Kernohan’s Notch – is actually the tentorium cerebelli contralateral to the site of the primary lesion
Kernohan’s Notch Phenomenon
- phenomenon with a false-localizing sign
- brain lesion is on one side, pupillary dilatation is on the contralateral side, and hemiparesis is on the ipsilateral side (both are reversed)
- etiology is mass effect from either a brain tumor or intracranial bleed, pushing the hemisphere (and the brainstem) contralaterally which leads to the contralateral brainstem being pushed against the tentorium cerebelli
- Compression of contralateral brainstem (where the corticospinal tract fibers are), leads to weakness on the side ipsilateral to the brain lesion (the fibers decussate further down in the medulla)
Peripheral Brain 