Elevation of extracellular glutamate in the final, ischemic stage of progressive epidural mass lesion in cats.

Epidural mass lesions may cause ischemia due to progressive intracranial hypertension. In order to investigate the impact of intracranial pressure on accumulation of neuroactive substances, we gradually raised intracranial pressure in five halothane anesthetized cats by inflation of an epidural balloon. We evaluated in the parietal cortex contralateral to the site of balloon inflation, alterations of extracellular glutamate and purine catabolites and of the lactate/pyruvate ratio in relation to changes of intracranial, cerebral perfusion and mean arterial blood pressure. In a complementary experiment, regional cerebral blood flow was assessed by sequential positron emission tomography. In this simplified mass lesion model, extracellular glutamate increased in all cats at a late, critical stage after tentorial herniation, when intracranial pressure had increased to more than 90 mm Hg, cerebral perfusion pressure had decreased below 40-50 mm Hg. Positron emission tomography assessments revealed that the ischemic threshold for glutamate accumulation was in the range of 15-20 mL/100 g/min. Purine catabolites and the lactate/pyruvate ratio increased somewhat earlier than glutamate, but also after reaching the critical, terminal stage. We conclude that in this model of progressive epidural compression, glutamate-mediated excitotoxic processes at sites remote from the initial focal lesion depend on processes such as delayed ischemia in combination with tentorial herniation and systemic hypotension. These processes seem to be initiated by a decrease of cerebral perfusion pressure below a threshold of 40-50 mm Hg.

In-vivo measurements of regional acetylcholine esterase activity in degenerative dementia: comparison with blood flow and glucose metabolism.

UNLABELLED: Memory and attention are cognitive functions that depend heavily on the cholinergic system. Local activity of acetylcholine esterase (AChE) is an indicator of its integrity. Using a recently developed tracer for positron emission tomography (PET), C-11-labeled N-methyl-4-piperidyl-acetate (C11-MP4A), we measured regional AChE activity in 4 non-demented subjects, 4 patients with dementia of Alzheimer type (DAT) and 1 patient with senile dementia of Lewy body type (SDLT), and compared the findings with measurements of blood flow (CBF) and glucose metabolism (CMRGlc). Initial tracer extraction was closely related to CBF. AChE activity was reduced significantly in all brain regions in demented subjects, whereas reduction of CMRGlc and CBF was more limited to temporo-parietal association areas. AChE activity in SDLT was in the lower range of values in DAT. Our results indicate that, compared to non-demented controls, there is a global reduction of cortical AChE activity in dementia. KEYWORDS: Dementia, cholinergic system, acetylcholine esterase, positron emission tomography, cerebral blood flow, cerebral glucose metabolism.

[F-qi-FDG PET of the thyroid gland in Graves' disease]. / F-18-FDG-PET der Schilddrüse bei Morbus Basedow.

AIM: This study evaluates F-18-FDG PET of the thyroid in Graves' disease. METHODS: Thirty patients were investigated the day before radioiodine therapy, 15 patients 3-10 days after radioiodine therapy. Twenty patients with cancer of the head or neck and normal thyroid function served as controls. RESULTS: F-18-FDG uptake was higher in Graves' disease patients than in controls. Negative correlations of F-18-FDG uptake with half-life of radioiodine and absorbed radiation dose due to radioiodine therapy were found along with a positive correlation to autoantibody levels. CONCLUSION: Thus F-18-FDG PET is likely to give information on the biological activity of Graves' disease as well as on early radiation effects.

Individual functional anatomy of verb generation.

Examination of the individual functional anatomy of language is of particular interest in clinical neurology to explain the variability of aphasic symptoms after focal lesions and to avoid damage of language-related brain areas by surgery. For a silent verb generation task, we examined whether activation PET with 3D data acquisition, multiple replication of conditions, and coregistration with MRI provides results that are consistent and reproducible enough to be useful clinically. Visual analysis was performed on PET-MRI fusion images, including renderings of the brain surface. Quantitative analysis was based on volumes of interest. In seven right-handed normals, activation of the triangular part of the left inferior frontal cortex [Brodman area (BA) 45] was the most significant finding that was present in each subject. Two subjects showed minor anatomical variants of the ascending or horizontal ramus of the sylvian fissure that were associated with the least activation of BA 45. In the left hemisphere the other frontal gyri, the superior temporal and posterior part of the middle temporal gyrus, and the paracingulate gyrus were also significantly activated. There was significant bilateral cerebellar activation, but it was significantly more intense on the right than on the left side. The consistency and high interindividual reproducibility of these findings suggest that this technique may be useful for clinical assessment of language-related areas.

(68Ga)-EDTA positron emission tomography in the diagnosis of brain tumors.

Fifty-two patients with active brain tumors and 8 patients with brain lesions from surgical treatment and/or radio- and/or chemotherapy of their brain tumors were examined by positron emission tomography (PET) using (68Ga)-EDTA in addition to conventional X-ray computed tomography (XCT). All patients with active brain tumors showed abnormal uptake of radioactivity in the tumor region, while all treated patients had normal PET scans. Site and shape of abnormal radioactivity accumulation were in good agreement with the tumor as demonstrated by XCT. Small tumors had a tendency to appear larger in PET than in XCT, while tumors with a mean largest diameter of more than 50.7 mm in XCT usually appeared smaller in PET. Despite considerable overlap to tumor classes with respect to their degree of tracer uptake a highly significant decreasing order of tumor-sagittal sinus ratios of radioactivity (TSR) was found, malignant gliomas ranking highest (median TSR 0.634), followed by meningiomas (median TSR 0.522) and metastases (median TSR 0.391), benign gliomas showing the least uptake (median TSR 0.307). These findings suggest that PET with (68Ga)-EDTA has a high sensitivity supplementing XCT in the diagnosis of brain tumors, and may be helpful in early detection of recurrent tumor growth after therapy.