Transtentorial herniation can occur when the brain moves either up or down across the tentorium, called ascending and descending transtentorial herniation respectively; however descending herniation is much more common.
General imaging features include
Flattening or reversal of the smile shaped quadrigeminal cistern.
Obliteration of the quadrigeminal and superior cerebellar cistern in severe cases
“spinning top” appearance of midbrain due to bilateral compression of the posterior aspect of the midbrain may be associated with infarct in the territory of posterior cerebral and superior cerebellar arteries hydrocephalus as the result of the pressure of the cerebellum on the cerebral aqueduct
Cranial shift of vermis and parts of superomedial cerebellar hemisphere through tentorium incisura
Compressed superior cerebellar, vermian cisterns and forth ventricle