What is an Astrocytoma/Glioma?
Astrocytoma, also called glioma, is the most common brain tumor, accounting for more than half of all Central Nervous System (CNS) malignancies. These tumors originate from astrocytes, which are star-shaped brain cells. Astrocytes are a type of glial cell which function to support the surrounding cells. Astrocytomas typically occur in the first decade of life with the peak age of occurrence at 5-9 years.
Astrocytomas comprise a wide range of tumors that are defined by their appearance and are graded according to the World Health Organization (WHO) classification system. The WHO grading system divides astrocytomas into four subsets, Grade I, Grade II, Grade III and Grade IV Astroctyoma. The grade of the tumor defines its growth potential and extent of invasiveness. WHO Grade I and II Astrocytomas are slow growing tumors frequently grouped together and termed “low grade gliomas”. WHO Grade III and IV Astrocytomas are fast growing tumors, usually termed “high grade gliomas”.
Grade I Astrocytomas (which include pilocytic astrocytomas, subependymal giant cell astrocytomas, angiocentric glioma, and subependymomas) are the most common astrocytoma seen in childhood. These tumors are commonly located in the cerebellum, cerebral hemisphere, brainstem, spinal cord, hypothalamus, and the optic tracts. Grade I astrocytomas tend to be well circumscribed and do not infiltrate into the surrounding brain. Typically Grade I astrocytomas can be completely removed surgically. The exception is an optic pathway astrocytoma, which is a juvenile pilocytic astrocytoma but it infiltrates throughout the visual tract.
Grade II Astrocytomas are infiltrative tumors, i.e. the tumor cells penetrate into the surrounding normal brain, making complete surgical resection more difficult. Grade II gliomas include fibrillary astrocytoma, gemistocytic astrocytoma, protoplasmic astrocytoma, pilomyxoid astrocytomas, pleomorphic xanthoastrocytomas and desmoplastic infantile astrocytoma. Grade II astrocytoma are mainly located in the cerebral hemispheres.
Grade III Astrocytoma (anaplastic astrocytoma) and Grade IV Astrocytoma (glioblastoma multiforme) are highly malignant tumors that penetrate deep among the white matter tracts of the brain and grow rapidly. High grade gliomas are typically found in the cerebral hemispheres or the brainstem.
For the majority of astrocytoma, the etiology is unknown. Children with a familial cancer predisposition have an increased risk for developing both low grade and high grade gliomas. Children with Neurofibromatosis Type I have an increased risk of developing astrocytomas, with low grade astrocytoma being the most common subtype and the optic pathway, hypothalamus and brainstem being the most common locations. Patients with Li-Fraumeni syndrome (germline deletion of p53) have an increased risk for developing high grade gliomas. The only known environmental cause for astrocytoma is previous exposure to ionizing radiation.
What are the symptoms of an Astrocytoma/Glioma?
Symptoms vary depending on where the tumor is located within the central nervous system, the aggressiveness or grade of the tumor, and the age of the patient. Tumors can cause non-specific symptoms due to pressure on the brain resulting in increased intracranial pressure (ICP). Symptoms due to ICP may include:
- subtle developmental delay
- poor balance
- incontinence of urine and behavioral changes
Infants tend to have more subtle symptoms because their skull bones have not fused together, therefore the skull can expand to make room for the growing tumor. Infants with a brain tumor tend to present with large heads and non-specific symptoms of irritability, vomiting, failure to thrive, and regression of developmental milestones. Tumors can also present with focal symptoms, which are due to the tumor’s effect on the nearby brain or spinal cord. Focal symptoms may include seizures, weakness, or impairment in speech, memory or vision. Spinal cord tumors frequently cause back pain, weakness, loss of sensation and bladder or bowel dysfunction.
How is an Astrocytom/Glioma diagnosed?
Patients who have a brain or spinal cord tumor require an MRI of the brain and spine to further define the location of the tumor and to assess if there is any metastasis (spread) of the tumor. Patients who present with seizures also undergo an EEG to locate the origin of the seizure. Patients with optic pathway gliomas undergo a thorough ophthalmology exam to get a good baseline evaluation. Patients who have tumors located in the cerebral hemispheres will frequently undergo functional studies (functional MRI or magnetoencephalogram) to map out the important brain function located around the tumor, which will ultimately help the surgeon avoid eloquent functional areas of the brain at the time of surgical removal of the tumor. A biopsy of the tumor is required to make the final diagnosis of an astrocytoma/glioma and to subtype it according to WHO guidelines.
How is an Astrocytoma/Glioma treated?
The treatment of astrocytoma depends on the size and location of the tumor, its type and grade, whether the tumor has spread, and the child’s overall health. Typically, three types of treatments are used to treat children with astrocytoma: surgery, radiation therapy, and chemotherapy.
Surgery is the most important treatment for astrocytomas. The goal of surgery is to get a piece of the tumor to make a diagnosis and to remove as much of the tumor as possible without causing significant neurological injury. All grades of astrocytoma have the best outcome following complete removal of the tumor. The only situations where surgical biopsy is not routinely performed are in tumors diffusely involving and intrinsic to the optic tract, tectum and the pons because the risk of neurological injury is high following a biopsy, and the histology is uniformly a low grade glioma (WHO I or II) in the optic tracts and tectum, and a high grade glioma (WHO II or IV) in the pons.
Chemotherapy has been found to be very effective for low-grade astrocytomas that are inoperable because of location (optic pathway and hypothalamus) or have demonstrated early recurrence or progression. Chemotherapy is typically preferred over radiation therapy in prepubertal children to avoid the long term side effects of radiation. Chemotherapy (along with surgery and radiation) is considered standard treatment for most high-grade glioma.
Radiation is very effective for the treatment of low-grade gliomas, but it has potential long term toxicities (cognitive impairment, secondary malignancies, and vascular injury), therefore it is typically reserved for older children or younger children who fail chemotherapy. Radiation is part of the standard treatment for high grade gliomas and is essential to improving the outcome in children with high-grade gliomas.
Surgical resection is the primary treatment modality. If feasible, complete surgical removal is the goal in order to minimize the risk of local recurrence. However, long-term control of low grade gliomas may ensue even after partial resection; therefore many patients can undergo observation without further treatment after partial resection if the risk of neurologic impairment from further growth is low. Low-grade tumors that progress or recur after surgery often can be cured by surgical resection depending on the location of the recurrent tumor.
Low-grade tumors that are inoperable (such as optic tract, hypothalamic and thalamic tumors), partially resected and posing a high risk of neurologic impairment if allowed to regrow, or demonstrate early progression or recurrence may be treated with chemotherapy or radiotherapy. Chemotherapy is typically preferred in young children to avoid or to delay radiotherapy, which has potential neurologic sequelae. There are several different chemotherapy regimens that are effective for low grade astrocytomas. Radiation therapy is usually reserved for older children or children who have failed chemotherapy. Radiation is given to the area of the tumor plus a margin. Radiotherapy is less commonly recommended in children with neurofibromatosis type 1 (NF1) due to risks of radiation-induced secondary high-grade brain tumors, mutagenesis and intracranial vasculopathy.
Surgical resection is the initial treatment modality. If feasible, complete surgical removal is the goal in order to minimize the risk of local recurrence. Following surgical resection, patients are treated with local radiotherapy and chemotherapy. Chemotherapy has been found to improve outcome in high grade astrocytomas, but these tumors are fairly resistant to chemotherapy. Current trials are testing new chemotherapy and biological agents in high-grade gliomas with the hope of improving the outcomes.
About treatment for Astrocytoma/Glioma at Children’s Minnesota
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