Mechanical displacement of normal brain relative to another anatomic region and is secondary to mass formation from trauma, malignancy, ischemia or infection.
5 categories: transtentorial, subfalcine/cingulate, foramen magnum/tonsillar, sphenoid and extra cranial herniation.
All categories are associated with a specific neurologic syndrome.
Transtentorial herniation refers to a downward or upward displacement of the brain via the tentorium at the level of the incisura.
Descending herniation occurs when the supratentorial brain herniates downward through the incisura.
An ascending transtentorial herniation occurs when the infratentorial herniation occurs upward through the incisura.
Uncal herniation is a subtype of descending transtentorial herniation.
Cerebral mass effect pushes the supratentorial brain through the incisura and causes neurologic symptoms.
Posterior fossa masses pushes the infratentorial brain through the incisura with ascending transtentorial herniation.
Ascending transtentorial herniation causes distortion of the midbrain with the flattening of the posterior quadrigeminal plate and narrowing of the bilateral ambient cisterns.
Ascending transtentorial herniation is caused most commonly by posterior fossa tumors and less commonly extra-axial and intra-axial hematomas of the posterior fossa.