Acta radiologica. Supplementum
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AIMS OF THE PRESENT INVESTIGATION: Observations made in a preliminary study of pulsatile cerebrospinal fluid (CSF) and brain motions using MR imaging called for a reconsideration of the CSF flow model currently accepted. The following questions were addressed: 1) The nature of the CSF-circulation, e.g., the magnitude and pattern of pulsatile and bulk flow; 2) The driving forces of the CSF circulation and assessment of the role of associated hemodynamics and brain motions; 3) The major routes for the absorption of CSF. ⋯ 1) The CSF-circulation is propelled by a pulsating flow, which causes an effective mixing. This flow is produced by the alternating pressure gradient, which is a consequence of the systolic expansion of the intracranial arteries causing expulsion of CSF into the compliant and contractable spinal subarachnoid space. 2) No bulk flow is necessary to explain the transport of tracers in the subarachnoid space. 3) The main absorption of the CSF is not through the Pacchionian granulations, but a major part of the CSF transportation to the blood-stream is likely to occur via the paravascular and extracellular spaces of the central nervous system. 4) The intracranial dynamics may be regarded as the result of an interplay between the demands for space by the four components of the intracranial content, i.e. the arterial blood, brain volume, venous blood and the CSF. This interaction is shown to have a time offset within the cerebral hemispheres in a fronto-occipital direction during the cardiac cycle (the fronto-occipital "volume wave"). 5) The outflow from the cranial cavity to the cervical subarachnoid space (SAS) is dependent in size and timing on the intracranial arterial expansion during systole. Similarly, the outflow from the aqueduct mirrors the brain expansion. The brain expansion is typically very small as evident from the minute aqueductal flow observed in healthy individuals. This expansion occurs simultaneously with an inflow of CSF and will be directed inwards towards the ventricular system. The brain expansion is of decisive importance for the formation of the normal transcerebral pressure gradient. 6) The instantaneous increase of flow in the superior sagittal sinus at the beginning of the systole reflects a direct pressure transmission via the SAS from the expanding arteries to the cerebral veins. It is contended that this early increase in venous pressure together with the volume wave is most likely an important prerequisite for sustaining normal intracranial pressure (ICP) and normal cerebral blood flow. This counter pressure should be reduced in hydrocephalus due to the decreased arterial expansion and could explain the reduced blood flow as well as an increased transmantle pressure gradient causing the ventricular dilatation. An increased pressure in the venous system is likely to be the cause of increases in ICP, including the increased pressure observed in benign intracranial hypertension (BIH).
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Multicenter Study
Radiological aspects of gamma knife radiosurgery for arteriovenous malformations and other non-tumoural disorders of the brain.
The aims of the thesis were to investigate stereotaxic procedures in radiosurgery for cerebral arteriovenous malformations (AVMs) and radiation effects of single session high-dose irradiation delivered by gamma knife on the human brain. Investigation of gamma knife radiosurgery in 1,464 patients constitutes the data base of this thesis. High quality stereotaxic angiography is the gold standard targeting imaging in radiosurgery for cerebral AVMs, particularly for small AVMs or residual AVMs after other treatments. ⋯ Volume effects and depreciation of the steep isodose gradient are hypothesised as the leading factors of the inconsistency. Based on the in vivo assessment of the radiation effects observed on the basically normal human brain it is concluded that irradiation volume is strongly related to the radiation effects and is one of the important considerations in decision making for radiosurgery. Volume of brain tissue exposed to irradiation could be minimised and precision of targeting could be maximised provided that a proper stereotaxic imaging is used.(ABSTRACT TRUNCATED AT 400 WORDS)