Introduction to CT Brain imaging. Download the presentation for best effect (animations don't function properly online).

1. Introduction to
Brain CT : Part 2
RAH Radiology

2. Introduction to Brain Imaging : CT scans
How to interpret CT brain:
• Film quality / technical factors
• Important anatomic structures
• Basic patterns of disease
Warning:
This is a big topic. Important phrases and
concepts are bolded.

3. Anatomy

4. Introduction to Brain Imaging : CT scans
• Important anatomic structures
• Describe cortical features
• Deep brain structures
• CSF spaces
• Vessels
There are many ways to describe
the organisation of the cerebrum
(upper brain).
The most common method is to
describe the cerebrum
anatomically; naming areas by
location. The major divisions are
the lobes.
These divisions are not particularly
useful for diagnosis.
Frontal lobe Parietal lobe
Temporal lobe
Occipital
lobe

5. Introduction to Brain Imaging : CT scans
• Important anatomic structures
• Describe cortical features
• Deep brain structures
• CSF spaces
• Vessels
The cerebrum can also be
described functionally. There are
many methods to do this, but the
important radiological elements
are fairly macroscopic:
Inputs / sensorium - blue
Output / motor - red
Complex functions - yellow

6. Introduction to Brain Imaging : CT scans
• Important anatomic structures
• Describe cortical features
• Deep brain structures
• CSF spaces
• Vessels
Several specific areas of interest
are shown on the diagram. These
regions help us identify areas to
focus on given the clinical
symptoms.
Note the proximity of Broca’s area
and the “mouth area” of the
motor cortex, and Wernicke’s area
and the auditory cortex. Areas
with similar functions are often co-
located.
1
3
4
6
1. Broca’s area – expressive dysphasia
2. Lower motor cortex (mouth/tongue) – dysarthria
3. Upper motor cortex (limbs) – hemi/monoparesis
4. Wernickie’s area – receptive dysphasia
5. Auditory cortex – cortical deafness
6. Visual cortex – homonymous hemianopia
5
2

7. Introduction to Brain Imaging : CT scans
• Important anatomic structures
• Describe cortical features
• Deep brain structures
• CSF spaces
• Vessels
The cerebrum can also be
described in terms of the blood
supply:
Anterior cerebral artery - red
Middle cerebral artery - green
Posterior cerebral artery - purple
These divisions can help
differentiate diagnosis, for
example embolic CVA vs
“watershed” CVA (global hypoxia).

8. Introduction to Brain Imaging : CT scans
• Important anatomic structures
• Describe cortical features
• Deep brain structures
• CSF spaces
• Vessels
Another useful way to describe the
blood supply is:
Anterior circulation - orange
Posterior circulation - blue
The anterior circulation is supplied
via the carotids, the posterior
circulation via the vertebral
arteries. This helps us identify a
likely source of embolus, e.g.
cardiac vs ICA origin.

9. Introduction to Brain Imaging : CT scans
From the skull base on the left to vertex on the right identify:
• Anterior and posterior circulation
• ACA, MCA and PCA territories
Click forward to highlight these distributions.

10. Introduction to Brain Imaging : CT scans
• Important anatomic structures
• CSF spaces
• Vessels
• Deep brain structures
One of the most useful diagnostic
features to assess an intracranial
abnormality is whether the
pathology is within the brain
tissue, or outside it.
These locations are called intra-
axial and extra-axial respectively.
The extra-axial spaces are the
meningeal spaces. These either
contain CSF or exist as potential
spaces.
Occipital
lobe

11. Introduction to Brain Imaging : CT scans
• Important anatomic structures
• CSF spaces
• Vessels
• Deep brain structures
The other major CSF spaces are
the ventricles.
These are technically in continuity
with the subarachnoid space, but
they are best thought of as
somewhere in between intra-axial
and extra-axial because pathology
from both locations can extend
into the ventricles.
Occipital
lobe

12. Introduction to Brain Imaging : CT scans
Occipital
lobe
The ventricles are somewhat difficult to understand anatomically, because the lateral
ventricles are oriented obliquely in the coronal plane. This is an important shape to
understand in relation to the deep brain structures.
The easiest way to think of the orientation of the lateral ventricles is as reversed “C “
shapes that are more lateral at inferiorly when seen from the front. This follows the
shape of the brain; the temporal lobes are more lateral than the frontal or parietal
lobes.

13. Introduction to Brain Imaging : CT scans
• Important anatomic structures
• CSF spaces
• Vessels
• Deep brain structures
The lateral ventricles are also
called the 1st and 2nd ventricles
(although which is which is not
important).
The 3rd and 4th ventricles are
unpaired CSF spaces, located in
the midline.
The 3rd is just below the lateral
ventricles, the 4th is at the level of
the medulla.
Occipital
lobe

14. Introduction to Brain Imaging : CT scans
• Important anatomic structures
• CSF spaces
• Vessels
• Deep brain structures
CSF flows between the ventricles
via small channels which can be
easily obstructed.
The communication between the
lateral ventricles and the 3rd
ventricle is via the paired foramina
of Monroe. These are at the front
of the third ventricle.
Occipital
lobe
Lateral ventricles
Third ventricle
Foramen of
Munroe

15. Introduction to Brain Imaging : CT scans
• Important anatomic structures
• CSF spaces
• Vessels
• Deep brain structures
CSF flows between the ventricles
via small channels which can be
easily obstructed.
The communication between the
3rd ventricle and 4th ventricle is via
the cerebral aqueduct, at the level
of the midbrain.
The fourth ventricle drains into the
subarachnoid space at the
craniocervical junction (blue circle)
Fourth ventricle
Third ventricle
Cerebral aqueduct

16. Introduction to Brain Imaging : CT scans
• Important anatomic structures
• CSF spaces
The extra-axial spaces are defined
by the meninges; connective tissue
layers between the brain and the
skull.
Dura - runs along the inner surface
of the skull. The inner layers run
along the falx and tentorium.
Arachnoid - runs loosely around
the outside of the brain.
Pia - is closely adherent to the
brain, following the gyri.
Occipital
lobe

17. Introduction to Brain Imaging : CT scans
• Important anatomic structures
• CSF spaces
The extra-axial spaces are
described by their relationship to
the meninges.
Extradural space - a potential
space between the bone and dura.
The outer part of the dura is
bound to the skull sutures.
Subdural space - a potential
between the dura and arachnoid.
Subarachnoid space - between the
arachnoid and pia. Contains CSF.
Subpial space – a potential space
between the pia and brain, of little
diagnostic significance.
Occipital
lobe

18. Introduction to Brain Imaging : CT scans
• Important anatomic structures
• CSF spaces
Of these meningeal spaces, only
the subarachnoid is normally
appreciated; it contains CSF.
This includes the CSF over the
cerebral convexities, in the sulci
and in the basal cisterns.
The most important basal cistern is
the suprasellar cistern. This is low
in the brain (just above the
pituitary fossa or sella) and looks
like a star.
Occipital
lobe

19. Introduction to Brain Imaging : CT scans
• Important anatomic structures
• CSF spaces
The CSF spaces (i.e. the
subarachnoid space) contains
most of the vessels that supply
and drain the brain.
The Circle of Willis matches the
“star” shape of the suprasellar
cistern.
The limbs of the star contain the
cerebral arteries.

20. Introduction to Brain Imaging : CT scans
• Important anatomic structures
• CSF spaces
• Vessels
Reviewing the arterial vascular
territories, you can appreciate how
the path of the vessel determines
the pattern of blood supply.
Click to show the territories in
relation to the vessels.
• ACA, MCA and PCA territories
Occipital
lobe

21. Introduction to Brain Imaging : CT scans
• Important anatomic structures
• CSF spaces
• Vessels
• Deep brain structures
There are important structures in
the brain other than the cerebral
cortex. These include aggregations
of neurons, called nuclei, and
communication pathways.
Nuclei, being the locations of
neurons, are part of the grey
matter. What central grey matter
can you see on this image?
The basal ganglia are partially
visible here. Notice the density is
the same as the cerebral cortex.

22. Introduction to Brain Imaging : CT scans
• Important anatomic structures
• CSF spaces
• Vessels
• Deep brain structures
The basal ganglia are a group of
deep brain nuclei clustered in the
lower cerebral hemispheres.
The parts of the basal ganglia seen
readily on CT imaging are the
lentiform nucleus and the head of
the caudate nucleus.
The lentiform nucleus is ‘lens-
shaped’ and is appreciated
alongside the third ventricle.
The caudate head sits against the
anterior lateral ventricle.

23. Introduction to Brain Imaging : CT scans
• Important anatomic structures
• CSF spaces
• Vessels
• Deep brain structures
The other major grey matter
structure associated with the basal
ganglia are the paired thalami,
which look like eggs along the
third ventricle.
The deep brain nuclei are similar,
in that they are multipurpose / not
specialised.
They are often thought of as
“integrating” other functions, with
major roles in sensation, motor
control and learning.

24. Introduction to Brain Imaging : CT scans
• Important anatomic structures
• CSF spaces
• Vessels
• Deep brain structures
There are also several major white
matter pathways in the brain,
communicating between brain
areas or to / from the spinal cord.
At the level of the basal ganglia,
the most important is the internal
capsule. This contains the axons of
the sensory and motor neurons. A
single insult here, like a stroke, can
cause severe disability.
Much like the cortex itself, the
anterior half carries motor fibres
and the posterior half carries
sensory fibres.

25. Introduction to Brain Imaging : CT scans
• Important anatomic structures
• CSF spaces
• Vessels
• Deep brain structures
There are also several major white
matter pathways in the brain,
communicating between brain
areas or to / from the spinal cord.
The major communication
between hemispheres is the
corpus callosum. This is best seen
on the sagittal view in the midline.
The corpus callosum is only rarely
involved with pathology.

26. Introduction to Brain Imaging : CT scans
• Important anatomic structures
• CSF spaces
• Vessels
• Deep brain structures
The corpus callosum can also be
seen on axial views. It curls around
the ventricles, so the superior
portion is hard to see, but the
anterior and posterior elements
are easily identified.

27. Pathology

28. Introduction to Brain Imaging : CT scans
The most important high density
pathology you will see is acute
haemorrhage.
There are many different types of
haemorrhage. Location is usually
the best clue to identify the cause
(aside from clinical history).
Extra-axial pathology pushes the
brain away. Intra-axial pathology
expands the brain.
This is an acute intra-axial
haemorrhage.
• Basic patterns of disease
• Approach to CT scans
• Low density pathology
• High density pathology

29. Introduction to Brain Imaging : CT scans
Intra-axial bleeds are inside the
brain, and are usually caused by
hypertension (deep brain regions),
underlying disease (e.g.
amyloidosis) or trauma (coup /
contrecoup injury, shown here).
Extra-axial bleeds within the
meningeal spaces, and are usually
traumatic or aneurysmal.
• Basic patterns of disease
• Approach to CT scans
• Low density pathology
• High density pathology

30. Introduction to Brain Imaging : CT scans
The shape of extra-axial bleeding
helps differentiate the source.
The outer layer of the dura is
strongly bound to the skull sutures,
so extradural blood cannot pass.
This creates the classic biconvex or
“lens shaped” appearance, as the
haematoma is pinned down at
either end.
This is an acute extradural
haemorrhage.
• Basic patterns of disease
• Approach to CT scans
• Low density pathology
• High density pathology

31. Introduction to Brain Imaging : CT scans
Subdural haematomas are not
bound by the skull sutures, so can
flow around the brain. This creates
the typical semilunar or “crescent
moon” appearance.
Blood outside vessels becomes less
dense over time, and can be similar
to brain tissue or even fluid.
This is an image of bifrontal chronic
subdural haematomas. Notice that
you can see the displaced arachnoid
mater on the left.
• Basic patterns of disease
• Approach to CT scans
• Low density pathology
• High density pathology

32. Introduction to Brain Imaging : CT scans
Subarachnoid haematomas follow
the shape of the brain.
This is an acute subarachnoid
haemorrhage.
In extra-axial bleeds, a central
location (the basal cisterns) is
suspicious for aneurysm rupture
(shown here).
A peripheral location is often
related to trauma.
• Basic patterns of disease
• Approach to CT scans
• Low density pathology
• High density pathology

33. Introduction to Brain Imaging : CT scans
The only other common high density
change you will see in the brain is
with calcification.
Throughout the body, calcification is
usually benign. In the brain, the
arteries, pineal gland, choroid plexus
and basal ganglia (shown here)
often calcify with age.
Some tumours calcify, such as
meningiomas. Again, calcified
tumour are usually benign.
• Basic patterns of disease
• Approach to CT scans
• Low density pathology
• High density pathology

34. Introduction to Brain Imaging : CT scans
CSF flows through the ventricular
system and extra-axial spaces,
constantly produced in the
ventricles and resorbed in the
peripheral subarachnoid spaces.
If the flow of CSF is obstructed, the
ventricles can dilate, this is called
hydrocephalus.
The most important causes are
tumours and subarachnoid blood
(which can block the resorption of
the CSF).
• Basic patterns of disease
• Approach to CT scans
• Low density pathology
• High density pathology

35. Introduction to Brain Imaging : CT scans
The obstruction can occur at any level. Most common locations are:
• mass at the foramen of Munroe (unilateral lateral ventricle hydrocephalus)
• stenosis at the cerebral aqueduct (lateral and 3rd ventricle dilatation)
• subarachnoid blood obstructing CSF resorption (global ventricular dilatation).
This case shows stenosis of the cerebral aqueduct.
Third ventricleFourth ventricle

36. Introduction to Brain Imaging : CT scans
As we have seen, expansion of CSV
spaces can also be due to volume
loss.
In this case the ventricles of this
elderly patient are larger than
expected, but the sulci are also
prominent. This suggest generalised
atrophy / volume loss.
Always look for enlargement of the
ventricles out of keeping with the
sulcal size.
• Basic patterns of disease
• Approach to CT scans
• Low density pathology
• High density pathology