Classification of brain tumours

The classification approaches towards the distinguishing of revealed brain tumours are mainly determined by two tasks. The first of them is denotation and estimation of an individual variant of anatomo-topographic peculiarities of the location of tumour in regard to the choice of a variant of operative intervention or determination of an individual tactics of the conservative treatment, prognostication of its outcomes. On the basis of this, the following variants of the classification of brain tumours have been developed.

In relation to the tentorium of the brain they distinguish supratentorial and subtentorial tumours, as well as tumours of the so called double localization: supra-subtentorial, craniospinal, extra-intracranial.

For the denotation of the width of the distribution of the tumour process in regard to the cranial cavity, they distinguish intracranial, extracranial, intra-extracranial, as well as craniospinal tumours.

For the denotation of the relation of the tumour node to the calvarium, it is accustomed to divide brain tumours into convexital ("convex" is a fornix) and basal ("basis" is a foundation).

The anatomic relationship of the tumour node and the brain allows to distinguish intracranial and extracranial tumours which are most often linked to craniocerebral nerves, arachnoid membranes, surrounding tissues.

To reflect the number of the tumour foci being determined, they use the concepts of singleness and multiplicity (as examples of the latter metastatic tumours, brain tumours in neuroblastomatosis and others can serve).

The anatomic relationship of the tumour focus being diagnosed to the focus of primary arising of tumour (which not necessarily can be outside the cranial cavity) allows to distinguish primary and secondary (metastatic) brain tumours. The second approach to classifying is determined by the necessity of reflection of pathogistologic and, thereby, biological properties of tumour, that in a clinical relation has a determining significance in the choice of a method of treatment, estimation of its possible volume and radicalism, as well as in the prognostication of the subsequent course of disease.

Roughly, the modern variant of histological classification of brain tumours looks as follows:

I. Tumours of neuroectodermal tissue.

1. Glial tumours:

a) astrocytary tumours (astrocytoma, astroblastoma, anaplastic astrocytoma);

b) oligodendrocytic tumours (oligodendroglioma, anaplastic oligodendroglioma);

c) undifferentiated malignant tumours ofthe glial type (glioblastoma, gliomatosis ofthe brain).

2. Tumours of ependima (ependymoma, subependymoma, malignant ependymoma) and a neuroepithelial component of vascular plexuses (papillomas, malignant papillomas).

3. Tumours of the pineal gland (pinealoma, pineablastoma).

4. Neuronal tumours (nuerocytoma, neuroblastoma).

5. Undifferentiated malignant tumours of the neuroectodermal type (medulloblastoma, inedulloepitelioma, primitive spongioblastoma).

6. Tumours of membranes of cranial nerves:

a) of the glial type (neurinoma (schwannoma), malignant schwannoma);

b) of the mesenchymal type (neurofibroma, malignant neurofibroma - neurogenic sarcoma).

II. Tumours consisting of cells of mesenchymal origin.

1. Tumours of arachnoid membranes (meningioma/arachnoidendothelioma), meningosarcoma, xantomatose tumours);

2. Vascular tumours (hemangioma, hemangiosarcoma, angioreticuloma).

3. Primary malignant lymphomas.

4. Tumours extending from surrounding tissues (chondroma, chordoma, sarcoma, osteoma, osteoblastoma, olfactory neuroblastoma and others).

III. Tumours of prepituitary: adenomas of the hypophysis (acidophilic, basophilic, chromophobic, mixed), adenocarcinoma of the hypophysis.

IV. Disontogenetic tumours and tumour-like processes, descending from cells of embryonic tissues: craniopharingioma, dermoid cyst, colloid cyst of III^d ventricle, heterogenous cyst, lipoma, neuronal hamartoma of the hypothalamus.

V. Disontogenetic tumours descending from highly potent germ cells: teratomas, germinomas, embryonic cancer, chorioid carcinoma.

VI. Metastatic tumours: cancer of the lungs (50%), cancer of the mammary gland (15%), hypernephroma (5-10%), melanoma of the skin (10,5%), malignant tumours of the gastrointestinal tract (9,5%), and urinary tracts (2%).

At the basis of this classification the relation of tumour cells to derivatives of a certain embryonic leaf is laid which is determined first of all on the basis of pathogistologic investigation with the help of general and special methods of staining and study at the level of a light microscope. Lately, the identification of a cellular type is performed on the basis of more clear criteria: by the study of expression of genes as markers for every cell type of a normal organism (immunochemical research).

In some cases, the given classification (or its variations) is denoted as histogenetic. But this in no way means that brain tumours, denoted in accordance with the type of cells determined in their structure, descend from mature cells of the same type. Referring the revealed tumour, for example, to neurocytomas just reflects the fact that its constituents have the origin and morphology similar to those the neurons of the brain. But it does not mean in any way that the cells of the mentioned tumour descended from the mature neurons of the brain.

Besides, in the histological classification there are other moments requiring further classification, that will be determined by the development of knowledge about the ontogenesis of the brain and biology of stem cells. For example, hormone-producing tumours of the adenohypophysis, as well as craniopharingiomas, can be defined as ectodermal tumours, as namely from this embryonic leaf Ratke's pouch is formed giving the beginning to the adenohypophysis.

So, among the primary brain tumours it is possible to distinguish tumours of the neuroectodermal, mesenchymal, ectodermal type, as well as tumours descending from stem cells with a high level of potency (pluripotent stem cells).

By the time of clinical display, it is accustomed to divide brain neoplasms into congenital (symptomatology is first displayed during 60 days after birth) and acquired.

As well as in general oncology, in relation to brain tumours the determination of the degree of malignantness is applicable, but here the quantitative characteristic of this quality is based exceptionally on histological, immunohistochemical criteria described for tumours of other localizations. A hard lying up of the concept of malignancy and the clinical picture reflecting its degree in tumours of other localizations is absent. The growth of any tumour within the limits of the cranial cavity, regardless of the degree of its malignancy after histological criteria, sooner or later (which is determined by the location of the tumour node or by the speed of the growth of tumour) results in a fatal outcome, which from the clinical point of view is one of the main displays of malignancy. Apart from this, intracranial neuroectodermal tumours are most often not surrounded by the capsule and characterized by the infiltrative diffuse type of growth which is characteristic of malignant tumours. And only for such brain tumours as, for example, meningiomas, neurinomas, ependimomas the expansive type of growth is characteristic.

Metastatic tumours are more frequently located on the border between the grey and white brain substance, in the tissue of craniocerebral nerves, along the course of the vessels of the brain and sinuses of the dura mater of the brain that is determined by metastasis of tumour cells from the primary focus. Multiple metastases are observed most frequently in tumours of the lungs and in melanoma, while single ones - in mammary tumour, hypernephroma.

Tumour cells get to the brain by the hematogenic way: through the arterial bloodstream, rarer - using the venous vessels of the spine. Brain tumours predominantly do not give metastatic growth, but in those rare cases when metastasis takes place it is performed through the system of CSF circulation (medulloblastoma) and, presumably, by tissue taxis and homing of tumour stem cells (glioblastoma).

Date: 2015-02-16; view: 1091