GLIOMA

This is a general name for any tumor that arises from the supportive tissue called glia, which help keep the neurons (“thinking cells”) in place and functioning well. There are three types of glial cells that can give rise to different tumors. An astrocyte (star-shaped cell) will give rise to astrocytomas (including glioblastomas), an oligodendrocyte (cell with short arms forming the insulation of neurons) will give rise to oligodendrogliomas, and lastly, tumors called ependymomas arise from ependymal cells (i.e., the cells that form the lining of the fluid cavities in the brain). Occasionally, tumors will display a mixture of these different cells and are called mixed gliomas.

Names such as “optic nerve glioma” and “brain stem glioma” refer to the location of these tumors, and not the type of tissue that gave rise to them. A specific diagnosis is only possible if a sample of the tumor is obtained during surgery or biopsy.

GLIOMA, BRAIN STEM

Brain-stem gliomas usually arise in the “stem of the brain” which contains all the “wires” converging from the brain to the spinal cord as well as important structures involved in eyes movements, face and throat muscle control and sensation. Between 10 and 20% of brain tumors in children are brain-stem gliomas. This tumor   most often affects children between 5 and 10 years old, but can also be found in adults generally between 30 and 40 years old. Most of these tumors are astrocytomas varying from localized grade I tumors (mostly in children) to infiltrating grade II or III tumors, although many are never biopsy-proven given the high-risk of performing any surgical procedure in that area. However, the diagnosis can usually be based on the MRI scan features.

Most of these tumors are classified by their location:

• Upper brain stem (midbrain or tectum)
• Middle brain stem (pons)
• Lower brain stem (cervico-medullary)

and MRI appearance:

• Localized or circumscribed
• Diffusely infiltrating
• Exophytic (meaning the tumor has a knob protruding outside the brainstem)

A majority of brain stem tumors occur in the pons, are diffusely infiltrating, and therefore not amenable to surgical resection. Few of these tumors are localized and may be reachable for   resection. The latter also tend to be very slow growing, not in the pons, and are exophytic – on the outer edges of the brain stem.

 

The symptoms of a brain-stem glioma depend on the location of the tumor. The most common symptoms are related to eye movement abnormalities and cause double vision. Other symptoms include weakness or sensation changes of the face, swallowing difficulty and hoarseness. Weakness, loss/changes in sensation or poor coordination on one side of the body may also occur. The tumor may also block the cerebrospinal fluid circulation resulting in hydrocephalus (dilatation of the fluid cavities in the brain) causing headache, nausea, vomiting and gait unsteadiness.

 

Treatment of brain-stem glioma is dictated by the tumor location, the grade and the symptoms. Surgery may be warranted if a tumor appears circumscribed (contained) or exophytic (on the outside of the brain stem). The goal of surgery is first to determine the grade and type of tumor and, sometimes, removal of the tumor. A shunt may also be placed if there is blockage of the cerebrospinal fluid circulation. Radiation therapy may be used early if the patient has a significant symptoms, or it may be postponed until the tumor grows on MRI scan or causes symptoms. A focal type of radiation, such as radiosurgery, can be considered if the tumor appears localized. Chemotherapy is used when the tumor progresses following radiation therapy. Drugs similar to those used to treat glioblastoma may be considered.

 

Radiation therapy with hyperfractionation (with smaller dose per treatment and many more doses) has been used in children in order to increase the effectiveness of the therapy and decrease side-effects. Unfortunately, this has not resulted in significant advantage over standard radiation. Clinical trials using various forms, doses and schedules of radiation therapy for newly diagnosed tumors, and chemotherapy for recurrent tumors are available.