Uncal herniation

Uncal herniation occurs when raised intracranial pressure forces the medial temporal lobe (uncus) downward through the tentorial notch. The displaced uncus may compress the ipsilateral oculomotor nerve (CN III), producing a dilated, poorly reactive pupil, and compress the midbrain, causing progressive loss of consciousness. Compression of the posterior cerebral artery may produce occipital infarction. With increasing pressure, brainstem distortion and secondary Duret hemorrhages may occur. It is a life-threatening form of transtentorial herniation and may rapidly progress to coma and death.