Brain herniation:

DEFINITION:

Displacement of brain tissue from one compartment to another in response to increase intracranial pressure .

Intracranial compartment is divided by rigid dural folds ,if pressure in increased portion of brain are displaced across thses rigid structures,herniation leads to compromise blood supply to compressed tissue producing infarction ,additional swelling and further herniation.

TYPES OF HERNIATION:

1. SUFBFALCIAN [CINGULATE] HERNIATION.

2. TRANSTENTORIAL[UNCINATE] HERNIATION.

3. TONSILLAR HERNIATION.

SUBFALCIAN HERNIATION:

DEFINITION:

Unilateral or asymmetrical expansion of cerebral hemisphere that causes cingulate gyrus to displace under edge of falx cerebri.

This herniation compress the anterior cerebral artery.

TONSILLAR HERNIATION:

DEFINITION:

Displacement of cerebral tonsils through foremen magnum.

This displacement cause compression of brain stem which comprises the vital respiratory and cardialC centers in medulla.

TRANSTENTORIAL HERNIATION:

DEFINITION:

Medial aspect of temporal lobe is compressed against free margins of tentorium.

This leads to compression of third cranial nerve and results in 

• Pupillary dilatation

• Blown pupil

This type of herniation also leads to compression of posterior cerebral artery resulting in ischemic injury of primary visual cortex.

Transtentorial herniation is often accompanied by linear or flame shaped hemorrhage in mid brain.

With further displacement of temporal lobe ,pressure on mid brain compress the contralateral cerebral peduncle against tentorium ,resulting in hemiparesis ipsilateral to the side of herniation.