Classification of brain tumors in children

In 1926, Bailey and Cushing developed a classification of brain tumors based on a general concept of oncology. According to this concept, tumors develop from cells that are at different stages of morphological and functional development. The authors suggested that each stage of glial cell development corresponds to its own tumor. The modification of the work of Bailey and Cushing is based on the majority of modern morphological and histological classifications.

The modern histological classification of CNS tumors (WHO, 1999) reflects more fully the histogenesis and malignancy of a number of neoplasms due to the use of new methods in neuromorphology, including immunohistochemistry and molecular genetic analysis. Tumors of the central nervous system in children are characterized by the heterogeneity of the cellular composition. They contain neuroectodermal, epithelial, glial and mesenchymal components. The definition of the histological type of the tumor is based on the identification of the predominant component of the cells. The following is a 1999 WHO classification with abbreviations.

Histological variants of tumors of the central nervous system

• Neuroepithelial tumors.
  • Astrocytic tumors.
  • Oligodendroglial tumors.
  • Ependymary tumors.
  • Mixed gliomas.
  • Tumors of the vascular plexus.
  • Glial tumors of unknown origin.
  • Neuronal and mixed neuronal-glial tumors.
  • Parenchymal tumors of the pineal gland.
  • Embryonic tumors.
• Tumors of the cranial and spinal nerves.
  • Schwannoma.
  • Neurofibroma.
  • Malignant tumor of the peripheral nerve trunk.
• Tumors of the meninges.
  • Tumors from meningoepithelial cells.
  • Mesenchymal non-meningoepithelial tumors.
  • Primary melanocytic lesions.
  • Tumors of unknown histogenesis.
• Lymphomas and tumors of the hematopoietic tissue.
  • Malignant lymphomas.
  • Plasmacytoma.
  • Granulocyte sarcoma.
• Tumors from germ cells (germinogenic).
  • The germinom.
  • Embryonic cancer.
  • Tumor of the yolk sac.
  • Choriocarcinoma.
  • Teratoma.
  • Mixed germ cell tumors.
• Tumors of the region of the Turkish saddle.
  • Craniopharyngioma.
  • Granular cell tumor.
• Metastatic tumors.

This classification provides for the definition of several degrees of malignancy of astrocytic and ependemic tumors. The following criteria are used:

• cell pleomorphism;
• mitotic index;
• atypia of nuclei;
• necrosis.

The degree of malignancy is defined as the sum of the four listed histological signs.

Phenotypic classification

In addition to exclusively morphological and histogenetic concepts, there is a phenotypic approach to the classification of CNS tumors. Immunohistochemical and molecular methods are used as a supplement to standard light and electron microscopy, which allows to more accurately and objectively determine the type of brain tumor cells. A number of tumors are phenotypically polymorphous, since they consist of tissues of various genesis. Immunohistochemical study of an atypical teratoid-rhabdomous tumor revealed that rhabdoid cells often express epithelial membrane antigen and vimentin, less often actin of smooth muscle cells. These cells can also express glial fibrillar acidic protein, neurofilaments and cytokeratins, but never express desmin and markers of germ cell-cell tumors. Small embryonic cells express the markers of neuroectodermal differentiation and desmin is unstable. The mesenchymal tissue expresses vimentin, and the epithelium expresses cytokeratins of different molecular weights. Teratoid-rhabdomous tumors have a significant proliferative activity, the labeling index of the proliferative marker Ki-67 in the vast majority of cases exceeds 20%.

Classification of brain tumors in children

Tumors of the brain in children differ from those of adults. Among adults, supratentorial tumors predominantly predominate, mainly gliomas. Most of the neoplasms in infants are infratentorial, about 20% are undifferentiated embryonic tumors. The prognosis determines the biological nature of the tumor and surgical accessibility, therefore, with a different arrangement of histologically similar tumors, the prognosis may be different.

Of the many histological types of brain tumors among children, the most common group of embryonic tumors, consisting of low-grade neuroepithelial cells. According to the WHO classification of 1999, this group includes a medulloblastoma, a supratentorial primitive neuroectodermal tumor, an atypical teratoid-rhabdomoid tumor, medulloepithelioma and ependymoblastoma. The vast majority of tumors are represented by the first three histological types.

Isolation of embryonic tumors is based on the following:

• they occur exclusively in childhood;
• have the same clinical course, characterized by a pronounced tendency to leptomeningeal distribution, which necessitates preventive craniospinal irradiation;
• most tumors of this group (medulloblastoma, supratentorial primitive neuroectodermal tumor and ependymoblastoma) consist mainly of primitive or undifferentiated neuroepithelial cells, although they also contain cells morphologically resembling neoplastic astrocytes, oligodendrocytes, ependymary cells, neurons or melanocytes (some tumors may contain smooth or cross-shaped myofibrils , fibro-collagenous tissue).

Tumors with the above characteristics are typical of the cerebellum (medulloblastoma). However, histologically identical tumors can also occur in the cerebral hemispheres, pituitary gland, brain stem, in the spinal cord. In this case, they are designated by the term "supratentorial primitive neuroectodermal tumor". The division of medulloblastoma and primitive neuroectodermal tumors is based on their molecular and biological properties. The group of embryonic tumors included, due to the high risk of their leptomeningeal spread, and the atypical teratoid-rhabdomous tumors recently identified in a separate histological variant. Histologically, these neoplasms differ from embryonic CNS tumors. They consist of tissues of various genesis - large rhabdoid cells in combination with areas of neuroectodermal, mesenchymal and epithelial origin. In some cases, the tumor can consist only of rhabdomoid cells, two-thirds of tumors have a pronounced small-cell embryonic component.

[1], [2], [3], [4]