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 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 Introduced in 1974 by Sir Jeffrey Hounsfield.
The original “Siretom” Circa 1974

14. 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.

15. 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.

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

17. 2 Sheet Head CT

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

19. CT Scan

20. CT Scan

21. Sagittal View

22. Cisterns

23. CT Scan

24. Brainstem Lateral View

25. 2nd Key Level Sagittal View

26. Cisterns at Cerebral Peduncles Level

27. CT Scan

28. Suprasellar Cistern

29. CT Scan

30. 3rd Key Level Sagittal View

31. Cisterns at High Mid-Brain Level

32. CT Scan

33. Ventricles

34. 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.

35. CT Scan

36. CT Scans 36
Andrew D. Perron, MD, FACEP

37. Trauma Pictures

38. PATHOLOGY

39. 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?

40. 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.

41. 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.

42. 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.

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

44. CT Scan

45. CT Scans

46. 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.

47. CT Scan 47
Andrew D. Perron, MD, FACEP

48. CT Scan 48
Andrew D. Perron, MD, FACEP

49. Subarachnoid Hemorrhage

50. 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

51. 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.

52. CT Scan 52
Andrew D. Perron, MD, FACEP

53. CT Scan 53
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54. Intraventricular/ Intraparenchymal Hemorrhage54
Andrew D. Perron, MD, FACEP

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

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

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

58. 58
Andrew D. Perron, MD, FACEP

59. 59
Andrew D. Perron, MD, FACEP

60. 60
Andrew D. Perron, MD, FACEP

61. B is for BRAIN
(Blood Can Be Very Bad) 61
Andrew D. Perron, MD, FACEP

62. 62
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63. Tumor 63
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64. Atrophy 64
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65. Abscess 65
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66. Hemorrhagic Contusion66
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68. 68
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69. Mass Effect 69
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70. Stroke 70
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71. 71
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72. 72
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73. Intracranial Air

74. Intracranial Air 74
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75. Intracranial Air 75
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76. V is for VENTRICLES
(Blood Can Be Very Bad)

77. 77
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78. 78
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79. Ex-Vacuo Phenomenon 79
Andrew D. Perron, MD, FACEP

80. 80
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81. 81
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82. BONE 82
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83. 83
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84. 84
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85. 85
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86. 86
Andrew D. Perron, MD, FACEP

87. Three Stooges

88. 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.

89. RIP

90. www.ferne.org ferne@ferne.org Andrew D. Perron, MD, FACEP
Questions
Andrew D. Perron, MD, FACEP
(207)
ferne_acep_2005_spring_perron_ich_bcbvb.ppt 4/24/ :18 PM
Andrew D. Perron, MD, FACEP 54 54 1