By Sally Robertson, BSc
A glioma is a type of tumor originating in the brain or spinal cord that arises from the glial cells. These cells form a tissue called “glia” that surrounds nerve cells to keep them in place and support their function.
Glioma is a common type of brain tumor and accounts for around one third of cases. The tumor may arise from different types of glial cells which include astrocytes, oligodendrocytes and ependymal cells. The tumor is named according to which cell type it originates from. Tumors that arise from a mixture of these cell types are referred to as mixed gliomas.
This tumor originates in the connective tissue cells called astrocytes. The tumor is usually found in the cerebrum, which is the large, external part of the brain. An astrocytoma may also occur in the cerebellum, which is at the back of the brain. Around half of all primary brain tumors are astrocytomas and these are the most common form of glioma. Astrocytomas can occur at any age.
This tumor occurs in the cells that line the brain ventricles or spinal cord. The tumor is soft, grey or red in color and may contain mineral calcifications or cysts. Different types of ependymoma occur in various locations of the brain or spinal cord. Tumors that arise near the ventricle are referred to as subependymomas, while those occurring at the lower end of the spinal column are referred to as myxopapillary ependymomas. These tumors are rare and account for less than 5% of all primary brain tumors. However, they do account for up to 10% of brain tumors that occur in children. In children, these tumors usually develop in those aged under ten years.
This tumor originates in the oligodendrocytes, the supportive tissue cells that are usually found in the cerebrum. Oligodendroglioma usually occurs in the frontal and temporal lobes. These tumors accounts for around 5% of primary brain tumors and they usually affect young or middle-aged adults. Oligodendroglioma is associated with a better patient outcome than most other types of glioma.
This form of glioma arises from more than one type of glial cell. These tumors are also referred to as oligoastrocytomas and they usually occur in the cerebrum, although they can spread to other areas of the brain. Mixed gliomas only account for around 1% of primary brain tumors and they usually develop in adult males.
As with many forms of cancer, the cause of glioma is not known and this type of tumor affects people of all ages, although it is more common in adults than children. A glioma is also more likely to occur in men than in women.
The glioma symptoms that develop depend on the size, grade and location of the tumor. Those occurring in the brain can cause vomiting, headache, seizures, dizziness, and fainting while those that grow and press on the optic nerve may cause vision loss and those growing in the spine can lead to pain and weakness in the limbs.
Some of the symptoms associated with the various different forms of glioma are described below.
- Behavioural changes
- Increased head size
- Inability to sleep
- Behavioral changes
- Weakness on one side of the body
- Loss of short-term memory
- Speech problems
Gliomas are not spread via the bloodstream but can metastasize via the cerebrospinal fluid and cause lesions in the spine referred to as “drop metastases.”
Gliomas are designated different grades according to their potential to grow and how aggressive they are. The tumors are graded I to V, where grade I represents the least serious type of tumor and grade V represents the most serious. However, gliomas are usually referred to as simply “low grade” or “high grade.”
Most high-grade or more aggressive gliomas have already developed their own blood supply and tend to infiltrate. The tumors can also break down the blood–brain barrier in areas near to the tumor. In addition, these tumors usually grow back after surgical removal and are often referred to as recurrent brain cancer.
Low-grade tumors, on the other hand, can take many years to grow back and may not require any follow-up treatment after surgical excision, unless symptoms begin to manifest.
The treatment of these tumors depends on the size, location and grade of the tumor. Often, treatment involves a combination of surgery, radiotherapy and chemotherapy. Those with high-grade tumors generally have a poor outcome due to the high rates of recurrence.