Cerebrospinal fluid circulation is a process of the central nervous system that permanently circulates cerebrospinal fluid in the inner and outer cerebrospinal fluid spaces around the brain and spinal cord. The CSF nourishes and protects the brain and spinal cord. Circulatory disturbances increase the volume of circulating CSF and can result in hydrocephalus.
What is cerebrospinal fluid circulation?
Cerebrospinal fluid (CSF) circulation is a process of the central nervous system that keeps cerebrospinal fluid constantly circulating in the inner and outer CSF spaces around the brain and spinal cord. CSF is also known as cerebrospinal fluid and corresponds to a clear fluid that nourishes the human central nervous system while protecting it from injury. The cerebrospinal fluid travels through a system of cavities around the brain and spinal cord. This process is known as cerebrospinal fluid circulation. CSF circulation occurs in both the internal and external CSF spaces, which are connected and communicate with each other via the aperturae laterales and mediana on the fourth ventricle of the brain. In an adult human, the CSF space contains a volume of up to 200 milliliters. This volume is involved in CSF circulation and thus supplies the central nervous system. Up to 700 milliliters of the fluid are newly formed day after day. Since only 200 of it circulate permanently, the rest is reabsorbed. Thus, the intracranial pressure caused by the fluid in the system of a healthy person does not rise to pathological levels.
Function and task
CSF is largely produced in the ventricles of epithelial cells in the choroid plexus. The cells perform ultrafiltration of the blood for this purpose. Ependymal cells are probably also involved in the secretion of the fluid. The CSF circulates around the brain and spinal cord. Originating in the lateral ventricles, the fluid reaches the interventricular foramen at the third ventricle. From there, CSF circulation continues via aqueduct at the fourth ventricle and reaches the central canal in the spinal cord. Via openings inform the foramina Luschkae and the foramen Magendii, the CSF passes into the external CSF space. The circulating fluid must be reabsorbed on a daily basis due to the high level of new formation so that hydrocephalus does not develop. Individual protrusions on the arachnoid take care of the reabsorption. These protuberances project into the venous dura mater of the cranial cavity and are also called arachnoidal villi, pacchioni granulations or granulationes arachnoideae. Similar projections are located in the root pockets on the spinal nerve roots. All of these filter CSF into the veins. Near the root pockets in the spinal canal, the arachnoid becomes the perineurium. Along this junction, a few milliliters of CSF pass every hour to the cranial and spinal nerves, around which they henceforth circulate and later drain to the periphery. In the periphery, the lymphatic system reabsorbs it. The internal CSF space is distinguished from the external CSF space in terms of CSF circulation. Both are located in the central nervous system. The inner CSF space consists of sequentially connected cavity systems from the four cerebral ventricles and the spinal central canal. The inner CSF space is in communication with the inner ear spaces. The spaces communicate specifically via the aquaeductus cochleae. Thus, there is a close relationship between the pressures of the perilymph and those of the CSF. The outer CSF space is spinal. The spinal cord in the vertebral space, like the brain in the skull, is protected by meninges known as the dura mater, the arachnoid mater and the pia mater. The arachnoid mater and pia mater are separated by a fissure-like subarachnoid space in which CSF circulation also occurs. This space corresponds to the outer CSF space.
Diseases and disorders
CSF circulation and especially reabsorption are impaired in so-called CSF outflow disorders. The result of a CSF outflow disorder can be hydrocephalus. The cerebrospinal fluid is formed especially in the two lateral ventricles of the brain. In addition, the third and fourth ventricles are involved in its production. Once the CSF has passed through the ventricles, it reaches the cisterna cerebellomedullaris of the outer CSF space. From this point, in a healthy person, it distributes in the interstitial space around the brain and spinal cord and is reabsorbed into the blood by the arachnoid villi at the superior sagittal sinus.Other outflow paths are present with the outlets of the spinal nerves in the venous plexus or with the lymphatic system. The total amount of CSF permanently circulating averages 150 milliliters and reaches highest 200 milliliters. Because of the high production of CSF in the choroid plexus, in a healthy organism there is a complete exchange of circulating CSF three times a day. The resorption and the production of the fluid are in balance with each other. As soon as a higher than usual amount of CSF is produced, if the connection of the CSF spaces is obstructed or if there is a resorption disorder, a hydrocephalus (water head) develops due to the increasing amount of CSF. When drainage or resorption obstructions are causative, the primary disease is usually meningitis, which manifests secondarily as hydrocephalus. Congenital or early childhood brain malformations or prenatal infections of the fetal brain are also conceivable. In certain cases, hydrocephalus is also preceded by hemorrhage into the brain structures where cerebrospinal fluid circulation occurs. Tumors can also cause problems. Once the intracranial pressure increases, the resistance to resorption also increases. Thus, hydrocephalus or the associated increase in intracranial pressure causes a steadily worsening resorption disorder, which in turn causes hydrocephalus to grow. All CSF circulation disorders can manifest as hydrocephalus and significantly increase the total volume of circulating CSF.