Types of Brain Tumors
A primary brain tumor is one that begins in the brain or spinal cord. These often do not spread (metastasize), even if they grow quickly. The few brain and spine tumors that do metastasize will usually spread only within the brain and spinal cord spaces and not to the rest of the body.
A brain tumor type called a glioma – even more specifically called glioblastoma – accounts for the majority of primary brain cancer and spine cancers in adults, while a tumor type called a meningioma makes up the large majority of noncancerous tumors. Complicating things is the observation that some meningiomas can behave like malignant tumors, and some gliomas can be treated effectively and remain in remission for many years, if not cured.
Lesion, tumor or cancer?
A lesion is an abnormality – anything from a spot on your skin to a shadow on a chest X-ray. Lesions can be scar tissue, infections, benign cysts or malignant tumors. Usually, a lesion is something your physician isn’t sure about and so recommends further tests.
A tumor is an overgrowth of cells causing an abnormal mass or lump in the body. Some tumors are very slow-growing, do not invade local structures (like bone) and do not spread (metastasize). These are referred to as benign tumors.
A cancer is a type of tumor that can grow quickly, invade local structures or metastasize. Sometimes it can do all of these things. These are referred to as malignant or high-grade tumors.
Gliomas or glial tumors
Gliomas are tumors that arise from glial cells, which make up the supporting architecture of the brain and spinal cord. The most common kinds of glial cells that form tumors are:
- Astrocytes resulting in astrocytomas
- Oligodendrocytes resulting in oligodendrogliomas
- Ependymomas, another type of glial tumor, but one that is grouped separately because it behaves differently
Gliomas can be further divided by their appearance under the microscope, which can relate to how aggressively they behave:
- Grade 1: These gliomas tend to be found mainly in children.
- Grade 2: These low-grade gliomas typically grow slowly.
- Grade 3: These anaplastic gliomas grow at a moderate rate.
- Grade 4: These gliomas are glioblastomas and grow the quickest.
Grade 2, 3 and 4 gliomas are more likely in adults.
All gliomas will infiltrate, or grow into the surrounding normal brain tissue (microscopic clusters of tumor cells migrate away from the main body of the tumor), making it impossible to remove all the tumor cells with surgery. The microscopic amounts of tumor cells remaining after surgery are the target of additional treatment, including radiation and/or chemotherapy.
An additional feature of lower grade gliomas is the possibility of transformation, or changing into a more aggressive type of glioma. This is a reason for ongoing MRI monitoring after initial treatment.
Meningiomas are usually nonmalignant, slow-growing tumors that begin in the meninges, the tissue that covers the brain and spinal cord. These tumors push the normal brain structures out of their way (much like a stone in your shoe will push from outside of your foot) as they grow.
Often, symptoms do not appear until many years have passed.
- Grade 1: These meningiomas are unlikely to regrow after complete removal by surgery.
- Grade 2: These meningiomas have a somewhat higher rate of local recurrence after complete resection.
- Grade 3: These meningiomas are malignant, grow fast and invade the local brain.