1. Dr lokesh kumar meena
Dept of Radiodiagnosis
MGIMS, Sevagram

2. About this presentation
This presentation will give you a systematic approach
to head CT
By the end you should be familiar with normal
anatomy and be able to identify classic abnormalities
on CT
You can test your knowledge with the short cases at
the end

3. Types of head CT’s
Non-contrast
Contrast
IV contrast is given to better evaluate:
 Vascular structures
 Tumors
 Sites of infection
Relative contraindications:
 Allergy, renal failure

4. Common Indications for Head CT
Cranial-facial trauma
Acute stroke
Suspected subarachnoid or intracranial hemorrhage
Evaluation of headache
Evaluation of sensory or motor function loss
Evaluation of sinus cavities

5. CT basics
Before we begin, there are key concepts you should
be familiar with:
Hounsfield units
Windowing & leveling
Planes

6. What’s a Hounsfield Unit?
Named after the inventor of CT
CT scanners record the attenuation (brightness) of each
pixel in Hounsfield Units (HU)
This number represents the relative density of the
scanned substance
Ranges from -1000 to +1000

7. Hounsfield Unit (HU)
Different substances have different relative densities and
thus, different Hounsfield units
 Air: -1000 HU
 Fat: -50 HU
 Water: 0 HU
 Soft tissue: +40 HU
 Blood: +40-80 HU
 Stones: +100 to +400 HU
 Bone: +1000 HU
Therefore, if you’re not sure what you’re looking at, measure
its Hounsfield Unit!

8. How to measure HU
In EFILM, you can
measure the HU using
the oval ROI tool:
On the right, you can
see sample
measurements of
different structures
Note how bone, CSF,
brain tissue, and air all
have different mean
HUs

9. Windowing
The human eye can only perceive ~ 16 shades of
gray
The CT scanner records levels of gray far beyond
what the eye can see
Therefore, to interpret images, we have to limit
the number of Hounsfield units shown
(windowing)
The computer then converts this set range of HU
into shades of gray we can see

10. Windows & levels
Window width:
The range of HU of all tissues of interest
Tissues in this range will be displayed in various shades
of gray
Tissues with HU outside the range are displayed as
black or white
Window level:
The central HU of all the numbers in the window width

11. Windowing
Wide Hounsfield Units Narrow
Window Window
+400
+300
+200
+100
0
-100
-200
-300
-400

12. Window examples
In head CT, 3 windows are commonly used
BRAIN window BONE window SUBDURAL window
W:80 L:40 W:2500 L:480 W:350 L:90

13. Plane
 Plane refers to how the picture slices are orientated
Transaxial plane
 used most often for head CT’s
Coronal plane
 good for evaluation of
pituitary/sella and sinuses
Saggital plane
 rarely used (more common in
MRI)

14. Plane examples
Axial plane Coronal plane Saggital plane

15. Identification
 Now we can begin our basic approach to the head CT
Start with the easy stuff:
PATIENT NAME (make sure you have the right patient !!)
MEDICAL RECORD # (MRN)
AGE
DATE OF EXAM

16. Previous studies
Always check for any previous scans for comparison
Findings can be very subtle
A good way to spot them is to look for changes between
the current and previous scans
Even old chest and abdominal films can give you clues to
possible brain pathology
 ie. Brain mets from lung cancer

17. Study parameters
Make note of the study technique:
Anatomic region of scan: head, neck, spine
Slice thickness (mm)
Window level & width
Plane: Transaxial, coronal, saggital
Use of contrast?
 Look for the Circle of Willis. It will be enhanced on studies using
contrast

18. Image analysis
Now that you have noted all the basic information
about the scan, it’s time to look at the scan itself
Use a systematic order & approach to what you look
at
Use the same approach for all scans to ensure that you
don’t miss anything

19. Regions to inspect
We will start from the inside and move outwards:
1. Midline structures & 5. Sulci
symmetry 6. Sinuses
2. Ventricles 7. Bones
3. Cisterns 8. Skin/soft tissue
4. Brain parenchyma

20. 1. Midline structures
Identify:
 Fornix
Falx Cerebri
 Pineal gland
(usually calcified)
 Great vein of Galen

21. Midline shift
Evaluate for midline shift:
The septum
between the
lateral ventricles
should not deviate
more than 5mm
from the midline
Find a slice where the 2 Draw a vertical line down
lateral ventricles are the middle joining the falx
prominent cerebri anteriorly &
posteriorly

22. Midline shift examples
R L R L
A right-sided abscess is causing a A left-sided tumor is causing a
midline shift to the left midline shift to the right

23. 2. Ventricles
 Identify:
Lateral ventricles x 2
 Third ventricle
 Cerebral aqueduct
 Fourth ventricle

24. Ventricles
Evaluate for any changes in
Symmetry
Size
Shape
Density
A displaced ventricle is often the product of mass
effect or atrophy

25. Ventricles
Common pathology:
 Mass effect
 Atrophy
 Hydrocephalus
 Intra-ventricular Hemorrhage

26. 3. Cisterns
 Identify:
 Supracellar cistern
 Ambient cistern
 Prepontine cistern
 Cisterna magna

27. Cisterns
Evaluate for any changes in
Symmetry
Size
Density
Cisterns often contain blood with subarachnoid
hemorrhage
Cisterns can fill with pus in the setting of meningitis

28. 4. Brain parenchyma – Lobes
First, identify the major lobes:
 Frontal lobe
 Temporal lobe
 Parietal lobe
 Occipital lobe

29. Brain Parenchyma - Brainstem
Then identify:
 Midbrain
 Pons
 Medulla
 Cerebellum

30. Brain parenchyma – Deep structures
Lastly, identify the deep structures:
 Corpus Callosum
 Caudate
 Thalamus
 Lentiform Nucleus
 Internal capsule
 External capsule

31. Parenchymal masses
Look for mass lesions
 Abscess
 Neoplasm
Note how the tumor becomes bright with contrast
Note the ring enhancing lesion consistent
Also note the surroundingof an abscess
with that dark area of edema

32. Acute Infarct
 Look for signs of acute infarction
 Hyperdense MCA sign  Loss of gray-white
differentiation
The middle cerebralto see
Click me artery (MCA) Click me to see
The usual border between grey and white
becomes hyperdense due to occlusion matter is lost due to vasogenic edema

33. Chronic Infarct
 Then, look for signs of chronic infarction:
Retractment of parenchyma
from skull due to atrophy
Focal area of
hypodensity
Mild midline shift to the
right due to atrophy

34. Infarction locations

35. Microangiopathic change
You may encounter the term
“microangiopathic change” in reports
and wonder what it is
Microangiopathic change refers to
age-related white matter ischemia due Normal
to microvessel disease
Very commonly seen in the elderly
Its clinical significance is still not
known
Microangiopathic change

36. Types of Hematoma
Look for evidence of a bleed:
Subdural Hematoma
Due to tear of bridging veins
Look for crescentic shape along brain surface
Crosses suture lines
Epidural Hematoma
Due to rupture of middle meningeal artery
Associated with skull fractures
Look for biconvex, lenticular shape
Does not cross suture lines

37. Subdural vs. Epidural
Note the cresentic shape Note the lenticular shape
SUBDURAL EPIDURAL

38. Subarachnoid Hemorrhage
Look for a subarachnoid hemorrhage
 Due to aneurysm rupture, trauma, or AVM
 Blood in the subarachnoid space and/or ventricles
 Blood can often first be seen in the inter-peduncular cistern
Blood in
subarachnoid
space
(Normal)
Blood in
sulci
Blood in ventricle

39. Intraparenchymal Hemorrhage
Look for intraparenchymal
hemorrhage:
blood (acute, subacute, or
chronic) located in brain
parenchyma
surrounding area of edema
may also be seen
Usually caused by
hypertension

40. Hemorrhage timeline
If you see a bleed, try to assess if its new or old:
ACUTE bleed (< 3 days)
 Hyperdense (80-100 HU) relative to brain
 Caused by protein-Hb component
 Can be hard to spot if hemoglobin is low (<80)
SUBACUTE bleed (3-14 days)
 Hyperdense, isodense, or hypodense relative to brain
 Density loss starts from periphery and goes to centre
CHRONIC bleed (>2 weeks)
 Hypodense (<40 HU) relative to brain

41. Density of blood over time in a
subdural hematoma
Hypodense
Hyperdens Isodense blood
e blood blood
Acute Sub-acute Chronic
(<3 days) (3-14 days) (>14 days)

42. 5. Sulci
Identify:
 Sulci
 Sylvian fissures
 Central sulcus
 Precentral
sulcus
 Postcentral sulcus

43. Sulci
Remember that sulci will become deeper and more prominent
with age
Look for blood in the sulci & Sylvian Fissure which are
indications of a sub-arachnoid bleed
Acute blood in
Sylvian fissure
Acute blood in
sulci

44. 6. Sinuses
Switch to Bone Window to better evaluate the sinuses
Identify:
 Superior Saggital Sinus
 Frontal Sinus
 Ethmoid Sinus
 Sphenoid Sinus
 Maxillary Sinus

45. Sinuses
Evaluate for any sinusitis:
fluid in sinuses
(notice the air/fluid level)
sinusitis normal

46. Sinuses
Also look for any:
Mucosal thickening
Blood in sinuses (especially with history of trauma)
Polyps or mucous retention cysts

47. 7. Bone
Stay on the Bone Window and look at the bones now
Identify:
 Skull
 Sutures
 Mastoid air cells

48. Bone
Evaluate for any:
 Fractures
 Surgical changes
(ie. craniotomies)

49. 8. Skin & Soft tissue
Evaluate for any:
 Sub-galeal hematoma
 Foreign body
 Surgical changes

50. Thank you……………

51. Recap
Begin with the basic identification
Remember to check for previous scans
Check the technique
Look at each region of the brain systematically
We started from the middle and worked out:
1. Midline structures 5. Sulci
2. Ventricles 6. Sinuses
3. Cisterns 7. Bones
4. Brain parenchyma 8. Skin/soft tissue

52. Recap
In each area, identify the major anatomy
Then look for findings
Below is a list of important things not to miss:
 Midline: midline shift
 Ventricles: blood and mass effect
 Cisterns: blood and pus
 Parenchyma: signs of ischemia and/or bleeding
 Sulci: for blood
 Sinuses: signs of sinusitis
 Bones: fractures
 Soft tissue: hematoma

53. Recap
Remember to use the same approach every time so
that you don’t miss anything!
Try out the cases in the next slides to test your
knowledge

55. Case #1
Mr A is an 80 y/o female presenting with:
Expressive aphasia/apraxia
Mild right facial droop
Atrial fibrillation
A non-contrast CT scan of her brain is performed

57. Your analysis
What are your findings?
What is your impression?
What would be your top diagnosis?

58. Normal

59. Case #1 - Answer
Mr A had an infarction of her Left
Parietal Lobe
The location is consistent with
MCA infarction
The cause was emboli related to
her atrial fibrillation

60. Case #2
Mr. B is a 56 y/o male presenting with:
A sudden onset 10/10 headache while running
Photophobia, nausea & vomiting
No history of trauma or LOC
Otherwise well
A non-contrast CT scan of his brain is performed

62. Your analysis
What are your findings?
What is your impression?
What would be your top diagnosis?
Is this pathology acute, subacute, or chronic

63. Case #2 - Answer
Mr. B had a large subarachnoid
hemorrhage
The bleed was acute
This was caused by rupture of an
ACA aneurysm
He was admitted to ICU where
his condition deteriorated
rapidly
He passed away shortly after
admission

64. Case #3
Mr C is a 66 y/o female who slipped down the stairs
yesterday and hit the back of her head.
She presents with
Generalized left sided weakness
Light headache
A non-contrast CT scan of her brain is performed

65. R L

66. Your analysis
What are your findings?
What is your impression?
What would be your top diagnosis?
Is this pathology acute, subacute, or chronic

67. Case #3 - Answer
Mr C had a large right-
sided subdural hematoma
The hematoma is acute
This was caused by
rupture of bridging veins
when she hit her head
A craniotomy was
performed and the bleed
was drained

68. Bonus case
Mr. X is a 80 y/o male presenting with:
3 month history of delirium
Recent fall from bed
Large scalp laceration
No focal neurological findings
An non-contrast CT scan of his brain is performed

69. Hint? Look closely at the midline structures
Subdural

70. Analysis
Can you spot the abnormalities?
What is your impression?
What would be your top diagnosis?

71. Bonus case - Answer
 Mr. X had a tiny right-sided
subdural hematoma
 Blood is seen along the left
subdural space as well as in the
falx cerebri anteriorly (arrows)
 The hematoma is acute
 Because of its small size, no
immediate treatment was
required
 Follow-up CT scans showed
resolution of the subdural
hematoma
Normal scan for comparison