BRAIN HAEMORRHAGE
deep within the brain. This leads to a
condition called
kernicterus.
Brain dam-
age that occurs before, during, or after
birth may result in
cerebral palsy.
OUTCOME
Diffuse damage to the brain may result
in
learning difficulties
and severe physical
disability. Localized brain damage may
cause specific deficits in brain function,
such as disturbances of movement or
speech (see
speech disorders).
Nerve cells
and tracts in the brain and spinal cord
cannot repair themselves once they have
been damaged, but some return of func-
tion may be possible with training, as
patients learn to use other parts of the
brain. (See also
Structure of the brain
box.)
brain death
abscess is an infection following a pene-
trating
brain
injury.
Multiple
brain
abscesses may
occur as a result of
blood-borne infection, most commonly
in patients with a heart-valve infection
(see
endocarditis).
Symptoms of a brain abscess include
headache, drowsiness, vomiting, visual
disturbances, fever, and seizures. There
may also be other symptoms, such as
speech disturbances, that are due to
local pressure. Treatment is with
anti-
biotic drugs
and surgery. A
craniotomy
may be needed to open and drain the
abscess. Untreated, brain abscesses can
cause permanent damage and can be
fatal. Despite treatment, scarring can
cause
epilepsy
in some cases.
brain contusion
Bruising of the brain accompanied by
loss of consciousness, which occurs as
the result of an injury. (See also
brain
damage; concussion.)
brain damage
Degeneration or death of nerve cells
and tracts within the brain that may be
localized to a particular area of the
brain or may be diffuse.
DIFFUSE DAMAGE
One of the most common causes of
diffuse
brain
damage
is
prolonged
cerebral
hypoxia
(an insufficient supply
of oxygen to the brain), which may
occur in a baby during a difficult birth.
Other causes of diffuse damage to the
brain tissue include
cardiac arrest
(cessa-
tion of the heartbeat),
respiratory arrest
(cessation of breathing), drowning, cer-
tain types
of poisoning,
and
status
epilepticus
(prolonged seizures). Diffuse
damage may also occur gradually as a
result of exposure to environmental
pollutants, such as lead or mercury
compounds (see
Minamata disease),
or
if nerve-cell poisons build up in the
brain, as occurs in untreated
phenylketo-
nuria.
Other possible causes of diffuse
brain damage include brain infections
such as
encephalitis
.
LOCALIZED DAMAGE
Localized brain damage may occur as
the result of a
head injury, stroke
(dam-
age to part of the brain caused by an
interruption to its blood supply),
brain
tumour,
or
brain abscess.
At birth, a
raised blood
level of bilirubin
(see
haemolytic disease of the newborn)
can
cause local damage to the
basal ganglia
The irreversible cessation of all func-
tions of the brain, including those of
the brainstem. (See also
death.)
Bleeding within or around the brain
caused either by injury or by the spon-
taneous rupture of a blood vessel. There
brain failure
See
brain syndrome, organic.
brain haemorrhage
DISORDERS OF THE BRAIN
Defects and disorders of the brain have
numerous causes, including infection,
injury,
brain tumour,
or a lack of blood
or oxygen (see
hypoxia).
Brain cells
destroyed by injury or disease cannot
be replaced, so any resulting loss in
function can be difficult to reverse.
Because the brain is encased within
the skull, any space-occupying tumour,
brain abscess,
or
haematoma
(large blood
clot) creates raised pressure, which can
impair the function of the whole brain.
Brain disorders that are localized
in a small region may affect a specific
function, such as speech (see
aphasia
).
However, more often, damage is more
diffuse and the symptoms can be varied
and numerous.
The brain may also be damaged by a
blow to the head (see
head injury
).
Congenitaldefects
Some brain disorders are congenital
(present from birth) due to genetic or
chromosomal disorders, as in
Down's
syndrome.
Structural defects during fetal
development include
hydrocephalus
(water on the brain) and
anencephaly
(congenital absence of the brain).
Impaired blood and oxygen supply
Brain cells can survive only a few minutes
without oxygen. A reduced supply may
occur at birth, causing
cerebral palsy.
Later
in life, choking or arrest of breathing and
heartbeat can cause hypoxia (oxygen lack).
From middle age onwards,
cerebro-
vascular disease,
which impairs the blood
supply to one or more regions of the
brain, is the most important cause of brain
disorders. If an artery within the brain
becomes blocked or ruptures, leading to
haemorrhage, the result is a
stroke
.
Infection
Encephalitis
(infection within the brain)
may be due to a virus.
Meningitis
(infection
of the membranes surrounding the brain)
is generally due to bacterial infection.
Creutzfeldt-Jakob disease
is a rare, fatal
brain disease associated with an infective
agent called a prion, which, in some cases,
has been linked with
bovine spongiform
encephalopathy
(BSE), a disease in cattle.
Degenerative disorders
Multiple sclerosis
is a progressive disease
of the brain and spinal cord. Degenera-
tive brain diseases include
Alzheimer's
disease
and
Parkinson's disease.
Other disorders
Emotional or behavioural disorders are
often called psychiatric illnesses, but the
distinction between these and
neurological disorders is unclear. In
many illnesses, such as
depression
and
schizophrenia,
there may be an under-
lying disturbance of brain chemistry.
INVESTIGATION
Procedures used to investigate brain
disorders and function include tests
o f reflexes and of mental and physical
abilities. Electrical activity may be
measured with an
EEG.
Physical
abnormalities can be found using
brain imaging
techniques such as
angiography, CTscanning,
or
MRI.
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