Approach to Head CT

1
Approach to Head CT

• Wesley Chan
• CC3 Queens University
• with
• Dr. Danny Mandell
• Dr. Nasir Jaffer
• Department of Medical Imaging
• University of Toronto

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 CTs

• 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
Whats 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 youre not sure what youre 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
Narrow Window
Hounsfield Units
Wide Window
400 300 200 100 0 -100 -200 -300 -400
12
Window examples

• In head CT, 3 windows are commonly used

BRAIN window W80 L40
BONE window W2500 L480
SUBDURAL window W350 L90
13
Plane

• Plane refers to how the picture slices are
  orientated

• Transaxial plane
• used most often for head CTs
• 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, its 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 dont miss anything

19
Regions to inspect

• We will start from the inside and move outwards

• Midline structures symmetry
• Ventricles
• Cisterns
• Brain parenchyma

• Sulci
• Sinuses
• Bones
• Skin/soft tissue

20
1. Midline structures

• Identify (click on the names to see their
  location)

• 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

• Draw a vertical line down the middle joining the
  falx cerebri anteriorly posteriorly

• Find a slice where the 2 lateral ventricles are
  prominent

22
Midline shift examples
L
R
R
L
Click me to see shift
Click me to see shift
A right-sided abscess is causing a midline shift
to the left
A left-sided tumor is causing a midline shift to
the right
23
2. Ventricles

• Identify (click on the names to see their
  location)

• 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 (click on name to see an
  example)

• Mass effect

• Atrophy

• Hydrocephalus

• Intra-ventricular Hemorrhage

26
3. Cisterns

• Identify (click on the names to see their
  location)

• 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
• (click on names to see their location)

• Frontal lobe

• Temporal lobe

• Parietal lobe

• Occipital lobe

29
Brain Parenchyma - Brainstem

• Then identify
• (click on the names to see their location)

• Midbrain

• Pons

• Medulla

• Cerebellum

30
Brain parenchyma Deep structures

• Lastly, identify the deep structures
• (click on the names to see their location)

• Corpus Callosum

• Caudate

• Thalamus

• Lentiform Nucleus

• Internal capsule

• External capsule

31
Parenchymal masses

• Look for mass lesions (click on the names to see
  example)

• Abscess

• Neoplasm

Note how the tumor becomes bright with
contrast Also note the surrounding dark area of
edema
Note the ring enhancing lesion consistent with
that of an abscess
32
Acute Infarct

• Look for signs of acute infarction

• Loss of gray-white differentiation

• Hyperdense MCA sign

Click me to see
Click me to see
The usual border between grey and white matter
is lost due to vasogenic edema

• The middle cerebral artery (MCA)
• becomes hyperdense due to occlusion

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 to microvessel disease
• Very commonly seen in the elderly
• Its clinical significance is still not known

Normal
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

Click me to see shape
Click me to see 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 (lt 3 days)
• Hyperdense (80-100 HU) relative to brain
• Caused by protein-Hb component
• Can be hard to spot if hemoglobin is low (lt80)
• SUBACUTE bleed (3-14 days)
• Hyperdense, isodense, or hypodense relative to
  brain
• Density loss starts from periphery and goes to
  centre
• CHRONIC bleed (gt2 weeks)
• Hypodense (lt40 HU) relative to brain

41
Density of blood over time in a subdural hematoma
Hypodense blood
Hyperdense blood
Isodense blood
Acute (lt3 days)
Chronic (gt14 days)
Sub-acute (3-14 days)
42
5. Sulci

• Identify
• (click on the names to see their location)

• 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 (click on the names to see their
  location)

• 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)
normal
sinusitis
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
• (click on the names to see their location)

• 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
Congratulations!

• You now know an easy, systematic approach to head
  CT!
• You have also learned how to identify normal
  anatomy and how to spot classic abnormalities on
  CT
• What follows is a brief summary of what you have
  learned followed by some short cases

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

• Midline structures
• Ventricles
• Cisterns
• Brain parenchyma

• Sulci
• Sinuses
• Bones
• 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 dont miss anything!
• Try out the cases in the next slides to test your
  knowledge

54
CASES
55
Case 1

• Ms. EW 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

56
(No Transcript)
57
Your analysis

• What are your findings?
• What is your impression?
• What would be your top diagnosis?

58
Normal
59
Case 1 - Answer

• Mrs. EW 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. GH 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

61
(No Transcript)
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. GH 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

• Ms. JH 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

• Mrs. JH 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. LR 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
Subdural
Look closely at the midline structures
Hint?
70
Analysis

• Can you spot the abnormalities?
• What is your impression?
• What would be your top diagnosis?

71
Bonus case - Answer

• Mr. LR 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