**Core Concept**
Increased intracranial pressure (ICP) following head injury can manifest through various clinical signs, but the earliest and most subtle indicator is often altered mental status. This is due to the compression of brain tissue and the disruption of normal cerebral function, which can affect cognitive processes before other signs become apparent. Altered mental status can range from mild confusion to coma, depending on the severity of ICP.

**Why the Correct Answer is Right**
Altered mental status is the earliest manifestation of increased ICP because as the intracranial pressure rises, it compresses the brain tissue, particularly the cerebral cortex. This compression disrupts normal neuronal function, leading to impaired cognitive processes, including attention, memory, and decision-making. The compression of the cerebral cortex also affects the brain's ability to regulate autonomic functions, such as blood pressure and respiratory rate, further contributing to altered mental status. The cerebral cortex is particularly susceptible to increased ICP due to its high metabolic demand and delicate blood supply.

**Why Each Wrong Option is Incorrect**
**Option A:** Ipsilateral papillary dilatation is a sign of third cranial nerve (oculomotor nerve) compression, typically seen in conditions such as aneurysms or tumors, rather than increased ICP following head injury.

**Option B:** Contralateral papillary dilatation is not a recognized sign of increased ICP or head injury.

**Option D:** Hemiparesis is a sign of focal brain injury, such as a stroke or traumatic brain injury, but it is not the earliest manifestation of increased ICP.

**Clinical Pearl / High-Yield Fact**
It is essential to recognize altered mental status as a sign of increased ICP, as it can progress rapidly to more severe and life-threatening complications, such as herniation. Early recognition and management of increased ICP are critical to preventing these complications and improving patient outcomes.

✓ Correct Answer: C. Altered mental status