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Head Injury
Published in Ian Greaves, Keith Porter, Jeff Garner, Trauma Care Manual, 2021
Ian Greaves, Keith Porter, Jeff Garner
Uncal herniation is the syndrome seen when an expanding mass lesion compresses the temporal lobe, pushing the uncus over the free edge of the tentorium cerebelli. This compresses the cerebral peduncle and ipsilateral oculomotor nerve, producing contralateral hemiparesis or hemiplegia and an ipsilateral oculomotor nerve palsy. The latter can present as just pupillary dilatation or progress to include ptosis and a ‘down and out’ pupil secondary to paralysis of the ocular muscles innervated by the third nerve. The Kernohan’s notch phenomenon refers to uncal herniation presenting with weakness ipsilateral to the mass lesion and results from compression of the contralateral cerebral peduncle against the contralateral tentorial edge.
Neurotrauma in the Field
Published in Mansoor Khan, David Nott, Fundamentals of Frontline Surgery, 2021
The immediate surgical consideration is whether there may be a localised haematoma that can be efficiently evacuated through a simple burr hole. This is much more likely if the patient has lowered GCS and lateralising signs, such as a unilateral weakness or unilateral pupillary dilatation. The haematoma is likely to be ipsilateral to the side of the impact or wound, with further clues coming from pupil dilation or motor weakness. However, it is possible to have false lateralising signs. Kernohan’s notch — which describes significant subfalcine herniation resulting in compression of the contralateral cerebral peduncle causing weakness that is ipsilateral to the weakness — may make the diagnosis difficult. See the later discussion for the actual procedure for burr-hole creation.
Raised Intracranial Pressure
Published in John W. Scadding, Nicholas A. Losseff, Clinical Neurology, 2011
Kernohan’s notch describes the situation in which lateral displacement of the midbrain by a supratentorial mass leads to impingement of the opposite cerebral peduncle onto the hard tentorial edge. This produces an indentation or ‘notch’ in the contralateral cerebral peduncle and can produce a hemiparesis ipsilateral to the causative supratentorial mass. Thus, hemiparesis can be misleading as a localizing clinical sign. Occasionally, a posterior fossa mass can produce transtentorial herniation upwards. Thus, there is a small but definite risk of producing this complication when associated obstructive hydrocephalus is relieved by shunting fluid from the lateral ventricles in the presence of a posterior fossa mass.
Chameleons, red herrings, and false localizing signs in neurocritical care
Published in British Journal of Neurosurgery, 2022
Boyi Li, Tolga Sursal, Christian Bowers, Chad Cole, Chirag Gandhi, Meic Schmidt, Stephan Mayer, Fawaz Al-Mufti
Kernohan’s Notch syndrome, also known as Kernohan-Woltman Notch Phenomenon (KWNP), is contralateral herniation of cerebral peduncles causing ipsilateral hemiparesis.59 KWNP is generally associated with acute space occupying lesions such as hematomas, neoplasms, and AVMs and may often be secondary to traumatic brain injury.59,60 Causes of insidious onset, though more rare, include chronic subdural hematoma, reabsorption bone syndrome, pressure necrosis, high grade glioma, and arachnoid cyst.59–61 Clinically, KWNP presents with the characteristic hemibody syndrome ipsilateral to the primary lesion, and may also present with ipsilateral oculomotor nerve involvement.59,60 A particularly concerning true localizing causes of ipsilateral hemiparesis is primary brain stem lesion, however primary brain stem lesions tend to produce more profound and prolonged impairment in level of consciousness.60,62,63