Brain herniation: a revision of classical concepts

Area of Science:

• Neurology
• Neurosurgery
• Radiology

Background:

• Traditional understanding of brain herniation, particularly transtentorial herniation, suggests it is a primary cause of irreversible brain stem damage.
• Cerebellar pressure coning has been historically considered a highly lethal consequence of increased intracranial pressure.

Purpose of the Study:

• To re-examine the role of herniation at the tentorium in critically damaging the brain stem.
• To clarify the mechanisms of brain stem injury in acute intracranial pressure events.
• To differentiate true herniation from other forms of brain compression.

Main Methods:

• Review and synthesis of clinical data.
• Analysis of pathological findings.
• Evaluation of computed tomography (CT) and magnetic resonance imaging (MRI) data.

Main Results:

• Temporal lobe herniation is not the primary cause of irreversible midbrain damage in acute settings.
• Lateral displacement of the brain at the tentorium is identified as the main driver of brain stem injury.
• Transtentorial herniation, as visualized by CT, could not be definitively documented in terms of descent through the tentorial opening.
• Upward cerebellar herniation is an indicator of posterior fossa volume excess.
• Subfalcine herniation is generally well-tolerated unless significant lateral displacement occurs.

Conclusions:

• Lateral brain displacement at the tentorium, rather than herniation itself, is the critical factor in acute brain stem damage.
• Bilateral brain stem compression requires distinction from herniation syndromes.
• Upward cerebellar herniation and subfalcine herniation have specific interpretations related to intracranial dynamics.