Transtentorial herniation is a type of cerebral herniation broadly divided into two major types based on the direction of herniation: downwards due to supratentorial mass effect and upward due to infratentorial mass effect.
Downward transtentorial herniation
Downward herniation occurs when there is mass effect upon or from within the cerebral hemispheres. The pattern of herniation can be divided into lateral and central herniation.
Lateral herniation occurs due to unilateral or asymmetric mass effect. The medial parts of the temporal lobe are pushed into the ambient cistern and up against the brainstem. This can be further divided according to whether the herniation is predominantly anterior (uncal herniation), which is most common, or posterior (posterior parahippocampal gyrus and anterior part of the lingual gyrus ) . Anterior and posterior herniation can occur separately or together .
Upward transtentorial herniation
Ascending transtentorial herniation occurs due to mass effect within the posterior fossa.