Overview
Brain herniation is a life-threatening event that occurs secondary to elevated intracranial pressure.
There are different types of brain herniation depending on ‘which way’ the brain herniates:
- Subfalcine herniation
- Central herniation
- Transtentorial/uncal herniation:
- Tonsillar herniation
- Transcalvarial herniation
General Features
Overview
General features suggesting brain herniation include:
- Cushing’s triad – suggests a pre-terminal state and indicates brain imminent herniation
- Irregular breathing
- Hypertension with a wide pulse pressure
- Bradycardia
- Reduced levels of consciousness
- Headaches
- Vomiting – due to compression of the vomiting centre in the medulla oblongata
- Papilloedema
More specific features are discussed below.
Types of Brain Herniation
Subfalcine (cingulate) herniation
The cingulate gyrus moves under the falx cerebri. It does not put as much pressure on the brainstem compared to other types of herniation. It may lead to central herniation and can interfere with the anterior cerebral arteries. This may present with lower limb weakness.
Central herniation
The diencephalon and parts of both temporal lobes are squeezed through the tentorium cerebelli. This can stretch basilar arteries and tear them.
Transtentorial/uncal herniation
The lower part of the temporal lobe (uncus) moves towards the tentorium and puts pressure on the brainstem. This may lead to:
- CN III compression:
- Fixed and dilated pupils initially due to compression of the parasympathetic nerve fibres
- As time progresses, motor effects may arise – ‘down and out eye’
- Brainstem dysfunction:
- As time goes on a decerebrate or decorticate posture may arise
- Respiratory centre depression
Tonsillar herniation
Also known as ‘coning’, this describes the downward displacement of the cerebellar tonsils through the foramen magnum. This can put pressure on the brainstem. Features include:
- Respiratory depression – due to pressure on cardiorespiratory centres
- Decerebrate posturing
- Blood pressure instability – due to pressure on cardiorespiratory centres
Congenital tonsillar herniation of the cerebellum is known as a Chiari malformation.
Transcalvarial herniation
This is where the brain squeezes through a fracture or surgical opening in the skull (calvarium).
Management
Management involves:
- Identifying and treating the underlying cause (e.g. tumour removal, haematoma removal, cerebrospinal fluid (CSF) drainage
- Supportive measures such as those mentioned in the management of elevated intracranial pressure.
