BRAIN HERNIATION - A REVISION OF CLASSICAL CONCEPTS

This paper is an update on evolving ideas about brain herniations. Fol lowing observations on cerebellar pressure coning that raised doubts a bout its reputed lethal connotations, herniation at the tentorium was re-examined for its role in critically damaging the brain stem. Combin ing clinical, pathologic, computed tomography and magnetic resonance i maging data, it is concluded that temporal lobe herniation is not the means by which the midbrain sustains irreversible damage in acute case s, but rather lateral displacement of the brain at the tentorium is th e prime mover and herniation a harmless accompaniment. Transtentorial herniation has been investigated with computed tomography using the th ree calcification relationship and descent through the tentorial openi ng could not be documented. Bilateral brain stem compression in acute bilateral cases must be distinguished from herniation. Upward cerebell ar herniation is only the sign of an overfull posterior fossa. Subfalc ial herniation is tolerated unless lateral displacement is excessive.