The term “herniation of the brain” has been used at least since Cushing’s article in 1905 , but the symptoms he associated with it have been observed at least since the 1850s. , Doctors who performed increasing amounts of autopsies were studying disease post mortem, and observed that in some individuals who had died from brain tumours and other intracranial masses, specific parts of the brain were deformed in a more or less repetitive pattern. A theory successively emerged: An expansive mass increases intracranial pressure locally, and owing to the compartmentalizing of the rigid cranial cavity, most notably the falx cerebri and the tentorium cerebelli, a localized pressure increase led to brain tissue protruding onto the adjacent compartment. The resulting distortion might induce symptoms and signs attributable to direct pressure on sensitive structures and / or to ischemia, symptoms like pupillary changes, decreasing level of consciousness, dysautonomia and characteristic posturing. Different clinical-anatomical concepts have been described, this paper describes subfalcine, transsphenoidal, uncal, transtentorial, cerebellar tonsillar and external herniation.
With the introduction of CT about 1975-80 and MRI about 1980-85 doctors could study the brain ante mortem as the symptoms progressed, and correlate symptoms with the pictures to form new theories about the mechanisms and course of the disease.
There have been at least three different approaches, or “schools”: The clinical, the anatomical-pathological and the radiological. The unavoidable result is three different ways of describing herniation, and all of them are found in recent literature. The author therefore has to conclude that herniation is not completely understood, and more research is needed. Some common ground could be attainable and lead to improved cross-disciplinary understanding.
As concerns “spinal tap” some attention will be given to some aspects of herniation of the cerebellar tonsils as a feared and potentially fatal complication. The author makes a swift review of literature on the subject, and finds recent studies suggesting a connection in about five percent of the cases.