Cerebrospinal Fluid – CSF
Copyright 2010
Definition
The cerebrospinal fluid is a transparent colored liquid that bathes the brain and spinal cord. It circulates through the subarachnoid space, cerebral ventricles and the central spinal canal constituting a volume of around 100-150 ml at normal conditions.
The fluid is composed of sodium, potassium, calcium, chlorine, inorganic salts (phosphates) and organic compounds (glucose).
It is produced by in the choroid plexus of the four brain ventricles, especially the lateral ventricles at a rate of 0.35 ml/min or 500 ml/day.
The circulation of cerebrospinal fluid starts in the lateral ventricles, continues into the third ventricle through the interventricular foramina (or foramina of Monro) and then passes through the cerebral aqueduct (aqueduct of Sylvius) to the fourth ventricle. From there it flows through a set of foramina – the median aperture (foramen of Magendie) and two lateral apertures (of Luschka), to enter the cisterna magna (cerebellomedullary cistern), a large fluid reservoir located behind the medulla oblongata and below the cerebellum.
Many diseases alter its composition and its study is important and often decisive in meningeal infections and bleeding carcinomatosis for example. It is also useful in the study of demyelinating diseases of the central or peripheral nervous system.
The cisterna magna is continuous with the subarachnoid space. Then, most of the cerebrospinal fluid flows through this space to the brain. From the subarachnoid spaces, the fluid flows in multiple arachnoid villi or granulations that project into the sagittal sinus and other venous sinuses. Finally, it drains into the venous system through the villi surface.
Third ventricle
The third ventricle represents the central cavity of the first brain vesicle. It is a narrow cavity in the diencephalon. It serves as a cushion to protect the brain from impacts that would otherwise damage the important structures contained in the diencephalon.
Shape
It is shaped like a triangle whose apex is at the bottom.
A longitudinal groove, the sulcus of Monro, which extends from the foramen of Monro to the aqueduct of Sylvius, divides the walls of the ventricle into two parts, one superior and inferior.
It has four major recesses, named after the structures they are related to: a suprapineal recess, and immediately posterior to it a pineal recess. Continuing further down, the infundibular recess is present, and finally, the optical recess.
Size
The upper part is oval and its long axis (anteroposterior) measures 7 to 8 millimeters; the lower part measures 15 mm, and has the form of a triangle with its base directed upward.
Position
It situated below the corpus callosum and between the thalami. Its floor is formed by the hypothalamus, the anterior wall by the lamina terminalis. It is middle and symmetrical. It communicates with the fourth ventricle through the aqueduct of Sylvius and with the lateral ventricles by the interventricular holes.
Character
Essentially a cavity whose walls are covered with ependyma, filled with CSF.
Lateral ventricles
The lateral ventricles are two cavities that are arranged symmetrically on either side of the midline, extending longitudinally from the frontal to the occipital lobe. Each begins at the front lobe, head back to the posterior pole of the thalamus, surround it and then go forward again to the anterior temporal lobe.
At the posterior pole of the optic thalamus, where the ventricle changes direction, it originates a horizontal extension that merges into the occipital lobe. Each ventricle has therefore three parts: the anterior or frontal horn, the posterior or occipital horn, and an inferior horn (also called temporal or sphenoid). Moreover, the three poles converge in a single cavity, at the posterior end of the thalamus.
The lateral ventricles are separated from each other, and both communicate with the third ventricle through the foramen of Monro, located approximately in the middle of the anterior horn.
Shape
Curved shape, like a horseshoe – C-shaped – corresponding to the shape of each half of the brain.
Position
It passes through the four lobes of the brain.
The anterior horn is inferior to the corpus callosum, is separated from the opposite ventricle in the midline by the septum pellucidum and fornix, and is bounded laterally and inferiorly by the head of the caudate nucleus.
The posterior horn remains inferior to the corpus callosum and the optic tracts; it is superior to the medulla and splenium of the corpus callosum.
The inferior horn is inferior to the white matter of the hemispheres and tail of the caudate nucleus. It is superior to the hippocampus.
Character
Essentially a cavity whose walls are covered with ependyma, filled with CSF.
Fourth ventricle
The fourth ventricle is a middle cavity located behind the brain stem.
It constitutes a dilation of the ependymal cavity at the medular-pontine level.
Like all the ventricles, it is lined by an ependymal epithelium that secretes CSF through the choroid plexus.
It communicates above with the third ventricle through the aqueduct of Sylvius, and also communicates with the subarachnoid spaces the foramens of Magendie and Luschka. Below, it continues with the central canal of the spinal cord.
Shape
It has a flattened form from front to rear.
Position
Its anterior face is formed by the dorsal surfaces of the pons and the medulla; a posterior that corresponds to the hilum of the cerebellum.
Character
Essentially a cavity whose walls are covered with ependyma, filled with CSF.
Cisterns
The arachnoid membrane lines the inner surface of the dura mater. By contrast, the pia mater adheres to the central nervous system. This organization implies that on superficial irregularities of the central nervous system, the subarachnoid space increases. The expansion forms a subarachnoid cistern.
Cerebellomedullary cistern
The cisterna magna (or cerebellomedullary cistern) is one of the three principal cisterns. It is located between the cerebellum and the dorsal surface of the medulla oblongata.
This large cistern communicates with the fourth ventricle through the foramen of Magendie. It contains large vessels and the inferior cerebellar tonsils.
In case of intracranial hypertension, these tonsils can migrate to the foramen magnum and compress the medulla located just in front. This constitutes a risk of lumbar punctures.
CSF provides buoyancy suspends it and protects
Allows internal mileu perfect for the brain PH osmolarity – different from other body systems – blood brain barrier