What is gliosis and what causes it?

• A. Astrocyte proliferation in response to CNS injury; a reactive, non-neoplastic process.
• B. Malignant tumor of glial origin.
• C. Autoimmune demyelination.
• D. Vascular malformation.

Answer: (A)

Gliosis is the reactive change of astrocytes that occurs after CNS injury. When the brain or spinal cord is damaged, astrocytes become activated, increase expression of GFAP, hypertrophy, and proliferate to form a dense network around the injury—the glial scar. This response is non-neoplastic, meaning it is not due to cancer, but a repair and protective attempt to contain damage and restore homeostasis. While this glial reaction helps seal off the lesion and limits spread of injury, it can also impede axonal regrowth in the central nervous system. The triggers are various forms of CNS damage such as trauma, ischemia, infection, or inflammation. In contrast, a malignant glial tumor would be a neoplastic process, autoimmune demyelination centers on myelin loss rather than primarily astrocyte proliferation, and vascular malformations are unrelated to this reactive glial change.