Low-Grade Glioma in Childhood

This article was written for The Childhood Brain Tumor Foundation,Germantown, MD 20876

Low-Grade Gliomas in Childhood

Eva Perdahl, M.D., Ph.D.
Pediatric Hematology/Oncology of Northern Virginia
8301 Arlington Boulevard #209
Fairfax, VA 22031

Brain tumors are the most common solid tumor during childhood. Only leukemia is a more common childhood cancer. Low-grade gliomas constitute a mixed group of brain tumors accounting for 40-50% of all central nervous system tumors. The group of low-grade glioma include diverse tumors such as juvenile pilocytic astrocytoma, fibrillary astrocytoma, oligodendroglioma and mixed glioma. There are other rare types, often only occurring in early childhood, such as dysembryoplastic neuroepithelial tumor and desmoplastic cerebral astrocytoma.

As with most childhood cancers, we do not know the causes of low-grade gliomas. The low-grade gliomas that occur in childhood are different from adult gliomas. They are more likely to involve the cerebellum(the part of the brain closest to the spinal cord that coordinates muscle movements), the midbrain(an area of hormone regulation) and the optic pathway - optic nerve, optic nerve crossing(chiasm) and behind the chiasm(posterior optic pathway). The type and grade of glioma are also different, as well as the survival.

Types of Low-Grade Gliomas

Pilocytic astocytoma is usually found in the cerebellum, has well-defined margins and can often be completely, or nearly completely removed by surgery with an excellent long-term survival.

Fibrillary astrocytomas are usually found in the mid-brain, has less well-defined margins and, because of the location, less likely to be completely removed.

Optic pathway gliomas are usually juvenile pilocytic astrocytomas but difficult to completely remove because of the delicate location. There is an association with neurofibromatosis, especially in isolated optic nerve gliomas(50-70%).

Oligodendroglioma and mixed glioma are often found in the outer layer of the brain(cortex) and seizures is often a presenting sign.

Tumor Biology

The tumor biology of low-grade gliomas is poorly understood. In neurofibromatosis 1 and neurofibromatosis 2 there are known chromosomal changes(17q and 22q). The tumor suppressor gene p53 is known to play a role in adult gliomas but does not seem to play a major role in childhood low-grade gliomas. There is data suggesting that testing for the rate of tumor cell division(labeling index) is predictive of how aggressively the tumor is growing. However, there are other reports that dispute those findings.

Signs and Symptoms

Presenting symptoms are usually insidious and dependent on the location of the tumor. Patients with the tumor in the cerebellum often complain of headaches, nausea and vomiting, mostly in the morning, changes in coordination and difficulty walking(wobbly, broad-based gait). Tumors in the cortex often present with seizures and loss of motor(movement) and/or sensory(feeling) function depending on the location of the tumor. Tumors in the midbrain usually have signs of hormone deficits and tumors affecting the optic pathway often present with visual impairment, crossed eyes(strabismus), rapid eye movements(nystagmus) and sometimes bulging of the eye(proptosis).

The work-up

To evaluate a patient with a suspected brain tumor, the patient has to undergo several tests. A thorough neurological exam by a Pediatric neurologist is usually the first step. A scan of the brain - CT(computerized tomography) scan or MRI(magnetic resonance imaging) are the most common forms of ìpicturesî of the brain. PET(positron emission tomography) is a rather new, and not commonly used, test where the metabolic rate of the tumor(how ìactiveî the tumor is) can be estimated. If the patient has had seizures, an EEG(electroencephalogram) is done, where the electrical activities of different parts of the brain is recorded through small wires pasted to the outside of the skull. A thorough eye exam by an ophthalmologist(eye doctor) is important for children with midbrain and optic pathway tumors. A neuro-psychological evaluation will help to recognize problems in many different areas of higher brain function. When problems are identified, the appropriate tools to help the child to cope can be instituted.

Treatment

The treatment of low-grade glioma depends on the location of the tumor, type of tumor and the age of the child.

Surgery is used to completely or partially remove(resect) the tumor and to obtain a piece of the tumor to confirm the diagnosis(biopsy). With technical development in neurosurgery such as stereotactic devices and monitoring of brain-waves during surgery(intra-operative corticography), the neurosurgeon is able to be more aggressive in taking out tumor and at the same time able to decrease the side-effects of surgery.

Radiation therapy is the most extensively used treatment for brain tumors, both for historical reasons and for known efficacy. There are several different techniques used to irradiate brain tumors. The most common is external beam radiation where the beam of radiation from a machine is directed towards the tumor and a margin of surrounding normal brain tissue. Stereotactic radiosurgery(also known as ìthe gamma-knifeî) is used for small tumors and delivers accurately very high doses of radiation to a small area in one treatment. Stereotactic radiotherapy delivers conventional doses of radiation during many treatment sessions to small localized tumors with less irradiation of normal tissue. Both stereotactic radiosurgery and radiotherapy requires the childís head to be in a special frame.

Chemotherapy is used to control tumor growth and shrink the tumor to allow surgical removal, delay radiation or limit the field of radiation needed. Chemotherapy alone very rarely cure low-grade glioma. Carboplatin with/without vincristine has been used in several treatment protocols showing efficacy in partially shrinking or stopping growth of the tumor.

Cerebellar astrocytomas are often completely removed by surgery resulting in an approximately 90 % chance of cure. If the tumor recurs an other attempt to completely remove the tumor is often successful. Tumors that are not completely removed tend to recur(relapse) more often. The slow, and sometimes absence of growth, of residual tumor can be followed closely and other treatments such as radiation and/or chemotherapy may be used if/when tumor growth is noted. Because of the significant effects of radiation therapy on the developing brain radiation will be delayed in the very young child (<3years) and chemotherapy may be used to delay, or even omit, the need for radiation.

Oligodendroglioma often require an attempt to complete resection to achieve seizure control. This may be difficult as the margins of the tumor are difficult to separate from normal brain tissue. Close monitoring after surgery and addition of radiation therapy and/or chemotherapy if tumor growth is noted is necessary.

The midbrain and optic pathway tumors often grow very slowly and do not grow at all for long periods of time without treatment. Therefore, no treatment but close observation is possible in some cases (especially cases associated with neurofibromatosis). Because of the delicate position of these tumors, radical surgery is very difficult without major side-effects. Debulking(removing parts of the tumor) may help to improve vision and postpone the occurrence of new symptoms. Radiation and/or chemotherapy is used when there is sign of tumor growth.

Most children with brain tumors are treated on specially designed treatment protocols at institutions which belong to one of the two large national groups of doctors specializing in treating children with cancer(Pediatric Oncologists), Childrenís Cancer Group(CCG) and Pediatric Oncology Group(POG).

Outcome

For the patients whose tumor can be completely removed the long-term survival is excellent. For those patients where complete tumor removal is not possible or when the tumor comes back the chance of long-term cure, at this time, is small, but with the appropriate treatment the child can survive and have a good quality of life for many years.

Long-Term Effects

Long-term effects of the treatment depend on the location of the tumor, the type of treatment and, in the case of radiation, the age of the patient at time of treatment. Patients with midbrain tumors and patient who have received radiation will often have hormone deficiencies causing stunted growth, delayed puberty and problems with salt-and water balance. Learning disabilities of different severity, is a common problem for children with brain tumors.

Long-Term Goals

Long-term goals for the treatment and care of children with low-grade gliomas are several:

To improve the understanding of tumor biology of low-grade gliomas and tailor treatment accordingly
To improve treatment and minimizing side-effects
To better detect children with long-term side-effects and and support them and their families

Dr. Perdahl is a Pediatric Hematologist/Oncologist practicing at Fairfax Hospital, VA and Shady Grove Hospital, MD. She received her M.D. and Ph.D. from University of Umeå, Sweden. Her research interests pursued at Yale University, The Rockefeller University and Mount Sinai School of Medicine(NY) include neurochemistry/neuropathology as well as bone marrow failures. Clinical interests include childhood brain tumors and bone marrow transplantation.