What Is an Astrocytoma?
Astrocytes are cells found in the central nervous system, which is composed of the brain and spinal cord. They are named for their appearance, astro for star, and cyte for cell. Thus, they are star-shaped cells. Unlike neurons, or nerve cells, they do not transmit electrical signals, but instead support the neurons. They help with detoxification, providing direction for migration, nutrients, and even healing.
They also help form the blood-brain-barrier, a tight seal that prevents unauthorized access to sterile nervous system components. An astrocytoma, or astrocyte tumor, forms when astrocytes grow and reproduce abnormally. When abnormal growth is slow and the tumor is non-invasive, the glioma is said to be benign. When abnormal growth is fast and the tumor is invasive, it is referred to as malignant.
A type of tumor called glioblastoma is thought to develop from astrocytes, although there are other candidates that can potentially cause this tumor as well. Glioblastomas are highly aggressive (cancerous) and make up approximately 16% of primary brain tumors (tumors originating in the brain).
What Causes Astrocytoma?
Various factors are thought to play roles in the development of astrocytomas. Genetic mutations are believed to contribute to astrocytoma formation. Rare types of genetic disorders may accelerate these mutations and their tumor-forming abilities. Exposure to ultraviolet radiation, ionizing radiation, and immunologic deficiencies have also been implicated in tumor formation. Occupational exposures to metals and paints, as well as agent orange, and stress have been implicated without clear evidentiary support.
What Are the Signs and Symptoms of an Astrocytoma?
Signs and symptoms of astrocytomas are similar to other tumors and largely depend on the area of brain impacted. The following are signs and symptoms (some of which are nonspecific) of an astrocytoma:
- Neck pain
- Loss of appetite
- Nausea and vomiting
- Loss of memory
- Double or blurred vision
- Difficulties with movement
- Abnormal reflexes
- Limb weakness
- Speech difficulties
How Is Astrocytoma Diagnosed?
Diagnosis begins with a medical history and physical examination. The physician will ask questions about when symptoms began, how severe they are, and what makes them better or worse. A thorough physical examination will emphasize and document neurological changes and may include testing reflexes, limb strength, vision, hearing, balance, sight, coordination, and other indications of how the nervous system is functioning.
The next step often includes imaging. Magnetic resonance imaging (MRI), magnetic resonance spectroscopy (MRS), computed tomography (CT), and positron emission tomography (PET) scans may be performed to show the location, size, and other characteristics of the tumor.
Figure 1: An axial MRI image demonstrates a large left frontal astrocytoma.
To learn about the grade or invasiveness of a tumor, neurosurgeons can remove a small specimen, called a biopsy, through a short surgery called stereotactic biopsy. A medical specialist called a pathologist will examine the biopsy specimen under a microscope to learn its grade. This will guide the patient and physician in planning treatment and knowing what to expect.
However, more often, the neurosurgeon will recommend removal of the tumor through a more definitive surgery called, craniotomy. Under general anesthesia and during the craniotomy, the patient undergoes opening of the skull and removal of the tumor. A biopsy is also done as part of the craniotomy.
The more tumor removed, the higher the chance of longer survival. The experience of the surgeon is important in making sure that a more extensive tumor removal does not pose more neurological risk to the patient.
How Is Astrocytoma Treated?
Surgery, radiation, and chemotherapy are the tools most often used to treat astrocytoma. Other medications are also available to make treatments more effective.
- Surgery is aimed at removing as much of the tumor as possible without endangering surrounding healthy brain or spinal cord tissue.
- Radiation works by damaging tumor cells directly.
- Dexamethasone, similar to the hormone cortisol, can be given temporarily to prevent and treat the brain swelling that may accompany certain treatment options.
- Temozolomide (TMZ) is an oral medication that binds to the tumor’s DNA and triggers cell death.
- Avastin (bevacizumab) works by inhibiting the growth of blood vessels that support the tumor tissue. Without blood vessels, the tumor has difficulty growing.
- Keppra (levetiracetam) is an anti-seizure medication that prevents seizures caused by tumor irritation or the treatment.
What Is the Prognosis for Astrocytoma?
Astrocytomas are classified into four grades, each with its own prognosis:
- Grade I: These are the least malignant tumors with slowly growing cells and no invasion of surrounding tissues. Grade I astrocytomas generally have a good prognosis. Surgery is often very effective, with 96% of patients alive at 5 years after diagnosis. Examples of Grade I astrocytomas include pilocytic astrocytoma, pleomorphic xantoastrocytoma, and subependymal giant cell astrocytoma (SEGA).
- Grade II: These tumors can become malignant with the possibility of invading healthy tissue. The average prognosis for patients with Grade II tumors is 8 years. An example of a Grade II astrocytoma is diffuse astrocytoma.
- Grade III: These tumors contain abnormally reproducing cells, infiltrating healthy tissue. For patients with Grade III tumors, the average survival is 3 to 5 years. Grade III tumors have the potential to transform into Grade IV tumors. Anaplastic astrocytoma is an example of a Grade III astrocytoma.
- Grade IV: This is the most malignant grade of tumor. They are composed of abnormal, rapidly reproducing cells that invade healthy tissue and often grow new blood vessels to nourish the growing tumor. Patients with Grade IV tumors survive 15 months on average. Glioblastoma (GBM) is a Grade IV astrocytoma.
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