Glioma is the name given to a primary brain tumor that arises from glial cells. Gliomas account for nearly one-quarter of all primary brain tumors and over 80% of malignant brain tumors. Glioma is an “umbrella” term that includes tumors more specifically labelled as astrocytomas, oligodendrogliomas and ependymomas.
Glial cells (also called glia or neuroglia) serve to support neurons (the actual nerve cells that produce the electrical impulses in the central nervous system). There are four types of glial cells in the brain: astrocytes, oligodendrocytes, ependymal cells and microglia. The glial support structure accounts for about 90% of the cells in the brain.
For the last century, pathologists have classified gliomas by their location, major cell type and general appearance using a microscope. Additionally, gliomas have been subclassified as low grade (Grades I-II) or slow-growing, and high grade (Grades III-IV) or “malignant.”
Currently, there is growing use of molecular markers which are being identified within the tumor. These markers pinpoint genetic mutations which may directly affect the gene code or how it is read and expressed by the cell (epigenetic mutation). Together with its microscopic appearance, these markers now provide a much more precise classification of the tumor which can give further information on how it may behave or respond to treatment.
Diffuse glioma is the most common adult glial tumor. These tumors grow within normal brain tissue and continue to expand by infiltrating or invading the area around the main tumor mass. This invasion by tumor cells makes it difficult to cure this type of tumor using surgery, despite an apparent complete removal on post-operative imaging studies.
- Grade I gliomas have the highest level of cell differentiation (specialized structure and function). These gliomas are slow-growing and less aggressive. Some specific types of grade I tumors can appear to be “encapsulated.”
- Grade II gliomas are also slower-growing tumors whose cells creep or infiltrate into the surrounding brain. Over the course of many years, more genetic mutations can accumulate. The cells become less differentiated (anaplastic) and transform into high-grade tumors. This process is termed malignant transformation.
- Grade III gliomas are also referred to as anaplastic or high-grade gliomas. These tumors are considered malignant or cancerous. They tend to grow rapidly and are more difficult to treat. Certain molecular features in these tumors are tied to the outlook (prognosis) and response to specific treatments.
- Grade IV gliomas are also referred to as glioblastoma. These are the most poorly differentiated glial tumors and, in general, carry the worst prognosis for progression-free and overall survival. Molecular markers are playing an increasingly important role in identifying these tumors’ behavior and their potential response to treatment.
Signs and Symptoms
Symptoms usually depend on the size and location of the tumor. Symptoms can be produced by altered brain function within the tumor area or by the tumor exerting pressure on normal areas. If edema (swelling) develops around a glioma, symptoms may increase or worsen.
Some of the more common symptoms associated with a glioma may include:
- New or worsening headache
- Nausea and vomiting
- Difficulty thinking
- Difficulty speaking or reading
- Blurry vision
- Weakness in an arm and/or leg
- Difficulty with balance or walking
- Confusion, irritability or personality change
- Drowsiness or lethargy
The causes of glioma are not fully understood. Gliomas result from an accumulation of genetic mutations in glial stem cells (which can replicate or make copies indefinitely) or glial progenitor cells (which only divide a limited number of times). The genes suffering a mutation may be involved in cell metabolism, DNA repair, regulation of cell growth and tumor suppression. The only known external cause is exposure to high doses of ionizing radiation.
The presence of symptoms often leads to a physician visit. Many other conditions can produce similar symptoms. Diagnosis begins with the medical history and physical examination. Other tests are then used to establish the diagnosis and help guide treatment. These may include computerized tomography ( CT ) scan of the brain, magnetic resonance imaging ( MRI ) scan, functional MRI ( fMRI ), MRI perfusion scan and/or a positron emission tomography ( PET ) scan. CT is often the first test obtained. Use of a stereotactic biopsy may be indicated in certain situations.
A customized treatment plan is put together for you based on:
- The type, location and size of your glioma
- Your age and general health
- Your ability to tolerate specific treatments
- Your preferences
Depending on the grade, size, location and molecular findings, treatment may include one or a combination of the following options:
- Craniotomy Direct surgery on the brain is called a craniotomy. This type of surgery may be open or minimally invasive. When possible, craniotomy to remove the tumor is often the first step. It establishes the definite diagnosis and provides initial treatment. This surgery is best performed by specialized neurosurgeons experienced in operating on brain tumors. Your neurosurgeon will use magnification, often with a high-powered operative microscope, and a computer-guided imaging system to navigate precisely around the tumor during the craniotomy. Fluorescence-guided resection incorporates a special dye to help define the tumor using the operative microscope. Unfortunately, individual tumor cells may already have crept beyond the apparent border of the tumor into normal brain, which means that additional treatments will be needed. Generally you will stay in the hospital for a few days after surgery, with the length of stay determined by the extent of surgery and your medical condition.
- Other treatments A variety of treatments may be employed to treat the tumor itself. These include chemotherapy, immunotherapy and radiation therapy.
- Steroids These medicines may improve or even provide temporary relief of symptoms from your glioma by reducing the edema (swelling) around the tumor. The most commonly used steroid in neurosurgery is dexamethasone (Decadron®).
- Anti-seizure medicine This type of medicine is used to prevent further seizures. Sometimes, anti-seizure medication may be used for a short period around the time of surgery. A tumor can alter normal electrical activity in the brain which may produce a seizure. This is a surge of synchronized electrical activity that may alter awareness or consciousness, produce repetitive shaking or stiffness or loss of bowel or bladder function.
- Therapies A brain tumor and its subsequent treatments may affect your motor skills, speech, swallowing or even cognitive abilities, depending on its size and location. Physical, occupational or speech therapies may be used to help regain or compensate for any diminished abilities. These rehabilitative therapies may be performed in an inpatient or outpatient setting.
Follow-up care includes regular monitoring of your clinical condition as well as routine surveillance of your imaging studies (usually MRI or CT scans). Often you may be seen in a coordinated fashion by the specialists who have been treating you (neurosurgeon, radiation oncologist and medical oncologist).