Uncal herniation

Uncal herniation

Involves herniation of the uncal portion of the medial temporal lobe.
Anteriorly, the uncus encompasses the amygdala, and posteriorly, it forms the anterior aspect of the hippocampus.
During medial temporal lobe (limbic lobe) herniation, the uncus herniates over the tentorium cerebelli and compresses the lateral aspect of the midbrain. It commonly compresses:

1. The ipsilateral CN 3 as it exits the midbrain, causing an oculomotor palsy.
2. Causes either direct compression of the ipsilateral cerebral peduncle or compresses the contralateral cerebral peduncle against the contralateral tentorium cerebelli, forming a so-called Kernohan's notch in that peduncle, affecting the corticospinal tract. Cerebral peduncle injury causes unilateral upper and lower extremity weakness. The laterality of the weakness depends on the side of cerebral peduncle that is injured.