Uncal herniation compresses which structures?

Uncal herniation compresses which structures?

• A. Midbrain structures and PCA
• B. Pons and basilar artery
• C. Cerebellum
• D. Thalamus and MCA

Answer: (A)

Uncal herniation occurs when the medial temporal lobe (the uncus) slides under the tentorium and presses against structures at the tentorial edge. The most vulnerable structures there are the ipsilateral midbrain and the posterior cerebral artery as it runs near that edge. Pressing on the midbrain can affect the oculomotor nerve pathways, producing a classic ipsilateral third‑nerve palsy with pupil dilation, and may also impact the crus cerebri leading to motor signs. Simultaneous compression of the posterior cerebral artery can cause ischemic effects in the occipital lobe, contributing to visual field deficits. Other options don’t fit the typical pattern of uncal herniation: the pons and basilar artery are more associated with downward or transtentorial lesions involving the brainstem or basilar system rather than the edge of the tentorium; the cerebellum is involved in tonsillar herniation, not uncus herniation; and the thalamus with the MCA isn’t the hallmark combination seen with uncal herniation.

Uncal herniation occurs when the medial temporal lobe (the uncus) slides under the tentorium and presses against structures at the tentorial edge. The most vulnerable structures there are the ipsilateral midbrain and the posterior cerebral artery as it runs near that edge. Pressing on the midbrain can affect the oculomotor nerve pathways, producing a classic ipsilateral third‑nerve palsy with pupil dilation, and may also impact the crus cerebri leading to motor signs. Simultaneous compression of the posterior cerebral artery can cause ischemic effects in the occipital lobe, contributing to visual field deficits.

Other options don’t fit the typical pattern of uncal herniation: the pons and basilar artery are more associated with downward or transtentorial lesions involving the brainstem or basilar system rather than the edge of the tentorium; the cerebellum is involved in tonsillar herniation, not uncus herniation; and the thalamus with the MCA isn’t the hallmark combination seen with uncal herniation.