Local cerebral blood volume in head-injured patients. Determination by emission computed tomography of 99mTc-labeled red cells

Regulation of brain fluid volumes and pressures: basic principles, intracranial hypertension, ventriculomegaly and hydrocephalus

The principles of cerebrospinal fluid (CSF) production, circulation and outflow and regulation of fluid volumes and pressures in the normal brain are summarised. Abnormalities in these aspects in intracranial hypertension, ventriculomegaly and hydrocephalus are discussed. The brain parenchyma has a cellular framework with interstitial fluid (ISF) in the intervening spaces. Framework stress and interstitial fluid pressure (ISFP) combined provide the total stress which, after allowing for gravity, normally equals intracerebral pressure (ICP) with gradients of total stress too small to measure. Fluid pressure may differ from ICP in the parenchyma and collapsed subarachnoid spaces when the parenchyma presses against the meninges. Fluid pressure gradients determine fluid movements. In adults, restricting CSF outflow from subarachnoid spaces produces intracranial hypertension which, when CSF volumes change very little, is called idiopathic intracranial hypertension (iIH). Raised ICP in iIH is accompanied by increased venous sinus pressure, though which is cause and which effect is unclear. In infants with growing skulls, restriction in outflow leads to increased head and CSF volumes. In adults, ventriculomegaly can arise due to cerebral atrophy or, in hydrocephalus, to obstructions to intracranial CSF flow. In non-communicating hydrocephalus, flow through or out of the ventricles is somehow obstructed, whereas in communicating hydrocephalus, the obstruction is somewhere between the cisterna magna and cranial sites of outflow. When normal outflow routes are obstructed, continued CSF production in the ventricles may be partially balanced by outflow through the parenchyma via an oedematous periventricular layer and perivascular spaces. In adults, secondary hydrocephalus with raised ICP results from obvious obstructions to flow. By contrast, with the more subtly obstructed flow seen in normal pressure hydrocephalus (NPH), fluid pressure must be reduced elsewhere, e.g. in some subarachnoid spaces. In idiopathic NPH, where ventriculomegaly is accompanied by gait disturbance, dementia and/or urinary incontinence, the functional deficits can sometimes be reversed by shunting or third ventriculostomy. Parenchymal shrinkage is irreversible in late stage hydrocephalus with cellular framework loss but may not occur in early stages, whether by exclusion of fluid or otherwise. Further studies that are needed to explain the development of hydrocephalus are outlined.

Novel Approach for 99mTc-Labeling of Red Blood Cells: Evaluation of 99mTc-4SAboroxime as a Blood Pool Imaging Agent

Angiography with radiolabeled red blood cells (RBCs) plays an important role in diagnosis and prognosis in vascular diseases. Both in vitro and in vivo methods have been developed for ^99mTc-labeling of RBCs. However, these methods are complicated and lack reproducibility. Therefore, it is highly desirable to develop an alternative method for routine ^99mTc-labeling of RBCs. In this report, we present a novel approach for ^99mTc-labeling of RBCs. We prepared a new ^99mTc(III) radiotracer [^99mTcCl(CDO)(CDOH)₂B-4AS] (^99mTc-4ASboroxime: 4AS-B(OH)₂ = 4-aminosulfonylphenyl)boronic acid, and CDOH₂ = cyclohexanedione dioxime) in >95% radiochemical purity. Imaging and biodistribution studies were performed in Sprague-Dawley (SD) rats. It was found that the blood radioactivity was ∼6.0%ID/g (∼90% injected dose for 200-225 g SD rats) for ^99mTc-4ASboroxime with low uptake in the myocardium, kidneys, liver, lungs, and muscle, most likely due to lack of leakage of ^99mTc-labeled RBCs from the intravascular space. The blood radioactivity was almost unchanged over the 2 h period, suggesting that the binding of ^99mTc-4ASboroxime to blood components (cells, proteins, and plasma) is stable. The results from γ-counting of the isolated blood components showed that ^99mTc-4ASboroxime had >95% of blood radioactivity binding to RBCs, ∼1% to albumin, and ∼3% remaining free in blood plasma, demonstrating its RBC-specificity. The results from imaging studies in SD rats indicated that ^99mTc-4ASboroxime is predominantly distributed in the blood pool. Main blood vessels were well delineated in the head/neck and abdominal regions. This statement was further substantiated by the results from imaging studies in pigs. ^99mTc-4ASboroxime is an excellent blood pool agent with the potential for diagnosis and prognosis of vascular diseases.

Prolonged Cerebral Hyperperfusion and Subcortical Low Intensity on Fluid-Attenuated Inversion Recovery Images: Unusual Manifestation After Removal of Organized Chronic Subdural Hematoma

BACKGROUND

Cerebral hyperperfusion sometimes occurs after removal of chronic subdural hematoma (CSH) and usually resolves within a few days without any symptoms. Subcortical low intensity (SCLI) on fluid-attenuated inversion recovery (FLAIR) magnetic resonance images is rare and has been reported in some diseases other than CSH. A case of organized CSH who suffered prolonged neurologic deterioration, SCLI, and cerebral hyperperfusion postoperatively is described.

CASE DESCRIPTION

An 81-year-old man, presenting with left hemiparesis, underwent craniotomy for right organized CSH after 2 burr-hole surgeries. After the craniotomy, the symptoms improved, but on postoperative day 2, left hemiparesis, hemispatial neglect, and hemiasomatognosia developed. Magnetic resonance imaging revealed SCLI on FLAIR images, and single-photon emission computed tomography with N-isopropyl-p-[¹²³I]-iodoamphetamine revealed cerebral hyperperfusion in the right hemispheric cortex. Antihypertensive treatment improved the symptoms gradually, which resolved completely 1 month postsurgery.

CONCLUSIONS

A case of organized CSH, which showed postoperative neurologic deterioration associated with prolonged cerebral hyperperfusion and SCLI on FLAIR images, is reported. Prolonged cerebral hyperperfusion could be a cause of postoperative neurologic deterioration in organized CSH.

Vessel-specific quantification of blood oxygenation with T2-relaxation-under-phase-contrast MRI

PURPOSE

Measurement of venous oxygenation (Yv) is a critical step toward quantitative assessment of brain oxygen metabolism, a key index in many brain disorders. The present study aims to develop a noninvasive, rapid, and reproducible method to measure Yv in a vessel-specific manner.

THEORY

The method, T2-Relaxation-Under-Phase-Contrast MRI, utilizes complex subtraction of phase-contrast to isolate pure blood signal, applies nonslice-selective T2-preparation to measure T2, and converts T2 to oxygenation using a calibration plot.

METHODS

Following feasibility demonstration, several technical aspects were examined, including validation with an established global Yv technique, test-retest reproducibility, sensitivity to detect oxygenation changes due to hypoxia and caffeine challenges, applicability of echo-planar-imaging (EPI) acquisition to shorten scan duration, and ability to study veins with a caliber of 1-2 mm.

RESULTS

T2-Relaxation-Under-Phase-Contrast was able to simultaneously measure Yv in all major veins in the brain, including sagittal sinus, straight sinus, great vein, and internal cerebral vein. T2-Relaxation-Under-Phase-Contrast results showed an excellent agreement with the reference technique, high sensitivity to oxygenation changes, and test-retest variability of 3.5 ± 1.0%. The use of segmented-EPI was able to reduce the scan duration to 1.5 minutes. It was also feasible to study pial veins and deep veins.

CONCLUSION

T2-Relaxation-Under-Phase-Contrast MRI is a promising technique for vessel-specific oxygenation measurement.

Measurement of parenchymal extravascular R2* and tissue oxygen extraction fraction using multi-echo vascular space occupancy MRI at 7 T

Parenchymal extravascular R2* is an important parameter for quantitative blood oxygenation level-dependent (BOLD) studies. Total and intravascular R2* values and changes in R2* values during functional stimulations have been reported in a number of studies. The purpose of this study was to measure absolute extravascular R2* values in human visual cortex and to estimate the intra- and extravascular contributions to the BOLD effect at 7 T. Vascular space occupancy (VASO) MRI was employed to separate out the extravascular tissue signal. Multi-echo VASO and BOLD functional MRI (fMRI) with visual stimulation were performed at 7 T for R2* measurement at a spatial resolution of 2.5 × 2.5 × 2.5 mm(3) in healthy volunteers (n = 6). The ratio of changes in extravascular and total R2* (ΔR2*) was used to estimate the extravascular fraction of the BOLD effect. Extravascular R2* values were found to be 44.66 ± 1.55 and 43.38 ± 1.51 s(-1) (mean ± standard error of the mean, n = 6) at rest and activation, respectively, in human visual cortex at 7 T. The extravascular BOLD fraction was estimated to be 91 ± 3%. The parenchymal oxygen extraction fraction (OEF) during activation was estimated to be 0.24 ± 0.01 based on the R2* measurements, indicating an approximately 37% decrease compared with OEF at rest.

Calibration and validation of TRUST MRI for the estimation of cerebral blood oxygenation

Recently, a T(2) -Relaxation-Under-Spin-Tagging (TRUST) MRI technique was developed to quantitatively estimate blood oxygen saturation fraction (Y) via the measurement of pure blood T(2) . This technique has shown promise for normalization of fMRI signals, for the assessment of oxygen metabolism, and in studies of cognitive aging and multiple sclerosis. However, a human validation study has not been conducted. In addition, the calibration curve used to convert blood T(2) to Y has not accounted for the effects of hematocrit (Hct). In this study, we first conducted experiments on blood samples under physiologic conditions, and the Carr-Purcell-Meiboom-Gill T(2) was determined for a range of Y and Hct values. The data were fitted to a two-compartment exchange model to allow the characterization of a three-dimensional plot that can serve to calibrate the in vivo data. Next, in a validation study in humans, we showed that arterial Y estimated using TRUST MRI was 0.837 ± 0.036 (N=7) during the inhalation of 14% O2, which was in excellent agreement with the gold-standard Y values of 0.840 ± 0.036 based on Pulse-Oximetry. These data suggest that the availability of this calibration plot should enhance the applicability of T(2) -Relaxation-Under-Spin-Tagging MRI for noninvasive assessment of cerebral blood oxygenation.

Determination of spin compartment in arterial spin labeling MRI

A major difference between arterial-spin-labeling MRI and gold-standard radiotracer blood flow methods is that the compartment localization of the labeled spins in the arterial-spin-labeling image is often ambiguous, which may affect the quantification of cerebral blood flow. In this study, we aim to probe whether the spins are located in the vascular system or tissue by using T2 of the arterial-spin-labeling signal as a marker. We combined two recently developed techniques, pseudo-continuous arterial spin labeling and T2-Relaxation-Under-Spin-Tagging, to determine the T2 of the labeled spins at multiple postlabeling delay times. Our data suggest that the labeled spins first showed the T2 of arterial blood followed by gradually approaching and stabilizing at the tissue T2. The T2 values did not decrease further toward the venous T2. By fitting the experimental data to a two-compartment model, we estimated gray matter cerebral blood flow, arterial transit time, and tissue transit time to be 74.0 ± 10.7 mL/100g/min (mean ± SD, N = 10), 938 ± 156 msec, and 1901 ± 181 msec, respectively. The arterial blood volume was calculated to be 1.18 ± 0.21 mL/100 g. A postlabeling delay time of 2 s is sufficient to allow the spins to completely enter the tissue space for gray matter but not for white matter.

Transient focal spinal cord hyperemia after resection of spinal meningioma: case report

OBJECTIVE

Transient postoperative focal hyperemia in the spinal cord is rare. We report 2 patients with transient focal hyperemia after the resection of a spinal meningioma that led to temporal neurological deterioration followed by complete recovery.

CLINICAL PRESENTATION

Two patients presented with cervical meningiomas at the C7 and C1-C2 levels. Preoperatively, both patients experienced gradual exacerbation of spastic tetraparesis. Magnetic resonance imaging revealed isointensity on T1-weighted images and high intensity on T2-weighted images with homogeneous enhancement.

INTERVENTION

Both patients underwent complete tumor removal. A histopathological examination revealed a meningothelial meningioma in both patients. Postoperative magnetic resonance imaging revealed transient focal hyperemia of the cervical cord.

CONCLUSION

Both patients manifested transient focal hyperemia of the spinal cord after acute decompression by resection of a spinal meningioma.

Does the brain become heavier or lighter after trauma?

An uncontrolled rise in intracranial pressure is probably the most common cause of death in traumatic brain-injured patients. The intracranial pressure rise is often due to cerebral oedema. Diffusion-weighted imaging has been extensively used to study cerebral oedema formation after trauma in experimental studies. Nevertheless, this technology is difficult to perform at the acute phase, especially in unstable head trauma patients. For these reasons, a safe examination allowing us to better understand the pathophysiology of cerebral oedema formation in such patients would be of great interest. Radiological attenuation is linearly correlated with estimated specific gravity in human tissue. This property gives the opportunity to measure in vivo the volume, weight and specific gravity of any tissue by computed tomography. We recently developed a software package (BrainView) for Windows workstations, providing semi-automatic tools for brain analysis from DICOM images obtained from cerebral computed tomography. In this review, we will discuss the results of the in vivo analysis of brain weight, volume and specific gravity and consider the use of this software as a new technology to improve our knowledge of cerebral oedema formation after trauma and to evaluate the severity of traumatic brain-injured patients.

A quantitative computed tomography assessment of brain weight, volume, and specific gravity in severe head trauma

BACKGROUND

Computed tomography DICOM images analysis allows a quantitative measurement of organ weight, volume and specific gravity in humans.

METHODS

The brain weight, volume and specific gravity of 15 traumatic brain-injury patients (3+/-2 days after trauma) were computed using a specially designed software (BrainView). Data were compared with those obtained from 15 healthy subjects paired for age and overall intracranial volume.

RESULTS

Hemisphere weight were 91 g higher in patients than in controls (1167+/-101 vs 1076+/-112 g; p<0.05). Specific gravity of hemispheres (1.0367+/-0.0017 vs 1.0335+/-0.0012 g/ml; p<0.001), brainstem (1.0302+/-0.0016 vs 1.0277+/-0.0015 g/ml; p<0.001) and cerebellum (1.0396+/-0.0020 vs 1.0375+/-0.0015 g/ml; p<0.05) was significantly higher in traumatic brain injury (TBI) patients than in controls (all p<0.0001 without interaction). This increase in specific gravity was evenly distributed between the hemispheres, the brainstem and the cerebellum, and the grey and white matter. It was more pronounced in the rostral than in the caudal areas of the hemispheres. It was independent of the volume of brain contusion, of the mechanism of head injury, of natremia and of initial Glasgow coma score.

CONCLUSION

Human TBI patients present a diffuse increase in specific gravity. This observation is in sharp opposition with the data derived from the experimental literature.

Chronic subdural hematoma following dural metastasis of gastric cancer: measurement of pre- and postoperative cerebral blood flow with N-isopropyl-p-[123I]iodoamphetamine--case report

A 58-year-old female with gastric cancer presented with left chronic subdural hematoma (CSH) without history of head injury. Magnetic resonance imaging revealed left CSH with atypical findings such as abnormal dural enhancement and swelling of the left cerebral hemisphere. One month after gastrectomy, motor aphasia and right hemiparesis developed. Irrigation of the left CSH was performed. The hematoma was abnormally mucinous and became solid immediately after irrigation. Histological examination showed that adenocarcinoma cells had metastasized to the dura mater and the outer membrane of the hematoma. The preoperative cerebral blood flow (CBF) in the affected cerebral hemisphere, measured by single photon emission computed tomography using N-isopropyl-p-[123I]iodoamphetamine, was much higher than that in the opposite hemisphere, whereas the postoperative CBF was almost equal in both hemispheres. Subdural hematomas secondary to dural metastases of extraneuronal malignancies are rare, and are usually the chronic type. Measurement of the pre- and postoperative CBF in the present patient with CSH following dural metastasis of the malignant tumor showed that preoperative hyperemia in the affected hemisphere may result from dilation of the cerebral vessels caused by the effects of the CSH.

There is no evidence of an association in children and teenagers between the apolipoprotein E epsilon4 allele and post-traumatic brain swelling

Traumatic brain injury (TBI) is an important cause of mortality and disability in children and teenagers. A particular feature of the neuropathology at post-mortem is brain swelling. The cause of the swelling in some cases is not known, while in others it is associated with traumatic axonal injury or hypoxia. Apolipoprotein E (APOE) epsilon4 allele is known to be an important genetic determinant of outcome in children after TBI. We hypothesized a relationship between possession of APOEepsilon4 and diffuse traumatic brain swelling. A total of 165 cases aged between 2 and 19 years were identified from the department's tissue archive. APOE genotype was determined by polymerase chain reaction (PCR) in 106 cases. Bilateral swelling was present in 44 cases (11 with APOEepsilon4), unilateral swelling in 25 cases (7 with APOEepsilon4) and in 36 cases (9 with APOEepsilon4) there was no evidence of brain swelling. There was no significant relationship between possession of APOEepsilon4 and the presence of cerebral swelling (chi(2) = 0.09, df = 2, P = 0.96). The 95% confidence interval for difference in proportions with swelling in those with and without the APOE epsilon4 is -19% to 22%. Thus, a significant relationship was not found between diffuse brain swelling and possession of APOEepsilon4, and in this cohort of patients there was an identifying cause of the brain swelling in all cases.

Experimental measurement of extravascular parenchymal BOLD effects and tissue oxygen extraction fractions using multi-echo VASO fMRI at 1.5 and 3.0 T

Quantitative interpretation of BOLD fMRI signal changes has predominantly employed empirical models for the whole parenchyma and a calibration step is usually needed to determine the physiological parameters during activation. Although analytical expressions are available for the extravascular and intravascular components of the BOLD effects, it is difficult to experimentally separate tissue from blood signal contributions at the low magnetic fields in which most fMRI studies are performed. Even if this can be achieved, an additional problem that remains is the separation of two types of extravascular BOLD effects, namely those around microvasculature (in the parenchyma close to the site of activation) and those around draining macrovasculature (e.g., in tissue and CSF more remote from the site of activation). In the recently developed vascular space occupancy technique, blood signals are nulled and the activations are localized predominantly in gray matter, allowing experimental measurement of parenchymal extravascular R(2)* and its changes accompanying activation. When comparing such data with total parenchymal R(2)* changes in BOLD fMRI, the extravascular fractions were found to be 47 +/- 7% (mean +/- SEM, n = 4) and 67 +/- 6% at 1.5 and 3.0 T, respectively, in line with expectations that intravascular BOLD contributions are reduced at higher field. The present approach provides a noninvasive means to determine parenchymal oxygen extraction fraction (OEF) in situ. During visual stimulation, OEF values measured at 1.5 and 3.0 T were in good agreement, giving 0.23 +/- 0.01 and 0.21 +/- 0.01, respectively.

Admission Perfusion CT: Prognostic Value in Patients with Severe Head Trauma

PURPOSE

To assess the prognostic value of admission perfusion computed tomography (CT) in patients with severe head trauma.

MATERIALS AND METHODS

This prospective study included 130 patients with severe trauma, aged 19-86 years, admitted with a Glasgow Coma Scale score of 8 or less. They underwent perfusion CT as part of their admission CT survey. Clinical data, unenhanced cerebral CT findings, and perfusion CT scans were evaluated with respect to the Glasgow Outcome Scale (GOS) score at 3 months. Perfusion CT features were evaluated in patients with intracranial hypertension, cerebral contusions, and juxtadural hematomas. Ordered logistic regression was used to determine risk factors for an unfavorable GOS score at 3 months.

RESULTS

Perfusion CT was more sensitive than conventional unenhanced CT in the detection of cerebral contusions. Perfusion CT featured specific patterns with respect to patient outcome, with normal brain perfusion or hyperemia in patients with favorable outcome, and oligemia in patients with unfavorable outcome. The number of arterial territories with low regional cerebral blood volume at perfusion CT was an independent prognostic factor (P =.008), as were mean arterial pressure at the scene of accident (P =.083), base excess at admission (P =.002), presence of skull fractures (P =.041), and signs of herniation (P =.013) at admission unenhanced cerebral CT. Perfusion CT also showed a range of brain perfusion alterations in patients with juxtadural collections, cerebral edema, or intracranial hypertension.

CONCLUSION

Perfusion CT in patients with severe head trauma provides independent prognostic information regarding functional outcome.

Circulatory basis of fMRI signals: relationship between changes in the hemodynamic parameters and BOLD signal intensity

Blood oxygenation level-dependent functional magnetic resonance imaging (BOLD-fMRI) is widely used as a tool for functional brain mapping. During brain activation, increases in the regional blood flow lead to an increase in blood oxygenation and a decrease in paramagnetic deoxygenated hemoglobin (deoxy-Hb), causing an increase in the MR signal intensity at the site of brain activation. However, not a few studies using fMRI have failed to detect activation of areas that ought to have been activated. We assigned BOLD-positive (an increase in the signal intensity), BOLD-negative (a decrease in the signal intensity), and BOLD-silent (no change) brain activation to respective circulatory conditions through a description of fMRI signals as a function of the concentration of oxygenated Hb (oxy-Hb) and deoxy-Hb obtained with near-infrared optical imaging (NIOI). Using this model, we explain the sensory motor paradox in terms of BOLD-positive, BOLD-negative, and BOLD-silent brain activation.

Hematoma intracerebral tras la evacuación de hematoma subdural crónico: descripción de dos casos y revisión de la literatura

Intracerebral hemorrhage ocurring after chronic subdural hematoma evacuation, is a rare and very serious postoperative complication. The sudden increase of cerebral blood flow in the hemisphere beneath the hematoma, is the most likely mechanism responsible for this situation. Two new cases of intracerebral hemorrage after evacuation of chronic subdural hematomas are reported.

Contribution of edema and cerebral blood volume to traumatic brain swelling in head-injured patients

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.

Postoperative hyperperfusion syndrome in elderly patients with chronic subdural hematoma

BACKGROUND

Temporary acute agitated delirium is a frequent complication after surgery for chronic subdural hematoma (CSH) in elderly patients. To clarify the pathogenic mechanism underlying this complication, we measured cerebral blood flow before and after surgery in elderly patients with CSHs.

METHODS

Twenty-seven patients aged 75 years or older with unilateral CSH underwent treatment involving a single burr hole craniostomy with continuous catheter drainage. Cerebral blood flow was measured using single photon emission computed tomography 1 day before surgery, and at 1 hour and 24 hours after surgery. Acute agitated delirium was diagnosed by the characteristic behavioral abnormality.

RESULTS

SPECT imaging 1 hour after surgery demonstrated hyperperfusion in the cerebral cortex beneath the CSH in 14 patients (51.9%). Of these 14 patients, five showed acute agitated delirium a few hours after surgery that persisted for 10 to 12 hours. A hematoma was detected in the right hemisphere in all five patients. Hyperperfusion was significantly more intense in patients with acute agitated delirium both 1 hour and 24 hours after surgery than in patients (n = 9) without acute agitated delirium. Moreover, mean arterial blood pressure during the first postoperative hour was significantly higher in patients with acute agitated delirium.

CONCLUSION

In elderly patients with CSH, intense and prolonged hyperperfusion after surgery induces temporary acute agitated delirium. This postoperative hyperperfusion syndrome is exacerbated by hypertension.

Severe pediatric head injury: the role of hyperemia revisited

Diffuse cerebral swelling is a frequent finding after severe pediatric head injury, and is two to five times as common in children as in adults. Hyperemia or cerebrovascular engorgement has long been considered by many as the cause of diffuse swelling and raised intracranial pressure (ICP). Consequently, reduction of the vascular compartment by institution of hyperventilation and avoidance of mannitol has been advocated for the intensive care management of severely head-injured children. Suzuki and colleagues (1990) studied cerebral blood flow (CBF) in 80 normal, unanesthetized children. It was shown that CBF in normal children may range from 40 mL/100 g per minute during the first 6 months of life to a peak of 108 mL/100 g per minute at age 3 to 4 years, and down to 71 mL/100 g per minute after age 9 years. Considering this large range, comparisons of CBF data in children are valid only when small, well-defined age ranges are selected. When the CBF values of children with severe head injuries (described in previous research) were compared with normal values in children, there did not seem to be a substantial increase of CBF. Hyperemia may therefore not be as common in severe pediatric head injury as previously thought. Until we acquire a better understanding of the pathophysiology of severe pediatric head injury, and what the optimal treatment in children would be, there is no reason to treat children differently from adults.

Transient hyperemia immediately after rapid decompression of chronic subdural hematoma

OBJECTIVE

Intracerebral hemorrhage occurring after removal of a chronic subdural hematoma (CSH) is a rare but usually devastating postoperative complication. In patients with CSH, we determined cerebral blood flow immediately after surgical decompression to clarify the pathogenic mechanism of this complication.

METHODS

In 22 patients with unilateral CSH, a catheter was inserted into the hematoma cavity through a single burr hole without leakage of the contents. Cerebral blood flow was measured using single-photon emission computed tomography 1 day before surgery, immediately after rapid decompression by opening the catheter, and 3 days after surgery.

RESULTS

Single-photon emission computed tomography imaging immediately after decompression demonstrated areas of hyperemia in nine patients (41%). In all nine patients, hyperemia was observed in the cortex beneath the CSH, and it disappeared on the 3rd postoperative day. The patients with hyperemia were significantly older than those without hyperemia. Other variables, including preoperative cerebral blood flow, intrahematoma pressure before decompression, and mean arterial blood pressure during decompression had no significant effect on the occurrence of hyperemia.

CONCLUSION

In elderly patients, rapid decompression of CSH frequently results in transient hyperemia in the cerebral cortex beneath the hematoma.

Pathogenesis of traumatic brain swelling: role of cerebral blood volume

The pathogenesis of traumatic brain swelling is unclear. Brain edema (increased water content) is considered an important cause of swelling, but there is also evidence that vasodilatation with increased cerebral blood volume (CBV) plays a role. We have evaluated early posttraumatic changes in CBV in 37 head-injured patients, using dynamic contrast-enhanced computerized tomography (CT) in combination with stable Xenon-enhanced CT for measurement of cerebral blood flow (CBF). This technique enables rapid determination of CBV without interfering with patient care. CBV values ranged from 2.0 to 10.1 ml/100 g. There was no relationship the time after injury at which the measurements were taken. CBV did not correlate with CBF in the early posttraumatic period. Patients with raised ICP (> 20 mm Hg) had significantly higher CBV that patients with normal ICP (5.4 +/- 2.1 vs 3.7 +/- 0.9 ml/100 g). Yet, the presence of signs of brain swelling on CT had no relation to the level of CBV. These data suggest that increased CBV may contribute to raised ICP, but that brain swelling is not caused by increased CBV alone, and is more likely accounted for by brain edema. We speculate that cerebral energy failure is the unifying cause of both intracellular edema and cerebral vasodilation leading to swelling of brain tissue.

Changes in blood-brain barrier permeability associated with insertion of brain cannulas and microdialysis probes

Blood-brain barrier (BBB) transcapillary transport was studied after insertion of cannulas and microdialysis probes into the brains of three groups of rats. Quantitative autoradiography was used to measure changes in BBB permeability around the insertion site. In the first group, BBB function was measured with 14C-sucrose at times from immediately, and up to 28 days, after insertion of a microdialysis probe. BBB function was disrupted biphasically: a 19-fold increase in the influx constant (K1) of sucrose occurred immediately after insertion with a second 17-fold increase at 2 days, followed by a slow decline to 5 times normal values at 28 days. In the second group, 14C-dextran (70 kDa) was used to measure BBB transcapillary transport; K1 was increased 90-fold after probe insertion. In the 3rd group, 14C-AIB (alpha-aminoisobutyric acid) was used to evaluate BBB transport after insertion of a 27 gauge cannula, which was used to infuse 1 microliter of saline over 5 min. The K1 of AIB was increased 25 times control values. We conclude that BBB transcapillary transport function is disturbed in response to insertion of brain cannulas and/or microdialysis probes, that BBB dysfunction is maximal at the cannula or probe tip, varies with time after insertion, may persist for at least 28 days after insertion, and occurs over a wide molecular range of solutes. These results suggest caution when using microdialysis as a method to study normal BBB function, and suggest that microdialysis may overestimate the rate of transfer into and out of the brain.

Regional cerebral blood volume after severe head injury in patients with regional cerebral ischemia

OBJECTIVE

Recent early cerebral blood flow (CBF) studies in cases of severe head injury have revealed ischemia in a substantial number of patients with a variety of computed tomographically demonstrated diagnoses. The underlying derangements causing this early ischemia are unknown, but cerebral blood volume (CBV) measurements might offer some insight into this pathological abnormality.

METHODS

For this purpose, stable xenon-enhanced computed tomography was used for assessment of CBF, and a dynamic computed tomographic imaging technique was used for determining CBV. Based on the occurrence of regional ischemia (CBF < 20 ml/100 g/min), seven patients with varying anatomic lesions revealed by computed tomography were identified for comparison between CBF and CBV in ischemic and nonischemic areas.

RESULTS

Both CBF (15+/-4.3 versus 34+/-11 g/min, P < 0.002) and CBV (2.5+/-1.0 versus 4.9+/-1.9 ml/100 g) exhibited significantly lower values in the ischemic zones than in the nonischemic zones (means+/-standard deviations). Among 26 patients with or without ischemia observed during their initial follow-up studies, which were conducted between Days 2 and 8, all patients showed CBF and CBV values within the low-normal range.

CONCLUSION

These data evidently support the suggestion that compromise of the microvasculature is the cause of early ischemia, rather than vasospasm of the larger conductance vessels.

Hypertonic/hyperoncotic saline reliably reduces ICP in severely head-injured patients with intracranial hypertension

Hypertonic saline (HS) has been shown to decrease intracranial pressure (ICP) and cerebral water content in experimental models of traumatic brain injury (TBI). The purpose of the present study was to test the efficacy of administration of HS (7.5%) combined with 6% hydroxyethyl starch (molecular weight 200.000/0.60-0.66; HHES) for the treatment of therapy-resistant intracranial hypertension in patients with severe TBI. Six patients with severe TBI (GCS < 8) who met the inclusion criteria (therapy resistant ICP > 25 mmHg, cerebral perfusion pressure (CPP) < 60 mmHg, plasma-Na+ < 150 mOsm and > 4 hours since the last HS/HHES treatment) were prospectively enrolled in the study and received between one and ten bolus infusions of maximal 250 ml HS/HHES at a rate of 20 ml/min. A total of 32 infusions were given. Administration of HS/HHES significantly lowered ICP by 44% and improved CPP by 38% to well above 70 mmHg at 30 min without affecting arterial blood pressure or blood gases. Plasma sodium normalized within 30 min. Experimental studies from our laboratory indicate that the ICP lowering effect is primarily due to dehydration of brain tissue and that cerebral blood volume remains largely unaffected by HS. In summary, HS/HHES reduces otherwise therapy-resistant intracranial hypertension and improves cerebral perfusion even after repeated administration without negatively affecting blood pressure or causing a rebound ICP increase.

A new method for quantitative regional cerebral blood volume measurements using computed tomography

BACKGROUND AND PURPOSE

Knowledge of cerebral blood volume (CBV) is invaluable in identifying the primary cause of brain swelling in patients with stroke or severe head injury, and it might also help in clinical decision making in patients thought to have hemodynamic transient ischemic attacks (TIAs). This investigation is concerned with the development and clinical application of a new method for quantitative regional CBV measurements.

METHODS

The technique is based on consecutive measurements of cerebral blood flow (CBF) by xenon/CT and tissue mean transit time (MTT) by dynamic CT after a rapid iodinated contrast bolus injection. CBV maps are produced by multiplication of the CBF and MTT maps in accordance with the Central Volume Principle: CBV = CBF x MTT. The method is rapid and easily implemented on CT scanners with the xenon/CBF capability. It yields CBV values expressed in milliliters of blood per 100 grams of tissue.

RESULTS

The method was validated under controlled physiological conditions causing changes that were determined both with our technique and from pressure-volume index (PVI) measurements. The two independent estimates of CBV changes were in agreement within 15%. CBV measurements using this method were carried out in normal volunteers to establish baseline values and to compare with values using the ratio-of-areas method for calculating both CBF and CBV from the dynamic study alone. Average CBV was 5.3 mL/100 g. The method was also applied in 71 patients with severe head injuries and in 1 patient with hemodynamic TIAs.

CONCLUSIONS

The primary conclusions from this study were (1) the proposed method for measuring CBV accurately determines changes in CBV; (2) the MTT x CBF determinations are in agreement with the ratio-of-areas method for CBV measurements in normal volunteers and are consistent with other methods reported in the literature; (3) MTTs are significantly prolonged early after severe head injury, which when combined with the finding of decreased CBF and increased arteriovenous difference of oxygen indicates increased cerebrovascular resistance due to narrowing of the microcirculation consistent with the presence of early ischemia; and (4) CBV in the patient with TIAs was increased in the hemisphere with the occluded internal carotid artery, indicating compensatory vasodilation and probable hemodynamic cause.

Brain incorporation of [1-11C]arachidonate in normocapnic and hypercapnic monkeys, measured with positron emission tomography

Positron emission tomography (PET) was used to determine brain incorporation coefficients k* of [1-11C]arachidonate in isoflurane-anesthetized rhesus monkeys, as well as cerebral blood flow (CBF) using [15O]water. Intravenously injected [1-11C]arachidonate disappeared from plasma with a half-life of 1.1 min, whereas brain radioactivity reached a steady-state by 10 min. Mean values of k* were the same whether calculated by a single-time point method at 20 min after injection began, or by least-squares fitting of an equation for total brain radioactivity to data at all time points. k* equalled 1.1-1.2 x 10(-4) ml x s(-1) x g(-1) in gray matter and was unaffected by a 2.6-fold increase in CBF caused by hypercapnia. These results indicate that brain incorporation of [1-11C]arachidonate can be quantified in the primate using PET, and that incorporation is flow-independent.

Focal cerebral hyperemia after focal head injury in humans: a benign phenomenon?

To assess the relationship between posttraumatic cerebral hyperemia and focal cerebral damage, the authors performed cerebral blood flow mapping studies by single-photon emission computerized tomography (SPECT) in 53 patients within 3 weeks of brain injury. Focal zones of hyperemia were present in 38% of patients. Hyperemia was correlated with clinical features and early computerized tomography (CT) and magnetic resonance (MR) imaging performed within 48 hours of the SPECT study and late CT and MR studies at 3 months. The hyperemia was observed primarily in structurally normal brain tissue (both gray and white matter), as revealed by CT and MR imaging, immediately adjacent to intraparenchymal or extracerebral focal lesions; it persisted for up to 10 days, but was never seen within the edematous pericontusional zones. The percentage of patients in the hyperemic group having brief (< 30 minutes) or no loss of consciousness was significantly higher than in the nonhyperemic group (twice as high, p < 0.05). Other clinical parameters were not significantly more common in the hyperemic group. The mortality of patients with focal hyperemia was lower than that of individuals without it, and the outcome of survivors with hyperemia was slightly better than patients without hyperemia. These results differ from the literature, which suggests that global post-traumatic hyperemia is primarily an acute, malignant phenomenon associated with increased intracranial pressure, profound unconsciousness, and poor outcome. The current results agree with more recent studies which show that posttraumatic hyperemia may occur across a wide spectrum of head injury severity and may be associated with favorable outcome.

Cerebral blood flow and oxygen metabolism in hemiparetic patients with chronic subdural hematoma. Quantitative evaluation using positron emission tomography

BACKGROUND

It remains unclear why chronic subdural hematoma (CSH) can cause hemiparesis, although the contribution of impaired cerebral blood flow and metabolism has been suggested.

METHODS

We studied six hemiparetic patients (five men, one woman; mean age 60.5 +/- 7.5 years) with unilateral CSH using positron emission tomography. The 15O2 steady state technique was used to measure regional cerebral blood flow (rCBF), regional oxygen extraction fraction (rOEF), and regional cerebral metabolic rate of oxygen (rCMRO2), followed by the 1-minute inhalation of C15O to measure regional cerebral blood volume (rCBV).

RESULTS

On the hematoma side, rCBF and rCMRO2 were significantly reduced in the caudate nucleus and the cingulate gyrus. We observed a tendency toward reduced levels of rCBF and rCMRO2 in the lentiform nucleus. rCBV was not elevated. rOEF was significantly elevated in the lentiform nucleus, the cingulate gyrus, the frontal gray matters under the hematoma and the semioval center. On the nonhematoma side, rCBF and rCMRO2 were normal except for the significant reduction in the cingulate gyrus. rCBV was elevated in the lentiform nucleus, the middle temporal gyrus and the inferior frontal gyrus. rOEF was elevated significantly in the cingulate gyrus, the precentral gyrus and the semioval center.

CONCLUSIONS

Our hemiparetic patients with CSH were observed to have a circulatory disturbance of blood; it was manifested by an elevation of rOEF, specifically in the hemisphere adjacent to the hematoma. This circulatory disturbance was highly pronounced and resulted in a consistent reduction in rCBF and rCMRO2 in the anterior central cerebral area such as the caudate nucleus, the lentiform nucleus and the cingulate gyrus.

Different cerebral hemodynamic responses following fluid percussion brain injury in the newborn and juvenile pig

The present study was designed to characterize the influence of early developmental changes on the relationship among systemic arterial pressure, cerebral hemodynamics, and cerebral oxygenation during the first 3 h following percussion brain injury. Anesthetized newborn (1-5 days old) and juvenile (3-4 weeks old) pigs equipped with a closed cranial window were connected to a percussion device consisting of a saline-filled cylindrical reservoir with a metal pendulum. Brain injury of moderate severity (1.9-2.3 atm) was produced by allowing the pendulum to strike a piston on the cylinder. Mean arterial blood pressure increased after brain injury in juveniles (68 +/- 4 to 93 +/- 2 mm Hg within 3 min, n = 6), whereas it decreased after injury in newborns (70 +/- 3 to 51 +/- 3 mm Hg within 3 min, n = 6). Fluid percussion brain injury decreased pial artery diameter more in newborns (132 +/- 5 to 110 +/- 5 microns within 10 min, n = 5) than in juveniles (141 +/- 3 to 133 +/- 3 microns within 10 min, n = 5). Pial arterioles constricted to a greater extent than small pial arteries following brain injury in both age groups. Within 30 sec, brain injury produced a transient increase in cerebral hemoglobin O2 saturation (27 +/- 4%, n = 5) that was reversed to a profound decrease in cerebral hemoglobin O2 saturation (45 +/- 2%, n = 5) in the newborn as measured by near infrared spectroscopy. In contrast, brain injury produced modest increases in hemoglobin O2 saturation (10 +/- 1%, n = 5), followed by mild desaturation (4 +/- 1%, n = 5) in juveniles. Additionally, regional cerebral blood flow was reduced within 10 min of injury in both newborn and juvenile pigs and remained depressed for 180 min in newborns. In contrast, cerebral blood flow returned to control values within 180 min in juveniles. These data show that the effects of comparable brain injury level were very different in newborn and juvenile pigs. Further, these data suggest that reductions in cerebral blood flow following brain injury are more dependent on changes in reactivity of arterioles. Finally, these data suggest that the decrease in cerebral oxygenation, an index of metabolism, coupled with reduced cerebral blood flow, could result in profound hypoperfusion after brain injury.

Non-invasive monitoring of brain oxygen sufficiency on cardiopulmonary bypass patients by near-infra-red laser spectrophotometry

A new portable high-performance apparatus for near-infra-red (NIR) laser spectrophotometry was developed to monitor the oxygenation state in the human brain. Three different wavelengths of 780, 805 and 830 nm of the NIR light illuminated the head using a fibre-optic bundle, and the transmitted or reflected light was detected by a photodiode placed on the forehead. The oxygenated Hb (oxy Hb), deoxygenated Hb (deoxy Hb) content and the Hb (blood) volume changes in the brain were continuously monitored in cardiopulmonary bypass (CPB) patients in the reflectance mode. In hypothermic CPB with selective brain perfusion, the brain bypass flow rates of 0.5 L min-1 at 24-25 degrees C and 0.3 L min-1 at 21-22 degrees C were confirmed as the safe lower limits by our NIR monitoring. During deep hypothermic circulatory arrest, the brain oxy Hb and blood volume decreased significantly. The result indicates that brain Hb oxygenation decreases significantly during circulatory arrest. In the adult patients group, during moderate hypothermic CPB, the brain blood oxygenation level was maintained roughly constant at mean arterial perfusion pressure of over 60 mm Hg, whereas below 50-55 mmHg a progressive decline in the brain Hb oxygenation was observed. These findings led us to conclude that non-invasive monitoring of brain oxygenation using NIR light can provide valuable data at the bed-side regarding tissue metabolism, and it can allow for the proper management of critical patients.

Selected cases of poor outcome following a minor brain trauma: comparing neuropsychological and positron emission tomography assessment

Neuropsychological residua are common particularly in the early stages following a minor traumatic brain injury (TBI), however, a minority of individuals complain of persistent deficits following months or years post-accident. Nine such cases are presented with little or no evidence of brain damage demonstrated according to non-functional neuroimaging (for example CT, MRI), yet their neuropsychological examinations were positive. Since the introduction of positron emission tomography (PET), which captures a functional approach, the question arose as to what extent the two techniques (i.e. PET and neuropsychological examination) are interrelated. All nine minor TBI cases revealed a corroboration between the positive neuropsychological findings confirmed on the PET. The PET procedure documented neuropathology which frequently was pronounced in the frontal and anteriotemporo-frontal regions. Moreover, no significant differences were evident between those five cases with reported loss of consciousness vs. those four cases without.

Diffuse brain swelling after head injury: more often malignant in adults than children?

A series of 118 patients with diffuse traumatic brain swelling was studied retrospectively in order to compare the clinical findings in children with those in adults, and to determine the occurrence of neurological deterioration and outcome. The computerized tomography (CT) picture of absent third ventricle and basal cisterns was used to identify the cases. Although this condition has been associated with children, we found the same number of children and adults (59 cases each). Secondary deterioration (decline in consciousness, the development of new focal neurological signs, or an increase in intracranial pressure) occurred in 40% of cases and was more common in adults than children. Features that were significantly associated with deterioration were the presence of prolonged coma (> 1 hour) after the injury, CT signs of diffuse axonal injury or subarachnoid hemorrhage, or a recorded episode of hypotension. A moderate or good recovery at 6 months was achieved by 70 patients (59%), but 45 patients had a poor outcome (severe disability in nine, vegetative state in three, and death in 33) and this was often a consequence of secondary deterioration. In three patients, the outcome was not known. The combination of a severe initial injury, secondary insult, and diffuse swelling is associated with a poor outlook, particularly in adults. The CT appearance of diffuse swelling may develop more readily in children because of the lack of cerebrospinal fluid available for displacement. In children, diffuse swelling may have a relatively benign course unless there is a severe primary injury or a secondary hypotensive insult.

Documented reversal of global ischemia immediately after removal of an acute subdural hematoma. Report of two cases

The authors report two cases of severe head injury with acute subdural hematoma, in which cerebral blood flow (CBF) and cerebral blood volume (CBV) measurements were obtained prior to evacuation of the subdural hematoma and again immediately after removal. The first patient, a 21-year-old man with a motor response localizing to pain, had a global CBF of 18.2 ml/100 gm/min and a decreased global CBV of 3.7 ml/100 gm at 2.3 hours after injury. Immediately after removal of the subdural hematoma (8.1 hours after injury), CBF and CBV measurements revealed increases to 35.5 ml/100 gm/min and 5.8 ml/100 gm, respectively. The second patient, a 49-year-old woman with a normal flexor motor response to pain, had preoperative global values of 15.8 ml/100 gm/min for CBF and 2.0 ml/100 gm for CBV at 3 hours after injury. Postoperatively (9.3 hours after injury), the CBF and CBV values increased to 41.6 ml/100 gm/min and 4.0 ml/100 gm, respectively. The first patient, with only borderline ischemia and removal of the subdural hematoma within 3 hours, made a good recovery, while the second patient, with prolonged lower levels of CBF, remained in a persistent vegetative state. The low values of preoperative CBV argue for compression of the microcirculation as the cause of ischemia.

Traumatic brain edema: an overview

This article provides a brief summary of concepts describing the formation and resolution of traumatic brain edema. Recent laboratory and clinical data are reviewed targeted toward resolving the contribution of edema to the swelling process. These data, indicate that blood volume is reduced in areas of ischemia following traumatic injury and edema volume is increased. Thus, edema is the major contributor to the swelling process in diffuse injury. As clinical MRI studies have not revealed barrier compromise in the presence of swelling, it is considered that other forms of edema, primarily ischemic and neurotoxic, make a substantial contribution to the edema volume.

The cause of acute brain swelling after the closed head injury in rats

The major component of acute brain swelling was determined using a new closed head injury (CHI) model in rats. Twenty seven Sprague-Dawley rats were separated into four groups (Sham, CHI, CHI combined with hypotension and CHI combined with hypoxia and hypotension). Hypoxia (pO2 of 40 mmHg) and hypotension (mean arterial blood pressure of 30 to 40 mmHg) were induced immediately after head injury and were maintained for 30 minutes. These experiments were terminated at two hours after CHI by transcalvarial freezing with liquid nitrogen. Blood pressure, intracranial pressure (ICP) and physiological parameters were monitored. Regional cerebral blood volume and water content were measured quantitatively. Rats with CHI, and with CHI and hypotension, had mild increase in ICP. Otherwise, rats with CHI, hypoxia and hypotension showed a significant increase in ICP (36.2 +/- 5.6 mmHg). Water content showed an increase of 1.6% in the estimated total brain and 2.4% in the cerebral cortex in those rats. Cerebral blood volume decreased by 61.4% in the total brain and 57.3% in the cortex. There was a reduction in the cerebral hematocrit of 2.4% in the total brain and 4.7% in the cortex. The main component of brain swelling in this head injury model was brain edema. Cerebral blood volume and hematocrit were reduced in the remarkable edematous brain.

Cerebral blood flow decreased by adrenergic stimulation of cerebral vessels in anesthetized newborn pigs with traumatic brain injury

Changes in cerebral blood flow (CBF), pial arteriolar diameter, and arterial blood pressure, gases, and pH were examined before and for 3 hours after fluid-percussion brain injury in alpha-chloralose-anesthetized piglets. The brain injury was induced by a percussion of 2.28 +/- 0.06 atm applied for 23.7 +/- 0.5 msec to the right parietal cortex. Regional CBF was measured with radiolabeled microspheres, and changes in pial arteriolar diameter were monitored in the left parietal cortex using closed cranial windows. Immediately following brain injury, mean blood pressure transiently (for approximately 10 minutes) either increased or decreased and then exhibited a prolonged decrease in all of the animals. The brains showed changes consistent with traumatic brain injury such as subarachnoid hemorrhage, contusions, or reactive axonal swelling; none showed histological evidence of a global alternative pathogenetic mechanism such as hypoxic ischemic damage. While CBF of uninjured control animals did not change over a 3-hour observation period, after brain injury blood flow decreased 30% +/- 1% below the baseline level within 10 minutes and remained there for 2 to 3 hours posttrauma. After adrenergic blockade, CBF did not decrease at any time during the 3-hour period in either the uninjured control or the injured animals. Concomitant with the decreased blood flow after brain injury, pial arteriolar diameter decreased 14% below the preinjury level. However, in piglets treated with adrenoceptor antagonists, uninjured control and brain-injured animals did not show a decrease in pial arteriolar diameter. The present results support the hypothesis that increased sympathetic outflow to the cephalic vasculature following the fluid-percussion brain injury causes cerebral vasoconstriction decreasing pial arteriolar diameter and regional CBF.

Changes in cerebral blood flow and metabolism related to the presence of subdural hematoma

Acute subdural hematoma (SDH) remains an important factor in head injury. The early effects of SDH on cerebral blood flow (CBF) and cerebral metabolic rate of oxygen consumption (CMRO2) in humans have not been clearly demonstrated. Patients admitted to the Medical College of Virginia with severe closed-head injury between 1982 and 1990 were studied with Xenon-133 regional CBF measurement. Data were reviewed retrospectively with regard to the presence of SDH (n = 54). A comparison group consisted of patients with head injuries without mass lesions or midline shift on admission computed tomographic scans (n = 76). CBF measurements made in patients less than 16 years of age, with concurrent administrations of mannitol or vasopressors, or with cerebral perfusion pressure under 50 mm Hg were excluded. CBF measurements were made on multiple occasions during the first 6 days after injury, and in many instances, simultaneous determinations of cerebral arteriovenous oxygen difference (AVDO2) were made through sampling of jugular bulb and arterial oxygen content. Not all patients underwent CBF measurements on each day. Differences in mean CBF, CMRO2, and AVDO2 were evaluated on each day after injury with the application of Student's t-test for independent groups. Significant reductions in CBF were demonstrated in patients with SDH on Days 1 (P < 0.0005) and 2 (P < 0.01). CMRO2 differed notably on Days 1 (P < 0.005) and 2 (P < 0.05) in patients with SDH, but when corrected for the lower Glasgow Coma Score in patients with SDH, the P values were only 0.07 and 0.12, respectively (analysis of covariance).(ABSTRACT TRUNCATED AT 250 WORDS)

Uncoupling between CBF and oxygen metabolism in a patient with chronic subdural haematoma: case report

The regional cerebral blood flow (rCBF) and oxygen metabolism of a patient with a chronic subdural haematoma were examined quantitatively, using positron emission tomography (PET). Before operation, the rCBF was decreased slightly throughout the brain, whereas the regional oxygen extraction fraction (rOEF) was increased throughout the brain, with values ranging from 0.36 to 0.60. One month after operation, the rCBF had recovered remarkably in almost all regions and rOEF had decreased to within the normal range.

Quantitative assessment of cerebral blood volume by single-photon emission computed tomography

We implemented a technique for measuring regional cerebral blood volume using single-photon emission computed tomography and in vivo technetium-99m-labeled red blood cells and then evaluated it in nine normal human volunteers (controls) and seven patients with bilateral occlusion or severe stenosis of the internal carotid artery. We also measured regional cerebral blood flow using single-photon emission computed tomography and intravenous xenon-133 in the same subjects. We studied regional cerebral blood flow, regional cerebral blood volume, and their ratio before and after the intravenous injection of 1 g acetazolamide. Mean +/- SD baseline regional cerebral blood volume was higher in the patients than in the controls (4.1 +/- 0.6 versus 3.2 +/- 0.3 ml/100 g, p less than 0.01), and mean +/- SD baseline regional cerebral blood flow was lower in the patients than in the controls (40.5 +/- 11 versus 55.6 +/- 11 ml/100 g/min, p less than 0.05). Acetazolamide induced similar mean +/- SD increases in regional cerebral blood volume in both the controls and the patients (0.3 +/- 0.1 and 0.3 +/- 0.2 ml/100 g), while the mean +/- SD regional cerebral blood flow reactivity was significantly less in the patients than in the controls (12.6 +/- 7.6 versus 24.5 +/- 9.6 ml/100 g/min, p less than 0.05). Our study shows that single-photon emission computed tomography can provide quantitative estimates of both regional cerebral blood volume and regional cerebral blood flow in humans.

Studies of central nervous system disorders with single photon emission computed tomography and positron emission tomography: evolution over the past 2 decades

Single photon emission computed tomography (SPECT) was introduced in the 1960s to detect breakdowns in the blood-brain barrier and was replaced by x-ray computed tomography in the mid-1970s. The development of the deoxyglucose (DG) technique to measure regional cerebral glucose metabolism by employing either autoradiography, using 14CDG, or positron emission tomography (PET), using 18FDG, added a major dimension to the investigation of brain function. In the late 1970s and early 1980s, the FDG-PET technique was widely used to examine a variety of neuropsychiatric disorders. It soon became apparent that functional imaging was more sensitive than anatomic imaging in detecting abnormalities of the brain related to aging, dementia, tumors, seizures, cerebral vascular accidents, and psychiatric problems. Because of its complexity and the cost involved, PET was used in a limited number of centers in the United States. However, the success of PET resulted in the resurgence of interest in SPECT as an alternative technology after almost a decade. This became possible because of the synthesis of iodine 123- and technetium 99m-labeled radiopharmaceuticals to determine regional cerebral blood flow. Since blood flow and metabolism are coupled in most pathological states, patterns of abnormality noted on SPECT were similar to those seen on PET in many disorders. Since the introduction of high resolution SPECT imaging instruments, the role of SPECT has been further enhanced. The successful synthesis of both positron and single emitting radioligands to image dopamine and other receptors has started a new era in neurosciences and will have a far-reaching impact on the day-to-day practice of neuropsychiatry.

Fatal head injury in children

A comprehensive neuropathological study was undertaken on 87 children aged between 2 and 15 years with fatal head injuries to identify those features which occurred at the time of head injury (fractured skull, contusions, intracranial haematoma and diffuse axonal injury) and those which were subsequently produced by complicating processes (hypoxic brain damage, raised intracranial pressure, infection and brain swelling). The types of brain brain damage identified were remarkably similar to those seen in adults. The only difference was the prevalence of diffuse brain swelling in children.

Determination of rat cerebral cortical blood volume changes by capillary mean transit time analysis during hypoxia, hypercapnia and hyperventilation

Changes in cerebral blood volume due to augmented or diminished numbers of blood-perfused capillaries can be studied in small animals by optical methods. Capillary mean transit time was determined by detection of the passage of a hemodilution bolus through a region of the parietal cerebral cortical surface, using a reflectance spectrophotometer through a small craniotomy in chloral hydrate-anesthetized rats. Local cerebral blood flow was determined in the same region by the butanol indicator-fractionation method. Blood volume was calculated from the product of blood flow and transit time. Normoxic, normocapnic values for these variables were blood flow = 144 ml/100 g/min; mean transit time = 1.41 s; and blood volume = 3.4 ml/100 g. Mean transit time reached a minimum (1.1 s) with moderate hypoxia or hypercapnia. Combined hypoxia and hypercapnia did not result in any further decrease in mean transit time although blood flow was much higher than either hypoxia or hypercapnia alone. The maximum blood volume recorded during hypercapnic hypoxia (12.1 ml/100 g) was 3.6 times greater than that at normoxic normocapnia, which suggests that under control conditions in the anesthetized rat considerably less than 100% of the cerebral capillaries were actively perfusing the tissue. These studies demonstrate that optical methods can be used to quantitatively measure blood volume. The data suggest that capillary recruitment is a physiologically significant phenomenon in rat cerebral cortex.

Head trauma in the child

Head injury, either alone or in combination with multiple injuries, is common in children. Its pattern is different in children compared to adults, with diffuse cerebral swelling rather than localized hematoma being most common. The pathophysiology of pediatric head trauma is not yet clearly elucidated, but may be closely related to changes in the regulation of cerebral blood flow. The initial management and subsequent care of the child with severe brain injury are discussed from a multisystem viewpoint. The prognosis for children with severe head injury seems brighter than for adults, but there are not yet enough data to allow prediction of outcome in any individual case. Efforts to prevent, rather than treat, head injury in childhood are more likely to be beneficial.

Effect of stimulation of the medullary reticular formation on cerebral vasomotor tonus and intracranial pressure

The authors report the results of a study to evaluate the effect of stimulation of the medullary reticular formation on cerebral vasomotor tonus and intracranial pressure (ICP) after the hypothalamic dorsomedial nucleus and midbrain reticular formation were destroyed. Systemic arterial pressure (BP), ICP, and local cerebral blood volume (CBV) were continuously recorded in 32 cats. To assess the changes in the cerebral vasomotor tonus, the vasomotor index defined by the increase in ICP per unit change in BP was calculated. In 29 of the 32 animals, BP, ICP, and CBV increased simultaneously immediately after stimulation. The increase in ICP was not secondary to the increase in BP, because the vasomotor index during stimulation was significantly higher than the vasomotor index after administration of angiotensin II. The vasomotor index was high during stimulation of the area around the nucleus reticularis parvocellularis. In animals with the spinal cord transected at the C-2 vertebral level, ICP increased without a change in BP. These findings indicate that the areas stimulated in the medullary reticular formation play an important role in decreasing cerebral vasomotor tonus. This effect was not influenced by bilateral superior cervical ganglionectomy, indicating that there is an intrinsic neural pathway that regulates cerebral vasomotor tonus directly. In three animals, marked biphasic or progressive increases in ICP up to 100 mm Hg were evoked by stimulation. The reduction of cerebral vasomotor tonus and concomitant vasopressor response induced by stimulation of the medullary reticular formation may be one of the causes of acute brain swelling.