Cerebral oedema is
accumulation of tissue fluid in between the cells of the nervous system.
after damage from many different causes, it is the result of breakdown of the
blood-brain barrier due to ischaemia, trauma, inflammation, and metabolic
disorders. This breakdown also occurs around tumours.
Severe cerebral swelling is associated with a rise in the pressure within the
skull (raised intracranial pressure).
Expanding intracranial lesions cause raised intracranial pressure
The cranial cavity is divided into three spaces by the falx and tentorium
If a lesion expands within the brain substance, there is only a
limited amount of room within the skull to accommodate it.
in the size of the ventricles and sub-arachnoid space occurs, but once this
volume is used, further increase in the size of a lesion is associated with
increase in intracranial pressure.
Swellings within the brain are particularly dangerous when they lead to rapid
local expansion of one part, causing it to shift from one brain compartment to
another, a process termed cerebral herniation.
There are four types of cerebral herniation:
is caused by lesions expanding in one cerebral
hemisphere. There is herniation of the medial part of the temporal lobe down
over the tentorium cerebelli to compress the upper brain stem.
The third cranial
nerve becomes first stretched, then compressed on the side of the lesion, giving
rise to a fixed dilated pupil.
Branches of the posterior cerebral artery are
also compressed as the brain herniates, causing secondary infarction of the
As the midbrain is distorted by compression, small vessels are
torn and secondary haemorrhage occurs into the brain stem leading to death.
Cerebellar tonsillar herniation
is caused by expanding lesions in the
posterior fossa. There is herniation of the lower part of the cerebellum (cerebellar
tonsils), which pushes down into the foramen magnum and compresses the medulla;
this process is also known as coning.
As the medulla is compressed, it causes
cessation of respiration and death.
This may be precipitated by performing a
lumbar puncture in a person with a mass in the brain. Withdrawal of CSF allows a
pressure gradient to develop and there is rapid coning with death.
puncture should never be performed until the possibility of a mass lesion in the
skull has been excluded.
Cingulate gyrus (subfalcial) herniation
is caused by a lesion in one of the cerebral
hemispheres, resulting in movement of the cingulate gyrus beneath the falx
This is often associated with compression of the adjacent anterior
cerebral artery, leading to secondary cerebral infarction.
is caused by generalized swelling of both
cerebral hemispheres. There is compression of the ventricles, with descent of
the thalamus and midbrain through the tentorial hiatus.
This causes tearing of
vessels in the midbrain, with secondary haemorrhage.