Generality
Glioma is a tumor that originates in some particular cells of the central nervous system, the so-called glia cells. Like any tumor, glioma is also caused by a genetic mutation, but the exact cause of this mutation is still being studied.
There are different types of gliomas: their characteristics depend mainly on the type of cell of the affected glia and on the growth rate of the tumor mass. More severe gliomas, such as glioblastoma multiforme, are characterized by a high growth rate.
Knowing a glioma in detail (therefore, location, size and severity) allows you to set the most appropriate therapy.
Severe gliomas always have a poor prognosis.
Brief reminder of what a brain tumor is
A brain tumor is a mass of cells that forms and grows inside the brain in a completely abnormal way, due to a genetic mutation.
Based on the characteristics with which it presents itself, a tumor can be defined in various ways:
- Benign or malignant. Brain tumors characterized by slow growth of the abnormal cell mass are considered benign; Brain neoplasms with fast growth are instead considered malignant.
- Primary or secondary. Primary brain tumors are those that arise directly in the brain or in parts adjacent to it (for example, the meninges or the pituitary gland). Secondary brain tumors, on the other hand, represent the result of a process of metastasis, in where the cells of a neoplasm that arose elsewhere (for example, in the lung) have moved and invaded the brain.
In addition, there is a third, more general classification criterion that distinguishes brain tumors according to the degree of severity. For more information on this, read the chapter on what is a glioma.
What is a glioma?
Glioma is defined as a tumor that develops from glial cells (or glial cells) of the central nervous system; it can therefore affect both the brain and the spinal cord, however, given the rarity with which it arises in the spinal cord, glioma tends to be considered an exclusive neoplasm of the brain.
Figure: a glioma, indicated by the red arrow. It is a multiform glioblastoma. From the site: http://en.wikipedia.org/
WHAT IS THE GLIA?
Inside the nervous system, the glia provides support and stability to the intricate network of neurons inside the human body (the network that has the task of transmitting nerve signals). Furthermore, the cells of the glia communicate with the same neurons. through growth factors and trophic factors (ie nourishment), to keep them healthy and direct their development.
The implantation of the glia is present, with different actors, both in the peripheral nervous system (PNS) and in the central nervous system (CNS): in the PNS, the cells that compose it are the so-called Schwann cells and satellite cells; CNS, on the other hand, its cellular elements are oligodendrocytes, microglia cells, astrocytes and ependymal cells.
Schwann cells (SNPs) and oligodendrocytes differ from the others for two reasons: in addition to wrapping themselves around extensions of neurons (axons), they produce a whitish substance called myelin. Myelin serves to increase the conduction speed of the nerve signal.
- Astrocytes
- Oligodendrocytes
- Microglia
- Ependymal cells
- Schwann cells
- Satellite cells
Figure: a neuron, its main components (body, dendrites, axon and axon terminals), and two glia cells of the CNS (an astrocyte and an oligodendrocyte). It can be seen that both glial cells connect to the neuron, but only the oligodendrocyte also wraps around the axon. From the site: www.monicamarelli.com
DIFFERENT TYPES OF GLIOMI
According to the affected glial cells, there are different categories of gliomas:
- Astrocytomas, because they arise at the level of astrocytes
- Oligodendrogliomas, because the site of origin are the oligodendrocytes
- Ependymomas, because they affect the ependymal cells
- Mixed gliomas, because they affect both oligodendrocytes and astrocytomas at the same time
GRAVITY OF A GLIOMA: THE FOUR DEGREES
As mentioned in the introductory part, brain tumors can also be distinguished according to the degree of severity. There are four grades, from I to IV, and - in addition to taking into account the growth rate - they also take into account the capacity for infiltration and diffusion.
Grade I and II neoplasms are tumors with slow growth and localized in one place; on the other hand, all infiltrating and rapidly growing tumors are considered to be grade III and IV. Over time, it is not excluded that a tumor mass of I or II degree evolves and becomes of III or IV degree.
This classification is very useful especially in the case of gliomas, as they can present with quite different connotations (different growth, different location, etc.).
Some examples of gliomas, divided by degree of severity
- Grade I: pilocytic astrocytoma, subependymoma
- Grade II: Diffuse astrocytoma, oligodendroglioma, pleomorphic xanthastrocytoma
- Grade III: Anaplastic astrocytoma, anaplastic ependymoma, anaplastic oligodendroglioma, anaplastic oligoastrocytoma
- Grade IV: glioblastoma multiforme (it is an astrocytoma)
N.B: pleomorphic xanthastrocytoma is a cross between grade I and grade II.
EPIDEMIOLOGY
Gliomas account for about 80% of primary brain tumors and about 30% of malignant ones.
glioblastoma multiforme, which is one of the most common and deadly brain neoplasms, mainly affects people aged 55 and over.
Grade I and II astrocytomas usually occur in individuals aged 20-30, while anaplastic astrocytomas and oligodendrogliomas predominantly affect individuals in their forties.
Causes
The exact causes, which cause gliomas, have not yet been fully clarified.
However, since it is a form of brain tumor, the researchers believe that at the origin there is a genetic mutation in the glia cells.
What triggered this mutation is still being studied: the only known risk factors are some rare genetic diseases, which due to their rarity cannot explain most gliomas and brain tumors.
KNOWN RISK FACTORS
After numerous scientific studies, researchers have discovered that there are rare conditions, of a genetic type, strongly linked to the onset of brain tumors (in general) and gliomas (in particular).
These predisposing circumstances are:
- Type 1 and 2 neurofibromatosis
- Tuberous sclerosis
What is neurofibromatosis?
Neurofibromatosis is a rare genetic disease that affects the nervous system and alters some functions. To trigger the disorder is the mutation of a gene with a fundamental role in regulating the growth of nerves.
Neurofibromatosis can be passed on from parents to a child, but it can also arise spontaneously at the embryonic level, due to a genetic error.
There are two types of neurofibromatosis, type 1 and type 2, each having their own specific characteristics.
Symptoms and Complications
The symptoms of a glioma are very varied and depend on the size, location and infiltration (grade) of the tumor.
To understand what has just been said, it may be useful to make the following example, which takes into consideration the position of the neoplasm. A tumor in the parietal lobe of the brain (ie in the lateral part) can cause difficulties in speaking, in understanding what is being said, in writing, in reading and in coordinating certain movements; a tumor in the occipital lobe (ie in the back) can cause a decrease in vision.
GENERAL SYMPTOMS
Bearing in mind what has just been stated, the symptoms that could arise are:
- Headache. It represents the most characteristic symptom and that distinguishes all brain tumors. It is caused by the push of the tumor mass against the skull and adjacent areas (intracranial pressure); for this reason, it tends to gradually increase in intensity, parallel to the growth of the tumor.
- Sense of nausea and vomiting
- Epilepsy attacks
- Visual disturbances
- Difficulty speaking
- Sudden personality changes in behavior
- Intracranial haemorrhage: especially in cases of glioblastoma multiforme.
Diagnosis
When symptoms lead to suspicion of a brain tumor, the diagnosis process begins with a thorough neurological examination. However, this does not allow us to understand whether it is a glioma or a "other brain neoplasm: to clarify this doubt, we need instrumental tests and the collection of a small sample of tumor tissue (brain biopsy).
NEUROLOGICAL EXAMINATION
During the neurological examination, the doctor subjects the patient to various checks, aimed at assessing vision, hearing, balance, coordination and reflexes. The partial or total loss of one of these abilities provides reliable information on the area. of the affected brain.
INSTRUMENTAL TESTS
Instrumental tests such as computerized axial tomography (CT) and nuclear magnetic resonance (MRI), ensure clear images of the brain and its internal anatomy.
Figure: nuclear magnetic resonance of a glioblastoma multiforme. The so-called enhacement ring, which surrounds the tumor, can be seen.
From the site: www.surgicalneurologyint.com
Through MRI and CT, in fact, information is obtained regarding the site, size and type of the tumor.
For example, glioblastoma multiforme is surrounded by a ring, the so-called ring of enhancement.
THE BRAIN BIOPSY
The brain biopsy takes place after identifying the area affected by the glioma; the examination consists of taking a small portion of the tumor mass and observing it under a microscope.
The characteristics of the tumor cells clarify the nature of the neoplasm: which cells were affected, the degree and malignancy.
Treatment
For the treatment of gliomas, there are several therapeutic approaches. The choice of a particular treatment path and the exclusion of another depends on the following factors:
- Location, size, grade and type of glioma
- Patient's age and state of health
The most commonly practiced treatment is surgical removal of the tumor mass (excision). This operation is very delicate, as it involves performing a craniotomy and removing the tumor without damaging the surrounding healthy parts.
The other treatments adopted consist of: radiotherapy, chemotherapy and radiosurgery. These can be applied either after the surgical removal operation, as a completion of it, or as a stand-alone treatment (for example, if the tumor is in a location inaccessible to the surgeon).
For more information about the aforementioned methods of treatment, the reader is advised to consult the page of the site dedicated to brain tumor (chapter on therapy).
Below, however, you can find the treatment methods implemented in the presence of certain gliomas.
TREATMENT OF I AND II DEGREE GLIOMI
Removal surgery is recommended for patients with grade I and II gliomas, as this operation is usually quite successful: the tumor masses, in fact, are not particularly large and infiltrating, therefore they can be completely removed. and without problems.
Should the surgeon opt for a partial resection of the tumor (for precautionary reasons or because the tumor is in a delicate position), at the end of the operation we proceed with radiotherapy or chemotherapy sessions.
When is surgery not recommended? The only situations that could lead to not operating are the advanced age or the precarious state of health of the patient.
TREATMENT OF GRADE III GLIOMI
The removal of grade III gliomas must always be carried out (if it is in an reachable site) and within the limits of the possible, ie as much tumor mass as possible must be removed.
At the end of the operation, the cycles of radiotherapy and / or chemotherapy are essential to eliminate (hopefully definitively) what remains of the neoplasm.
Unfortunately, even when the surgery is performed in a precise and timely manner, the chances of recovery are very low.
THE TREATMENT OF GLIOBLASTOMA
Glioblastoma multiforme is, as mentioned, the most common severe glioma. It has a fast growth rate and a remarkable infiltration capacity.
The only feasible cure, in these unfortunate situations, consists in the removal of the most consistent part of the tumor, combined with radiotherapy and chemotherapy (exactly as in the case of grade III gliomas, with the only difference that, for glioblastomas, success of the intervention is lower, as well as the subsequent life expectancy).
If there should be a recurrence, it is possible to intervene again and perform another resection of the tumor.
Prognosis
The prognosis for an individual with glioma depends on the type of glioma itself.
As we have seen, in fact, the forms of grade III and IV, in addition to having much more dramatic effects than the forms of grade I and II, are also more difficult to treat.
Another factor not to be overlooked is the age of the patient: young patients have a longer life expectancy after surgery than elderly patients, even if they have been affected by a grade III or IV glioma.
Below is a brief account of the life expectancy of those who have been operated on for glioma.
- Grade I and II gliomas (for example, pilocytic astrocytoma): post-operative life expectancy is high; usually, no relapse occurs.
- Grade III gliomas (for example, anaplastic astrocytoma): the average survival is about 2-3 years.
- Grade IV gliomas (for example, glioblastoma multiforme): the survival rate, after one year, is 30%; after two years, it is 14%.
