BRAIN ABSCESS
BRAIN, DISORDERS OF
balance, posture, and muscular coordi-
nation. Both of these regions operate at
a subconscious level.
The brain and spinal cord are encased
in 3 layers of membranes, known as
meninges. Cerebrospinal fluid
circulates
between the layers and within the 4 main
brain cavities called
ventricles.
This fluid
helps to nourish and cushion the brain.
The brain receives about 20 per cent of
the blood from the heart's output.
brain abscess
A collection of pus, sur-
rounded by inflamed tissues, within the
brain or on its surface. The most com-
mon sites are the frontal and temporal
lobes of the
cerebrum
in the forebrain.
Brain abscesses may occur after a
head injury, but most cases result from
the spread of infection from elsewhere
in the body, such as the middle ear or
sinuses. Another cause is an infection
following a penetrating 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
include headache, drowsiness, vomiting,
visual disturbances, fever, seizures, and
symptoms, such as speech disturbances,
that are due to local pressure. Treatment
is with
antibiotic drugs
and surgery. A
craniotomy
may be needed to open and
drain the abscess. Untreated, brain abs-
cesses can cause permanent damage or
can be fatal. Despite treatment, scarring
can cause
epilepsy
in some cases.
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 diffuse. Diffuse
damage most commonly results from
prolonged cerebral
hypoxia
(which may
occur in a baby during a difficult birth),
cardiac arrest
,
respiratory arrest
,
or
causes such as poisoning or
status
epilepticus
(prolonged convulsions). The
damage may also occur gradually due
to environmental pollutants such as lead
or mercury compounds (see
Minamata
disease
) or if nerve-cell poisons build up
in the brain, as in untreated
phenylketo-
nuria.
Other possible causes include
brain infections such as
encephalitis
.
Localized brain damage may occur as
a result of a
head injury, stroke, brain
tumour
, or
brain abscess
. At birth, a
raised blood level of bilirubin (in
haem -
olytic disease o f the newborn)
causes
local damage to the
basal ganglia
deep
within the brain. This leads to a condi-
tion called
kernicterus
. Brain damage
that occurs before, during, or after birth
may result in
cerebral palsy
.
Damage to the brain may result in dis-
abilities such as
learning difficulties
or
disturbances of movement or speech.
Nerve cells and tracts in the brain and
spinal cord cannot repair themselves
once they have been damaged, but some
return of function may be possible.
brain death
The irreversible cessation
of all functions of the brain, including
the brainstem. (See also
death.)
brain, disorders of
Defects and disor-
ders of the brain, which may have one of
numerous causes including infection, inj-
ury,
brain tumour
, or a lack of blood or
oxygen (
hypoxia
). Because the brain is
encased in the skull, any space-occupy-
ing tumour,
brain abscess
, or
haematoma
creates raised pressure, which impairs
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
). More
often, damage is more diffuse and the
symptoms can be varied and numerous.
Some brain disorders are
congenital
due to genetic or chromosomal disor-
ders, as in
Down's syndrome.
Structural
defects that arise during the develop-
ment of the fetus in the womb include
hydrocephalus and anencephaly
.
Reduced oxygen supply may occur at
birth, causing
cerebral palsy
. Later in
life, cerebral hypoxia can result from
choking or from arrest of breathing and
heartbeat. From middle age onwards,
cerebrovascular disease
is the most
important cause of brain disorder. If an
artery within the brain becomes blocked
or ruptures, leading to haemorrhage,
the result is a
stroke.
The brain may also
be damaged by a blow to the head see
head injury
).
Infection within the brain
(enceph-
alitis)
may be due to viral infection.
Infection of the membranes surrounding
the brain (
meningitis
) is generally due
to bacterial infection.
Creutzfeldt-Jakob
B
91
previous page 89 BMA Illustrated Medical Dictionary read online next page 91 BMA Illustrated Medical Dictionary read online Home Toggle text on/off