What are astrocytomas?

Related conditions:
Primary brain tumors

Definition:


Astrocytomas, the most common gliomas, are primary malignant brain tumors that can occur in most parts of the brain and occasionally in the spinal cord. As the name implies, astrocytomas are derived from astrocytes nonneural support cells of the central nervous system. The types of astrocytomas based on clinical pathology include pilocytic astrocytoma, fibrillary astrocytoma, anaplastic astrocytoma, and glioblastoma multiforme. Because astrocytomas are primary brain tumors formed in the brain, they rarely spread to other parts of the body; however, they usually grow rapidly and invade surrounding normal brain tissue and therefore are life-threatening.

Risk factors: Brain tumors are caused by mutated or missing genes that result in abnormal cells. High-dose ionizing radiation used over time to treat brain tumors may on occasion cause secondary tumors. Exposure to certain chemicals such as pesticides, petrochemicals, and formaldehyde, and to electromagnetic fields over time increase the risk of developing astrocytomas.

Etiology and the disease process: Generally, malignant brain tumors are caused by changes in genetic structure due to inherited or environmental factors. It was thought that only 5 percent of primary brain tumors, including astrocytomas, are inherited; however, one study has shown that 80 percent of patients with grade IV astrocytoma (glioblastoma multiforme) had anomalous copies of chromosome 7. Familial clustering of gliomas is also associated with defined inherited tumor syndrome, including Li-Fraumeni syndrome, Turcot syndrome, and the neurofibromatosis I syndrome.

Incidence:
Gliomas of both benign and malignant tumors account for 45 to 50 percent of all primary brain tumors; grade I and II astrocytomas account for 25 to 30 percent of all gliomas. Approximately 13,000 people in the United States die of malignant brain tumors every year, which represents about 2 percent of all cancer-related deaths.

Symptoms: Various symptoms may occur with astrocytomas, which depend largely on the location and size of the tumor. Seizure, focal neurologic deficits such as weakness or speech problems, and headaches are common symptoms. The headaches that are associated with brain tumors are typically worse in the morning and accompanied by vomiting. Sometimes increased pressure on the brain tissue can cause blurred, double, or even loss of vision. Behavioral changes may also follow with changes in mood and general state of well-being.

Screening and diagnosis: Methods of screening and diagnosing astrocytomas include computed tomography (CT) scans, magnetic resonance imaging (MRI), angiograms, X rays of the head and skull, and biopsies. Other brain scans, such as magnetic resonance spectroscopy (MRS), single-photon emission computed tomography (SPECT), or positron emission tomography (PET), provide a gauge of brain activity and blood flow. Brain tumors are graded based on the following criteria: mitotic index (growth rate), vascularity (blood supply), presence of necrotic center, invasive potential (border distinctness), and similarity to normal cells.

Accordingly, astrocytomas can be graded into four levels. Pilocytic astrocytoma are grade I tumors that are slow growing and do not invade the surrounding normal tissue, and are commonly diagnosed in children and young adults. Low-grade astrocytomas, including fibrillary or protoplasmic astrocytomas, are grade II tumors that grow slightly faster than grade I tumors and are invasive, with high incidence in the cerebrums of young adults and in the brain stems of children. Anaplastic astrocytomas are grade III, malignant and invasive tumors that occur in the same location as the low-grade astrocytomas and have a high recurrence rate. Glioblastomas multiforme are grade IV, a malignant type that is by far the most common glioma: Approximately 50 percent of astrocytomas are glioblastomas. The common sites of tumors are cerebral hemispheres in adults and the brain stem in children, and they typically contain more than one cell type.

Treatment and therapy: Treatment options differ according to size, grade, and location of the tumor. Tumors may be removed by craniotomy, an open-skull procedure. They may also be removed by ultrasonic aspiration, in which ultrasonic waves fragment the tumors, which are then aspirated. Alternatively, stereotactic radiosurgery may be performed with a Gamma Knife on benign, malignant, or metastatic tumors that are around 4 centimeters (cm) in size. Chemotherapy may be used as a primary therapy in young children or as an adjuvant after tumor removal with radiosurgery. For pilocytic and fibrillary astrocytomas, complete resection of the tumor is achieved; however, if excision is not possible because of the tumor’s location, chemotherapy is indicated in young children and radiotherapy in adults. The treatment options for anaplastic astrocytoma and glioblastoma multiforme include total resection followed by radiotherapy and chemotherapy after surgery.

Prognosis, prevention, and outcomes: The prognosis and outcome of astrocytomas largely depend on the age of the patient, histological features of the tumor, and degree of neurologic or functional impairment. In low-grade astrocytomas, the mean survival time after surgery is six to eight years with the prognosis depending on whether the tumor undergoes progression to a malignant phenotype. Complete recovery is possible in pilocytic astrocytoma if total resection is achieved, while fibrillary astrocytomas show frequent recurrence. In patients with anaplastic astrocytomas and glioblastoma multiforme, the extent of resection is a prognostic factor; generally, younger patients below the age of forty-five have a better prognosis.

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