By Dr. Loice Swisher, M.D.,Parent/Family Advocate, Website Advisor
Understanding glioma terminology is one of the toughest things about deciphering brain tumors.
Medicine is an evolving science and art, and while much progress has been made in the past decade to help better classify brain tumors, the system is still under constructionђ.Traditionally, pathologists have ownedђ the brain tumor classification system and have based the name of the tumor on the tumor cells from which it is derived.For example, tumor cells that are embryonicђ give rise to medulloblastoma brain tumors.Ependymal tumor cells are the line for ependymomas, and to the point, glial cells are the tumor cells, which directly correlate to glioma brain tumors.
So what is a glial cell?Glial cells are the cells that support the neurons of the brain.There are two different types of glial cells the astrocyte and the oligodendrocyte.The former are the cells that provide the framework for neuron lay out and also nourish these cells.The latter are the cells that wrap around the neuron֒s axon to make the myelin.Following the pathologists logic from above, the astrocyte cells give rise to astrocytomas and the oligodendrocyte tumor cells give rise to oligodendroglioma.(While these cells are in fact quite distinct, there are cases where a tumor can be made up of a mix of the astrocyte and oligodendrocyte cells as well as a mix of neuronal and glial components.When this happens, the tumor is classified as a ganglioglioma.)
Glioma is a broad umbrella and while it gives an overall direction, it does not tell the whole story.To get more specific details about a glioma tumor, there is also a grading system, which is used to further identify a glioma brain tumor.The system is based on a scale of 1 Җ 4 where grades 1 and 2 are generally considered benignђ or low gradeђ (that is the tumor cells look closest to normal cells and tissue architecture under the microscope), grades 3 and 4 are considered higher risk, or high gradeђ as they are faster growing, more infiltrative and more likely to spread (and not surprisingly, these cells tend to have a more abnormal appearance). The World Health Organization updated its brain tumor classification system in 2007 and included astrocytoma brain tumors within the grading structure as follows:
- Grade 1: juvenile pilocytic astrocytoma (JPA), pilomyxoid astrocytoma (PMA), pleomorphic xantrastrocytoma (PXA) and DNETs
- Grade 2: fibrillary astrocytoma
- Grade 3: anaplastic astrocytoma
- Grade 4: glioblastoma multiforme
While cell type and grade provide the rough framework for identifying a glioma brain tumor, there is a third, and final component, which is used to classify a tumor typelocation in the brain.To copy a popular real estate mantra œIt all boils down to location, location, location.Low grade gliomas can occur in essentially any part of the brain, brainstem, cerebellum, thalamus, hypothalamus, optic pathways and cerebral hemispheres.
In conclusion, to fully decipher the type of brain tumor one will benefit from knowing BOTH the tumor type and classification AS WELL as the tumor location.