Anatomy
The brain ventricles or cerebral ventricles are fluid-filled cavities surrounded by brain tissue and connected to each other by small holes. In them, the so-called cerebrospinal fluid is produced and stored (colloquially called nerve fluid), a nutrient medium for nerve cells, which also serves to protect the brain and nerve structures. The cerebrospinal fluid system consisting of a total of four ventricles is called the inner cerebrospinal fluid space.
The corresponding outer cerebrospinal fluid space runs between the middle and inner meninges. The cerebrospinal fluid flows down from the brain through the spinal canal and surrounds the spinal cord. It can be reached by needle puncture between the vertebral bodies, which is a typical examination option for nerve disorders.
The lateral ventricles or ventriculi laterales are arranged in pairs and located in the two halves of the cerebrum. They are divided into an anterior and posterior horn and a middle section. The so-called plexus choroidei are vein plexuses that extend into the ventricles and are located, among other things, on the inner wall of the two lateral ventricles.
Their task is to produce the liquor. Via the interventricular hole or foramen interventriculare, each lateral ventricle is connected to the third ventricle in the diencephalon. The fourth ventricle is located in the rhombic brain and is connected to the third ventricle via a kind of water channel (aequaductus). It also represents the transition to the outer cerebrospinal fluid space, which is reached via three openings.
Function
The function of the brain’s ventricles is based on the production and unhindered transport of cerebrospinal fluid. It protects the brain and spinal cord from external forces by absorbing shocks from the fluid. At the same time, the cerebrospinal fluid also serves as a nutrient medium for the nerve cells and for the removal of various substances.
Other tasks are still the subject of research at the present time. The cerebrospinal fluid is colloquially known as cerebral fluid and is formed in the plexus choroidei. Each ventricle has a delimited area of this vein plexus on its inner wall.
The vascular cluster produces a so-called ultrafiltrate of the blood by carefully filtering the blood plasma. Around 600 milliliters of cerebrospinal fluid are produced daily in the vascular plexus. The blood-cerebrospinal fluid barrier between capillary blood and cerebrospinal fluid cannot be passed by most substances.
For oxygen, carbon dioxide and water, however, it is continuous. Without continuous absorption (reabsorption) of the nerve water into the bloodstream, the cerebrospinal fluid space would enlarge and lead to a massive increase in pressure within the brain and spinal canal. The cerebrospinal fluid flows out of the cerebrospinal canal into the spinal cord canal on the one hand and into the outer cerebrospinal fluid space between the meninges on the other.
The middle meninges have protuberances, which are also called villi. They absorb the cerebrospinal fluid and conduct it into the veins of the outer meninges and into the lymphatic system. This prevents an increase in intracranial pressure and ensures that the cerebrospinal fluid is exchanged up to four times a day.
A pathological dilatation or enlargement of the cerebral ventricles is colloquially known as hydrocephalus. An internal hydrocephalus is an enlargement of the internal cerebrospinal fluid (within the brain). Accordingly, hydrocephalus externus means an enlargement of the external cerebrospinal fluid space (between the meninges).
An internal hydrocephalus usually occurs as a result of an obstruction of the outflow. The causes can be tumors, bleeding and inflammatory processes. So-called colloid cysts are among the most common causes of cerebrospinal fluid congestion in the ventricle system.
These benign masses grow in the third ventricle. If they lie down in front of the inter-ventricular hole, the outflow of cerebrospinal fluid is no longer guaranteed. Symptoms of colloidal cysts are vomiting, headaches and balance disorders.
In the worst case, they cause an increase in intracranial pressure, which can be life-threatening. Dilatations of the external and internal cerebrospinal fluid space are also a possible consequence when the resorption villi become sticky. A resorption disorder also leads to an increase in intracranial pressure.
Another cause of one of the ventricles is increased cerebrospinal fluid production, for example in the context of an inflammation. If the dilated cavities are in unrestricted communication with each other and there is no increased intracranial pressure, this is called normal pressure hydrocephalus. The following symptoms are typical: Urinary incontinence, gait disorders and dementia.