Brain stem tumors are neoplasms of the bridge, middle and medulla oblongata. There are many variable symptoms, such as: strabismus, hearing disorder, nystagmus, choking, facial asymmetry, discoordination and gait disorder, dizziness, lower or upper monoparesis, hemiparesis, cerebrospinal hypertension syndrome. The only informative method for diagnosing neoplasms of the trunk to date, which allows determining the presence of a tumor, its nature and prevalence, is MRI of the brain. The possibility of surgical treatment exists only in 20% of cases of stem tumors. In the remaining patients, radio and chemotherapy are used. The prognosis is unfavorable, the majority of patients die in the first year from the manifestation of the disease.
General information
A brain stem tumor occurs mainly in childhood. Children under 15 years of age make up about 70% of patients operated with this diagnosis. The peak occurrence occurs in the 5th-6th year of life. Among cerebral tumors in children, stem neoplasms occupy 10-15%, the vast majority (90%) of them are represented by brain glioma. Localization of neoplasms in the structures of the brain stem is distributed as follows: bridge tumors — 40-60%, midbrain tumors — 15-20%, medulla oblongata tumors — 20-25%. The difficulties of early diagnosis and treatment, morbidity in childhood, high mortality — all these factors put stem tumors among the most pressing problems of oncology, neurology, pediatrics and neurosurgery.
Pathogenetic mechanisms and morphology
The brain stem performs many tasks, the overall result of which is to integrate the work of all departments of the central nervous system with the peripheral NS to regulate the main functions of the body: movement, respiration, cardiac activity, vascular tone, etc. Such interaction is achieved through the pathways leading from the cerebellum, cerebral cortex and lobes of the brain through the trunk to the spinal cord. In addition, the nuclei of the III-XII pairs of cranial nerves are located in the brain stem. The vital importance of the trunk is due to the presence of cardiovascular and respiratory centers in it.
The diversity of both nuclear and conductive structures of the cerebral trunk causes a large variability in the symptoms of its lesion. However, unlike cerebellar tumors, a brain stem tumor is rarely accompanied by cerebrospinal fluid disorders leading to hydrocephalus. The only exception is the neoplasms of the midbrain, localized next to the Sylvian water supply.
Morphologically, in about half of cases, a brain stem tumor is a benign, but diffusely spreading, astrocytoma. From 15 to 30% of stem neoplasms are malignant astrocytomas — glioblastoma and anaplastic astrocytoma. Hemangioblastoma, ependymoma, medulloblastoma, ganglioglioma, astroblastoma, melanoma metastases, etc. are more rarely observed.
Classification
It is generally accepted to divide the neoplasms of the trunk according to the localization principle. In accordance with this, primary and secondary stem tumors of the brain stem are isolated. The first originates directly in the stem tissue, it can be intra-stem and exophytic-stem. The second grows from the membranes of the IV ventricle and cerebellar tissues, then spreading into the brain stem. There are also parastolic tumors, which are classified into closely fused with the trunk and deforming the trunk.
Specialists of the Institute of Neurosurgery have developed a classification of stem neoplasms depending on the type of their growth. It distinguishes nodular tumors, diffuse and infiltrative. Nodular neoplasms are expansively growing, separated from the brain tissues by a capsule of tightly intertwining processes of tumor cells, often having a cystic component. Diffuse brain stem tumor occurs in 80% of cases. Its elements are scattered among the brain tissue so that the boundaries of the tumor are not determined even microscopically. In this case, the elements of the stem tissue are disintegrated and partially destroyed. The most rare is an infiltrative brain stem tumor. Macroscopically, it looks like a formation with well-defined boundaries, for which it received the name “pseudonuclear tumor”. Microscopic examination reveals the infiltrative nature of the growth of the neoplasm with the destruction of the adjacent nervous tissue.
Symptoms
The presence of many structures in the brain stem (CN nuclei, pathways, nerve centers) causes a wide variety of symptoms of its lesion. It should be noted that in children, due to the large compensatory capabilities of the nervous tissue, a brain stem tumor can have a long inapparant course. The symptoms of the onset of the disease largely depend on the location of the stem neoplasm, and the further course depends on the type of tumor process.
There may be a central paresis of the facial nerve, manifested by facial asymmetry, nystagmus, strabismus, staggering when walking, discoordination of movements, dizziness, tremor of the hands, hearing loss, difficulty swallowing and choking. In some cases, muscle weakness (paresis) appears in the arm, leg, or half of the body. As the tumor process progresses, an increase in these symptoms and the addition of new manifestations is observed. In most clinical cases, signs of hydrocephalus (headache, nausea, vomiting) appear in the later stages of the disease. The death of patients occurs due to disorders in the cardiovascular and respiratory centers of the brain stem.
Diagnostics
A preliminary diagnosis is made by a neurologist based on the patient’s medical history and clinical neurological examination. However, the leading importance in diagnostics belongs to neuroimaging studies — CT, MSCT and MRI of the brain. Among them, the most informative is MRI, enhanced by the introduction of a contrast agent. The resolution of MRI makes it possible to detect small tumors that are not visualized during CT. MRI makes it possible to assume the histological type of tumor, determine the presence and prevalence of the exophytic tumor component, pre-evaluate the nature of the growth of the neoplasm and the degree of infiltration of brain tissue. All this information is extremely necessary to assess the possibility and expediency of surgical treatment.
The analysis of MRI data is carried out with the determination of the density of formation, the form of accumulation of contrast (uniform, ring-shaped, uneven), and other parameters. In diffuse and infiltrative tumors, the contrast boundaries often do not correspond to the existing size of the neoplasm. It is possible to propagate changes in the MP signal (mainly in T2 mode) to zones where there is no accumulation of contrast. Such areas can be a zone of edema of brain tissue, a zone of its infiltration, or both at once. The detection of implantation metastases in the walls of the ventricular system and in the spinal subarachnoid spaces during MRI indicates that the tumor belongs to primitive neuroectodermal formations.
According to neuroimaging data, it is possible to differentiate a brain stem tumor from multiple sclerosis, stem encephalitis, demyelinating encephalomyelitis, ischemic stroke, intracerebral hematoma, lymphoma, etc.
Treatment
According to the previously existing opinion, any brain stem tumor appeared to be an infiltrative formation, diffusely sprouting stem structures and therefore not subject to surgical removal. Currently, it has become clear that in addition to diffusely spreading neoplasms (which, unfortunately, are the majority), there are delimited nodular tumors in the trunk, the removal of which is quite possible. In such cases, to decide on the feasibility of surgical treatment, the patient needs a consultation with a neurosurgeon. The dominant principle of stem tumor removal is maximum resection of its tissues with minimal injury to brain structures. In this regard, great hopes are pinned on the development of microneurosurgical techniques of operations.
Unfortunately, about 80% of trunk neoplasms are inoperable. In relation to them, as well as as pre- and postoperative therapy, chemotherapeutic and radiation exposure can be used. Chemotherapy is carried out by a combination of various cytostatic drugs. Radiation therapy makes it possible to achieve symptomatic improvement in 75% of patients. However, in the early stages after the treatment, many of them have a fatal outcome. The radiotherapy technique with an increase in the total radiation dose allowed to slightly increase the life expectancy of children with stem tumors. In 30% of children, the life expectancy after radiotherapy was 2 years.
Stereotactic radiosurgery is an innovative method of treating stem neoplasms today. It is possible to carry out 2 types of procedures: gamma knife and cyber knife. In the first case, a helmet is put on the patient’s head, irradiation is carried out from a variety of sources so that their rays converge at one point corresponding to the localization of the tumor. The effect is achieved due to the total exposure of radiation sources, while the irradiation of healthy brain tissues is minimal, since each beam carries a small gamma energy. The procedure for influencing the tumor with a cyber knife is more automated. The robotic device itself directs radiation to the area of the tumor location, while taking into account its movements in connection with the patient’s breathing or movements. However, so far these methods are effective mainly against benign tumors up to 3-3.5 cm in size.
Forecast
Benign neoplasms of the brain stem, due to their slow growth, can exist for up to 10-15 years, more often having a subclinical course. But, unfortunately, most tumors in this area are malignant in nature and cause death within a few years or months from the onset of symptoms. The treatment carried out in such cases only prolongs the life of patients for a short time.
