The pathology of cerebral edema

[Postmortem assessment of cerebral edema]

An analysis of literature data on the methods of post-mortem assessment of cerebral edema is presented. Based on the mechanisms of development, two main types of cerebral edema are distinguished: cytotoxic (intracellular) and vasogenic (extracellular). To determine cerebral edema, a number of methods are used, both direct and indirect, invasive and non-invasive assessment. Direct methods for assessing cerebral edema are based on determining the amount of water in its tissue. Indirect methods include morphological and radiation studies. Traditionally, the most evidence-based criteria for the diagnosis of cerebral edema are macroscopic and microscopic changes determined at autopsy. Methods are also indicated for determining the content of water in brain tissue by comparing the mass of wet and dry brain, as well as estimating the specific density of brain tissue.

Tissue sample analysis for post mortem determination of brain edema

The post mortem evaluation of a brain edema is routinely performed by pathologists based on the macroscopic signs during autopsy. This method represents the current gold standard, but is subjective and observer dependent. Therefore, three post mortem evaluation methods of brain samples were analyzed in this work: histology, wet-dry weight and normalized cerebral weight, which was described in 2020 by Bauer et al. Tissue samples from six different regions of 34 brains were collected and examined both by rating of histological slides and by measuring the water content by using a drying oven. The rating of the histological slides, stained with hematoxylin and eosin, was performed by two pathologists independently. For the water content, the wet weight and the dry weight of each sample were set in relation. The normalized cerebral weight was calculated by dividing the brain weight by the brain volume, which were both determined during autopsy and in computed tomography images, respectively. A fair to moderate interrater agreement was obtained for the histologic evaluation and a significant correlation was present between one rater and the wet-dry weight and the normalized cerebral weight method. When classifying according to the gold standard, a significant difference was detected between the edematous and nonedematous cases by using the wet-dry weight method in the cerebral cortex and by using the normalized cerebral weight method. However, the significant correlations and group differences were limited to the aforementioned results. In conclusion, both the histological and the wet-dry weight method show limited benefits for the classification of brain edema and the histology analysis is highly observer dependent. The normalized cerebral weight method, however, reveals a significant effect between the edematous and nonedematous cases when classifying according to the gold standard. Therefore, we suggest to apply this method for the assessment of brain edema since it is objective and rater independent. Nevertheless, the exact evaluation of brain edema remains a challenging task, especially due to the continuous transition between no edema and edema.

Analysis of different post mortem assessment methods for cerebral edema

While cerebral edema is a live-threatening condition in living persons, also an edema-like fluid redistribution can occur post mortem. In deceased, usually macroscopic signs are evaluated during autopsy in order to determine the presence or absence of cerebral edema. As a quantitative and objective classification is beneficial, an already existing method (Radojevic et al., 2017), which is based on a mathematical formula using the intracranial dimensions and the cerebral weight, was compared to the evaluation of macroscopic signs in 31 cases. The results showed an excellent agreement for the comparison between the raters as well as the measurement methods (at opened skull or in CT images). However, both measurement methods only poorly agree with the macroscopic edema evaluation. In order to find a more concordant method, the normalized cerebral weight, which puts the cerebral weight in relation to the intracranial volume, was calculated for 115 cases. This method resulted in an excellent agreement with the macroscopic rating and showed a clear numerical difference between the edematous and nonedematous group. While the influence of the post mortem time and the cooling time was found to be negligible, the age at death might confound the edema classification due to pre-existing cerebral atrophy leading to lower cerebral weights. In summary, the present study compared different assessment methods to classify cerebral edema and developed a rater independent, objective and quantitative classification method, which was as reliable as the rating of the forensic pathologists.

Value of morphological parameters for grading of brain swelling

This study investigated the value of both gross features and histological findings for grading of brain swelling. For this purpose, the grooving of the temporal gyri (unci) as well as the extension of the cones at the basal part of the cerebellum were measured in 42 brains obtained at autopsy. Furthermore, the distension of perivascular spaces in tissue samples from seven different regions of the brains was evaluated histologically, assisted by an automatic image processing and analysis system. In each individual, the normal range of brain weight was calculated on the basis of the body height, using the formulae by Röthig and Schaarschmidt. The difference between this calculated (normal) value and the brain weight evaluated at autopsy was considered as a reliable criterion for the grade of brain swelling. There was no statistical evidence of a positive correlation between the various parameters. Hence, it can be concluded that both gross section and histological findings are of minimal significance for grading of brain swelling.

Spatial and temporal expression of P-glycoprotein in the congenitally hydrocephalic HTX rat brain

The purpose of the present study is to examine spatial and temporal expression of P-glycoprotein in the brain of congenitally hydrocephalic HTX rats. P-glycoprotein has been reported not only as a drug efflux pump but also one of the factors that restricts brain edema. We examined the rat brain from postnatal day 1 to 60 using light and electron microscopy, immunohistochemistry, Western immunoblot and reverse transcriptase-polymerase chain reaction (RT-PCR) methods with monoclonal antibody specific for P-glycoprotein. Immunohistochemically, the positive anti-P-glycoprotein reactivity was found in capillaries of the normal control rat cerebrum. In the hydrocephalic HTX rat brains, it was also found in the capillaries, but only very weak to no reactivity was found in the capillaries of the spongy changes and cystic wall in the subcortical and lateral periventricular white matter. Immunoelectron microscopically, the reaction product was found exclusively on the luminal surface of the capillary endothelium in control rats. A tracer study with intracardiac perfusion of lanthanum chloride showed that lanthanum penetrated the tight junctions and passed through the intercellular space. In the Western immunoblot analysis, P-glycoprotein of 170 kDa was detected clearly in most normal control rat brains but it was not found in the hydrocephalic HTX rat brains. Moreover, mdr1 P-glycoprotein gene expression in the subcortical white matter was examined by RT-PCR. It was detected in all normal control rat brains, but not found in the hydrocephalic HTX rat brains. The results suggested that the absence of P-glycoprotein expression in the capillaries of deep subcortical and lateral periventricular white matter of hydrocephalic HTX rats led to a deficiency of the blood-brain barrier and might be related to vasogenic edema and to the formation of the spongy changes and cystic cavities.

The multidrug-resistance gene MDR1 is expressed in human glial tumors

The most consistantly reported alteration of multidrug-resistant carcinoma cells is the overexpression of a membrane glycoprotein, termed P-glycoprotein. In this study we examined whether the strong intrinsic chemotherapy resistance of glial tumors might be related to the expression of the MDR1 gene which codes for P-glycoprotein. Fourteen glial tumors were examined immunohistochemically using the monoclonal antibody C219. In addition, RNA samples of 11 of these tumors were analysed using a sensitive Northern blot assay. P-glycoprotein is expressed in all 14 glial tumors; the number of stained tumor cells, however, varied considerably ranging from 0.3% to 15%. There was no correlation between the number of MDR1-positive cells and the histological malignancy. Varying amounts of MDR1 mRNA were detectable in 7 from 11 examined tumors. The results of our study show that the MDR1 gene is expressed in human glial tumors and suggest that the multidrug transporter may contribute to the clinical non-responsiveness of these tumors to chemotherapy.

Immunohistochemical demonstration of serum proteins in human cerebral gliomas

The leakage of different serum proteins, including immunoglobulins, into human cerebral gliomas was studied by use of the unlabeled peroxidase-antiperoxidase (PAP) method on cryostat and paraffin sections. Our series of 50 tumour biopsies included 21 isomorphic astrocytomas and oligodendrogliomas (grade II), 19 anaplastic astrocytomas and oligodendrogliomas (grade III), and 10 glioblastomas (grade IV). The immunohistochemical staining of the serum proteins was similar on paraffin and cryostat sections and graded with respect to occurrence, distribution, and intensity. Serum proteins of a small hydrodynamic radius with a low serum concentration (prealbumin) or with a high serum concentration (albumin) were diffusely present in the interstitial spaces of all glioma types. Serum proteins with a medium molecular size and variable serum concentrations, i.e. IgG, IgA, and ceruloplasmin, were detected preferentially in anaplastic gliomas and in glioblastomas (grade III and IV) displaying comparable distribution patterns but different intensities. Alpha-2-macroglobulin a serum protein with a large hydrodynamic radius was also demonstrated in grade III and IV gliomas, whereas IgM and beta-lipoprotein being the largest serum proteins tested were almost restricted to blood vessels and tumour necroses. In addition, most serum proteins occurred with high intensities in those areas of isomorphic grade II gliomas that showed a macro- or microcystic or mucinous tissue degeneration. The varying immunohistochemical staining results for the serum proteins studied indicate that the blood-brain barrier within isomorphic and anaplastic gliomas is not completely disturbed. It appears that the vascular permeability is preferentially increased for small-sized serum proteins, whereas the leakage of larger serum proteins into the glioma interstitium seems to depend on the tumour type and on increasing malignancy.

Pathology and pathophysiology of brain ischaemia

The current views on the pathophysiology of cerebral ischaemia have recently been challenged by the new experimental results and animal models devised in recent years. These data are briefly reviewed. Ischaemic macroscopical and microscopical lesions in the human brain are outlined. Ischaemic changes can be either regional or total. The types, topography and aetiology of cerebral infarcts, lacunes and venous infarcts are described. The consequences of marked or total ischaemia affecting the whole cerebral blood supply are mentioned.

Disruption of the blood-brain barrier in hyperammonemic coma and the pharmacologic effects of dexamethasone and difluoromethyl ornithine

Both hyperammonemia and blood-brain barrier (BBB) breakdown have been implicated in the evolution of hepatic encephalopathy. To define a possible relationship, Swiss Albino mice were subjected to sublethal encephalopathic doses of ammonium acetate; the integrity of the BBB was determined grossly with Evans blue and quantitatively with [14C]-alpha-aminoisobutyrate (AIB). Some animals were injected with a dose of ammonium acetate sufficient to maintain coma for 1 hr (AC group). One group, termed stuporous (AS), received only enough ammonium acetate to interfere with grooming and exploratory activity; this dosage was insufficient to completely block the righting response, which was absent in the AC group. When compared to that of controls (CON) receiving normal saline instead of ammonium acetate, cerebral tissue from the AC group was stained blue and contained nearly double the amount of AIB; AS group brain tissue was unstained and the AIB content did not differ significantly from normal. Some of the AC group were pretreated with drugs known to retard BBB breakdown; one set received dexamethasone (AC-DXMN), another the ornithine decarboxylase inhibitor difluoromethyl ornithine (AC-DFMO), and a third L-ornithine (AC-ORN). Brain tissue from the AC-ORN group stained blue and AIB content did not differ significantly from that of the untreated AC group. Cerebral tissue of the AC-DXMN pretreatment group stained light blue; AIB content was significantly lower than in the AC group and greater than the CON group. The AC-DFMO brains were unstained and AIB content was significantly lower than in the AC group but did not differ significantly from CON. These results indicate that hyperammonemia may induce BBB breakdown but that the disruption of barrier integrity is not antecedent to the development of coma, although it seems to coincide with coma in time.(ABSTRACT TRUNCATED AT 250 WORDS)

Histopathological changes in the brain of mice given Clostridium perfringens type D epsilon toxin

The distribution, severity and frequency of brain lesions produced in mice by the administration of Clostridium perfringens Type D epsilon toxin were examined by light microscopy. The granular layer of the cerebellum was the area most frequently affected in mice given single doses of toxin. Sequential changes in brain morphology were examined from 1 h to 7 days after injection of toxin. Lesions progressed from an initial vasogenic oedema to malacic foci which commonly were focal and bilaterally symmetrical, with a predilection for white matter. The topographical distribution of these malacic areas is discussed.

Ultrastructural changes in the brain of mice given Clostridium perfringens type D epsilon toxin

Mice were given lethal and sublethal doses of Clostridium perfringens Type D epsilon toxin and the early morphological changes in perfusion-fixed intoxicated brains were examined from 30 min to 6 h post-inoculation. The initial ultrastructural finding was swelling of astrocytes, especially the perivascular extensions of these cells. Astrocytes in the cerebellum appeared to be particularly sensitive to this toxin. These changes were quickly followed by evidence of severe endothelial damage, with the endothelial cytoplasm becoming attenuated, vacuolated and very electron-dense. A pathogenetic sequence of events leading to malacia, derived from ultrastructural observations, is proposed.

Status spongiosus in the course of treatment of malignant gliomas

Two cases of fatal encephalopathy which appeared in the course of treatment of malignant gliomas are described. CT scan showed diffuse, low density, non-enhanced lesions of the white matter. Pathological findings showed that the CT scan aspects corresponded to status spongiosus without demyelination. We were unable to find similar reports in the literature.

Neuropathology, pathogenesis, and neuropsychiatric sequelae of Reye syndrome

A clinico-pathologic correlation can be established for those survivors of Reye syndrome in the higher clinical stages who have sustained irreversible and often major neuropsychiatric deficits. The neuropathologic substrate for the clinical manifestations of mental retardation, recurrent seizures, movement disorders, sensori-motor deficits, psychobiologic maladjustment, and mediocre performance in school and on formal psychometric tests consists of multifocal infarction and astrocytosis in cerebral cortex, diencephalon, basal ganglia, and brainstem. While the mortality rate of Reye syndrome in acute stages is still significantly high (25% in our 20 cases, 52% in the tabulated cases in the higher clinical grades), the occurrence of permanent psychomotor deficits is an equally tragic socioeconomic and medical problem. Of our 15 survivors, 3 have suffered major and 1 has sustained minor brain damage. From a review of the literature, over one-third of survivors are consigned to cerebral malfunction, hence their potential for full enjoyment of life and their intellectual, emotional, and economic contributions to their families and society are sadly curtailed.

Pathophysiology and management of raised intracranial pressure

The mechanism of cerebral homeostasis is reviewed, paying particular attention to the way blood-brain barrier, cerebrospinal fluid and cerebral blood flow contribute to the maintenance of normal intracranial pressure. The pathophysiology of raised intracranial pressure is outlined delineating the different types of cerebral oedema. Guidelines for the management of patients with raised intracranial pressure are presented as well as the techniques of intracranial pressure monitoring.

Radio- and chemotherapy of malignant gliomas. Pathological changes in the normal nervous tissue

The pathological effects of radio- and chemotherapy on the normal nervous tissue have been studied in 42 brains with malignant gliomas. The brains have been examined by means of the complete study technique. In seven cases the picture of delayed radionecrosis has been found. Apart from this, many histological features have been related to post-operative survival, radiation dose, interval between radiation and death, chemotherapy, steroids, size and activity of the tumour. Some alterations, such as peritumoural necroses, macrophage areas, vessel wall degenerations etc. result from radiotherapy. The relations and pathogenesis are discussed.

Cerebral damage in paraquat poisoning

This is the first report on cerebral changes in eight patients who died of paraquat poisoning. These included generalized oedema, haemorrhages (both subependymal and subarachnoid), glial reactions (microglial activity and astrocytic response) and meningeal inflammation. Oedema and haemorrhage were the most consistent and significant findings; they suggest that paraquat may damage the cerebral blood vessels. The distribution of haemorrhages was unusual and resembled that seen in thiamine deficiency.

The role of biotransformation in organic mercury neurotoxicity

Although the clinical patterns of organic and inorganic mercury poisoning are very different, systemic toxicity experiments have shown that the histological changes in the kidneys and dorsal root ganglia neurones are identical with the 2 classes of compounds. It has been further suggested that the toxicity of organic mercurials is the result of biotransformation to inorganic mercury. To test this hypothesis, between 10(-7) and 10(-10) mol of mercuric chloride and methyl mercuric acetate were injected directly into the cerebrum of rats. The comparative size of lesions was estimated anatomically and by reference to blood brain barrier dysfunction. Inorganic lesions were only slightly larger than those produced by equimolar amounts of organic mercury. Consequently both organic and inorganic mercury must be regarded as neurotoxic in their own right. Conversion of organic mercury certainly occurs but is not the only mechanism by which organic mercury exerts its toxicological effect.

Effects of prolonged cyanide and thiocyanate feeding in rats

Male weaning rats were fed a semipurified diet containing 10% casein; this diet restricted in methionine, vitamin B12, and iodine; or the complete and restricted diets supplemented with either 1500 ppm potassium cyanide or 2240 ppm potassium thiocyanate for 11.5 mo. There were no deaths or clinical signs of toxicity. Cyanide, but not thiocyanate, caused a consistent reduction in weight gain in the complete and restricted groups. Both cyanide and thiocyanate caused decreased thyroid gland activity in young rats, particularly in the restricted groups. Plasma thyroxine concentrations were maintained in the mature cyanide-treated rats, even though secretion rates were decreased. However, the mature thiocyanate-treated animals showed decreased plasma thyroxine concentrations, despite thyroid gland enlargement. Modest primary myelin degeneration in the spinal cord white matter was found in the restricted group and in rats receiving this diet supplemented with either cyanide or thiocyanate. The lesions did not resemble those of a vitamin B12 deficiency in appearance or those of acute cyanide intoxication in distribution. Because of tissue autolysis, it could not be determined whether these changes resulted from histotoxic anoxia or an alteration of oligodendroglial myelin metabolism.

Chlorpromazine treatment of blood-brain barrier dysfunction. A quantitative and fluorescence microscopical study on small cerebral stab wounds in the rat

The extravasation of albumin around small cerebral stab wounds in the rat frontal cortex was studied by fluorescence microscopy after i.v. injection of Evans blue-labeled albumin and by quantitative immunoelectrophoresis after i.v. injection of bovine albumin, in both nonintoxicated and ethanol-intoxicated rats. The extravasion of albumin was enhanced in ethanol-intoxicated compared to nonintoxicated rats, as studied both by immunoelectrophoresis and by fluorescence microscopy. Administration of chloropromazine (2 mg/kg body weight i.v.) 16 h after inflicting cerebral stab wounds decreased the area around the wound showing extravasation of Evans blue-labeled albumin as studied by fluorescence microscopy both in nonintoxicated and in ethanol-intoxicated rats. Quantitative studies showed a significanct decrease in the amount of extravasated albumin around cerebral stab wounds in ehtnaol-entoxicated rats, while the extravasation in nonintoxicated rats was not significantly changed by chlorpromizine treatment.

Intracellular serum proteins in cerebral gliomas and metastatic tumours: an immunoperoxidase study

An immunoperoxidase technique was used to compare the presence of serum proteins in tumour cells in twenty cerebral gliomas and four intracerebral metastatic carcinomas, with the serum protein content of reactive astrocytes around four cerebral infarcts. Rabbit antiserum to human immunoglobulins and albumen was applied to paraffin sections of tumour biopsies and of infarcts from postmortem brains. All the reactive astrocytes surrounding infarcts stained positively for immunoglobulins and albumen. In the gliomas, a continuous range of staining was observed in plump astrocytic tumour cells varying from strongly positive to unstained. Very few poorly-differentiated glioma cells stained for serum proteins; metastatic tumour cells, areas of capillary endothelial proliferation, and spindle cells in gliosarcomas remained unstained. These results suggest that the astrocytic function of serum protein uptake from the extracellular fluid is often lost in poorly-differentiated glioma cells, but is retained to a variable degree by those tumour cells which histologically resemble reactive astrocytes.

Ultrastructural studies on blood-brain barrier dysfunction around cerebral stab wounds, aggravated by acute ethanol intoxication

Ethanol-intoxicated and non-intoxicated albino rats subjected to cerebral stab wounds were injected with Evans blue-labelled albumin (EBA) and horseradish peroxidase (HRP) 24 hours after the injury. The tracers were injected 30 and 2 minutes before perfusion fixation with glutaraldehyde and then prepared for light microscopy and electron microscopy. There was prominent leakage of peroxidase through chains of pinocytotic vesicles and transendothelial channels from blood, through the endothelial cells, into the brain. There was no difference in the way of peroxidase leakage through the endothelial cells between ethanol-intoxicated and control rats, but the area containing leaking blood vessels was greater in intoxicated rats. Furthermore, the number of trans-endothelial channels, vesicles and caveolae per unit length of capillaries and venules was increased in ethanol-intoxicated rats. Injured neurons with a diffuse distribution of peroxidase in their cytoplasm were observed within a greater area around the stab wound in ethanol-intoxicated than in control rats.

Brain monoamines in metabolic (endotoxic) coma. A preliminary biochemical study in human postmortem material

Spectrofluorometric assays of DA, 5-HT and 5-HIAA were performed in different areas of postmortem brains of humans who died in hepatic and uremic coma. Brain DA showed a mild general decrease, the average reduction being 20 to 30 percent of the controls. By contrast, 5-HT and 5-HIAA were markedly increased in most brain areas, most significantly in the reticular and raphé nuclei of the brainstem and in some parts of the limbic system. Despite individual and regional differences, the monoamine changes had similar patterns in both hepatic and uremic coma. These data in human brain which confirm previous clinical and experimental studies in hepatic encephalopathy suggest some common disorders of central monoamine metabolism in endotoxic coma of different origin. Brain edema, a constant feature in toxic coma, is probably due to increased 5-HT content in the brain, the pathophysiologic effect of 5-HT on the blood-brain barrier being well established. The prominent changes of indoleamine metabolism in the reticular brainstem and limbic systems may be related to disorders of consciousness.

Report of Joint Committee for Stroke Resources. IV. Brain edema in stroke

A classification of brain edema is provided as well as an extensive review of the animal models from which we have derived most of the basic information we have about the formation and resolution of edema. The clinical aspects of cerebral edema in stroke are discussed and also modern methods for identifying cerebral edema in the human. Attention is given to computed tomography and enhanced CT and advances in their application to this condition. Treatment of cerebral edema in the stroke patient using glycerol, dextran 40, mannitol, steroids, and other drugs is discussed and the need pointed out for controlled clinical trials of the therapeutic effectiveness of these agents.

Increased blood-brain barrier permeability around cerebral stab wounds, aggravated by acute ethanol intoxication

Control and ethanol-intoxicated rats were injured with a small cerebral stab wound and the extravasation of Evans blue-labelled albumin (EBA) was studied. Control rats displayed an extravasation of EBA in the immediate peri-traumatic area with subsequent uptake of EBA in neurons and glia. Ethanol-intoxicated rats showed a greater leakage of EBA as well as a wider area of leaking blood vessels around the stab wound, both in the peri-traumatic and in the early post-traumatic period. Neuronal uptake of EBA was enhanced and observed in a wider area in intoxicated than control rats. The difference in distribution of EBA among neurons and glia between intoxicated and control rats was partly a consequence of the difference in leakage of EBA in the experimental groups. However, part of the increased neuronal uptake of EBA might be explained by an effect of ethanol on nueronal plasmalemma. The results obtained indicated a more pronounced injury to endothelial and neuronal cells after small cerebral stab wounds in ethanol-intoxicated compared to control rats.

Enhanced blood-brain barrier leakage to evans blue-labelled albumin after air embolism in ethanol-intoxicated rats

Control and ethanol-intoxicated rats were given a small air embolus in the right common carotid artery after ligation of the external carotid branch. The extravasation of Evans blue-labelled albumin (EBA) was studied. Control rats dispalyed a slight extravasation of EBA through arteries and arterioles at the surface of the right hemisphere with a slight spread into adjacent brain parenchyma. Additionally, ethanol-intoxicated rats showed a great leakage through small blood vessels even deep in the right hemisphere and a blue-staining of most of the embolized hemisphere. Thus it was shown that during embolization, ethanol increases the vascular permeability to macromolecules. It is proposed that this phenomenon mainly is due to injury to the endothelial cells.

Vacuolation of oligodendroglia in neoplastic perifocal edema

Vacuolation of oligodendroglia, a new type of cytopathological change, has been described. The change is observed frequently at the perifocally edematous cerebral white matter adjacent to the metastatic lesions of carcinoma from the lung in all three cases examined. It is also present occasionally in association with astrocytoma. This condition is characterized by swelling of oligodendroglias due to numerous cytoplasmic vacuolations which contain the material identical with that of the extracellular edema fluid. In such cells, the nucleus is displaced and deformed by vacuoles but the nuclear chromatin and envelopes are arranged normally. By occupation of numerous large vacuoles the cytoplasm is divided into small areas, but the individual organelles are only minimally altered. The oligodendroglial vacuolation seems to be a phagocytic response to the edema fluid which contains proteinous macromolecules derived from blood-borne protein and necrotic material of brain tissue and neoplastic cells. The vacuolation may result in some oligodendroglial dysfunction in maintenance of myelin and probably be related with diffuse loss of myelin sheath in the longstanding brain edema secondary to neoplastic invasion. The vacuolated cells can be identified with light and electron microscopes in Epon-embedded sections of surgically removed tissue but not in paraffin sections.

XIII. Cerebral circulation and metabolism in stroke. Cerebral circulation and metabolism in stroke study group

An understanding of the cerebral circulation is so fundamental to comprehension of the pathogenesis of stroke that cerebral blood flow and metabolism merit review in this series of reports. The authors recognize that the research described here is very technical in nature and may appear to have little practical application to clinical medicine. Nevertheless, these matters are basic to the development of precise methods for the measurement of regional cerebral blood flow in man which could be used to monitor the therapy of stroke with greater success than is possible at present.