Astrocytoma is a brain tumor arising from astrocytes, which are supportive cells in the brain and spinal cord.
These tumors can develop in various locations across the nervous system, including the cerebral hemispheres, cerebellum, and brainstem. Certain astrocytoma subtypes tend to occur in specific parts of the brain.
Because astrocytes are a type of glial cell, astrocytomas are a specific type of glioma (tumors that arise from glial cells). In general, glial cells provide support to neurons and perform a variety of functions across the nervous system. Astrocytomas, including glioblastomas, account for about 75.5% of all gliomas.1
While imaging studies (including CT scans and MRIs) can characterize the size, location, and spread of an astrocytoma, surgical biopsy may be required to further classify certain astrocytoma subtypes. Each astrocytoma subtype can have very different symptoms and does not occur equally – some are much more rare than others. Accordingly, treatment options and patient outcomes also vary by astrocytoma subtype.
Overview of Astrocytomas
First, astrocytomas can be classified by grade, which is a measure how abnormal the tumor cells look, and how quickly they grow. Grade I and II astrocytomas are the slowest growing, and are collectively classified as low-grade astrocytomas. Grade III astrocytomas grow at an intermediate rate, while grade IV astrocytomas (also called glioblastoma) grow rapidly and are the most aggressive.
Next, tumors can also be classified based on their location. For example, the following subtypes of pediatric astrocytomas are classified by their location in the brain:
- Cerebellar astrocytoma
- Optic pathway glioma
- Hypothalamic/thalamic glioma
- Tectal glioma
- Brainstem glioma
Finally, astrocytomas can be further classified into more specific subtypes based on how the cells look under a microscope (its histological characteristics), and the specific mutations it has (its genetic characteristics):
These slow-growing tumors usually occur in children, and are considered the most benign type of astrocytoma. Because these tumors typically have well-defined boundaries, surgery alone may be sufficient treatment. Typically, pilocytic astrocytomas arise in the cerebellum, the part of the brain involved in balance and motor coordination.
These slow-growing tumors typically arise in the ventricles, the fluid-filled cavities in the brain and spinal cord.
Ventricles are filled with cerebrospinal fluid (CSF), which helps cushion the brain from trauma. When subependymal giant cell astrocytomas develop, they often interfere with the flow of CSF within the brain, causing a buildup of CSF and an increase in pressure. This condition, also called hydrocephalus, is often associated with headaches (or a rapidly increasing head size in infants) which may be included in the first symptoms.
Subependymal giant cell astrocytomas are relatively rare tumors that primarily occur in people with tuberous sclerosis complex (TSC), a rare genetic condition that predisposes patients to develop tumors throughout the body.
These are rare brain tumors that primarily affects children and young adults.
Pleomorphic xanthoastrocytomas typically arise in the cerebral hemispheres or the leptomeninges (two of the membrane layers that surround the surface of the brain). Symptoms may include seizures, headaches, nausea, and vomiting.
This type of tumor can be benign or malignant: pleomorphic xanthoastrocytoma (grade II) is the benign form, while anaplastic pleomorphic xanthoastrocytoma (grade III) is considered malignant, and grows more quickly. Anaplastic pleomorphic xanthoastrocytomas also have “anaplastic” features, meaning that the tumor extends tentacle-like projections of cells that grow into neighboring tissue.
These tumors tend to arise in the cerebral hemispheres of the brain, and typically have diffuse borders, with clusters of tumor cells growing into neighboring tissue.
Diffuse astrocytomas are primarily found in young adults, although children and adults may also be affected. Initial symptoms include seizures, headaches, and weakness on one side of the body.
These rare, malignant tumors tend to grow in cerebral hemispheres. Occasionally, they may arise in other parts of the brain. Anaplastic astrocytomas have “anaplastic” features, meaning that the tumors extend tentacle-like projections of cells that grow into neighboring tissue.
Anaplastic astrocytomas are most common in adults, although children may also be affected. Common symptoms may include headaches, fatigue, and nausea, with more specific symptoms depending on the size and location of the tumor.
Glioblastomas are the most aggressive type of astrocytomas. These highly malignant tumors typically grow rapidly and are supported by a large network of blood vessels. Glioblastomas tend to arise in the cerebral hemispheres, although they can grow in other parts of the brain as well.
Glioblastomas typically occur in adults, and occur very rarely in children. Many symptoms result from the tumor’s rapid growth, which can increase pressure in the brain. These include headache, nausea, vomiting, and fatigue. Other common symptoms depend on the location of tumor, for example progressive neurological deficits such as weakness on one side of the body.
Therefore, with all these classification systems, it is important to remember that your doctors could call the same tumor by several different names. For example, a grade 1 astrocytoma that is located in the optic pathway could be called a pilocytic astrocytoma, a grade 1 glioma, or an optic pathway glioma.
- Ostrom, Q.T., et al., CBTRUS Statistical Report: Primary brain and other central nervous system tumors diagnosed in the United States in 2010-2014. Neuro Oncol, 2017. 19(suppl_5): p. v1-v88.
This content was reviewed by UCSF Neuro-oncology Fellow, Sarah Lapointe MD.