Examples include complete 3rd nerve palsy accompanied by contralateral limb ataxia and tremor from involvement of the red nucleus (Claude syndrome) or by contralateral hemiparesis from involvement of descending motor (eg cortico-spinal) axons in the cerebral peduncle
(Weber syndrome) or in combination with both types of motor disorder affecting the opposite limb(s) (Benedict syndrome).
The deficits are attributed to pressure on the contralateral cerebral peduncle
, which leads to an indentation in the crus, called Kernohan's notch.
Mild atrophy was seen in ipsilateral cerebral peduncle
, thalamus, and contralateral cerebellar hemisphere.
This was first described by Kernohan et al (1) in 1929 after an autopsy study revealed a notched cerebral peduncle
from a contralateral herniation syndrome.
1) The 'roots' of the molar tooth are represented by thick, perpendicular, non-decussated superior cerebellar peduncles, while the 'body' of the molar tooth is formed by the cerebral peduncles
of the brainstem with a deep interpeduncular fossa (Fig.