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How to Read a Head CT. (or “How I learned to stop worrying and love computed tomography”). Andrew D. Perron, MD, FACEP. EM Residency Program Director Department of Emergency Medicine Maine Medical Center Portland, ME. Andrew D. Perron, MD, FACEP. 2. Head CT.

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how to read a head ct

How to Read a Head CT

(or “How I learned to stop worrying and love computed tomography”)

andrew d perron md facep
Andrew D. Perron, MD, FACEP

EM Residency Program Director

Department of Emergency Medicine

Maine Medical Center

Portland, ME

Andrew D. Perron, MD, FACEP

2

head ct
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.

head ct1
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.

head ct2
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.
head ct3
Head CT
  • The intent of this session is to introduce a similar systematic method of cranial CT interpretation, based on the mnemonic…
head ct4
Head CT

“Blood Can Be Very Bad”

b lood c an b e v ery b ad
Blood Can Be Very Bad
  • Blood
  • Cisterns
  • Brain
  • Ventricles
  • Bone
b lood c an b e v ery b ad1
Blood Can Be Very Bad
  • Blood
  • Cisterns
  • Brain
  • Ventricles
  • Bone
b lood c an b e v ery b ad2
Blood Can Be Very Bad
  • Blood
  • Cisterns
  • Brain
  • Ventricles
  • Bone
b lood c an b e v ery b ad3
Blood Can Be Very Bad
  • Blood
  • Cisterns
  • Brain
  • Ventricles
  • Bone
b lood c an b e v ery b ad4
Blood Can Be Very Bad
  • Blood
  • Cisterns
  • Brain
  • Ventricles
  • Bone
ct scan basics
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.
ct scan basics1
CT Scan Basics
  • The denser the object, the whiter it is on CT
    • Bone is most dense = + 1000 Hounsfield U.
    • Air is the least dense = - 1000H Hounsfield U.
ct scan basics windowing
CT Scan Basics: Windowing

Focuses the spectrum of gray-scale used on a particular image.

posterior fossa
Posterior Fossa
  • Brainstem
  • Cerebellum
  • Skull Base
    • Clinoids
    • Petrosal bone
    • Sphenoid bone
    • Sella turcica
    • Sinuses
sagittal view
Sagittal View

C Circummesencephalic Cistern

ct diagnostics
CT Diagnostics

Where is the most sensitive area to examine the CT for increased ICP?

  • Lateral Ventricles
  • IVth ventricle
  • Basilar Cisterns
  • Gyral pattern
2 nd key level sagittal view
2nd Key Level Sagittal View

2nd Key Level

Circummesencephalic Cistern

ct diagnostics1
CT Diagnostics

Where is the most sensitive area to examine the CT for ventricular dilation?

  • IIIrd ventricle
  • IVth ventricle
  • Temporal horns of lateral ventricles
3 rd key level sagittal view
3rd Key Level Sagittal View

Circummesencephalic Cistern

csf production
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. 500-700 cc’s per day.
ct scans
CT Scans

Andrew D. Perron, MD, FACEP

37

a few kid specific thoughts1
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.

slide39

1 day 1 year 2 years

Andrew D. Perron, MD, FACEP

40

b is for blood
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?
ct diagnostics2
CT Diagnostics

At what point does blood become isodense with brain?

  • About 48 hours
  • About 1 week
  • About 2 weeks
  • After 1 month
b is for blood1
B is for Blood
  • Acute blood is bright white on CT (once it clots).
  • Blood becomes hypodense at approximately 2 weeks.
  • Blood becomes isodense at approximately 1 week.
b is for blood2
B is for Blood
  • Acute blood is bright white on CT (once it clots).
  • Blood becomes hypodense at approximately 2 weeks.
  • Blood becomes isodense at approximately 1 week.
b is for blood3
B is for Blood
  • Acute blood is bright white on CT (once it clots).
  • Blood becomes hypodense at approximately 2 weeks.
  • Blood becomes isodense at approximately 1 week.
epidural hematoma
Epidural Hematoma
  • Lens shaped
  • Does not cross sutures
  • Classically described with injury to middle meningeal artery
  • Low mortality if treated prior to unconsciousness

( < 20%)

subdural hematoma
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.
ct scan6
CT Scan

Andrew D. Perron, MD, FACEP

50

subarachnoid hemorrhage1
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
ct diagnostics3
CT Diagnostics

What is the sensitivity of CT for SAH?

  • 100%
  • 95%
  • 80%
  • Depends…I need a lot more information to answer.
ct scan sensitivity for sah
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.
ct scan7
CT Scan

Andrew D. Perron, MD, FACEP

55

ct scan8
CT Scan

Andrew D. Perron, MD, FACEP

56

ct scan9
CT Scan

Andrew D. Perron, MD, FACEP

58

c is for cisterns
C is for CISTERNS

(Blood Can Be Very Bad)

  • 4 key cisterns
    • Circummesencephalic
    • Suprasellar
    • Quadrigeminal
    • Sylvian

Circummesencephalic

cisterns1
Cisterns
  • 2 Key questions to answer regarding cisterns:
    • Is there blood?
    • Are the cisterns open?
b is for b rain
B is for BRAIN

(Blood Can Be Very Bad)

tumor
Tumor

Andrew D. Perron, MD, FACEP

66

atrophy
Atrophy

Andrew D. Perron, MD, FACEP

67

ct diagnostics4
CT Diagnostics

What percentage of mass lesions will require IV contrast to be identified?

  • 100%
  • 50%
  • 30-40%
  • 10-20%
abscess
Abscess

Andrew D. Perron, MD, FACEP

69

hemorrhagic contusion
Hemorrhagic Contusion

Andrew D. Perron, MD, FACEP

70

mass effect
Mass Effect

Andrew D. Perron, MD, FACEP

72

stroke
Stroke

Andrew D. Perron, MD, FACEP

73

intracranial air1
Intracranial Air

Andrew D. Perron, MD, FACEP

75

intracranial air2
Intracranial Air

Andrew D. Perron, MD, FACEP

76

v is for v entricles
V is for VENTRICLES

(Blood Can Be Very Bad)

ex vacuo phenomenon
Ex-Vacuo Phenomenon

Andrew D. Perron, MD, FACEP

80

slide83
BONE

Andrew D. Perron, MD, FACEP

84

b lood c an b e v ery b ad5
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.

questions
Questions

www.ferne.orgferne@ferne.orgAndrew D. Perron, MD, FACEP

perroa@mmc.org(207) 662-7015

ferne_acep_2005_peds_perron_ich_bcbvb_fshow.ppt 11/27/2014 4:13 PM