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

[Acute traumatic subdural haematomas: study of 110 cases]

We report a series of 110 patients with acute traumatic subdural hematoma (ASDH) admitted at HBDF emergency within 1994 (January 1st to December 1st). All patients were treated according to the same protocol. There was a predominance of males (79%), with ages ranging from 14 to 70, being car accidents (20%) and car-pedestrian accidents (34%) the most frequent causes. The majority of patients (85.7%) was admitted in very serious condition, with a score of 8 points on the Glasgow Coma Scale (GCS) or lesser, which directly influenced the mortality rates. CT scan was the diagnostic procedure of choice, and it showed contusion and brain swelling to be the most frequent associated intracranial lesions. Surgery was carried out in 45.1% of cases and, in most instances, through an ample fronto-temporo-parietal craniotomy, with hematoma drainage and dural reconstitution. In 54.9% of cases, clinical conditions did not allow surgery and in this group, 69.6%.

Glutamate release and cerebral blood flow after severe human head injury

Elevations of extracellular glutamate have been found in patients with prolonged brain ischemia and focal cerebral contusions, following severe head injury. About 30% of severely head injured patients develop cerebral ischemia, defined as CBF < 18 ml/100g/min. Patients with both global and regional cerebral ischemia have the worst outcome. However, the relationship between CBF and EAA release is not well understood in head injured humans, and may differ from the findings in normal animals. To study the relationship between EAA release and CBF after severe head injury, we performed cerebral blood flow measurements using stable xenon enhanced computed tomography and correlated these with glutamate release in the extracellular fluid, measured by continuous microdialysis, in 25 severely head injured patients. Sustained cerebral blood flow reductions below the threshold for ischemic neuronal damage was closely related to massive excitatory amino acid release, as in previous animal studies. In patients without secondary ischemia, or focal contusions, delayed post-traumatic glutamate release appeared to be only transient or did not occur at all.

Thresholds for cerebral ischemia after severe head injury: relationship with late CT findings and outcome

Cerebral ischemic insults in at least 30% of severely head injured patients at a very early stage following trauma and are associated with early death. To date, the threshold for ischemia of 18 mL/100g/min used in human head injury studies has been adopted from animal studies (by temporary occlusion of the middle cerebral artery). Since the traumatized brain becomes more susceptible to irreversible damage if accompanied by ischemia one may question whether the threshold for ischemic vulnerability is higher than 18 mL/100 g/min. Cerebral ischemia can cause atrophy. Therefore, the authors obtained computerized tomography (CT) scans in 33 comatose head-injured patients (Glasgow Coma Score of 8 or less) at least 3 months following injury and compared ventricle sizes (as a reflection of atrophy) with cerebral blood flow (CBF) obtained within 4 h (average 2.3 +/- 0.8 h) after injury. Ventricular measurements were performed in three fashions: the third ventricular size (cm), the bicaudate cerebral ventricular index (BCVI), and the hemispheric ventricular index (HCVI). No significant correlation was found between early CBF and any of the ventricule sizes. Applying a multiple correlation analysis with four independent parameters [CBF, CBF/time postinjury, CBF/(time postinjury)2, age], only age emerged as a significant indicator for predicting ventricle size (p < 0.001). We also compared CBF data, obtained within 4 h after trauma, from survivors at 3 months after injury (mean CBF of 32 mL/100 g/min) with CBF data from non-survivors (CBF 20 mL/100 g/min). The difference in CBF between survivors and nonsurvivors was significant at p < 0.001 (Wilcoxon rank-sum test). The proportion of patients with CBF less than or equal to 20 mL/100 g/min was 56% in the nonsurvivors and only 5% in survivors. The difference in the proportions was significant at p < 0.001 (chi-square test). We conclude that a measure of atrophy does not correlate with ultra-early CBF. However, based on the clear distinction between survivors and nonsurvivors, we suggest the threshold for ischemia after head injury be redefined as a CBF of 20 mL/100 g/min.

The rationale for glutamate antagonists in the treatment of traumatic brain injury

The recent development of potent antagonists for the most widespread neurotransmitter in the mammalian brain has opened up possibilities for many forms of therapy. The excitotoxic hypothesis implicates excessive release of excitatory amino acids (EAAs) as an important cause of brain damage, especially in acute ischemia, and chronic neurodegeneration. Focal ischemic damage and diffuse axonal injury are the major causes of brain damage after traumatic human brain injury. Evidence from animal models has shown that excitatory amino acid-induced events maybe responsible for a proportion of the posttraumatic sequelae and that these effects can be blocked by EAA antagonists. This evidence is reviewed, and the implications for human pathophysiology and treatment are discussed.

The role of excitatory amino acids in severe brain trauma: opportunities for therapy: a review

Severe brain trauma remains poorly understood, because of its pathophysiological complexity, and this has so far thwarted our attempts to improve outcome by means of drug therapy, although better understanding of the role of ischemic events has led to improved mortality rates, in some centers. With regard to excitatory amino acid antagonists, new mechanistic insights from both animal models, and human monitoring has enabled better trial design, which may allow the tremendous laboratory neuroprotective potency of this group of compounds to be translated to clinical benefit.

A new application for near-infrared spectroscopy: detection of delayed intracranial hematomas after head injury

Clinical studies have documented the importance of secondary brain insults in determining neurologic outcome after head injury. Delayed intracranial hematomas are one of the most easily remediable causes of secondary injury if identified early, but can cause significant disability or death if not promptly recognized and treated. Early identification and treatment of these lesions that appear or enlarge after the initial CT scan may improve neurological outcome. Serial examinations using near-infrared spectroscopy (NIRS) to detect the development of delayed hematomas were obtained in 167 patients. The difference in absorbance of light (deltaOD) at 760 nm between the normal and the hematoma side was measured serially during the first 3 days after injury. Twenty-seven (16%) of the patients developed some type of late hematoma: an intracerebral hematoma in 8 patients, an extracerebral hematoma in 6 patients, and a postoperative hematoma in 13 patients. Eighteen of the delayed hematomas caused significant mass effect and required surgical evacuation. The hematomas appeared between 2 and 72 h after admission. In 24 of the 27 patients, a significant increase (>0.3) in the deltaOD occurred prior to an increase in intracranial pressure or a change in the neurological examination, or a change on CT scan. Early diagnosis using MRS may allow early treatment and reduce secondary injury caused by delayed hematomas.

Focal ischemia due to traumatic contusions documented by stable xenon-CT and ultrastructural studies

A traumatic cerebral contusion causes a zone of perifocal neuronal necrosis, the cause of which is not known; the surgical management of these lesions remains controversial. To determine the pathophysiological mechanisms responsible for brain damage after contusions, the authors performed cerebral blood flow (CBF) mapping studies and related these to change in local cerebral blood volume (CBV) and ultrastructure. In 11 severely head injured patients with contusion, CBF and CBV were measured in pericontusional areas using stable xenon-computerized tomography (CT). These studies demonstrated a profound reduction in perilesional CBF (mean 17.5 +/- 4 ml/100 g/min), which was always accompanied by a zone of edema defined by CT density measurements. Mean CBV in these regions was 2.3 +/- 0.4 ml/100 g, a reduction to approximately one-half the value of 4.8 ml/100 g found in the nonedematous regions, and to approximately 35% of the value of 6.0 ml/100 g found in normal volunteers. Ultrastructural analysis of the pericontusional tissue, taken at surgery in four patients with high intracranial pressure showed glial swelling with narrowing of the microvascular lumina due to massive podocytic process swelling. Additionally, some suggestion of vascular occlusion due to erythrocyte and leukocyte stasis was seen. These data support the conclusion that microvascular compromise by compression and/or occlusion is a major event associated with profound perilesional hypoperfusion, which is a uniform finding within edematous pericontusional tissue.

Acute subdural hematoma: is the blood itself toxic?

Recently developed rodent models of acute subdural hematoma have shown an associated large area of infarction underlying the clot. Excitotoxic processes have been postulated to play an important role in the extensive cell death seen with these models. However, whether increased pressure, vasoactive effects, or toxicity of the blood itself is responsible for initiating or sustaining these processes remains unclear. To study the effect of blood itself, an opaque layer of autologous clot was placed on the widely exposed parietal cortex of 15 Long-Evans rats and left in place for 72 h. In control animals the cortical surface was exposed but no blood was placed and contact with blood products was carefully limited. These animals were compared to a group in whom blood was injected into the closed subdural space. Histologic analysis showed that the majority of the cortex in both control and experimental animals in the open cranial model group appeared normal. Scattered small, discrete hemorrhagic lesions on the cortical surface of both control and experimental animals were seen, which had the appearance of focal mechanical trauma or vessel avulsion. There was no significant difference in average volume of lesions between experimental and control animals (9.1 versus 9.7 mm3, p = 0.85). No areas of infarction or selective neuronal loss were seen. In comparison, animals in which blood was injected into the subdural space had significantly larger lesions underlying clot, averaging 133.6 mm3 in volume (p < 0.0003). Blood in prolonged contact with the cortical surface in the absence of increased pressure, ischemia, or other insult is insufficient to cause underlying infarction like that seen when a similar volume of blood is injected into the closed subdural space.