Morphological responses of cerebral tissues to temporary ischemia

Thrombolytic therapy in cerebrovascular disorders

The knowledge obtained from the ongoing investigational trials of tPA for acute ischemic stroke will not only help establish the appropriate dose range and complication rates but will also further develop the clearly mandatory rapid, aggressive team approach needed to truly treat acute ischemic strokes successfully. Experimental cerebral ischemia data have pointed to the need to treat acute clinical stroke within only a few hours or less to effectively reduce stroke morbidity and mortality. Specifically, with reversible MCA occlusion models of focal cerebral ischemia (dogs and cats), the animals uniformly survive without neurological deficit if the occlusion is for less than 2 to 3 hours. Similarly in primates, MCA occlusion for 3 hours or less will lead to clinical improvement and a decrease in infarct size, with complete recovery generally associated with less than 2 hours of MCA occlusion. Therefore, it appears unlikely that ischemic brain can be salvaged if vascular occlusion persists longer than 4 to 6 hours (similar to the pathophysiology of myocardial ischemia). Further, at least one third of ischemic stroke patients reperfuse spontaneously (and obviously too late) within 48 hours of stroke onset. Several factors believed to be related to successful outcome after thrombolytic therapy are summarized in Table 16. A schematic approach to determining the response to thrombolytic agents in acute ischemic stroke is outlined in Table 17. Zivin succinctly reviews thrombolysis for stroke, both experimental and clinical, and summarizes some of the difficulties of the early clinical stroke trials with thrombolytic agents and speculates about future prospects. He believes tPA may prove valuable in the treatment of some forms of thromboembolic stroke. Its usefulness may depend in part on how quickly the drug can be initiated and the risk of side effects; factors that will require further study. The currently used doses of tPA may be too low to lyse large cerebral arterial clots and, therefore, if current trials do not show a positive treatment response, further trials with higher doses may be indicated. The implications of a potentially effective treatment for truly acute stroke are enormous: stroke will need to be considered by all (lay public through to caregivers) as a true medical emergency, analogous to MI and trauma.(ABSTRACT TRUNCATED AT 400 WORDS)

An intravascular technique to occlude the middle cerebral artery in baboons

A technique is described for occlusion of the middle cerebral artery in the baboon by an intravascular approach. A torque catheter is introduced under fluroscopic control into the internal carotid artery by transfemoral catheterization. In conjunction with a guide wire an infusion microcatheter with increasing stiffness from the distal tip to the proximal shaft is positioned in the proximal part of the middle cerebral artery via the introducer system. N-Butyl-2-cyanoacrylate-monomers are injected into the microcatheter for permanent occlusion of the middle cerebral artery. The procedure was successfully completed in 21 out of 24 baboons. In 3 baboons the occlusion could not be achieved since the torque catheter could not pass proximal extreme tortuosities of possibly arterisclerotic internal carotid arteries. Infarcts in the 21 animals were confirmed by computerized tomography and/or autopsies in all animals.

Fatal ischaemic brain oedema after early thrombolysis with tissue plasminogen activator in acute stroke

Two patients with acute major, disabling cerebral infarction with presumed middle cerebral artery occlusion were treated with the clot specific thrombolytic agent tissue plasminogen activator roughly three and a half hours after the onset of symptoms. Both patients had a normal computed tomography (CT) scan before treatment. No appreciable systemic bleeding complications occurred, apart from bruising. One patient had bleeding into the subarachnoid space from a microscopic angioma, which was found at necropsy. Haematological monitoring of the two patients showed pronounced fibrinogenolysis and alpha 2 antiplasmin consumption in one. One patient showed transient improvement during the infusion. In both cases extensive infarction, partly haemorrhagic in one, with massive concomitant oedema was found on repeated CT. Both patients deteriorated and eventually died as a consequence of transtentorial herniation. In the one patient who came to necropsy a moderate, probably pre-existing smooth stenosis of the ipsilateral carotid artery was found, all cerebral vessels being patent. It is concluded that thrombolytic treatment with a clot specific agent such as tissue plasminogen activator started three to four hours after a major ischaemic stroke may be hazardous, not because of haemorrhagic transformation of the original ischaemia but because early reperfusion may promote massive, potentially fatal cerebral oedema.

Multiparametric imaging of blood flow and metabolism after middle cerebral artery occlusion in cats

In anesthetized adult cats, acute stroke was produced by transorbital occlusion of the left middle cerebral artery. A battery of imaging techniques was used for simultaneous evaluation of regional blood flow, glucose utilization, protein synthesis, pH, and the regional tissue content of glucose, ATP, and potassium. The electrophysiological impact of stroke was monitored by EEG frequency analysis and recording of somatosensory evoked potentials. Two hours after vascular occlusion, a close correlation existed between the degree of electrophysiological changes and biochemical alterations, in particular with the extent of tissue acidosis, ATP depletion, decrease of tissue potassium content, and suppression of protein synthesis. However, there was only a poor correlation with blood flow and glucose utilization. Both of these exhibited a greatly inhomogeneous pattern with regions of reduced, normal, or increased rates. In areas remote from the infarct, the content of biochemical substrates was normal but blood flow was reduced globally by approximately 50% and glucose utilization by approximately 20%. An anatomically defined regional pattern of cerebral or cerebellar diaschisis was not observed. It is concluded that during the acute phase of stroke, imaging of blood flow and glucose utilization does not provide an accurate estimate of the actual functional or metabolic disturbance. For the clinical evaluation of the development or treatment of stroke, in consequence, alternative noninvasive techniques such as imaging of protein synthesis and/or pH may be more relevant.

Cerebral tissue response to electrode implantation

Tissue response to platinum electrodes was assessed after an eight-day implantation period. The regions of study included the cortical areas at the opercular gyri and at the sulcus parieto-occipitalis externus, as well as the sub-cortical white matter in these cases. Perivascular and intraparenchymal hemorrhagic lesions as well as edematous changes characterized both by extensive intra and extracellular swelling were noted. Numerous phagocytic elements and degenerative strucutres were present at the electrode/parenchymal interface. Tissue alterations were asymmetrical as observed both around and at the tip of the implanted electrode. The parenchymal alterations extended from 0.2mm to 3.5mm distance from the electrode path/parenchymal interface. Greater tissue involvement was found in the subcortical white matter as compared to the adjacent cortical gray matter.

Acute tissue response to cerebral ischemia in the gerbil. An ultrastructural study

The Mongolian gerbil, because of the uniqueness of the anatomical features of its circle of Willis, has become an increasingly useful model in the study of cerebrovascular disease. The present work defines acute changes at the ultrastructural level following ischemic insult. The pathomorphological responses include initial astrocytic involvement and, when the degree of insult is increased, a progression of morphological changes is evident in neuronal and other parenchymal elements. Animals with vessels occluded for more than 3 hr without neurological signs suggestive of ischemia exhibited limited perivascular edema. Contralateral changes (perivascular astrocytic) were observed in the basal ganglia at 24 hr in animals with neurological deficit. Astrocytic and basal ganglia susceptibility to ischemia was consistent with previous findings in primate models. An additional association was found in that limited edematous involvement could exist in animals without neurological deficit but neuronal changes were only present in animals with signs of ischemic neurological deficit.

An ultrastructural assessment of an embolic method of producing cerebral ischemia

This study presents ultrastructural confirmation of the embolic method of producing an ischemic lesion. The embolic method was shown to produce more advanced parenchymal changes than those reported for the same postocclusion period following vascular clipping. With this method there was less alteration in the morphological intergrity of occluded extraparenchymatous areas of the arterial bed, especially in the associated nerve bundles.