Chiasmal glioma
Chiasmal glioma is a tumor formation based on glial cells located in the area of the visual intersection. The main symptomatic manifestation of chiasmal glioma will be a decrease in vision and a narrowing of its field. Some parts of the field of view may fall out altogether. Symptoms of hydrocephalus or neuroendocrine disorders are also inherent in chiasmal glioma.
The content of the article:
Anatomy of the chiasm
Symptoms of chiasm glioma
Diagnosis of chiasmal glioma
Treatment of chiasmal glioma
Prognosis of chiasmal glioma
Chiasmal glioma
Diagnosis of chiasmal glioma involves conducting visiometry, perimetry, ophthalmoscopy, as well as brain examination by MRI, CT and VP. Stereotactic biopsy is also possible.
Treatment of chiasmal glioma will depend on the characteristics of the patient’s condition and the localization of the tumor itself. The age of the patient is of great importance. Treatment of chiasmal glioma also involves surgical intervention in the form of removal or resection of the tumor. In the future, chemotherapy or radiotherapy may be performed.
Chiasmal glioma accounts for no more than 2% of the total number of brain gliomas. Very often, in its histological structure, the glioma of the chiasm corresponds to an astrocytoma. If we compare chiasmal glioma with other types of optic nerve gliomas, it occurs much more often in patients older than 20 years, and not only in childhood.
It should also be said that in 30% of cases, chiasmal glioma proceeds in parallel with Recklinghausen’s neurofibromatosis, which is a phacomatosis in the form of pigmented formations and clusters of neurofibromas. There may also be the appearance of neurinomas, meningiomas and gliomas localized in different places.
When diagnosing chiasmal glioma in children or young people, treatment should be carried out immediately. The latter is in the competence of neurologists, neurosurgeons and ophthalmologists.
Anatomy of the chiasm
The structure of the chiasm resembles a partial intersection of the optic nerves located at the base of the brain. The hypothalamus is located above the chiasm level, its function is neuroendocrine regulation, which affects the secretory mobility of the pituitary gland. Not far from the most visual intersection is the third ventricle.
In the area of the chiasm, the fibers of the optic nerve begin to cross, which come from the nasal halves of the retina, both on the right and on the left eye. Those fibers that begin in the temporal parts of the retina still remain in their place.
As is known, the visual pathways of the right and left types depart from the surface of the chiasm. They contain the nerve fibers of the medial side of the retina of the eye located on the opposite side, as well as the lateral part of the retina of the eye on its side.
Since the image falling on the retina of the eye has an inverted appearance, information from the opposite half of the field of view of the two eyes enters the cerebral cortex via visual pathways.
Symptoms of chiasm glioma
Chiasmal glioma develops primarily or as a result of the spread of optic nerve glioma into the thickness of the optic junction. In practice, it has been proven that chiasmal glioma spreads along the optic nerve, getting into the orbital cavity, which is dangerous in the form of its germination into the hypothalamus or into the cavity of the third ventricle.
Very often, chiasmal glioma can be accompanied by such a phenomenon as optochiasmal reactive arachnoiditis, which leads to the appearance of adhesive structures or, alternatively, subarachnoid cysts.
According to its clinical manifestations, chiasmal glioma will differ from any other ocular tumor in the direction of its growth and localization.
The main symptoms of chiasm glioma are:
decreased visual acuity;
modification of visual fields;
cerebrospinal hypertension syndrome;
endocrine-metabolic failures.
The cause of visual impairment will be the effect of compression of the optic nerve by a tumor. Another reason may be the destruction of the visual fibers, in which the germinating glioma is involved.
In the case of an increasing proliferation of chiasmal glioma in the direction of the optic nerve, thickening of infiltrated optic fibers is usually observed. This leads to compression of the nerve in the area of the optic canal.
The deterioration of vision in this case can be explained in two ways. It happens that visual acuity decreases even at the initial stage of the development of chiasmal glioma. At the same time, there is a deterioration of one—sided type of vision, whereas the deterioration of vision in the second eye manifests itself only after a while (from several months to several years).
The main characteristic feature of chiasm glioma is its slow but progressive effect, expressed in an asymmetric decrease in the patient’s vision. With the spread of glioma to the level of the eye socket, in addition to a drop in visual acuity, the patient also has a progressive type of exophthalmos.
Changes occurring within the visual fields primarily depend on the localization of the tumor itself. Most often, the glioma is located in the front of the visual intersection, thereby affecting the visual fibers to the site of their transition to the other, opposite side. In this case, they speak of a bitemporal character inherent in the narrowing of the field of vision of one and the second eye. A concentric narrowing of the field of view with partial loss of the image is also possible. In the case of the location of the chiasm glioma in the posterior part (behind the intersection of the optic nerves), homonymous hemianopia occurs — the loss of individual halves of the visual field.
Among other symptomatic manifestations that accompany the growth of chiasmal glioma, contributing to its germination into the hypothalamus region, one can distinguish:
hypersomnia;
fatness;
hypothalamic syndrome;
diencephalic syndrome;
diabetes insipidus type;
hypercorticism;
mental disorder;
early puberty.
Among other symptoms accompanying chiasmal glioma, there are: nausea, a characteristic acute headache and heaviness in the area of the eyeballs. All these symptoms are explained by reactive arachnoiditis. The most pronounced symptoms will be if the glioma grows into the cavity of the third ventricle, while contributing to the onset of occlusive cerebrospinal fluid disorders with a further transition to hydrocephalus.
Diagnosis of chiasmal glioma
Since the first and most important clinical manifestation of chiasmal glioma will be visual impairment, most often the patient at the beginning turns to an ophthalmologist for help. The specialist prescribes an ophthalmological examination, which involves conducting tests to determine visual acuity, as well as conducting computer perimetry and a simple examination of the eyeball.
Perimetry is one of the most important research methods that helps to find out the extent of damage to the visual pathways, getting a clear idea of the location of the glioma.
As is known, at the initial stage of its formation, the glioma of the chiasm does not manifest itself symptomatically in any way. With further ophthalmoscopy, stagnant discs (optic nerves) may be detected, as well as the first signs of primary optic nerve atrophy. Through the examination of the visual VP, the doctor determines the level of the affected area of the optic nerve.
The obtained results of a comprehensive examination by an ophthalmologist, indicating the presence of an extensive process of visual pathways inside the skull, will be a reason to consult a neurologist with further examination of the brain through MRI or CT.
If it is not possible to carry out CT or MRI of the brain, then the doctor prescribes the passage of X-ray of the skull in order to identify the deformation of the Turkish saddle, which with glioma of the chiasm acquires a pear-shaped shape.
In addition, an X-ray of the orbits (oblique projection) can be carried out. If the glioma of the chiasm grows into the plane of the orbit, then the X-ray indicates a corresponding expansion of the visual openings, which can be one- or two-sided, and be about 9 mm.
Tomographic studies of chiasmal glioma
However, it should be remembered that CT or MRI will give a much more accurate result than an X-ray examination. Tomographic methods will help to identify the presence of glioma, its location, the degree of germination in the direction of the optic nerves and the nature of development. In addition, it will be possible to determine the ability of the tumor to germinate into the brain tissue (or hypothalamus).
The main disadvantage of tomography is that this method does not allow to distinguish chiasmal glioma from other types of gliomas of a similar location, because in its place there may be both a teratoma and a ganglioneuroma. It will be possible to carry out a differential diagnosis only through histological examination on the material of the taken tumor cells, which I receive, as a rule, with the help of stereotactic biopsy.
Treatment of chiasmal glioma
Surgical treatment
The main method of treatment of chiasmal glioma will be surgical intervention. It is prescribed in the case of exophytic tumor growth, when visual impairment occurs due to compression of the optic nerve. In the case of germination of chiasmal glioma into the plane of the optic nerve, it is completely removed. However, such a measure is resorted to if there is a danger of complete blindness for the patient.
If the glioma of the chiasm is of a common type, then it is subject to partial resection. If it is removed completely, then the patient may become blind in two eyes. Also, such an operation will lead to endocrine disorders.
If the chiasmal glioma has managed to germinate into the cavity of the third ventricle, then an operation is prescribed to eliminate the progressive type of hydrocephalus. To perform such an operation, an additional operation for dissection of adhesions and further opening of cysts may be prescribed. Usually such cysts are formed as a result of the course of reactive arachnoiditis.
What kind of therapeutic tactics will be chosen by a specialist depends on the localization of the chiasm glioma, its size, the nature of germination, histological content and the age of the patient. The choice of the type of treatment is prescribed by the neurosurgeon.
Conducting radiation or chemotherapy
In addition to surgical treatment of chiasmal glioma, chemotherapy or radiation therapy may be prescribed. If such a diagnosis was made to a child, then radiation therapy will be undesirable, since it can contribute to pronounced endocrine disorders due to the high sensitivity of the diencephalic region to radiation. In addition, radiation therapy can negatively affect intellectual abilities and affect behavioral disorders. The most severe side effect of radiation will be expressed in young children. Therefore, for them, the best solution for the treatment of chiasmal glioma is chemotherapy, whereas radiation therapy is used as a last resort.
Prognosis of chiasmal glioma
The most favorable prognosis for chiasmal glioma will be an exophytically growing type of this tumor, eliminated by surgical intervention.
A partial resection of the tumor with further use of chemotherapy will help stop the germination of glioma. But it should be said that in 20-25% of cases, patients are characterized by the growth of a tumor of a progressive nature.
