BRAIN IMAGING
B
SITES OF BRAIN HAEMORRHAGE
Haemorrhages within the skull fall into four main categories - extradural, subdural,
subarachnoid, and intracerebral - according to the site of the bleeding in relation
to the brain and its protective coverings (the meninges). The causes and effects of
the bleeding and the outlook for the patient vary depending on which category the
haemorrhage falls into.
Haemorrhage
, S c a l p
S u b c u t a n e o u s
l a y e r
S k u l l
D u ra m a t e r
A r a c h n o i d
P ia m a t e r
B r a in
S u b a r a c h n o i d
E x t r a d u r a l
S u b d u r a l
I n t r a c e r e b r a l
Intracerebral haemorrhage
This CT scan shows bleeding in the
brain tissue (cerebral haemorrhage).
are four possible types of brain haemor-
rhage:
subdural, extradural, subarachnoid,
and
intracerebral
(see the illustrated box).
Extradural and subdural haemorrhages
are usually caused by a blow to the head
(see
head injury).
Subarachnoid and intra-
cerebral haemorrhages tend to occur
spontaneously due to rupture of
aneur-
ysms
or small blood vessels in the brain.
brain imaging
Techniques that can provide pictures of
the brain. Brain imaging techniques are
used to detect injury or disease of the
brain and include
X-rays
,
angiography
,
CT
scanning, MRI
(magnetic resonance imag-
ing),
PET
(positron emission tomography)
scanning,
and
SPECT
(single photon
emission CT).
INVESTIGATION OF BRAIN STRUCTURE
CT scanning gives images of the brain
substance; it provides clear pictures of
the ventricles (fluid-filled cavities) and
can reveal tumours, blood clots, strokes,
aneurysms,
and abscesses.
MRI (magnetic resonance imaging)
produces very detailed images of the
brain’s structure. This technique is also
used to detect patches of abnormal
brain tissue, as seen in
multiple sclerosis
.
Angiography involves the injection of
a contrast medium that shows up the
blood vessels in the brain on
X-ray.
It is
used to investigate aneurysms and other
circulatory disorders.
INVESTIGATION OF BRAIN FUNCTION
PET and SPECT scanning are specialized
forms of
radionuclide scanning
that use
small amounts of radioactive material to
provide information about brain func-
tion as well as structure. They enable
blood flow and metabolic activity in the
brain to be measured.
Functional magnetic resonance imag-
ing (fMRI) can be used to determine
which parts of the brain are activated by
different sensations or activities, such as
sight or movement of the fingers. This
technique is used to assess how the
brain is working.
Ultrasound scanning,
through the fon-
tanelles (holes where the skull bones
have yet to fuse), can detect bleeding in
the brain only in premature or very
young babies; ultrasound waves cannot
penetrate the bones of a mature skull.
brainstem
A stalk of nerve tissue that forms the
lowest part of the brain and links with
the spinal cord. The brainstem acts partly
as a highway for messages travelling
between other parts of the brain and
spinal cord. It also connects with 10 of
the 12 pairs of
cranial nerves
(which
emerge directly from the underside of
the brain) and controls basic functions
such as breathing, vomiting, and eye
reflexes. Brainstem activities are below
the level of consciousness, and they
operate mainly on an automatic basis.
STRUCTURE
The brainstem is composed of three
main parts: the midbrain, pons, and
medulla. Attached to the back of the
brainstem is a separate part of the brain,
the
cerebellum,
which is concerned with
balance
and
coordinated
movement.
Running
longitudinally
through
the
middle of the brainstem is a canal; this
widens in the pons and medulla to
form the fourth ventricle (cavity) of the
brain, which contains the circulating
cerebrospinal fluid
.
Midbrain
The midbrain is the smallest
section of the brainstem. This part con-
tains the nuclei (nerve-cell centres) of
the third and fourth cranial nerves,
which control eye movements and the
size and reactions of the pupil. It also
contains cell groups, such as the sub-
stantia
nigra,
involved
in
smooth
coordination of limb movements.
Pons
The pons contains thick bundles of
nerve fibres that connect with the
cere-
bellum.
It also houses the nuclei for the
fifth to eighth cranial nerves, and relays
sensory information from the ear, face,
and teeth, as well as the signals that
move the jaw, adjust facial expressions,
and produce some eye movements.
Medulla
The medulla resembles a thick
extension of the spinal cord. It contains
the nuclei of the ninth to 12th cranial
nerves. by which it receives and relays
taste sensations from the tongue and
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