Types of brain tumor

Classification approaches to the division of detected brain tumors are determined mainly by two tasks. The first of them is the designation and assessment of the individual variant of the anatomical and topographic features of the location of the brain tumor in relation to the choice of the variant of surgical intervention or the determination of the individual tactics of conservative treatment, the prediction of its outcomes. Based on this, the following variants of the classification of brain tumors have been developed.

In relation to the tentorium cerebelli, supratentorial and subtentorial tumors are distinguished, as well as tumors of the so-called dual localization: supra-subtentorial.

To indicate the breadth of the spread of the tumor process relative to the cranial cavity, intracranial, extracranial, intra-extracranial, and craniospinal tumors are distinguished.

To indicate the relationship of the tumor node to the cranial vault, brain tumors are usually divided into convexital and basal (basis - base).

The anatomical relationship of the tumor node and the brain allows us to distinguish between intracerebral and extracerebral tumors, which are most often attached to the cranial nerves, membranes of the brain, and surrounding tissues.

To display the number of identified tumor foci, the concept of (singularity and plurality) is used; examples of the latter include metastatic tumors, brain tumors in neurofibromatosis, etc.

The anatomical relationship of the diagnosed tumor focus to the primary tumor focus (which may not necessarily be located outside the cranial cavity) allows us to distinguish between primary and secondary (metastatic) brain tumors.

The second approach to Classification is determined by the need to display the pathohistological and, therefore, biological properties of the tumor, which in clinical terms is of decisive importance when choosing a treatment method, assessing its possible scope and radicality, and also when predicting the further course of the disease. In general terms, the modern version of the histological classification of brain tumors has the following form.

I. Tumors of the brain neuroectodermal tissue.

• Glial tumors:
  • astrocytic tumors (astrocytoma, astroblastoma, anaplastic astrocytoma);
  • oligodendrocytic tumors (oligodendroglioma, anaplastic oligodendroglioma);
  • undifferentiated malignant tumors of the glial type (glioblastoma, gliomatosis cerebri).
• Tumors of the ependyma (ependymoma, subependymoma, malignant ependymoma) and neuroepithelial component of the vascular plexus (papilloma, malignant papilloma).
• Tumors of the pineal gland (pinealoma, pinealoblastoma).
• Neuronal tumors (neurocytoma, neuroblastoma),
• Undifferentiated malignant tumors of the neuroectodermal type (medulloblastoma, medulloepithelioma, primitive spongioblastoma).
• Tumors of the cranial nerve sheaths;
  • glial type (neurinoma (schwannoma), malignant schwannoma);
  • mesenchymal type (neurofibroma, malignant neurofibroma - neurogenic sarcoma).

II. Brain tumors consisting of cells of mesenchymal origin.

• Tumors of the meninges (meningioma, arachnoid endothelioma), meningosarcoma, xanthomatous tumors);
• Vascular tumors (hemangioma, hemangiosarcoma, angioreticuloma),
• Primary malignant lymphomas.
• Tumors growing from surrounding tissues (chondroma, chordoma, sarcoma, osteoma, osteoblastoma, olfactory neuroblastoma, etc.).

III. Tumors of the anterior pituitary gland: pituitary adenomas (acidophilic, basophilic, chromophobe, mixed), pituitary adenocarcinoma.

IV. Dysontogenetic tumors of the brain and tumor-like processes originating from cells of embryonic tissues: craniopharyngioma, dermoid cyst, colloid cyst of the third ventricle, heterogeneous cyst, neuronal hamartoma of the hypothalamus.

V. Dysontogenetic brain tumors originating from highly potent germ cells: teratomas, germinoma, embryonic cancer, choroid carcinoma).

VI. Metastatic brain tumors: lung cancer (50%), breast cancer (15%), hypernephroma (5-10%), skin melanoma (10.5%), malignant tumors of the gastrointestinal tract (9.5%) and urinary tract (2%),

This classification is based on the ratio of tumor cells to derivatives of a particular germ layer, which is determined primarily on the basis of pathohistological examination using general and special staining methods and examination at the level of a raccoon microscope. Recently, the identification of the cell type has been carried out on the basis of more precise criteria: by studying the expression of marker genes for each type of normal cells (immunohistochemical examination).

In some cases, the given classification (or its variations) is designated as histogenetic. But this does not mean that brain tumors, designated according to the type of cells defined in their structure, originate from mature cells of the same type. The classification of the identified tumor, for example, as a neurocytomas reflects only the fact that the cells that make it up have an origin and morphology similar to neurons of the brain. But this does not mean that the cells of the said tumor originated from mature neurons of the brain.

In addition, there are other aspects of the histological classification that require further clarification, which will be determined by the development of knowledge about the ontogenesis of the brain and stem cell biology. For example, hormone-producing tumors of the adenohypophysis, as well as craniopharyngiomas, can be defined as ectodermal tumors, since it is from this germ layer that Rathke's pouch is formed, giving rise to the adenohypophysis.

Thus, among primary brain tumors, we can distinguish tumors of the neuroectodermal, mesenchymal, ectodermal type, as well as tumors originating from stem cells with a high level of potency (pluripotent stem cells).

Based on the time of clinical manifestation, brain tumors are usually divided into congenital (symptoms first appear within 60 days after birth) and acquired.

As in general oncology, the definition of the degree of malignancy is applicable to brain tumors, but the quantitative characteristics of this quality are based exclusively on histological, immunohistochemical criteria described for tumors of other localizations. There is no strict link between the concept of malignancy and the clinical picture reflecting its degree in tumors of other localizations. The growth of any tumor within the cranial cavity, regardless of the degree of its malignancy according to histological criteria, sooner or later (determined by the location of the tumor node or the rate of tumor growth) leads to a lethal outcome, which is one of the main manifestations of malignancy from a clinical point of view.

In addition, intracerebral neuroectodermal tumors are most often not surrounded by a capsule and are characterized by an infiltrative diffuse type of growth, which is typical for malignant tumors. And only for such brain tumors as, for example, meningiomas, neurinomas, ependymomas, an expansive type of growth is more typical.

Metastatic brain tumors are most often located at the border between the gray and white matter of the brain, in the tissue of the cranial nerves, along the course of the brain vessels and sinuses of the dura mater, which is determined by the metastasis of tumor cells from the primary focus. Multiple metastases are most often observed in lung tumors and melanoma, while single metastases are observed in breast tumors and hypernephroma.

Tumor cells enter the brain hematogenously, through the arterial bed, and less frequently, using the venous vessels of the spine. In the majority of cases, brain tumors do not produce metastatic growth, but in those rare cases when metastasis occurs, it occurs through the cerebrospinal fluid circulation system (medulloblastoma) and, apparently, by tissue taxis and homing of tumor stem cells (glioblastoma).