Classification of gliomas

Gliomas are classified according to the morphology of the tumor cells, the degree of malignancy of the tumor cells, and the location of the tumor. Gliomas are classified according to the degree to which their tumor cell morphology resembles that of normal brain glial cells (and not necessarily their true cellular origin) as follows major classifications:

- Astrocytomas - astrocytes

- Oligodendrogliomas - oligodendroglial cells

- Mixed gliomas, e.g., oligodendroglial - - astrocytomas, contain mixed types of glial cells

- Ventricular meningiomas - ventricular meningiocytes Gliomas can be further classified according to the degree of malignancy of the tumor cells on a pathologic basis.

- Low-grade gliomas (WHO grades 1-2), which are well-differentiated gliomas; although these tumors are not biologically

benign, the prognosis for patients is relatively good.

- High-grade gliomas (WHO grades 3-4), which are poorly differentiated gliomas; these tumors are malignant, and patients survive

a poorer prognosis.

Although there are many grading systems for gliomas, the most commonly used is the grading system developed by the World Health Organization (WHO). According to this grading system, gliomas are classified as grades 1 (least malignant and best prognosis) to 4 (most malignant and worst prognosis). Of these, the so-called mesenchymal gliomas of conventional cytopathology correspond to WHO grade 3; glioblastomas correspond to WHO grade 4. Gliomas can be categorized according to where they are located in the brain. The cerebellar vermis (a layer of connective tissue that wraps around the cerebellum) divides brain tissue into supratentorial and infratentorial regions. Accordingly, gliomas are also classified as supratentorial and infratentorial gliomas.

- Supratentorial glioma: Located on the cerebellar vermis, mainly in the cerebral hemispheres, supratentorial gliomas are the most common gliomas in adults (70%).

- Subtentorial gliomas: located under the cerebellar vermis, mainly in the cerebellar hemispheres, are the most common gliomas in children (70%).

- Pontine glioma: located in the brainstem. The brainstem consists of three parts: the mesencephalon, the pontine brain, and the medulla oblongata, with the pontine brain controlling

important functions that include breathing. Surgery in the pontine brain carries significant risks.