Development of hydrocephalus and classical hypothesis of cerebrospinal fluid hydrodynamics: facts and illusions

According to the classical hypothesis of the cerebrospinal fluid (CSF) hydrodynamics, CSF is produced inside the brain ventricles, than it circulates like a slow river toward the cortical subarachnoid space, and finally it is absorbed into the venous sinuses. Some pathological conditions, primarily hydrocephalus, have also been interpreted based on this hypothesis. The development of hydrocephalus is explained as an imbalance between CSF formation and absorption, where more CSF is formed than is absorbed, which results in an abnormal increase in the CSF volume inside the cranial CSF spaces. It is believed that the reason for the imbalance is the obstruction of the CSF pathways between the site of CSF formation and the site of its absorption, which diminishes or prevents CSF outflow from the cranium. In spite of the general acceptance of the classical hypothesis, there are a considerable number of experimental results that do not support such a hypothesis and the generally accepted pathophysiology of hydrocephalus. A recently proposed new working hypothesis suggests that osmotic and hydrostatic forces at the central nervous system microvessels are crucial for the regulation of interstial fluid and CSF volume which constitute a functional unit. Based on that hypothesis, the generally accepted mechanisms of hydrocephalus development are not plausible. Therefore, the recent understanding of the correlation between CSF physiology and the development of hydrocephalus has been thoroughly presented, analyzed and evaluated, and new insights into hydrocephalus etiopathology have been proposed, which are in accordance with the experimental data and the new working hypothesis

The formation of cerebrospinal fluid: nearly a hundred years of interpretations and misinterpretations

The first scientific and experimental approaches to the study of cerebrospinal fluid (CSF) formation began almost a hundred years ago. Despite researchers being interested for so long, some aspects of CSF formation are still insufficiently understood. Today it is generally believed that CSF formation is an active energy consuming metabolic process which occurs mainly in brain ventricles, in choroid plexuses. CSF formation, together with CSF absorption and circulation, represents the so-called classic hypothesis of CSF hydrodynamics. In spite of the general acceptance of this hypothesis, there is a considerable series of experimental results that do not support the idea of the active nature of CSF formation and the idea that choroid plexuses inside the brain ventricles are the main places of formation. The main goal of this review is to summarize the present understanding of CSF formation and compare this understanding to contradictory experimental results that have been obtained so far. And finally, to try to offer a physiological explanation by which these contradictions could be avoided. We therefore analyzed the main methods that study CSF formation, which enabled such an understanding, and presented their shortcomings, which could also be a reason for the erroneous interpretation of the obtained results. A recent method of direct aqueductal determination of CSF formation is shown in more detail. On the one hand, it provides the possibility of direct insight into CSF formation, and on the other, it clearly indicates that there is no net CSF formation inside the brain ventricles. These results are contradictory to the classic hypothesis and, together with other mentioned contradictory results, strongly support a recently proposed new working hypothesis on the hydrodynamics of CSF. According to this new working hypothesis, CSF is permanently produced and absorbed in the whole CSF system as a consequence of filtration and reabsorption of water volume through the capillary walls into the surrounding brain tissue. The CSF exchange between the entire CSF system and the surrounding tissue depends on (patho)physiological conditions that predominate within those compartments