Astrocytomas are tumors that arise from astrocytes—star-shaped cells that make up the “glue-like” or supportive tissue of the brain.
These tumors are “graded” on a scale from I to IV based on how normal or abnormal the cells look. There are low-grade astrocytomas and high-grade astrocytomas. Low-grade astrocytomas are usually localized and grow slowly. High-grade astrocytomas grow at a rapid pace and require a different course of treatment. Most astrocytoma tumors in children are low grade. In adults, the majority are high grade.
Below are descriptions of the various grades of these tumors:
Pilocytic Astrocytoma (also called Juvenile Pilocytic Astrocytoma)
These grade I astrocytomas typically stay in the area where they started and do not spread. They are considered the “most benign” (noncancerous) of all the astrocytomas. Two other, less well known grade I astrocytomas are cerebellar astrocytoma and desmoplastic infantile astrocytoma. Pilocytic Astrocytomas generally form sacs of fluid (cysts), or may be enclosed within a cyst. Although they are usually slow-growing, these tumors can become very large.
Diffuse Astrocytoma (also called Low-Grade or Astrocytoma Grade II)
These grade II astrocytomas tend to invade surrounding tissue and grow at a relatively slow pace. Diffuse Astrocytomas tend to contain microcysts and mucous-like fluid. They are grouped by the appearance and behavior of the cells for which they are named.
An anaplastic astrocytoma is a grade III tumor. These rare tumors require more aggressive treatment than benign pilocytic astrocytoma. Anaplastic Astrocytomas tend to have tentacle-like projections that grow into surrounding tissue, making them difficult to completely remove during surgery.
Astrocytoma Grade IV (also called Glioblastoma, previously named “Glioblastoma Multiforme,” “Grade IV Glioblastoma,” and “GBM”)
There are two types of astrocytoma grade IV—primary, or de novo, and secondary. Primary tumors are very aggressive and the most common form of astrocytoma grade IV. The secondary tumors are those which originate as a lower-grade tumor and evolve into a grade IV tumor. Astrocytoma Grade IV may contain cystic material, calcium deposits, blood vessels, and/or a mixed grade of cells.