Brain herniation is the pathologic displacement of brain tissue driven by pressure gradients between compartments (Image. Brain Herniation). The brain is encased within the skull; any rise in intracranial pressure is limited to some extent by the compensatory displacement of cerebrospinal fluid (CSF) and changes in cerebral blood volume, as evident by the Monro-Kellie doctrine. When intracranial pressure increases despite these compensatory mechanisms, certain parts of the brain herniate across rigid dural folds (falx or tentorium) or through skull openings (eg, the foramen magnum), producing characteristic herniation syndromes. Brain herniation is a life-threatening event and needs urgent attention. Common clinically described types of brain herniation include:
Subfalcine herniation: This type of herniation involves the cingulate gyrus, which is pushed against the falx cerebri (Image. Subfalcine Hernation).
Uncal herniation: This herniation involves the medial temporal lobe, which is often squeezed by a mass under and across the tentorium (Image. Subdural Hematoma and Uncal Herniation)
Central descending transtentorial herniation: This herniation involves the downward displacement of the diencephalon and midbrain through the tentorial notch, typically due to diffuse cerebral edema or bilateral mass effect.
Tonsillar herniation: This type of herniation forces the cerebellar tonsils through the foramen magnum.
Upward (ascending) transtentorial herniation: This occurs when a posterior fossa mass effect drives cerebellar structures upward through the tentorial notch, distorting the midbrain and potentially obstructing CSF pathways and venous drainage.
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