What is the choroidal plexus?
The plexus choroideus is a collection of intertwined blood vessels. Both veins (running towards the heart) and arteries (running away from the heart) are involved in the formation of the plexus. They are all located in cavities inside the brain (brain ventricles), which are filled with cerebrospinal fluid (liquor). The function of the choroideal plexus is to form the cerebrospinal fluid and deliver it to the ventricles.
Anatomy of the choroidal plexus
The plexus choroideus is composed of two layers. The inner layer (lamina propria) consists of a specialized form of the soft meninges (pia mater). It contains richly branched, tiny blood vessels (capillaries).
The capillaries represent the transition between veins and arteries. The outer layer (lamina epithelialis) consists of likewise specialized supporting cells of nerve tissue. This special type of cells is called ependym cells.
They filter the blood from the inner layer and thus produce the cerebrospinal fluid (liquor). There are several plexus choroideus. They are located in liquor-filled cavities inside the brain (brain ventricle).
There are 4 brain ventricles. The first two (lateral ventricles) are located next to each other, one in each hemisphere of the brain. The third and fourth ventricles are located below the lateral ventricles.
The fourth ventricle is connected to the spinal canal (Canalis centralis). The cavities are interconnected by holes and small passages. The plexus choroideus is located in the lateral ventricles, mainly on the inside of the underside.
In the third and fourth ventricles it is located more on the upper side. The fourth ventricle has a special feature: small holes (Apertura lateralis, Foramen Luschkae) are found on the sides of the fourth ventricle. A part of the choroidal plexus passes through these holes to the outside. This structure is called Bochdaleck’s flower basket because of its shape.
Function of the choroidal plexus
The task of the choroidal plexus is to form the cerebrospinal fluid. It produces about 500 ml of cerebrospinal fluid per day. The choroid plexus thus renews the entire cerebrospinal fluid several times a day.
The cerebrospinal fluid is essential for the brain to survive. It contains the brain as if it were floating in water. This protects it from shocks.
In addition, the buoyancy of the cerebrospinal fluid reduces the weight of the brain. This also prevents injuries caused by the effect of pressure. Another important function of the cerebrospinal fluid is the disposal of waste products from the nerve cells of the brain.
During the metabolism of the nerve cells, substances are produced which the nerve cells can no longer use. They are released into the cerebrospinal fluid. This transports them with its flow direction into the lymphatic system.
The plexus choroideus ensures that there is enough cerebrospinal fluid to perform these tasks. It produces cerebrospinal fluid by filtering the blood from the capillaries of its inner layer. The liquid of the blood (the blood plasma) is separated from the solid components of the blood (the blood cells).
The ependymal cells of the choroid plexus also release other substances into the fluid obtained in this way, such as sodium, magnesium, chloride, glucose and vitamins. This leads to an increased concentration of these substances in the liquor and serves to supply the nerve cells with an optimal amount of these substances. Plexus choroideus cysts are cysts in the tissue of the plexus chroideus.
Cysts are closed, newly formed cavities in an organ. In the plexus choroideus they are found almost exclusively in unborn children. They can occur singly or in several places.
They are usually only a few millimeters in size. In most cases, the cysts do not cause any problems. They occur relatively frequently in 1-2:100 children.
In the course of pregnancy (until the 28th week of pregnancy) they usually recede on their own. In most cases, the plexus-choroidal cysts are noticed during an ultrasound examination (sonography) of the pregnant woman and the child. Such findings can lead to great uncertainty and concern.
However, plexus-choroidal cysts do not represent a disease. The cyst itself does not affect the child’s brain development before birth. In extremely rare cases, the cysts can be so unfavorably located that they block the outflow of cerebrospinal fluid and accumulate cerebrospinal fluid in the child’s head (internal hydrocephalus).
This rare complication usually only occurs after birth and can be treated. If the plexus choroidal cysts occur during an otherwise unremarkable pregnancy, they are usually completely harmless.Statistically, however, they are associated with an increased risk of chromosomal aberration. Especially the risk for trisomy 18 (Edwards syndrome), i.e. the presence of three chromosomes 18, is increased in this case.
This risk is slightly increased again when the mother is over 35 years old or the plexus-choroidal cysts appear on both sides. Therefore, a more detailed ultrasound examination (fine ultrasound) of the child should be performed. In addition, the existence of the cysts should be checked via the 28th SSW.
Invasive diagnostics (amniocentesis or chorionic villus sampling) can also be used to exclude chromosomal aberration. In these examination methods, the amniotic fluid or part of the placenta is punctured. This increases the risk of miscarriage by up to 2%.
The risk of having a child with chromosomal aberration is significantly lower if the findings are inconspicuous. Therefore, if the findings are inconspicuous, such an examination should be considered very critically. If the findings are conspicuous, there is the possibility of having an invasive diagnostic consultation.
This should be done by a human geneticist or a physician with appropriate training. The individual risk should be calculated and explained during the consultation. Tumors in the plexus choroideus can be benign or malignant.
The benign form is known as plexus papilloma, the malignant form as plexus carcinoma. In 80% of cases, a plexus choroideus tumor is a plexus papilloma. Tumors of the choroideal plexus usually occur in infancy or childhood, later they become significantly less frequent.
The tumor often produces liquor. It can also block the outflow path of the liquor. This leads to an accumulation of fluid in the brain, the so-called hydrocephalus.
This can lead to increased pressure on the brain and other symptoms such as headaches, nausea, vomiting and seizures. The diagnosis is made by imaging procedures such as computer tomography, magnetic resonance imaging or a biopsy of the tumor. The therapy consists of a possibly complete microsurgical removal of the tumor, possibly followed by radiotherapy.
In the case of plexus papilloma, the chances of survival after therapy are good. Only rarely does the tumor metastasize or cannot be completely removed. The plexus carcinoma, on the other hand, often metastasizes.
Therefore, the prognosis is unfortunately not favorable. The diagnosis is made by imaging techniques such as computer tomography, magnetic resonance imaging or a biopsy of the tumor. The therapy consists of a possibly complete microsurgical removal of the tumor, possibly followed by radiotherapy.
In the case of plexus papilloma, the chances of survival after therapy are good. Only rarely does the tumor metastasize or cannot be completely removed. The plexus carcinoma, on the other hand, often metastasizes.
Therefore, the prognosis is unfortunately not favorable. Calcification of the plexus choroideus is the deposition of solid substances in the area of the plexus choroideus. This does not necessarily have to be calcification, proteins can also lead to this picture.
Calcifications are usually noticed as a random finding in imaging procedures such as magnetic resonance imaging or computer tomography. Since calcification occurs in a relatively large number of people, especially at an advanced age, it is currently assumed that it has no disease value. In some cases, calcification may indicate vascular calcification of the vessels of the brain (arteriosclerosis) or minor trauma. Very rarely, an increased incidence of brain tumors has also been observed.
