Measurement of cerebrospinal fluid formation and absorption by ventriculo-cisternal perfusion: what is really measured?

The generally accepted hypothesis on cerebrospinal fluid (CSF) hydrodynamics suggests that CSF is actively formed mainly by the choroid plexuses, circulates unidirectionally along the brain ventricles and subarachnoid space, and is passively absorbed mainly into the dural venous sinuses. CSF formation rate (Vf ) has been extensively studied using the ventriculo-cisternal perfusion technique and the results have been used as the key evidence confirming the mentioned hypothesis. This technique and the equation for Vf calculation are based on the assumption that the dilution of the indicator substance is a consequence of the newly formed CSF, ie, that a higher CSF formation rate will result in a higher degree of dilution. However, it has been experimentally shown that the indicator substance dilution inside the CSF system does not occur because of a “newly formed” CSF, but as consequence of a number of other factors (departure of substances into the surrounding tissue, flowing around the collecting cannula into the cortical and spinal subarachnoid space, departure into the contralateral ventricle, etc). This technique allows “calculation” of the CSF formation even in dead animals, in an in vitro model, and in any other part of the CSF system outside the ventricles that is being perfused. Therefore, this method is indirect and any dilution of the indicator substance in the perfusate caused by other reasons would result in questionable and often contradictory conclusions regarding CSF formation rates

New experimental model of acute aqueductal blockage in cats: effects on cerebrospinal fluid pressure and the size of brain ventricles

It is generally assumed that cerebrospinal fluid (CSF) is secreted in the brain ventricles, and so after an acute blockage of the aqueduct of Sylvius an increase in the ventricular CSF pressure and dilation of isolated ventricles may be expected. We have tested this hypothesis in cats. After blocking the aqueduct, we measured the CSF pressure in both isolated ventricles and the cisterna magna, and performed radiographic monitoring of the cross-sectional area of the lateral ventricle. The complete aqueductal blockage was achieved by implanting a plastic cannula into the aqueduct of Sylvius through a small tunnel in the vermis of the cerebellum in the chloralose-anesthetized cats. After the reconstitution of the occipital bone, the CSF pressure was measured in the isolated ventricles via a plastic cannula implanted in the aqueduct of Sylvius and in the cisterna magna via a stainless steel cannula. During the following 2 h, the CSF pressures in the isolated ventricles and cisterna magna were identical to those in control conditions. We also monitored the ventricular cross-sectional area by means of radiography for 2 h after the aqueductal blockage and failed to observe any significant changes. When mock CSF was infused into isolated ventricles to imitate the CSF secretion, the gradient of pressure between the ventricle and cisterna magna developed, and disappeared as soon as the infusion was terminated. However, when mock CSF was infused into the cisterna magna at various rates, the resulting increased subarachnoid CSF pressure was accurately transmitted across the brain parenchyma into the CSF of isolated ventricles. The lack of the increase in the CSF pressure and ventricular dilation during 2 h of aqueductal blockage suggests that aqueductal obstruction by itself does not lead to development of hypertensive acute hydrocephalus in cats

Physiological Characteristics of Some Monoamine Metabolites in Cat Cerebrospinal Fluid

The concentrations of main metabolites of serotonin and dopamine, 5-hydroxyindoleacetic acid and homovanillic acid, respectively, were measured in cisternal cerebrospinal fluid of cats by high performance liquid chromatography with an electrochemical detector. Higher concentrations of homovanillic acid and a wide interindividual oscillation for both parameters have been found. However, samples collected at four different time intervals showed stabile intraindividual concentrations of the metabolites. The existence of a concentration gradient of both parameters inside the cat cerebrospinal fluid system was confirmed in experiments with a provoked artificial flow of cerebrospinal fluid inside physiological limits. These experiments also suggested that the hydrodynamics of cerebrospinal fluid is the factor responsible for the concentration gradient existence. It appears that the absence of cerebrospinal fluid circulation is the main hydrodynamic reason for the maintenance of 5-hydroxyindoleacetic acid and homovanillic add gradients between various parts of the cerebrospinal fluid system

The application of ultrasound in neuroendoscopic procedures: first results with the new tool »NECUP-2« [Upotreba ultrazvuka u neuroendoskopskim procedurama: prvi rezultati s novim uređajem »NECUP-2«]

In this paper, our experience with originally constructed Neurosurgical Endoscopic Contact Ultrasound Probe »NECUP-2« in neuroendoscopy is reported. Between June 1997 and June 2007, 132 neuroendoscopic procedures have been performed: 102 endoscopic thrid ventriculostomies (ETV), 15 arachnoid cysts and 5 intraventricular tumours operations. The »NECUP-2« was applied effectively in all cases in which blunt perforation was not possible: 38/102 ETV, 10/10 septostomies, 15/15 arachnoid cysts. In five cases of intraventricular tumours, neuroendoscopic procedure was combined with open microsurgery for tumour removal with preservation of vascular structures. There were no »NECUP-2« related complications. Of postoperative complications, we had liquorrhea (9 patients), and symptoms of meningitis (6 patients). In the follow-up period (6 months to 6 years), we had a patency rate of 80% (50/63 patients). All patients improved in clinical status. According to the first results, it seems that ultrasonic contact probe NECUP-2 presents a new device in neurosurgical armamentarium that can be used in various fields of neurosurgery. With minimal and controlled lesion that is produced at the tip of the probe, it can be used in highly demanding operations such as third ventriculostomy and tumour resection

The effects of lumboperitoneal and ventriculoperitoneal shunts on the cranial and spinal cerebrospinal fluid volume in a patient with idiopathic intracranial hypertension

Lumboperitoneal (LP) and ventriculoperitoneal (VP) shunts are a frequent treatment modality for idiopathic intracranial hypertension (IIH). Although these shunts have been used for a long time, it is still not clear how they change the total craniospinal CSF volume and what portions of cranial and spinal CSF are affected. This report for the first time presents the results of a volumetric analysis of the total cranial and spinal CSF space in a patient with IIH. We performed an automated segmentation of the cranial and a manual segmentation of the spinal CSF space first with an LP shunt installed and again after the LP shunt was replaced by a VP shunt. When the LP shunt was in place, the total CSF volume was smaller than when the VP shunt was in place (222.4 cm(3) vs 279.2 cm(3)). The difference was almost completely the result of the spinal CSF volume reduction (49.3 cm(3) and 104.9 cm(3) for LP and VP, respectively), while the cranial CSF volume was not considerably altered (173.2 cm(3) and 174.2 cm(3) for LP and VP, respectively). This report indicates that LP and VP shunts in IIH do not considerably change the cranial CSF volume, while the reduction of CSF volume after LP shunt placement affects almost exclusively the spinal part of the CSF system. Our results suggest that an analysis of both the cranial and the spinal part of the CSF space is necessary for therapeutic procedures planning and for an early recognition of numerous side effects that often arise after shunts placement in IIH patients

The influence of body position on cerebrospinal fluid pressure gradient and movement in cats with normal and impaired craniospinal communication

Intracranial hypertension is a severe therapeutic problem, as there is insufficient knowledge about the physiology of cerebrospinal fluid (CSF) pressure. In this paper a new CSF pressure regulation hypothesis is proposed. According to this hypothesis, the CSF pressure depends on the laws of fluid mechanics and on the anatomical characteristics inside the cranial and spinal space, and not, as is today generally believed, on CSF secretion, circulation and absorption. The volume and pressure changes in the newly developed CSF model, which by its anatomical dimensions and basic biophysical features imitates the craniospinal system in cats, are compared to those obtained on cats with and without the blockade of craniospinal communication in different body positions. During verticalization, a long-lasting occurrence of negative CSF pressure inside the cranium in animals with normal cranio-spinal communication was observed. CSF pressure gradients change depending on the body position, but those gradients do not enable unidirectional CSF circulation from the hypothetical site of secretion to the site of absorption in any of them. Thus, our results indicate the existence of new physiological/pathophysiological correlations between intracranial fluids, which opens up the possibility of new therapeutic approaches to intracranial hypertension

How to teach personcentered medicine during the coronavirus disease 2019 pandemic?

Personalized medicine refers to sophisticated diagnostic and therapeutic interventions tailored to the patient’s individual needs. The development of personalized medicine in the last two decades created a global movement of person-centered medicine and health care. Prominent medical organizations and institutions that advocate a personalized approach to medicine established an international network called the International College of Person-Centered Medicine (1,2)