Spinal contribution to CSF pressure lowering effect of mannitol in cats

The possible impact of cervical stenosis on cephalad neuronal dysfunction

Earlier observers have speculated on the causal relationships between abnormal CSF circulation and a variety of neurological dysfunctions. Such speculations have been at least partially validated by recent evidence and inquiries contravening the traditional static viewpoint of CSF circulation. More contemporary inquiries establish a number of factors which influence both CSF production and absorption (sleep disturbance, neck position, cerebral metabolism, brain atrophy, medications, etc.). Thus, transient periods of abnormality are possibly mingled with periods of normality. Such episodic alterations suggest that the physiological arrangements which underpin CSF circulation may be in some ways likened to blood pressure alterations, in that long-standing CSF abnormalities may be both unappreciated and gradual, though virulent enough to cause substantial neurological injury. We suggest that cervical stenosis (blocking an important CSF decompressive pathway into the vertebral canal) is among the largely unappreciated causes of abnormal CSF circulation and may play a role in cephalad neuronal dysfunction. Such a blockage is correlated with age and easily assessed by cine MRI study. Indeed, episodic disturbances can diminish CSF cerebral flow circulation increasing deposition in cerebral parenchyma of contrary metabolic products (e.g. beta Amyloid), possibly having a causal influence on senile dementia. Additionally, cervical stenosis, by increasing posterior fossa cerebral pressure, could play a causal role in a number of afflictions, among them sleep apnea, concomitant respiratory and circulatory dysfunction, hypertension, chronic occipital headaches, tinnitus, etc. We further suggest that among those patients with substantial cervical stenosis (extensive enough to block CSF circulation in the cervical area as identified by cine MRI) appropriate comparative clinical studies could be undertaken to demarcate associations with presenile dementia, sleep disturbance and posterior fossa dysfunction. Additionally, we suggest that an intracranial monitoring implant be perfected to chronically monitor both intracranial pressure and CSF flow - a monitoring device comparable to the rather less invasive sphygmometric evaluation of blood pressure. If such speculations prove correct, different therapeutic regimens which might improve outcome could be imagined. Among them better sleep hygiene (to by position maximize CSF flow) and possibly more aggressive operative decompressive intervention to diminish cervical obstruction.

Experimental Spinal Stenosis in Cats: New Insight in Mechanisms of Hydrocephalus Development

In our new experimental model of cervical stenosis without inflammation we have tested hypothesis that cranio-spinal communication impairment could lead to hydrocephalus development. Spinal and cranial cerebrospinal fluid (CSF) space separation was obtained with positioning of plastic semiring in epidural space at C2 level in cats. Brain ventricles planimetry, and CSF pressure recording in lateral ventricle (LV) and lumbar subarachnoid space (LSS) were performed in acute and subchronic experiments. In all experiments opening CSF pressures were normal. However, in acute experiments, an infusion of artificial CSF into the LV led to increase of CSF pressure and significant gradient pressure development between LV and LSS due to limited pressure transmission. After 3 or 6 weeks spinal cord atrophy was observed at the site of cervical stenosis, and pressure transmission from LV to LSS was improved as a consequence of spinal tissue atrophy. Planimetry of both the coronal brain slices and the ventricles' surface showed that control ventricular surface was 0.6 ± 0.1% (n = 5), and 1.6 ± 0.2% (n = 4) in animals with subchronic cervical stenosis (P < 0.002). These results support the mentioned hypothesis claiming that CSF volume cranio-spinal displacement impairment could start pathophysiological processes leading to development of hydrocephalus.

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.

Reassessing cerebrospinal fluid (CSF) hydrodynamics: a literature review presenting a novel hypothesis for CSF physiology

The traditional model of cerebrospinal fluid (CSF) hydrodynamics is being increasingly challenged in view of recent scientific evidences. The established model presumes that CSF is primarily produced in the choroid plexuses (CP), then flows from the ventricles to the subarachnoid spaces, and is mainly reabsorbed into arachnoid villi (AV). This model is seemingly based on faulty research and misinterpretations. This literature review presents numerous evidence for a new hypothesis of CSF physiology, namely, CSF is produced and reabsorbed throughout the entire CSF-Interstitial fluid (IF) functional unit. IF and CSF are mainly formed and reabsorbed across the walls of CNS blood capillaries. CP, AV and lymphatics become minor sites for CSF hydrodynamics. The lymphatics may play a more significant role in CSF absorption when CSF-IF pressure increases. The consequences of this complete reformulation of CSF hydrodynamics may influence applications in research, publications, including osteopathic manual treatments.

Direct venous spinal reabsorption of cerebrospinal fluid: a new concept with serial magnetic resonance cisternography in rabbits

OBJECT

For nearly 100 years it has been believed that the main reabsorption of CSF occurs in arachnoid projections into the superior sagittal sinus, but a significant number of experiments and cases conflict with this hypothesis. According to recently published studies, CSF is permanently produced and absorbed in the whole CSF system. Clusters of arachnoidal villi, which are speculated to have a role in the reabsorption of CSF, have recently been revealed in the dorsal root of the spinal nerves. Huge absorptive surface areas of microvessels have been suggested to serve a putative role in reabsorption. The authors' aim was to observe direct venous connections between the subarachnoid space and the perispinal veins.

METHODS

Eleven adult (6 months old) New Zealand white male rabbits weighing approximately 3.0 kg each were used in this experiment. After obtaining precontrast MR cisternography images, subarachnoid access was gained percutaneously via a cisternal approach by using a 20-gauge intravenous indwelling cannula. One rabbit died as a result of brainstem trauma during percutaneous cannulation before contrast administration, but contrast agent was still injected to see the possible MR imaging results of spinal CSF reabsorption after death. Magnetic resonance imaging was performed at 15, 60, 120, and 180 minutes after the administration of contrast agent. After intramuscular injections of anesthetic, 2 rabbits died 120 and 150 minutes after contrast injection, but the MR imaging study at 180 minutes after contrast injection was still performed.

RESULTS

Direct connections between the subarachnoid space and the perispinal veins were observed in all rabbits during serial MR cisternography. The enhancement power was not affected by the amount of injected contrast agent or by cervical or lumbar penetration but was increased at higher contrast concentrations or upon seizure (physical activity).

CONCLUSIONS

Extracranial reabsorption of CSF has been finally proved with direct radiological confirmation of spinal venous reabsorption of CSF using serial MR cisternography. The authors believe that this study can help to develop a more accurate model of CSF dynamics, which will allow understanding of many CSF-related diseases, as well as the development of new strategies for treatment.