Common Terminology with Tumor Description
- Astrocyte- One of two types of glial cells in the central nervous system that help support the neural cells. The other type of glial cell is called an oligodenrocyte.
- Astrocytoma- A tumor developed from the glial type of cell called an astrocyte. These tumors are often times further described by location or appearance under the microscope. The microscopy appearance can be into one of 4 grades using the World Health Organization classification.
- Anaplastic Astrocytoma- A synonym used interchangeably for WHO grade 3 astrocytoma.
- Brainstem Glioma- The broadest term to describe all histologic grades of glial tumor that are located in any part of the brainstem (pons, medulla, tectum and cervicomedullary junction). Brainstem gliomas can always be classified more specifically by particular location (e.g.- pontine glioma, tectal glioma, cervicomedullary glioma) and by certain descriptive terms (e.g. diffuse, infiltrative, focal, intrinsic, exophytic and extrinsic).
- Diffuse- An adjective that can be used to describe an infiltrative nature of a tumor as opposed to focal tumors which are more confined or circumscribed. Diffuse tumors are usually a higher histologic grade (3 or 4) but can be low grade. Except in the cases of leptomeningeal spread or gliomatosis cerebri, diffuse is also intrinsic. These tumors cannot be removed as they are like ‘sand in grass’. It has also be described as tentacles in brain tissue being too hard to remove the tumor without severely disturbing the normal tissue.
- Diffuse Brainstem Glioma- This is an infiltrative tumor of glial origin located anywhere in the brainstem. Approximately 80% of these tumors will be in the pons. Thus most, but not all, diffuse brainstem glioma can be more specifically called diffuse pontine gliomas or diffuse intrinsic pontine gliomas.
- Diffuse Pontine Glioma- A glioma (usually an astrocytoma) located in the pons which intermingles and infiltrates normal pontine tissue. Synonyms include diffuse intrinsic pontine glioma or diffuse infiltrative pontine glioma.
- Diffuse Intrinsic Pontine Glioma (DIPG)- A glioma (usually an astrocytoma) located in the pons which intermingles and infiltrates normal pontine tissue. Synonyms include diffuse pontine glioma or diffuse infiltrative pontine glioma.
- Extrinsic- an adjective to describe a tumor that is located on the outside- in this case of the outside of the pons.
- Exophytic- an adjective to describe a tumor that is growing out of the brainstem- like the top part of an iceberg sticking out of the water.
- Focal- An adjective used to describe a tumor that is well defined and does not seem to intertwine with normal tissue. Focal brainstem gliomas are usually histologically grade 1 (also called pilocytic astrocytoma).
- Glial Cell- One of the supportive cells in the central nervous system. These can be either astrocytes or oligiodendrocytes.
- Glioma- A tumor arising from glial cells- either astrocytes or oligodentroctyes. If one can differentiate the cell line from which the tumor derived from then it may be called by a more specific name- an astrocytoma, oligodendroglioma or a mixed tumor. Different adjectives can be applied to the term glioma to convey a more descriptive, specific understanding of the tumor.
- Glioblastoma Multiforme- A synonym used interchangeably for WHO grade 4 astrocytoma.
- Histologic- A term referring to the classification of tissue based on microscopic examination. With gliomas, there are 4 grades based on the WHO classification.
- Intrinsic- An adjective used to describe that a tumor is located on the inside- in this case inside the pons.
- Infiltrative- An adjective used to describe a tumor that is intermixed with normal tumor. A synonym for diffuse.
- Pilocytic Astrocytoma- The lowest histologic grade of tumor. When in the brainstem these tumors tend to be more confined and less infiltrative. They possibly could be operable. These are WHO grade 1 astrocytomas.
- Pons- A specific area of the brainstem located below the midbrain and above the medulla and is connected to the cerebellum through the cerebellar peduncles.
- Pontine- A adjective used to describe the specific location in the pons.
- Pontine Glioma- A tumor of glial origin which is located in the pons.
- WHO Grading of Glial Tumors- The World Health Organization has criteria in categorizing glial tumors by the way they appear under the microscope. Those that appear closer to normal cells are lower grade (1 or 2) and are generally considered less aggressive. Those that look more bizarre/abnormal are higher grades (3 or 4) and typically act as more aggressive.
The number grade and the corresponding terms are considered synonymous and used interchangeably.
- Grade 1-pilocytic astrocytoma
- Grade 2- fibrillary astrocytoma
- Grade 3- Anaplastic Astrocytoma
- Grade 4- Glioblastoma Multiforme