Acute microvascular platelet aggregation after subarachnoid hemorrhage

Long-term assessment of motor and cognitive behaviours in the intraluminal perforation model of subarachnoid hemorrhage in rats

The endovascular perforation model of subarachnoid hemorrhage (SAH) is a commonly used model in rats as it is performed without a craniotomy and accurately mimics the physiological effects of SAH in humans. The long-term behavioural profile of the model, however, has not been characterized. Given that humans often have cognitive deficits following SAH, we set out to characterize the behavioural profile as well as the spontaneous temperature changes of rats following intraluminal perforation. Rats were pre-trained on three motor tasks (tapered beam, limb-use asymmetry and the horizontal ladder tasks) prior to receiving a SAH. The animals were then assessed on post-surgical days 3, 7, 14 and 21 on these tasks. At the completion of motor testing, the rats were assessed on a moving platform version of the Morris water task. Despite significant mortality (33%), SAH did not result in lasting motor deficits on any of the tasks examined. However, the SAH group did show a minor cognitive impairment in the Morris water task. In addition, SAH produced a slight, but significant elevation in body temperature (vs. sham operated rats) despite an acute decrease in general home cage activity. The majority of the animals did not have any observable infarcts and the SAH did not significantly affect cortical thickness. In summary, the endovascular perforation model of SAH results in no lasting motor deficits and only minor cognitive impairment in survivors, which alone would be difficult to evaluate in neuroprotection or rehabilitation studies.

ACUTE RELATIVE ADRENAL INSUFFICIENCY AFTER ANEURYSMAL SUBARACHNOID HEMORRHAGE

OBJECTIVE

The hypothalamic-pituitary-adrenal axis is an important part of the body's natural response to acute illness. Adrenal insufficiency has the potential to lead to hemodynamic instability and electrolyte imbalances, limit the body's ability to respond to stress, and worsen overall clinical outcome. In this case series, we describe 16 patients evaluated for acute adrenal insufficiency after aneurysmal subarachnoid hemorrhage.

CLINICAL PRESENTATION

Over a 2-year period, the medical records of 16 patients admitted to the adult neurosurgery service for aneurysmal subarachnoid hemorrhage who were nonresponsive to vasopressor therapy and received cosyntropin for the evaluation of adrenal insufficiency within 14 days of their event were reviewed.

INTERVENTION

The median baseline cortisol in this population was 22.5 μg/dL, with a poststimulation cortisol level of 31 μg/dL. Of the population surveyed, a total of 11 patients met the preestablished criteria for adrenal insufficiency, 3 with baseline cortisol levels of less than 15 μg/dL and 11 with poststimulation concentration changes of less than 9 μg/dL. Baseline serum cortisol concentrations were significantly correlated with hospital stay (P = 0.045), intensive care unit stay (P = 0.005), and ventilator days (P = 0.006).

CONCLUSION

To date, this is the only investigation evaluating the incidence of acute relative adrenal insufficiency in this population. In our cohort, 69% of the patients met the preestablished criteria for relative adrenal insufficiency. The impact of low-dose corticosteroid therapy in this population also needs review, as it could have significant implications for the management of cerebral vasospasm.

Cerebral infarction associated with acute subarachnoid hemorrhage

BACKGROUND

Cerebral infarction is a common complication of aneurysmal subarachnoid hemorrhage (SAH), but usually occurs several days after onset as a complication of vasospasm or aneurysm repair. The frequency, causes, and clinical impact of acute infarction associated with the primary hemorrhage are poorly understood.

METHODS

We evaluated the presence of cerebral infarction on admission CT in 487 patients admitted within 3 days of SAH onset to our center between July 1996 and September 2002. Infarctions due to angiography or treatment complications were rigorously excluded. Outcome at 3 months was assessed with the modified Rankin Scale.

RESULTS

A total of 17 patients (3%) had acute infarction on admission CT; eight had solitary and nine had multiple infarcts. Solitary infarcts usually appeared in the vascular territory distal to the ruptured aneurysm, whereas multiple infarcts tended to be territorial and symmetric. Global cerebral edema (P < 0.001), coma on presentation (P = 0.001), intraventricular hemorrhage (P = 0.002), elevated APACHE-II physiological subscores (P = 0.026) and loss of consciousness at onset (P = 0.029) were associated with early cerebral infarction. Mortality (P = 0.003) and death or moderate-to-severe disability (mRS 4-6, P = 0.01) occurred more frequently in the early cerebral infarction group.

CONCLUSIONS

Early cerebral infarction on CT is a rare but devastating complication of acute SAH. The observed associations with coma, global cerebral edema, intraventricular hemorrhage, and loss of consciousness at onset suggest that intracranial circulatory arrest may play a role in the pathogenesis of this disorder.

Focal laminar cortical infarcts following aneurysmal subarachnoid haemorrhage

INTRODUCTION

The aim of this prospective study was to analyse small band-like cortical infarcts after subarachnoid haemorrhage (SAH) using magnetic resonance imaging (MRI) with reference to additional digital subtraction angiography (DSA).

METHODS

In a 5-year period between January 2002 and January 2007 10 out of 188 patients with aneurysmal SAH were evaluated (one patient Hunt and Hess grade I, one patient grade II, four patients grade III, two patients grade IV, and two patients grade V). The imaging protocol included serially performed MRI with diffusion- and perfusion-weighted images (DWI/PWI) at three time points after aneurysm treatment, and cerebral vasospasm (CVS) was analysed on follow-up DSA on day 7+/-3 after SAH.

RESULTS

The lesions were located in the frontal lobe (n=10), in the insular cortex (n=3) and in the parietal lobe (n=1). The band-like infarcts occurred after a mean time interval of 5.8 days (range 3-10 days) and showed unexceptional adjacent thick sulcal clots. Seven out of ten patients with cortical infarcts had no or mild CVS, and in the remaining three patients DSA disclosed moderate (n=2) or severe (n=1) CVS.

CONCLUSION

The infarct pattern after aneurysmal SAH includes cortical band-like lesions. In contrast to territorial infarcts or lacunar infarcts in the white matter which develop as a result of moderate or severe proximal and/or distal vasospasm visible on angiography, the cortical band-like lesions adjacent to sulcal clots may also develop without evidence of macroscopic vasospasm, implying a vasospastic reaction of the most distal superficial and intraparenchymal vessels.

The systemic implications of aneurysmal subarachnoid hemorrhage

Aneurysmal subarachnoid hemorrhage (SAH) is analogous to a pathophysiological watershed, disrupting brain integrity and function and precipitating an array of systemic derangements including cardiovascular, respiratory, endocrine, hematological, and immune dysfunction. Extracerebral organ dysfunction is closely linked to the magnitude of the primary neurological insult, suggesting neurogenic, neuroendocrine and neuroimmunomodulatory mechanisms. Systemic organ involvement is associated with increased mortality and neurological impairment, even after adjustment for other outcome predictors such as the severity of the initial neurological injury. This may be a reflection of secondary brain injury precipitated by hypoxemia, circulatory failure, fever, or hyperglycemia, all of which have been linked to adverse clinical outcomes. Interventions to avert or reverse these and other perturbations need to be tested in clinical trials as they represent opportunities to improve survival and neurological recovery in patients with SAH.

Cerebral vasospasm after subarachnoid hemorrhage: the emerging revolution

Cerebral vasospasm is the classic cause of delayed neurological deterioration after aneurysmal subarachnoid hemorrhage, leading to cerebral ischemia and infarction, and thus to poor outcome and occasionally death. Advances in diagnosis and treatment-principally the use of nimodipine, intensive care management, hemodynamic manipulations and endovascular neuroradiology procedures-have improved the prospects for these patients, but outcomes remain disappointing. Recent clinical trials have demonstrated marked prevention of vasospasm with the endothelin receptor antagonist clazosentan, yet patient outcome was not improved. This Review considers possible explanations for this result and proposes alternative causes of neurological deterioration and poor outcome after subarachnoid hemorrhage, including delayed effects of global cerebral ischemia, thromboembolism, microcirculatory dysfunction and cortical spreading depression.

Acute cerebral vascular injury after subarachnoid hemorrhage and its prevention by administration of a nitric oxide donor

Object

Structural changes in brain parenchymal vessels occur within minutes after subarachnoid hemorrhage (SAH). These changes include platelet aggregation, activation of vascular collagenases, and destruction of perivascular collagen IV. Because collagen IV is an important component of the basal lamina, the authors attempted to further define changes in vascular structure (length and luminal diameter) and their relationship to vascular permeability immediately after SAH. In addition, the authors explored whether such alterations were attenuated by administration of a nitric oxide (NO) donor.

Methods

Endovascular perforation was used to induce SAH in rats. Two sets of experiments were performed. The first established changes in vascular structure and permeability (collagen IV and endothelial barrier antigen [EBA] dual immunofluorescence) during the first 24 hours after SAH. In the second, the investigators examined the effects of an NO donor on vascular structure, permeability, and collagenase activity (in situ zymography). In this second study, animals received intravenous infusion of the NO donor S-nitrosoglutathione (GSNO, 1 μM/8 μl/min) 15 minutes after induction of SAH and were killed 3 hours after SAH onset. Controls were naive unoperated animals for the first study and saline-infused SAH animals for the second.

The authors found a time-dependent decrease in area fraction, length, and luminal diameter of collagen IV– and EBA-immunofluorescent vessels after SAH. The greatest change occurred at 3 hours after onset of SAH. Administration of GSNO was associated with striking preservation of collagen IV and EBA immunofluorescence compared with saline treatment. Zymography indicated decreased collagenase activity in GSNO-treated SAH animals compared with saline-treated SAH animals.

Conclusions

These results demonstrate changes in the structure and permeability of brain parenchymal microvessels after SAH and their reversal by treatment with an NO donor.

Mechanism of cerebral fat embolism in subarachnoid hemorrhage: An experimental study

Subarachnoid hemorrhage (SAH) may cause neurogenic pulmonary edema (NPE), and chylomicron metabolism may be destroyed in injured lungs. We aimed to investigate the effect of neurogenic pulmonary edema (NPE), if present, on the development of cerebral fat embolism. This study has been conducted on 20 rabbits. Experimental SAH has been applied to half of the animals by injecting homologous blood into the cisterna magna, and the remaining half was applied only isotonic saline solution in the same manner under general anesthesia. After 20 days, all animals were killed. Their lungs and brains were examined histopathologically. Six animals died of SAH between 16 and 20 days, and foamy hemorrhagic parenchymal lesions and intra-alveolar hemorrhage were observed in their lungs. Fat globules were abundantly found in cerebral arteries of six of all the non-surviving animals. But, minimal histopathological changes were found in the lungs and brains of the surviving animals. Cerebral fat embolism was detected in only one animal that was given isotonic solution. SAH may cause NPE and result in lung tissue destruction. Chylomicron metabolism may be disordered in the destructed lungs and leakage of chylomicrons into systemic circulation may be facilitated via destroyed lung barrier. These pathologic processes may lead to cerebral fat embolism.

Thromboembolism and delayed cerebral ischemia after subarachnoid hemorrhage: an autopsy study

OBJECTIVE

Recent findings have cast doubt on vasospasm as the sole cause of delayed cerebral ischemia after subarachnoid hemorrhage.

METHODS

We reviewed the medical records of 29 patients who died after subarachnoid hemorrhage. Brain sections were taken from the insula, cingulate gyrus, and hippocampus. Adjacent sections were stained with hematoxylin-eosin and immunostained for thromboemboli. The density (burden) of the latter was calculated blindly and correlated with evidence for ischemia and with the amount of subarachnoid blood.

RESULTS

There is a strong correlation between microclot burden and delayed cerebral ischemia. Patients with clinical or radiological evidence of delayed ischemia had mean microclot burdens of 10.0/cm2 (standard deviation [SD], +/-6.6); those without had mean burdens of 2.8 (SD, +/-2.6), a highly significant difference (P = 0.002). There is also significant association (P = 0.001) between microclot burden and histological evidence of ischemia, with the mean burdens being 10.9 in sections exhibiting severe ischemia and 4.1 in those in which ischemia was absent. Microclot burden is high in patients who died within 2 days of hemorrhage, decreasing on Days 3 and 4. In delayed ischemia, the numbers rise again late in the first week and remain high until after the second week. In contrast, the average clot burden is low in patients dying without developing delayed ischemia. The amount of blood on an individual slide influenced the microclot burden on that slide to a highly significant extent (P < 0.001).

CONCLUSION

Thromboembolism after subarachnoid hemorrhage may contribute to delayed cerebral ischemia, which parallels that caused by vasospasm. The pathogenesis of thromboembolism is discussed.

Vasospasm as the sole cause of cerebral ischemia: how strong is the evidence?

✓ The authors review literature that challenges the view that vasospasm involving large arteries is the exclusive cause of delayed ischemic neurological deficits (DINDs) following subarachnoid hemorrhage. They discuss alternative mechanisms and review the evidence supporting a potential role for thromboembolism. They conclude that vasospasm and thromboembolism play interrelated and additive roles in the development of DINDs, and that this interaction provides opportunities for novel therapeutic approaches.

Molecular mechanisms of early brain injury after subarachnoid hemorrhage

OBJECTIVES

Increasing body of experimental and clinical data indicates that early brain injury after initial bleeding largely contributes to unfavorable outcome after subarachnoid hemorrhage (SAH). This review presents molecular mechanisms underlying brain injury at its early stages after SAH.

METHODS

PubMed was searched using term 'subarachnoid hemorrhage' and key words referring to molecular and cellular pathomechanisms of SAH-induced early brain injury.

RESULTS

The authors reviewed intracranial phenomena and molecular agents that contribute to the early development of pathological sequelae of SAH in cerebral and vascular tissues, including cerebral ischemia and its interactions with injurious blood components, blood-brain barrier disruption, brain edema and apoptosis.

DISCUSSION

It is believed that detailed knowledge of molecular signaling pathways after SAH will serve to improve therapeutic interventions. The most promising approach is the protection of neurovascular unit including anti-apoptosis therapy.