induced cell body injury and diffuse axonal damage. The consequences of axonal damage in terms of subsequent deafferentation and any potential retrograde cell death and atrophy are addressed. The regional and global metabolic sequelae are also considered. This detailed presentation of the neuropathological consequences of traumatic brain injury is used to set the stage for better appreciating the neurological recovery occurring after traumatic injury. Although the pathological and clinical effects of focal and diffuse damage are usually intermingled, the different clinical manifestations of recovery patterns associated with focal versus diffuse injuries are presented. The recognizable patterns of recovery, involving unconsciousness, posttraumatic confusion/amnesia, and postconfusional restoration, that typically occur across the full spectrum of diffuse injury are described, recognizing that the patient's long-term recovery may involve more idiosyncratic combinations of dysfunction. The review highlights the relationship of focal lesions to localizing syndromes that may be embedded in the evolving natural history of diffuse pathology. It is noted that injuries with primarily focal pathology do not necessarily follow a comparable pattern of recovery with distinct phases. Potential linkages of these recovery patterns to the known neuropathological sequelae of injury and various reparative mechanisms are considered and it is proposed that potential biological markers and newer imaging technologies will better define these linkages.

Proton MR spectroscopy detected glutamate/glutamine is increased in children with traumatic brain injury

Adults with traumatic brain injury (TBI) have been shown by invasive methods to have increased levels of the excitatory neurotransmitter glutamate. It is unclear whether glutamate release contributes to primary or secondary injury and whether its protracted elevation is predictive of a poor outcome. Preliminary studies at our institution in adults found that early increases in magnetic resonance spectroscopy (MRS)-detected glutamate/glutamine (Glx) were associated with poor outcomes. We therefore studied 38 children (mean age, 11 years; range, 1.6-17 years) who had TBI with quantitative short-echo time (STEAM, TE = 20 msec) proton MRS, a mean of 7 +/- 4 (range, 1-17) days after injury in order to determine if their occipital or parietal Glx levels correlated with the severity of injury or outcome. Occipital Glx was significantly increased in children with TBI compared to controls (13.5 +/- 2.4 vs. 10.7 +/- 1.8; p = 0.002), but there was no difference between children with good compared to poor outcomes as determined by the Pediatric Cerebral Performance Category Scale score at 6-12 months after injury. We also did not find a correlation between the amount of Glx and the initial Glasgow Coma Scale score, duration of coma, nor with changes in spectral metabolites, including N-acetyl aspartate, choline, and myoinositol. In part, this may have occurred because, in this study, most patients with poor outcomes were studied later than patients with good outcomes, potentially beyond the time frame for peak elevation of Glx after injury. Additional early and late studies of patients with varying degrees of injury are required to assess the importance to the pathophysiology of TBI of this excitatory neurotransmitter.

Sex differences in N-acetylaspartate correlates of general intelligence: an 1H-MRS study of normal human brain

Researchers have long attempted to determine brain correlates of intelligence using available neuroimaging technology including CT, MRI, PET, and fMRI. Although structural and functional imaging techniques are well suited to assess gross cortical regions associated with intelligence, the integrity and functioning of underlying white matter networks critical to coordinated cortical integration remain comparatively understudied. A relatively recent neuroimaging advance is magnetic resonance spectroscopy (MRS) which allows for interrogation of biochemical substrates of brain structure and function in vivo. In this study, we examined twenty-seven normal control subjects (17 male, 10 female) to determine whether N-acetylaspartate (NAA), a metabolite found primarily within neurons, is related to intelligence as assessed by the Wechsler Adult Intelligence Scale-III. Of the three white matter regions studied (i.e., left frontal, right frontal, left occipito-parietal), we found that a model including only left occipito-parietal white matter predicted intellectual performance [F(1,25) = 8.65, P = .007; r2 = .26], providing regional specificity to our previous findings of NAA-IQ relationships. Moreover, we found that a complex combination of left frontal and left occipito-parietal NAA strongly predicted performance in women, but not men [F(2,7) = 21.84, P < .001; adjusted r2 = .82]. Our results highlight a biochemical substrate of normal intellectual performance, mediated by sex, within white matter association fibers linking posterior to frontal brain regions.

Quantitative neuropathologic correlates of changes in ratio of N-acetylaspartate to creatine in macaque brain

PURPOSE

To elucidate the neuropathologic basis of transient changes in the ratio of N-acetylaspartate (NAA) to creatine (Cr) in the primate brain by using a simian immunodeficiency virus (SIV)-infected macaque model of the neurologic manifestation of acquired immune deficiency syndrome.

MATERIALS AND METHODS

This study was approved by the Massachusetts General Hospital Subcommittee on Research and Animal Care and the Institutional Animal Care and Use Committee of Harvard University. Rhesus macaques infected with SIV were evaluated during the 1st month of infection. A total of 11 animals were studied, including four control animals, three animals sacrificed 12 days after infection, three animals sacrificed 14 days after infection, and one animal sacrificed 28 days after infection. All animals underwent in vivo proton ((1)H) magnetic resonance (MR) spectroscopy, and postmortem frontal lobe tissue was investigated by using high-spectral-resolution (1)H MR spectroscopy of brain extracts. In addition, quantitative neuropathologic analyses were performed. Stereologic analysis was performed to determine neuronal counts, and immunohistochemical analysis was performed to analyze three neuronal markers: synaptophysin, microtubule-associated protein 2 (MAP2), and calbindin. Analysis of variance (ANOVA) was used to determine substantial changes in neuropathologic and MR spectroscopic markers. Spearman rank correlations were calculated between plasma viral load and neuropathologic and spectroscopic markers.

RESULTS

During acute infection with SIV, the macaque brain exhibited significant changes in NAA/Cr (P < .02, ANOVA) and synaptophysin (P < .013, ANOVA). There was no significant change in the concentration of Cr. No significant changes were found in neuronal counts or other immunohistochemical neuronal markers. With the Spearman rank test, a significant direct correlation was detected between synaptophysin and ex vivo NAA/Cr (r(s) = 0.72, P < .013). No correlation between NAA/Cr and neuronal counts, calbindin, or MAP2 was found.

CONCLUSION

NAA/Cr is a sensitive marker of neuronal injury, not necessarily neuronal loss, and best correlates with synaptophysin, a marker of synaptodendritic dysfunction.

Proton spectroscopy detected myoinositol in children with traumatic brain injury

Previous studies have shown that proton magnetic resonance spectroscopy (MRS) is useful in predicting neurologic prognosis in children with traumatic brain injury (TBI). Reductions in N-acetyl derived metabolites and presence of lactate have been predictive of poor outcomes. We examined another spectroscopy metabolite, myoinositol (mI), to determine whether it is altered after TBI. Found primarily in astrocytes, mI functions as an osmolyte and is involved in hormone response pathways and protein-kinase C activation. Myoinositol is elevated in the newborn brain and is increased in a variety of diseases. We studied 38 children (mean age 11 y; range 1.6-17 y) with TBI using quantitative short echo time occipital gray and parietal white matter proton MRS at a mean of 7 d (range 1-17 d) after injury. We found that occipital gray matter mI levels were increased in children with TBI (4.30 +/- 0.73) compared with controls (3.53 +/- 0.48; p = 0.003). We also found that patients with poor outcomes 6-12 mo after injury had higher mI levels (4.78 +/- 0.68) than patients with good outcomes (4.15 +/- 0.69; p < 0.05). Myoinositol is elevated after pediatric TBI and is associated with a poor neurologic outcome. The reasons for its elevation remain unclear but may be due to astrogliosis or to a disturbance in osmotic function.

Diffuse axonal injuries: pathophysiology and imaging

Diffuse axonal shear injury is a common traumatic brain injury, with significant neurologic and behavioral impact on patients. Radiologic recognition of this entity and understanding of its sequelae can be of utmost importance in the prediction of outcome and planning for rehabilitation. MRI has proven to be the optimal means of detection and characterization of DAI lesions, with GRE and FLAIR sequences being particularly helpful, and more advanced techniques such as MRS show preliminary evidence of some utility in determining outcome.