This document provides an overview of common CT findings in acute intracranial pathology, including trauma and stroke. Key points include: - Extradural hematomas appear as biconvex lenses, while subdural hematomas are crescent shaped. Intraparenchymal hemorrhages can cause mass effect. - Ischemic strokes appear as low density areas that obscure gray-white matter differentiation. Hemorrhagic strokes are centered in basal ganglia. - Subarachnoid hemorrhage has a classic "five-pointed star" appearance around the circle of Willis. It can extend into ventricles and cause hydrocephalus. - Vasogenic edema spares

1. CT of Acute Intracranial
Pathology
Dr Anne Carroll
Dr Eric Heffernan
Department of Radiology
St Vincent’s University Hospital
Dublin, Ireland
www.svuhradiology.ie

2. Introduction
• Head CT is one of the most frequent studies
performed on-call by Radiologists
• The main indications for on-call head CT are
for trauma and for suspected stroke
• This tutorial will illustrate the most common
pathological appearances that we encounter
in these conditions

3. Introduction
• Unlike most CT examinations performed on other
parts of the body, head CT for trauma or stroke is
performed without IV contrast, as the
abnormalities we look for are readily visible on
unenhanced CT
• In some circumstances, IV contrast will
subsequently be injected:
– To perform CT angiography in patients with acute
stroke who may be candidates for thrombectomy
– When the initial non-contrast CT raises the possibility
of an underlying tumour or infection

4. What to look for on head CT
• Haemorrhage
– Acute haemorrhage is bright on CT
– When describing this we can call it ‘dense’, ‘high
attenuation’, or ‘hyperattenuating’
• Oedema
– This is less dense than normal brain and appears
relatively dark (‘decreased density’, ‘low attenuation’)
– Oedema can be ‘cytotoxic’ (grey and white matter
involved, seen in strokes), or vasogenic (white matter
only, seen around tumour, abscess and
intraparenchymal haemorrhage)

5. What to look for on head CT
• Mass effect
– Effacement of sulci (compare to opposite side)
– Effacement of ventricles
– Midline shift
• Hydrocephalus
– Can develop acutely in the setting of subarachnoid
haemorrhage

6. What to look for on head CT
• Skull fracture
– Frequently associated with intracranial
haemorrhage and occasionally pneumocephaly
(intracranial air – most commonly seen when a
fracture extends through the frontal sinus)
– Skull fractures are often difficult to see when
reviewing a CT on regular soft tissue windows so
we need to switch to a bone window to pick them
up*
*’Windows’ are explained in
the CT section of our website

7. Trauma
• Pathology to look for in patients with a history
of head injury:
– Extradural haematoma
– Subdural haematoma
– Subarachnoid haemorrhage
– Intraparenchymal haemorrhage
– Skull fracture
– Combinations of the above

8. Extradural haematoma
• Young patients
• Often associated with a skull fracture
– Injury to middle meningeal vessels
• Characteristic biconvex (‘lens’) shape
• Extension is limited by dural attachments at
skull sutures
• Mass effect including midline shift are usually
present

9. Two different patients with extradural haematomas – these often look exactly like
this and tend not to present much of a diagnostic challenge. Note the scalp haematoma
in the patient on the left (arrow), indicating the site of injury. A skull fracture was also
present in this case (seen on bone windows). Note the mass effect on the left-hand image –
the right lateral ventricle is effaced (compressed) and there is mild midline shift.

10. Midline shift

11. Subdural haematoma
• Older patients/alcoholics
• Due to tearing of bridging veins in subdural
space
• Not limited by sutures so can extend all the
way along the cerebral hemisphere
– Typically crescentic in shape
• Underlying brain is usually atrophic therefore
haematoma needs to be larger before it will
cause midline shift

12. Acute subdural haemorrhage. Note how this crescent shaped
haematoma is not limited by the sutures and in fact has
extended along the cerebellum (arrowhead). Note the midline
shift (dotted line = midline).

13. Subdural haematoma
• Unlike extradural haematomas, subdural
haemorrhages often don’t present in acute phase
• This is important as subacute or chronic subdural
haemorrhage appears different to acute
– Subacute – lower attenuation than acute blood, may
be very similar density to normal brain making it hard
to spot
– Chronic – similar attenuation to CSF, which can also
make this hard to spot
• A mixed picture (e.g. acute on chronic subdural)
is frequently present

14. Chronic subdural haematoma
• The haematoma is less
dense than the adjacent
brain parenchyma
• Note the effaced left
lateral ventricle (*)
*

15. Chronic subdural
haemorrhage is often
bilateral as in this
example

16. Bilateral subacute subdural
haemorrhage
The haematomas in this
case are almost the same
density as the adjacent grey
matter, which can make
them difficult to spot

17. Traumatic subarachnoid haemorrhage
• This is usually confined to a small number of
sulci and can be quite subtle
• It looks very different to the classic picture of
non-traumatic subarachnoid haemorrhage
(see later)
• Look for linear high density between gyri

18. Acute traumatic
subarachnoid haemorrhage
Note the scalp haematoma at the
site of injury (*). The linear high
density extending along several
sulci represents subarachnoid
blood (arrows). There is also some
subdural haemorrhage extending
between the occipital lobe and
the cerebellum (arrowhead).
*

19. Intracerebral haemorrhage
• Following head injury, one or more areas of
intraparenchymal haemorrhage may be visible on
CT
• The typical sites for these ‘contusions’ is in the
inferior aspects of the frontal lobes and the
anterior aspects of the temporal lobes
• They frequently occur directly opposite the side
of the traumatic force to the head (‘contre-coup
injuries’)
• When large, they may rupture into the
subarachnoid space or ventricles

20. Multiple intraparenchymal
haemorrhagic contusions of
varying sizes in the inferior
aspects of both frontal lobes.

21. Skull fracture on bone windows
Depressed skull fracture
Pneumocephaly

22. Head injury with multiple findings:
Depressed skull fracture
Extradural haematoma (yellow)
Intraparenchymal haemorrhage (*)
*
*

23. Acute ischaemic stroke
• Non-contrast CT brain is the initial imaging
modality of choice in suspected CVA
• CT is often normal in the first few hours after
onset of symptoms
– Main role of CT is to exclude haemorrhage, in
order to guide treatment
• Majority of strokes will be visible on CT after
24 hours

24. Acute ischaemic stroke
• CT signs
– Low attenuation in infarcted parenchyma
– Loss of grey-white matter differentiation
– Obscuration of basal ganglia
– Loss of visualization of insula (‘insular ribbon’ sign)
– Dense MCA sign or dot sign
– Mass effect (sulcal +/- ventricular effacement)
– Haemorrhagic transformation may occur

25. Acute left-sided CVA
• Low density parenchyma
• Loss of grey-white matter
differentiation
• Sulcal effacement

26. Subacute (>24 hours) MCA
infarct
• Loss of grey-white
matter differentiation
• Obscured basal ganglia
(normal outlined on left
side)
• Midline shift
• Effaced right lateral
ventricle

27. More examples of subacute infarcts

28. Subtle early left MCA infarct – slightly reduced parenchymal density. Note how the
usually bright grey matter of the insula (the ‘insular ribbon’) has become
indistinguishable on the left (normal right insular ribbon indicated by arrows). This
patient has had previous infarcts – these are the very low density areas in the
occipital lobes (*).
Right Left
*
*

29. MCA dot sign (due to thrombus) Acute MCA infarct (same patient)

30. Dense MCA sign

31. Dense MCA sign with corresponding occlusion on CT angiogram

32. Occipital infarct (left) with subsequent haemorrhagic
transformation (right, arrows)

33. How to tell that an infarct is old:
• This patient has an old right
frontal infarct (yellow arrows)
• Very low density (similar to
CSF)
• No mass effect
• Instead, nearby sulci become
widened and ventricle
enlarges (white arrows)

34. Haemorrhagic stroke
• Hypertensive patients
• Typically centred in basal ganglia

35. Haemorrhagic stroke
• Centred in left basal ganglia and
extending into temporal lobe
• Note mass effect – effaced sulci and
left lateral ventricle
• Also has small haemorrhage on right
side (arrow)

36. Atraumatic subarachnoid
haemorrhage
• Usually due to ruptured
aneurysm
• Dense blood accumulates around
circle of Willis
• Classical appearance is a 5-
pointed star, with blood
extending along left and right
posterior cerebral arteries, left
and right middle cerebral arteries
and anterior cerebral arteries
(these run alongside each other)

37. Atraumatic subarachnoid
haemorrhage
• Haemorrhage may extend into ventricles and
can cause acute hydrocephalus
• CT can be normal with small bleeds, hence
need for lumbar puncture when clinically
suspected
• When a subarachnoid haemorrhage is
detected on CT, a CT angiogram is performed
to search for a treatable aneurysm

38. Classic 5-pointed star appearance of acute subarachnoid haemorrhage
This patient also has acute hydrocephalus (dilated ventricles - *)
* *
*

39. Often, there will be uneven
distribution of blood which
can be a clue to the
location of the causative
aneurysm, as in this case
where it was located at the
tip of the left middle
cerebral artery

40. Subarachnoid haemorrhage with intraventricular extension
(orange arrows) and acute hydrocephalus (yellow arrows)

41. Massive subarachnoid haemorrhage with causative
aneurysm on CT angiography
ACA – anterior cerebral artery, MCA – middle cerebral artery, large arrow - aneurysm

42. The last few examples have shown
dramatic subarachnoid haemorrhage,
however they are often much more
subtle, as in this case
• Linear high density in a small
number of sulci (yellow arrows)
• Small amount of blood in right
lateral ventricle (orange)

43. • Remember, cytotoxic oedema causes low
attenuation in both grey and white matter
– strokes
• Vasogenic oedema only affects the white
matter, sparing the grey matter
– Suggests more sinister pathology
• Primary brain tumour
• Metastases
• Abscess

44. Vasogenic oedema in right frontal lobe (*), sparing the grey matter (arrows)
*

45. (Same patient as previous slide)
• MRI shows how extensive the vasogenic oedema is, and that it also involves white
matter of the left frontal lobe (arrows, left image - this is a FLAIR image, which is
explained in the MRI section of the www.svuhradiology.ie website)
• Post-contrast image on the right shows that there is an enhancing underlying mass,
which turned out to be a glioblastoma (arrows)

46. In this patient, the non-contrast CT image on the left shows extensive vasogenic oedema
with mass effect and midline shift.
IV contrast-enhanced CT on the right shows a huge underlying ring-enhancing mass
(arrows) which turned out to be an abscess. The patient was an intravenous drug abuser.

47. www.svuhradiology.ie