Which of the following is a major secondary brain injury mechanism after TBI?

• A. Hypoxic-ischemic injury due to respiratory failure or hypotension
• B. Direct neuronal injury from the initial impact
• C. Cerebral edema and inflammatory cascades
• D. Chronic neurodegeneration

Answer: (C)

Secondary brain injury after TBI is driven by processes that unfold after the initial impact, notably cerebral edema and inflammatory cascades. Edema raises water content in brain tissue, increasing intracranial pressure and impairing cerebral perfusion, which can worsen ischemia and expand the injury beyond the primary lesion. Inflammatory responses, including microglial activation and cytokine release, disrupt the blood-brain barrier and recruit cells that amplify injury and edema. These evolving inside-the-brain processes are central to secondary injury, explaining why cerebral edema with inflammatory cascades is the best choice. By contrast, direct neuronal injury from the initial impact is a primary event, not a secondary mechanism; chronic neurodegeneration is a longer-term outcome rather than an acute secondary process. Hypoxic-ischemic injury due to systemic factors can contribute to brain damage but is not the core evolving mechanism described here.