Gray matter – what is it? How it behaves? What is heterotopia?

The human nervous system is a very complex system in the body that is responsible for many different bodily functions. It is in the brain that the processes that are responsible for movement, the functioning of individual organs, speech, thinking and much more take place. One of the elements found in the central nervous system, apart from white matter, is gray matter. What is gray matter? What functions is it responsible for? What diseases and ailments are associated with changes in the gray matter. You can learn all of this in the article below.

What is gray matter?

Gray matter is made of the bodies of nerve cells and in the brain it forms the so-called the cortex of the brain, that is, it is located on the outside. The situation is different in the spinal cord, where the gray matter is inside and the outside is made of white matter. Gray matter plays a very important role in the human body.

What are the functions of gray matter?

Gray matter plays a very important role in the human body. It builds the central nervous system and this is where the popular phrase “gray cells” comes from. The cerebral cortex, which consists of gray matter, is responsible for memory, intelligence, language use, abstract thinking, reading, writing and many other similar mechanisms.

How does gray matter behave?

Although few people know about it, it turns out that gray matter is not a part of our brain that remains unchanged throughout our lives. Scientists have proved that gray matter can shrink, and the efficiency of our brain decreases from around the age of 25. There are many reasons why gray matter shrinks. First of all, it is worth noting that it is adversely affected by: alcohol, drugs and even stress. Fortunately, it also turns out, although for many years it was thought differently, that gray matter also has the ability to regenerate, so some of the so-called gray cells can just recreate.

Features of the structure and function of the gray matter of the brain

Gray matter (substantia grisea) is one of the components of the human central nervous system, which consists of cell bodies (neuron bodies), neuropils (clusters of unmyelinated axons, dendrites, processes of glial cells), synapses, glial cells (astrocytes and oligodendrocytes), and also capillaries.

Gray matter in living tissues is characterized by a gray-brown color, thanks to which it got its name and which is due to its blood capillaries and cell bodies of neurons.

The gray matter in the brain is represented by numerous areas that perform a wide variety of functions:

  • the cerebral cortex, areas of which are the highest centers of various activities and feelings;
  • cerebellar cortex;
  • thalamus (thalamus);
  • subthalamus (nucleus of Lewis – nucleus subthalamicus Luisi);
  • hypothalamus (hypothalamus);
  • basal ganglia;
  • pale ball (globus pallidus);
  • shell(putamen);
  • nucleus accumbens septi;
  • septum core (nucleus septi pellucidi);
  • cerebellar nuclei (spherical (nucleus globosus cerebelli), dentate (nucleus dentatus), tent nucleus (nucleus fastigii cerebelli), corky (nucleus emboliformes));
  • brainstem nuclei (red nucleus (nucleus ruber), black substance (substantia nigra), olive kernels (oliva), etc.;
  • cranial nerve nuclei.

The function of the gray matter of the brain is to control all bodily functions: muscle activity, sensory perception (eg, vision, hearing), memory, emotions, and speech.

Separately, it is worth mentioning the cortex covering the cerebral hemispheres (Latin cortex hemispheria cerebri) and represented, as mentioned earlier, by a layer of gray matter. In another way, it is also called a cloak, or pallium. Its thickness is in different areas, as well as depending on individual characteristics, from 1 to 5 mm.

This structure of the brain developed at the later stages of evolution and is of exceptional importance for the implementation of higher nervous activity, and also ensures the regulation and coordination of all body functions.

Almost half (approximately 44%) of the total volume of the cerebral hemispheres in humans is the cortex, its surface area averages from 1468 to 1670 cm2.

A significant increase in the surface of the human cortex in the absence of a significant increase in the volume of the skull is associated with an uneven growth of individual structures of the gray matter, as a result of which the surface of the cortex becomes covered with convolutions and furrows, folded. As a result, about two-thirds of the entire surface of the cortex is located in the depths of the convolutions and furrows.

The cerebral cortex is closely interconnected with various underlying structures of the brain, from which nerve fibers are sent to it, transmitting information, and which, in turn, are also under the control of the corresponding cortical zones, receiving regulatory responses from them along the nerve pathways.

Heterotopic Gray Matter

What is heterotopia?

As we mentioned in the previous paragraph, gray matter resides on the outside of the brain and the inside of the spinal cord. Sometimes, however, it also appears in other places, and still performs its physiological function. Heterotopias appear in the brain as specific plaques, nodules or streaks of various dimensions. They appear both in groups and independently. The cause of gray matter heterotopia is the migration of the so-called neuroblasts, which most often occurs between the seventh and sixteenth week of gestation.

Subependymal heterotopia (periventricular heterotopia) is the most common form of gray matter (SG) heterotopia, characterized by SG nodules located directly below the ependyma of the lateral ventricles. According to morphology can be divided into:

  • unilateral focal
  • bilateral focal
  • bilateral diffuse: a wavy strip of SW surrounding the ventricles.

Epidemiology

Most cases are sporadic, some are X-linked recessive (Xq28). Women have relatively mild cognitive impairment, subsequently developing epilepsy. In the case of boys, spontaneous abortion occurs, usually due to malformations of the cardiovascular system. The survivors are severely disabled.

Clinical picture

Most often, subependymal heterotopia is associated with epilepsy and developmental delay.

Pathology

Like other types of heterotopias, this type is the result of a violation of neuronal migration. In some cases, the cause of the development of subependymal heterotopia is a violation of cell proliferation.

Gray matter nodules are composed of clusters of neurons and glial cells. It is interesting to note that they are most often found on the right side, presumably due to later migration of neuroblasts from the right side.

X-linked cases show mutations in the gene for filamin-1, a protein that cross-links intracellular actin. In addition, filamin-1 also plays an important role in vascular development.

Diagnostics

MRI is the modality of choice, although periventricular heterotopia is seen on CT and ultrasonography (if the size is very large).

Ultrasound

Subependymal SW nodules are usually hyperechoic compared to normal white matter, and they may also protrude into the ventricular lumen (ventricular undulations).

CT

On CT scan, subependymal heterotopia appears as a non-calcified area of ​​tissue that does not accumulate contrast agent, in density similar to normal gray matter, around the lateral ventricles.

MRI

Antenatal MRI

In late pregnancy, the diagnosis of subependymal heterotopia is relatively clear. Before 26 weeks of gestation, the presence of a normal teleencephalic periventricular germinal matrix makes it difficult to detect, as does fetal movement.

Postnatal MRI

Small nodules of gray matter are observed in the ependymal layer and distort the contour of the ventricles. Most often, localization is in the region of the triangle and occipital horns. Other areas of the brain appear normal.

Gray matter nodules are visualized on all sequences, including post-contrast ones, where, like normal gray matter, they do not accumulate contrast agent.

Differential Diagnosis

  • norm
    • caudate nuclei
    • thalamus
  • subependymal giant cell astrocytoma
    • has a pronounced accumulation of contrast
    • localized near the foramen of Monroe
  • subependymal nodes in  tuberous sclerosis
    • usually calcified (except in early childhood)
    • higher T2 signal than gray matter signal
  • subependial hemorrhage on ultrasound and antenatal MRI [4]
    • although the picture may be similar, the control study in the case of hemorrhage determines the evolution of changes

What types of heterotopias are known and what are their symptoms?

There are three types of heterotopias: subcortical, sub-lined, and banded. The first type is characterized by, inter alia, very early occurrence, already in the first decade of life. Most often it manifests itself with severe developmental disorders, intellectual disability, as well as partial epileptic seizures. This heterotopia differs from the others in that the gray matter, which is usually on the outside of the brain, is inside.

Sub-lining heterotopia is diagnosed, inter alia, on the basis of magnetic resonance imaging, which shows the enlarged walls of the lateral ventricles of the brain. It affects both sexes, although in men the first symptoms, usually in the form of epileptic seizures, usually appear before the age of twenty, and in women after the age of twenty.

The last type are streaked heterotopias, which are the result of genetic mutations. They usually concern women. The name of this heterotopia comes from the fact that the magnetic resonance image shows alternating bands of gray matter and white matter.

Detection of gray matter heterotopia

Gray matter heterotopy can be detected using the magnetic resonance imaging method. However, it is also possible to diagnose these types of changes already in the womb. For this purpose, the so-called aminopuncture, which is usually performed between the 16th and the 20th week of pregnancy. These tests are most often confirmed by computed tomography after the baby is born.

Treatment of gray matter heterotopia

Treatment of gray matter heterotopia is based primarily on the inhibition of the occurrence of epileptic seizures. This can be done with drugs or, for example, by surgical removal of lesions, if we are dealing with drug-resistant epilepsy. In more serious cases of gray matter heterotopia, surgery may be necessary, even in the first hours of a child’s life. Therefore, heterotopia should be detected as early as possible in order to be able to initiate appropriate treatment promptly.

Prevention, or how to prevent gray matter heterotopia?

In the prevention of gray matter heterotopia, folic acid is of particular importance, which should be taken by pregnant women. Your doctor may recommend that your dose of folic acid be increased if the woman has previously given birth to a child with heterotopia. However, it is worth remembering that folic acid is also of great importance in the period before pregnancy.

Sources

  1. Varun Babu, Frank Gaillard et al. Subpendymal gray matter heterotopia. Radiopedia

  2. Barkovich AJ, Kjos B.O. Gray matter heterotopias: MR characteristics and correlation with developmental and neurological manifestations. (1992) Radiology. 182(2): 493-9. doi:10.1148/radiology.182.2.1732969 – Pubmed

  3. Abdel Razek AA, Kandell AY, Elsorogy LG, Elmongy A, Basett AA. Disorders of cortical formation: MR imaging features. (2009) AJNR. American journal of neuroradiology. 30(1):4-11. doi:10.3174/ajnr.A1223 – Pubmed

  4. Mitchell LA, Simon EM, Filly RA, Barkovich AJ. Antenatal diagnosis of subependymal heterotopia. (2000) AJNR. American journal of neuroradiology. 21(2): 296-300. pubmed

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