Uncal Transtentorial Herniation

Uncal transtentorial herniation is a serious brain condition where part of the brain called the uncus is pushed downward through an opening in the brain's protective covering called the tentorium. This happens when there is increased pressure inside the skull, often due to swelling or bleeding in the brain. The pressure causes the brain tissue to shift, which can compress important nerves and blood vessels. This affects the brainstem, which controls vital functions like breathing and heart rate. Symptoms may include sudden changes in consciousness, abnormal pupil size, and weakness on one side of the body. Because it involves critical areas of the brain, this condition can rapidly become life-threatening. Immediate medical evaluation is essential to understand the cause and severity.

Uncal transtentorial herniation is a subtype of brain herniation characterized by the medial displacement of the uncus of the temporal lobe through the tentorial notch. It typically results from increased intracranial pressure due to mass lesions such as epidural or subdural hematomas, tumors, or cerebral edema. The herniation compresses the ipsilateral third cranial nerve, causing pupillary dilation and impaired eye movement, and may compress the contralateral cerebral peduncle, leading to hemiparesis (Kernohan's notch phenomenon). Additionally, compression of the posterior cerebral artery can cause occipital infarction. This condition is a neurosurgical emergency due to the risk of brainstem compression and subsequent respiratory and cardiovascular collapse.