Chiasmal glioma is a tumor formation originating from glial cells located in the area of the visual intersection. Disease is manifested by a decrease in visual acuity, narrowing or loss of part of the visual fields, symptoms of hydrocephalus and neuroendocrine disorders. The complex of diagnostic examinations for chiasmal glioma includes visiometry, ophthalmoscopy, perimetry, examination of visual VEP, MRI and CT of the brain, stereotactic biopsy. Pathology is treated depending on its characteristics, localization and age of the patient. This may be surgical intervention (removal or partial resection of glioma, restoration of cerebrospinal fluid circulation), chemo- or radiotherapy.
C72 Malignant neoplasm of the optic nerve
Chiasmal glioma accounts for about 2% of brain gliomas. Most often it has a histological structure corresponding to an astrocytoma. Unlike most optic nerve gliomas, chiasmal glioma occurs not only in childhood, but also in patients older than 20 years. In approximately 33% of cases, chiasmal glioma is accompanied by Recklinghausen’s neurofibromatosis — phacomatosis, characterized by the formation of pigment spots and numerous neurofibromas, the appearance of neurinomas, gliomas and meningiomas of various localization.
The development of chiasmal glioma in children and young people makes its timely diagnosis and effective treatment an important task, which neurology, ophthalmology and neurosurgery are working together to solve.
Anatomy of the chiasm
Chiasm is a partial intersection of the optic nerves located at the base of the brain. Above the chiasm is the hypothalamus, which carries out neuroendocrine regulation and primarily affects the secretory activity of the pituitary gland. Near the visual intersection, the III ventricle is localized.
In the chiasm area, the fibers of the optic nerve intersect, coming from the nasal (medial) halves of the retina of the right and left eyes. The fibers originating in the temporal (lateral) halves of the retina remain on their side. The right and left visual pathways depart from the chiasm, containing nerve fibers from the medial part of the retina of the opposite eye and the lateral part of the retina of the eye on its side. Since the image falls on the retina in an inverted form (from the right field of vision to the left half of the retina and vice versa), each visual pathway carries information to the cerebral cortex from the opposite halves of the visual fields of both eyes.
Chiasmal glioma can occur primarily and as a result of the spread of optic nerve glioma to the area of the optic intersection. For its part, chiasmal glioma is able to spread along the optic nerve into the orbital cavity, germinate into the hypothalamus and III ventricle. Most authors indicate that chiasmal glioma is usually accompanied by optochiasmal reactive arachnoiditis, leading to the formation of adhesions and subarachnoid cysts. Clinical manifestations of chiasmal glioma depend primarily on the location of the tumor and the direction of its growth. They are mainly represented by a decrease in visual acuity, changes in visual fields, endocrine-metabolic disorders and cerebrospinal hypertension syndrome (intracranial hypertension).
Visual disturbances can be caused by both compression of the optic nerve chiasm by glioma and destruction of its optic fibers by a sprouting tumor. With the proliferation of chiasmal glioma along the optic nerve, thickening of the optic fibers infiltrated by the tumor occurs, which leads to compression of the nerve in the optic canal. The decrease in visual acuity is more often bilateral in nature. Sometimes, in the initial period, chiasmal glioma gives only a unilateral deterioration of vision, and the lesion of the second eye manifests itself after several months or even years. Chiasmal glioma is characterized by a slowly progressive and often asymmetric decrease in visual acuity. If the chiasmal glioma spreads to the eye socket, then along with the weakening of vision, progressive exophthalmos is observed.
The change in visual fields directly depends on the location of the chiasm glioma. Most often, the chiasmal glioma is located in the anterior part of the visual intersection and affects the visual fibers before they pass to the opposite side. In such cases, the bitemporal nature of the narrowing of the visual fields of both eyes is noted. There may be a concentric narrowing of the visual fields and the formation of centrally located cattle (areas of image loss). If the glioma of the chiasm is located in its posterior part behind the intersection of the optic nerves, then there is a loss of the eponymous halves of the visual fields (homonymous hemianopia).
Endocrine-metabolic disorders that accompany chiasmal glioma when it germinates into the hypothalamus may include: hypothalamic syndrome, diabetes insipidus, hypersomnia, diencephalic syndrome, obesity, hypercorticism, premature puberty, mental disorders.
Chiasmal glioma may occur with signs of increased intracranial pressure: headache, heaviness in the eyeballs, nausea. Often these symptoms are caused by reactive arachnoiditis. They are most pronounced when the glioma of the chiasm grows into the region of the III ventricle and, causing occlusive cerebrospinal fluid disorders, leads to the development of hydrocephalus.
Since chiasmal glioma begins to manifest itself with visual disturbances, the initial treatment of patients occurs mainly to an ophthalmologist. The doctor conducts ophthalmological testing: determination of visual acuity, conventional or computer perimetry, as well as examination of eye structures. Perimetry is of great importance in the diagnosis of chiasmal glioma, the results of which allow us to determine the level of damage to the visual pathways and get an approximate idea of the localization of the tumor. In the initial period of growth, chiasmal glioma may not produce any changes on the fundus. In the future, during ophthalmoscopy, stagnant discs of the optic nerves are noted, signs of primary atrophy of the optic nerve. To determine the degree and level of damage to the optic nerves allows the study of visual VEP.
The results of a comprehensive ophthalmological examination, indicating the presence of an intracranial volumetric process of the visual pathways, is a reason for consulting a neurologist and conducting an MRI or CT scan of the brain. In the absence of the possibility of tomographic examination, an X-ray of the skull is performed, which reveals a pear-shaped deformation of the Turkish saddle characteristic of chiasm glioma. Additionally, an X-ray of the orbits is performed in an oblique projection. In cases where the chiasmal glioma sprouts into the orbit, one- or two-sided expansion of the visual openings up to 9 mm is determined on radiographs.
Tomographic methods of brain research are much more informative. They allow you to accurately determine the presence of a tumor, its location, size and degree of germination along the optic nerves, in the brain tissue and hypothalamus. However, tomography does not make it possible to distinguish chiasmal glioma from other tumors of this localization (ganglioneuromas, teratomas, reticuloendotheliomas, etc.). This can be done only by histological examination of tumor cells obtained by stereotactic biopsy or during surgery.
Surgical treatment of chiasmal glioma can be used with its exophytic growth, when visual disturbances are caused mainly by compression of the optic nerve. If the chiasmal glioma grows inside the optic nerve, then its complete removal is usually resorted to only in the case of blindness. A common chiasmal glioma is subject to only partial resection, since its complete removal leads to bilateral blindness and significant endocrine disorders. With the germination of chiasmal glioma into the III ventricle, surgical intervention is necessary to eliminate progressive hydrocephalus. For the same purpose, it may be necessary to perform an operation to dissect adhesions and open cysts formed as a result of reactive arachnoiditis. The choice of therapeutic tactics in patients with a diagnosis of “chiasmal glioma” is carried out by a neurosurgeon depending on the localization and size of the tumor, the patient’s age, histological type of tumor, etc.
Along with surgical treatment for chiasmal glioma, radiation therapy and chemotherapy can be used. However, in childhood, due to the high radiosensitivity of the diencephalic region, radiation therapy leads to pronounced endocrine disorders, behavioral and intellectual disorders. The younger the child’s age, the more pronounced the side effects of tumor irradiation are. Therefore, in children with chiasmal glioma, chemotherapy (carboplatin, vincristine) is mainly used, and radiation exposure is carried out only in the absence of the effect of chemotherapy drugs.
The most favorable prognosis has an exophytically growing limited glioma of the chiasm, for which complete surgical removal was possible. Partial resection and subsequent chemotherapy in most cases can stop the growth of glioma. However, in 20-30% of cases, progressive tumor growth is observed after such treatment.