A 16-year-old boy suffers a concussion during an ice hockey game and is rushed to the emergency room. A CT scan of the brain reveals a cerebral contusion of the left frontal lobe. The boy lies comatose for 3 days but eventually regains consciousness. Which of the following cells is the principal mediator of scar formation in the central nervous system of this patient?

Damage to the brain or spinal cord is followed by the growth of capillaries and gliosis (i.e., the proliferation of astrocytes and microglia). Gliosis in the central nervous system is the equivalent of scar formation elsewhere; once established, it remains permanently. In spinal cord injuries, axonal regeneration can be seen up to 2 weeks after injury. After 2 weeks, gliosis has taken place and attempts at axonal regeneration end. In the central nervous system, axonal regeneration occurs only in the hypothalamohypophysial region, where glial and capillary barriers do not interfere with axonal regeneration. Axonal regeneration seems to require contact with extracellular fluid containing plasma proteins Diagnosis: Cerebral contusion, gliosis