**Core Concept**
Secondary brain injury refers to the exacerbation of brain damage following the initial traumatic event, often due to complications arising from the primary injury. This concept is crucial in understanding the complex pathophysiology of traumatic brain injury (TBI) and the importance of prompt and effective management.

**Why the Correct Answer is Right**
Secondary brain injury can occur due to various mechanisms, including increased intracranial pressure (ICP), cerebral edema, seizures, hypoxia, and hypotension. These factors can further compromise brain function and lead to permanent damage. The release of excitatory neurotransmitters, such as glutamate, and the subsequent activation of N-methyl-D-aspartate (NMDA) receptors can also contribute to secondary brain injury. This complex interplay of factors highlights the need for close monitoring and aggressive treatment to prevent further brain damage.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because primary brain injury refers to the immediate damage caused by the initial traumatic event, such as lacerations, contusions, or fractures. While primary injury is devastating, it is not a secondary brain injury.
**Option B:** This option is incorrect because cerebral vasospasm is a complication that can occur after a subarachnoid hemorrhage, but it is not a secondary brain injury in the context of TBI. Vasospasm can lead to decreased blood flow and further brain damage, but it is a distinct entity.
**Option C:** This option is incorrect because hypotension can contribute to secondary brain injury by reducing cerebral perfusion pressure and exacerbating cerebral edema. However, hypotension is a potential cause of secondary brain injury rather than an example of it.

**Clinical Pearl / High-Yield Fact**
It is essential to distinguish between primary and secondary brain injury, as the management strategies differ significantly. Prompt recognition and treatment of secondary brain injury can significantly impact patient outcomes.

**Correct Answer: C. Hypotension.**