Final answer:
The first sign of uncal (transtentorial) herniation is usually pupillary changes, such as dilation and unresponsiveness to light. Other signs may include contralateral hemiparesis, altered consciousness, and abnormal posturing. Uncal herniation is a medical emergency.
Step-by-step explanation:
The first sign of uncal (transtentorial) herniation, specifically the medial temporal lobe over the tentorium cerebelli, is usually pupillary changes.
This can manifest as the pupil on the side of the herniation becoming dilated and unresponsive to light.
The herniation causes pressure on the oculomotor nerve, leading to dysfunction and subsequent changes in pupil size and reactivity.
In addition to pupillary changes, other signs of uncal herniation may include contralateral hemiparesis (weakness on the opposite side of the body), altered consciousness, and abnormal posturing.
These symptoms may be accompanied by headache, nausea, and other signs of increased intracranial pressure.
It is important to note that uncal herniation is a medical emergency and requires immediate medical attention.