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This note outlines the origins of the recognition of brain herniation caused by raised pressure. Observers in the 19th century failed to recognise the importance of the signs accompanying brain herniation. James Collier described cerebellar tonsillar herniation in 1904. He observed false localising signs in consecutive cases of intracranial tumour that were examined clinically and pathologically. Later accounts of Kernohan’s notch were followed by the newer concept that decreased alertness corresponded to a distortion of the brain by horizontal rather than vertical displacement.
The clinical signs and physical mechanisms underlying intracranial hypertension and brain swelling were not understood until the mid-20th century. Why patients, subsequently shown to harbour brain swellings, suddenly became comatose and then usually perished was a mystery. One of the first references to causal brain herniation was made by Collier,1 who clearly described cerebellar tonsillar herniation in 1904. He observed accompanying false localising signs in 20 of 161 (12.4%) consecutive cases of intracranial tumour examined clinically and pathologically. He commented:
In many cases of intracranial tumour of long duration, it was found postmortem that the posterior inferior part of the cerebellum had been pushed down and backwards into the foramen magnum and the medulla itself somewhat caudally displaced, the 2 structures together forming a cone-shaped plug tightly …