1. (or “How I learned to stop worrying and love computed tomography”)
How to Read a Head CT
(or “How I learned to stop worrying and love computed tomography”)

2. Andrew D. Perron, MD, FACEP
EM Residency Program Director
Department of Emergency Medicine
Maine Medical Center
Portland, ME
Andrew D. Perron, MD, FACEP 2 54 54 1

3. Head CT
Has assumed a critical role in the daily practice of Emergency Medicine for evaluating intracranial emergencies. (e.g. Trauma, Stroke, SAH, ICH).
Most practitioners have limited experience with interpretation.
In many situations, the Emergency Physician must initially interpret and act
on the CT without specialist assistance.

4. Head CT
Most EM training programs have no formalized training process to meet this need.
Many Emergency Physicians are uncomfortable interpreting CTs.
Studies have shown that EPs have a significant “miss rate” on cranial
CT interpretation.

5. Head CT
In medical school, we are taught a systematic technique to interpret ECGs (rate, rhythm, axis, etc.) so that all aspects are reviewed, and no findings are missed.

6. Head CT
The intent of this session is to introduce a similar systematic method of cranial CT interpretation, based on the mnemonic…

7. Head CT
“Blood Can Be Very Bad”

8. Blood Can Be Very Bad
Blood
Cisterns
Brain
Ventricles
Bone

9. Blood Can Be Very Bad
Blood
Cisterns
Brain
Ventricles
Bone

10. Blood Can Be Very Bad
Blood
Cisterns
Brain
Ventricles
Bone

11. Blood Can Be Very Bad
Blood
Cisterns
Brain
Ventricles
Bone

12. Blood Can Be Very Bad
Blood
Cisterns
Brain
Ventricles
Bone

13. CT Scan Basics
A CT image is a computer-generated picture based on multiple x-ray exposures taken around the periphery of the subject.
X-rays are passed through the subject, and a scanning device measures the transmitted radiation.
The denser the object, the more the beam is attenuated, and hence fewer x-rays make it to the sensor.

14. CT Scan Basics The denser the object, the whiter it is on CT
Bone is most dense = Hounsfield U.
Air is the least dense = H Hounsfield U.

15. CT Scan Basics: Windowing
Focuses the spectrum of gray-scale used on a particular image.

16. 2 Sheet Head CT

17. Posterior Fossa Brainstem Cerebellum Skull Base Clinoids Petrosal bone
Sphenoid bone
Sella turcica
Sinuses

18. CT Scan

19. CT Scan

20. Sagittal View
C Circummesencephalic Cistern

21. CT Diagnostics
Where is the most sensitive area to examine the CT for increased ICP?
Lateral Ventricles
IVth ventricle
Basilar Cisterns
Gyral pattern

22. Cisterns

23. CT Scan

24. Brainstem Lateral View

25. 2nd Key Level Sagittal View
Circummesencephalic Cistern

26. Cisterns at Cerebral Peduncles Level

27. CT Scan

28. Suprasellar Cistern

29. CT Diagnostics
Where is the most sensitive area to examine the CT for ventricular dilation?
IIIrd ventricle
IVth ventricle
Temporal horns of lateral ventricles

30. CT Scan

31. 3rd Key Level Sagittal View
Circummesencephalic Cistern

32. Cisterns at High Mid-Brain Level

33. CT Scan

34. Ventricles

35. CSF Production
Produced in choroid plexus in the lateral ventricles  Foramen of Monroe  IIIrd Ventricle  Acqueduct of Sylvius  IVth Ventricle  Lushka/Magendie
0.5-1 cc/min
Adult CSF volume is approx. 150 cc’s.
Adult CSF production is approx cc’s per day.

36. CT Scan

37. CT Scans 37
Andrew D. Perron, MD, FACEP

38. A Few Kid-Specific Thoughts

39. A Few Kid-Specific Thoughts
Premature Infants (30-34 weeks):
Larger sylvian, basilar (circummesencephalic) cisterns.
Larger subarachnoid spaces
Thin cerebral cortex (Gray matter)
Prominent white matter (with higher water content)
Limited cortical gyral pattern
Ventricles are variable: slit-like to well-developed
Term Infant (36-41 weeks):
Small, slit-like lateral ventricles
Continued white-matter prominence
More prominent sulcal pattern
Temporal horns unlikely to be seen
1st & 2nd years of Life:
Marked growth of all lobes of the brain (proportionally greatest in frontal lobes)
Wide variation in lateral ventricle size (3rd and 4th fairly constant)
Temporal horns unlikely to be seen.

40. 1 day year years 40
Andrew D. Perron, MD, FACEP

41. Trauma Pictures

42. B is for Blood 1st decision: Is blood present?
2nd decision: If so, where is it?
3rd decision: If so, what effect is it having?

43. CT Diagnostics At what point does blood become isodense with brain?
About 48 hours
About 1 week
About 2 weeks
After 1 month

44. B is for Blood Acute blood is bright white on CT (once it clots).
Blood becomes isodense at approximately 1 week.
Blood becomes hypodense at approximately 2 weeks.

45. B is for Blood Blood becomes hypodense at approximately 2 weeks.
Acute blood is bright white on CT (once it clots).
Blood becomes isodense at approximately 1 week.
Blood becomes hypodense at approximately 2 weeks.

46. B is for Blood Blood becomes hypodense at approximately 2 weeks.
Acute blood is bright white on CT (once it clots).
Blood becomes isodense at approximately 1 week.
Blood becomes hypodense at approximately 2 weeks.

47. Epidural Hematoma Lens shaped Does not cross sutures
Classically described with injury to middle meningeal artery
Low mortality if treated prior to unconsciousness
( < 20%)

48. CT Scans

49. Subdural Hematoma Typically falx or sickle-shaped.
Crosses sutures, but does not cross midline.
Acute subdural is a marker for severe head injury. (Mortality approaches 80%)
Chronic subdural usually slow venous bleed and well tolerated.

50. CT Scan 50
Andrew D. Perron, MD, FACEP

51. Subarachnoid Hemorrhage

52. Subarachnoid Hemorrhage
Blood in the cisterns/cortical gyral surface
Aneurysms responsible for 75-80% of SAH
AVM’s responsible for 4-5%
Vasculitis accounts for small proportion (<1%)
No cause is found in 10-15%
20% will have associated acute hydrocephalus

53. CT Diagnostics What is the sensitivity of CT for SAH? 100% 95% 80%
Depends…I need a lot more information to answer.

54. CT Scan Sensitivity for SAH
98-99% at 0-12 hours
90-95% at 24 hours
80% at 3 days
50% at 1 week
30% at 2 weeks
Depends on generation of scanner and who is reading scan and how much blood there is.

55. CT Scan 55
Andrew D. Perron, MD, FACEP

56. CT Scan 56
Andrew D. Perron, MD, FACEP

57. Intraventricular/ Intraparenchymal Hemorrhage

58. CT Scan 58
Andrew D. Perron, MD, FACEP

59. C is for CISTERNS (Blood Can Be Very Bad) 4 key cisterns
Circummesencephalic
Suprasellar
Quadrigeminal
Sylvian
Circummesencephalic

60. Cisterns 2 Key questions to answer regarding cisterns: Is there blood?
Are the cisterns open?

61. 61
Andrew D. Perron, MD, FACEP

62. 62
Andrew D. Perron, MD, FACEP

63. 63
Andrew D. Perron, MD, FACEP

64. B is for BRAIN
(Blood Can Be Very Bad)

65. 65
Andrew D. Perron, MD, FACEP

66. Tumor 66
Andrew D. Perron, MD, FACEP

67. Atrophy 67
Andrew D. Perron, MD, FACEP

68. CT Diagnostics
What percentage of mass lesions will require IV contrast to be identified?
100%
50%
30-40%
10-20%

69. Abscess 69
Andrew D. Perron, MD, FACEP

70. Hemorrhagic Contusion70
Andrew D. Perron, MD, FACEP

71. 71
Andrew D. Perron, MD, FACEP

72. Mass Effect 72
Andrew D. Perron, MD, FACEP

73. Stroke 73
Andrew D. Perron, MD, FACEP

74. Intracranial Air

75. Intracranial Air 75
Andrew D. Perron, MD, FACEP

76. Intracranial Air 76
Andrew D. Perron, MD, FACEP

77. V is for VENTRICLES
(Blood Can Be Very Bad)

78. 78
Andrew D. Perron, MD, FACEP

79. 79
Andrew D. Perron, MD, FACEP

80. Ex-Vacuo Phenomenon 80
Andrew D. Perron, MD, FACEP

81. 81
Andrew D. Perron, MD, FACEP

82. 82
Andrew D. Perron, MD, FACEP

83. 83
Andrew D. Perron, MD, FACEP

84. BONE 84
Andrew D. Perron, MD, FACEP

85. 85
Andrew D. Perron, MD, FACEP

86. 86
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87. 87
Andrew D. Perron, MD, FACEP

88. 88
Andrew D. Perron, MD, FACEP

89. Blood Can Be Very Bad
If no blood is seen, all cisterns are present and open, the brain is symmetric with normal gray-white differentiation, the ventricles are symmetric without dilation, and there is no fracture, then there is no emergent diagnosis from the CT scan.

90. RIP

91. www.ferne.org ferne@ferne.org Andrew D. Perron, MD, FACEP
Questions
Andrew D. Perron, MD, FACEP
(207)
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