Kernohan’s Notch Phenomenon

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)




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