Kernohan phenomenon

Case contributed by Dr Erik Ranschaert


Patient with large brain tumour in right temporal and parietal lobe, with sudden weakness in the limbs on right side.


See image/stack specific findings.

Case Discussion

Kernohan phenomenon is caused by an uncal transtentorial herniation causing compression of a cerebral peduncle (part of the mesencephalon). Consequently the contralateral side of the brainstem is pressed against the free edge of the tentorium, resulting in an indentation called Kernohan notch.

The left cerebral peduncle contains motor fibers that cross over to the right side of the body. Thus, if you have a right hemisphere trans-tentorial herniation, it causes a Kernohan notch in the left cerebral peduncle which results in right-sided motor impairment. This phenomenon can be clinically confusing since it is a secondary condition caused by a primary condition (tumour) on the opposite hemisphere of the brain.

With courtesy of Dr R Noordveld.

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Case information

rID: 10967
Published: 4th Oct 2010
Last edited: 13th Mar 2016
Inclusion in quiz mode: Excluded

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