Brain stem activation in spontaneous human migraine attacks

Evidence from animal experiments shows that the brain stem is involved in the pathophysiology of migraine. To investigate human migraine, we used positron emission tomography to examine the changes in regional cerebral blood flow as an index of neuronal activity in the human brain during spontaneous migraine attacks. During the attacks, increased blood flow was found in the cerebral hemispheres in cingulate, auditory and visual association cortices and in the brain stem. However, only the brain stem activation persisted after the injection of sumatriptan had induced complete relief from headache and phono- and photophobia. These findings support the idea that the pathogenesis of migraine is related to an imbalance in activity between brain stem nuclei regulating antinociception and vascular control.

Recovery from Wernicke's aphasia: a positron emission tomographic study

Changes in the organization of the brain after recovery from aphasia were investigated by measuring increases in regional cerebral blood flow (rCBF) during repetition of pseudowords and during verb generation. Six right-handed patients who had recovered from Wernicke's aphasia caused by an infarction destroying the left posterior perisylvian language zone were compared with 6 healthy, right-handed volunteers. In the control subjects, strong rCBF increases were found in the left hemisphere in the posterior part of the superior and middle temporal gyrus (Wernicke's area), and during the generation task in lateral prefrontal cortex (LPFC) and in inferior frontal gyrus (Broca's area). There were some weak right hemisphere increases in superior temporal gyrus and inferior premotor cortex. In the patients, rCBF increases were preserved in the frontal areas. There was clear right hemisphere activation in superior temporal gyrus and inferior premotor and lateral prefrontal cortices, homotopic to the left hemisphere language zones. Increased left frontal and right perisylvian activity in patients with persisting destruction of Wernicke's area emphasizes redistribution of activity within the framework of a preexisting, parallel processing and bilateral network as the central mechanism in functional reorganization of the language system after stroke.

Review: does measurement of regional cerebral blood flow reflect synaptic activity? Implications for PET and fMRI

The energy metabolism of the adult human brain almost completely depends on glucose. The functional coupling of regional cerebral blood flow and local cerebral glucose metabolism has been established in a wide range of experiments using autoradiographic techniques in rats, cats, and monkeys as well as double-tracer techniques in humans. Glucose utilization in turn reflects neuronal activity and more specifically synaptic, mainly presynaptic, activity. The majority of glucose is needed for the maintenance of membrane potentials and restoration of ion gradients. PET as well as fMRI may be used to study changes in blood flow or flow-related phenomena in human subjects in vivo. Both techniques monitor changes of synaptic activity in a population of cells. These changes may be due to excitation or inhibition. More than 85% of cerebral glucose is used by neurons (mainly presynaptic axon terminals), while the remainder may at least partly account for metabolic processes in glial cells. Monitoring of regional cerebral blood flow with PET or fMRI thus mainly reflects neuronal and more specifically (pre-) synaptic activity.

Comparison of magnetic and metabolic brain activity during a verb generation task

The magnetic and metabolic activational patterns of the brain during the perception, generation and silent articulation of words overlap to some extent, yet also measure concrete activational patterns. In the present study, auditory evoked magnetic fields (MEG) and changes in regional cerebral blood flow (PET) were examined in healthy subjects during a verb generation task. The aim of the study was to determine whether the advantages of both recording techniques can be combined so as to identify distributed sources of brain activity during particular tasks such as language processing. Given the currently observed disparity of the results from the two types of brain imaging we conclude that PET data will most likely not provide physiologically meaningful constraints for the distributed source analysis of MEG data, and may not necessarily validate results of distributed source analyses.

Elevation of intracranial pressure in acute AIDS-related cryptococcal meningitis

Prior to the AIDS-era, elevation of intracranial pressure was known to be a typical complication of cryptococcal meningitis associated with an increased risk of early death. In AIDS-patients, however, the prevalence and clinical significance of this complication are as yet unclear. We analysed clinical features and courses, CSF findings, serological results and neuroimaging scans in acute cryptococcal meningitis in eight patients with AIDS. Five showed symptoms and signs compatible with raised intracranial pressure, which was life-threatening in one and the most probable cause of death in another. Serial monitoring of intracranial pressure together with repeated CSF analysis revealed that severe intracranial pressure elevation in AIDS related cryptococcal meningitis can occur in spite of effective antimycotic treatment, does not depend on an increased CSF/serum osmolality ratio or CSF overproduction and can be associated with normal cranial computed tomography and magnetic resonance imaging findings. Our data support the hypothesis that CSF reabsorption failure plays the crucial role in the pathophysiological mechanism. External lumbar drainage may be of benefit in selected cases of acute AIDS related cryptococcal meningitis with persisting life threatening elevation in intracranial pressure and normal computed tomogram.

[Progress in vascular dementia--an overview of vascular dementia from past to new concepts]

This article summarizes various concepts (Binswangers encephalopathy, multiinfarct-dementia, lacunar state, mixed dementia, dementia due to amyloid angiopathy or vasculitis) and classifications (DSM, ICD, ADDTC) on vascular dementia. It reviews historical, clinical, and diagnostic aspects (i.e. neuroradiology, SPECT, PET) as well as therapeutic approaches. The confusing nomenclature on vascular dementia is discussed, considering especially the non-convincing concept of multiinfarct-dementia that often has been misused as a synonym for vascular dementia. Multiinfarct-dementia is now restricted to a syndrome of vascular dementia due to several large vessels strokes. A current definition and classification of vascular dementia as suggested by NINDS-AIREN international workshop is described. It defines criteria consistent with the diagnosis of "possible", "probable" and "definite" vascular dementia based on clinical, radiologic and neuropathologic features. The criteria of "probable" vascular dementia include all the following: 1. the presence of dementia and cerebrovascular disease defined by focal signs on neurologic investigation and evidence of relevant cerebrovascular disease by brain imaging (multiple lacunae, extensive white matter lesions, multiple large-vessels infarcts or a strategically placed infarct) 2. A relationship between dementia and cerebrovascular disease (onset of dementia within 3 months following a recognized stroke; abrupt deterioration, stepwise progression). This classification of vascular dementia emphasises pathogenetic aspects and includes dementia resulting from small- and large-vessels disease as well as hypoperfusion, haemorrhagic dementia and dementia due to still unknown factors. Operational criteria for the frequent Binswangers encephalopathy--a prototype of vascular dementia--are presented. Thereby a basis for further research and discussion in this exciting area should have been formed.

Imaging recovery of function following brain injury

The past years have seen significant advances in our understanding of recovery of function after brain lesions. This results from the development of sophisticated methods for exploring the human living brain, especially by using positron emission tomography scans. From the recent literature, it appears that two main mechanisms may participate in the recovery process: recruitment of cortical areas in the undamaged hemisphere and extension of specialized areas adjacent to the lesioned site.

[Cerebral angiitis or central side effects after lumbar myelography (with intracerebral vascular spasm)]

This is a case report of severe neurological complications following lumbar radiculography with the non-ionic x-ray contrast agent Iopamidol. The complication, which consisted of serious mnestic disturbances and various neurological deficits including hemiparesis, was due to intracerebral vascular spasms, demonstrated by cerebral angiography, and TCD followed by multiple cerebral infarctions, demonstrated by MRI. A possible causal relationship between the cerebral vascular spasm and intrathecal administration of Iopamidol is discussed.

Cerebral vasomotor reactivity is significantly reduced in low-flow as compared to thromboembolic infarctions: the key role of the circle of Willis

To test the hypothesis that cerebral vasomotor reactivity (CVMR) is significantly more reduced in patients with hemispheric low-flow infarctions than in brain infarctions due to arterio-arterial embolism, a series of 64 consecutive patients with internal carotid artery occlusions were studied. CVMR was calculated from relative changes of blood flow velocity within the middle cerebral artery (MCA) measured by transcranial Doppler ultrasonography (TCD) during hypo- and hypercapnia. The configuration of the circle of Willis (COW) was also determined by TCD using common carotid artery compression tests. Anterior, posterior or ophthalmic artery collateral flow, and absence or combinations of these, were differentiated. CT scans were categorized as showing either no infarction (group I; n = 20) or territorial (group II; n = 28), or low-flow infarctions (group III; n = 16). As compared to normal, CVMR was significantly reduced but equal in groups I and II, however, even more reduced in group III. CVMR was lowest, and low-flow infarctions were most frequent in patients whose collateral hemispheric blood supply was from the ophthalmic artery as opposed to patients with a complete or nearly complete COW. Our findings indicate that low-flow infarctions in extracranial ICA occlusions represent brain damage due to a critical reduction in cerebral perfusion pressure, as opposed to thromboembolically induced lesions. The configuration of the COW seems to play the key role. Our findings also support the view that the pattern of hemispheric infarction seen on CT indicates the pathogenesis of stroke.

The case of aphasia or neglect after striatocapsular infarction

The occurrence of aphasia or neglect was related to anatomo-structural (CT/MRI), functional [regional cerebral blood flow (rCBF)] and pathogenetic features [duration of middle cerebral artery (MCA) occlusion and degree of cortical leptomeningeal anastomoses] in 57 cases (26 with and 31 without aphasia or neglect) with strictly subcortical infarcts of one defined type, i.e. striatocapsular infarcts. No distinct pattern of language disturbances was found. Aphasic syndromes did not differ in the amount of involvement of the putamen, pallidum, head of caudate nucleus and white matter. Patients with aphasia or neglect had larger infarcts than those without. However, there was no specific involvement of the basal ganglia, the internal capsule or the deep white matter in patients with aphasia or neglect. Patients with aphasia or neglect had a significantly longer duration of MCA occlusion and mostly poor leptomeningeal collaterals. The cortical rCBF was significantly decreased in the cortical MCA territory in the patients with aphasia or neglect only. The rCBF remained low at follow-up after 1 year and corresponded to focal cortical atrophy on MRI, although neglect had subsided completely in all patients and aphasia had improved considerably in almost 75% of the cases. Aphasia or neglect after striatocapsular infarcts are most likely due to selective neuronal loss of the cerebral cortex due to prolonged MCA occlusion and insufficient collateral blood flow. Individual differences in recovery from aphasia after striatocapsular infarction can be explained in terms of the number of surviving cortical neurons.

Individual patterns of functional reorganization in the human cerebral cortex after capsular infarction

We have previously shown bilateral activation of motor pathways and the recruitment of additional motor areas in studies of groups of patients with recovery from motor stroke. We have now developed a new positron emission tomographic technique to measure the changes in regional cerebral blood flow elicited during a motor task in individual patients, relative to the cerebral activation found in normal subjects. The patterns of cerebral activation in each of 8 individual patients with capsular lesions of the pyramidal tract and complete recovery from hemiplegia are described by comparison with the pattern found in a representative sample of 10 normal subjects. We found a large ventral extension of the hand field of the contralateral (sensori)motor cortex in all patients with lesions of the posterior limb of the internal capsule. Greater activation than in normal subjects was found in variable combinations of the supplementary motor areas, the insula, the frontal operculum, and the parietal cortex. Structures belonging to motor pathways ipsilateral to the recovered limb were also more activated in the patients than in normal subjects. However, additional activation of the ipsilateral (sensori)motor cortex was only found in the 4 patients who exhibited associated movements of the unaffected hand when the recovered hand performed the motor task. We conclude that recovery from motor stroke due to striatocapsular damage is associated with individually different patterns of functional reorganization of the brain. These patterns are dependent on the site of the subcortical lesion and the somatotopic organization of the pyramidal tract, both of which may determine the precise potential for recovery of limb function following this type of brain injury.

The cortical localization of the lexicons. Positron emission tomography evidence

Positron emission tomography was used to investigate changes in regional cerebral blood flow (rCBF) in neurologically normal subjects during word reading and word repetition. The blood flow in these conditions was compared with control conditions where subjects were presented with stimuli of comparable auditory and visual complexity to real words and said the same word on presentation of each stimulus. The control condition for word repetition (hearing spoken words presented backwards) resulted in bilateral activation of the superior temporal gyrus. Word repetition caused a significant increase in rCBF over this control condition in the left superior and middle temporal gyri. The control condition for word reading (seeing stimuli written in 'false fonts', i.e. non-existent letter-like forms) resulted in significant changes in rCBF bilaterally in the striate and extrastriate cortex. Word reading caused a significant increase in blood flow relative to this control in the posterior part of the left middle temporal gyrus. The implications of these results are discussed, and it is argued that they are consistent with localization of a lexicon for spoken word recognition in the middle part of the left superior and middle temporal gyri, and a lexicon for written word recognition in the posterior part of the left middle temporal gyrus.

Functional reorganization of the brain in recovery from striatocapsular infarction in man

We used positron emission tomography (PET) to study organizational changes in the functional anatomy of the brain in 10 patients following recovery from striatocapsular motor strokes. Comparisons of regional cerebral blood flow maps at rest between the patients and 10 normal subjects revealed significantly lower regional cerebral blood flow in the basal ganglia, thalamus, sensorimotor, insular, and dorsolateral prefrontal cortices, in the brainstem, and in the ipsilateral cerebellum in patients, contralateral to the side of the recovered hand. These deficits reflect the distribution of dysfunction caused by the ischemic lesion. Regional cerebral blood flow was significantly increased in the contralateral posterior cingulate and premotor cortices, and in the caudate nucleus ipsilateral to the recovered hand. During the performance of a motor task by the recovered hand, patients activated the contralateral cortical motor areas and ipsilateral cerebellum to the same extent as did normal subjects. However, activation was greater than in normal subjects in both insulae; in the inferior parietal (area 40), prefrontal and anterior cingulate cortices; in the ipsilateral premotor cortex and basal ganglia; and in the contralateral cerebellum. The pattern of cortical activation was also abnormal when the unaffected hand, contralateral to the hemiplegia, performed the task. We showed that bilateral activation of motor pathways and the recruitment of additional sensorimotor areas and of other specific cortical areas are associated with recovery from motor stroke due to striatocapsular infarction. Activation of anterior and posterior cingulate and prefrontal cortices suggests that selective attentional and intentional mechanisms may be important in the recovery process. Our findings suggest that there is considerable scope for functional plasticity in the adult human cerebral cortex.

Type and extent of hemispheric brain infarctions and clinical outcome in early and delayed middle cerebral artery recanalization

We evaluated the influence of time of recanalization or degree of initial leptomeningeal collateral blood flow in cardioembolic or arterio-arterial middle cerebral artery (MCA) occlusion on infarct size and clinical outcome in a series of 34 consecutive acute stroke patients with main stem (N = 31) or major branch (N = 3) occlusions using CT, initial cerebral arteriography (N = 21), repetitive close-meshed transcranial Doppler ultrasonography, and a neurologic stroke scale. We treated 15 patients with tissue plasminogen activator intravenously within the first 6 hours. The type and size of infarction depended on the location of the occluding lesions within the MCA trunk. Proximal MCA occlusion always led to infarction involving the striatum and internal capsule. Sixty-five percent of patients showed recanalization of the occluded MCA within 1 week. Following MCA recanalization, hyperperfusion was present in 38 to 44% of cases. There was a marginally significant relation between size of infarction on CT and recanalization time within the first 24 hours. The more rapidly recanalization occurred, the smaller the size of the infarct. When recanalization time was greater than 8 hours, the lesions always extended to the cortex. An additional good leptomeningeal collateral blood flow significantly reduced the size of the infarct and improved clinical outcome after 17 days and after 10 months. Early recanalization of embolic MCA occlusions within up to 8 hours, in conjunction with good transcortical collateralization, has a favorable impact on infarct size and outcome and may constitute the therapeutic window of opportunity.

[A comparison of MRT and SPECT findings in patients with cerebral microangiopathy]

Lacunar infarctions and periventricular hypodensity are assumed to be typical CT patterns of cerebral microangiopathy (MA). In 17 patients with such findings and in 6 controls without any signs of central nervous system disease cranial CT, MRT and 99mTc-HMPAO-SPECT were employed. Seven patients with CT findings of minor MA demonstrated in comparison to controls no significant difference. In 10 cases with CT findings of pronounced MA periventricular rCBF was significantly reduced compared to controls. rCBF of temporal and parietal cortex was not diminished compared to controls. In 14 patients studied with MRT deep white matter lesions were found which appeared solitary, multiple or confluent. Employing 99mTc-HMPAO-SPECT, cerebral MA revealed rCBF reduction in periventricular brain tissue by cerebellar standardization.

Clinical and hemodynamic aspects of low-flow infarcts

We used single-photon emission computed tomography to measure cerebral blood flow, cerebral blood volume, and cerebral perfusion reserve and transcranial Doppler sonography with CO2 stimulation to assess hemispheric vasomotor reactivity in 37 patients and in normal controls. Computed tomography and magnetic resonance imaging were performed to differentiate morphologically low-flow infarcts (n = 17) from territorial infarcts (n = 20). In patients with either type of infarct, blood flow was decreased and blood volume was increased in the infarcted areas compared with the same areas in the controls. Perfusion reserve and vasomotor reactivity were significantly reduced in patients with territorial infarcts and carotid artery occlusions (n = 12) and even more reduced in patients with low-flow infarcts (p less than 0.001). Both parameters were normal in patients with cardiac embolic territorial infarcts (n = 8). In patients with territorial infarcts, blood flow and perfusion reserve changes were restricted to the infarcted areas, whereas in patients with low-flow infarcts, regions of decreased perfusion reserve considerably exceeded the area of the infarct. Low-flow infarcts are related to the hemodynamic effects of severe extracranial carotid artery disease.

[Anticoagulation in acute cerebral infarct. Benefits, risks, therapeutic failures]

We studied 2 groups of ischemic stroke patients who received therapeutic heparinization during the acute phase in order to prevent thromboembolic reinfarction. 530 patients were studied retrospectively (Group B) and 127 prospectively (Group A). Doses of 24,000-38,000 IE/24 h of heparin were given i.v., resulting in a partial thromboplastin time 2-3 times that of normal controls. Three patients from Group A suffered a massive intracranial hemorrhage. All of them had a large infarction (greater than 5 cm in diameter). They had been given anticoagulants within the first 12 h. Two of them presented with uncontrollable hypertension (systolic BP up to 240 mm Hg). Ischemic reinfarction during the first two weeks occurred in 2.3% and 2.4% of subgroups, respectively. This was less than would have been expected from the literature (approx. 14-15%). Features of these patients were 1.) insufficient heparin dosage, 2.) progression of hemodynamically relevant internal carotid artery lesions leading to critical low-flow or 3.) embolization of a floating thrombus from the internal carotid artery in the middle cerebral artery. It appears that therapeutic heparinization reduces the rate of reinfarction within the acute phase of ischemic strokes. This type of treatment should, however, be confined to patients with an embolic stroke mechanism. Careful surveillance of blood pressure and PTT are prerequisites. Anticoagulation should be avoided in patients with massive infarctions (greater than 5 cm in diameter) or uncontrollable hypertension.