Kernohan’s notch: Uncal Herniation

• Notching of the midbrain is seen on the opposite side of the lesion with uncal herniation(Kernohan’s notch). This damages the contralateral pyramidal tract fibers in the midbrain and causes hemiparesis on the ipsilateral side.
• The corticospinal tracts originate in the motor cortex in the frontal lobes and descend through the internal capsules and subsequently through the midbrain and pons, before the majority of the fibers (80%) decussate in the medulla.
• In the midbrain, the pyramidal tract courses anteriorly in the crus cerebri. Due to the crossing of pyramidal tract fibers downstream in the medulla, damage of the fibers in the midbrain results in paralysis of the opposite side of the body.
• Kernohan and Woltman  reported the presence of a notch in the midbrain contralateral to the side of the space occupying lesion due to compression of the midbrain against tough dural reflection tentorium cerebelli