How to Read a Head CT

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How to Read a Head CT

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

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Andrew D. Perron, MD, FACEP

• EM Residency Program Director
• Department of Emergency Medicine
• Maine Medical Center
• Portland, ME

Andrew D. Perron, MD, FACEP
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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.

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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.

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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.

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Head CT

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

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Head CT

• Blood Can Be Very Bad

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Blood Can Be Very Bad

• Blood
• Cisterns
• Brain
• Ventricles
• Bone

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Blood Can Be Very Bad

• Blood
• Cisterns
• Brain
• Ventricles
• Bone

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Blood Can Be Very Bad

• Blood
• Cisterns
• Brain
• Ventricles
• Bone

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Blood Can Be Very Bad

• Blood
• Cisterns
• Brain
• Ventricles
• Bone

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Blood Can Be Very Bad

• Blood
• Cisterns
• Brain
• Ventricles
• Bone

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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.

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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.

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CT Scan Basics Windowing
Focuses the spectrum of gray-scale used on a
particular image.
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2 Sheet Head CT
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Posterior Fossa

• Brainstem
• Cerebellum
• Skull Base
• Clinoids
• Petrosal bone
• Sphenoid bone
• Sella turcica
• Sinuses

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CT Scan
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CT Scan
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Sagittal View
C Circummesencephalic Cistern
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CT Diagnostics

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

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Cisterns
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CT Scan
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Brainstem Lateral View
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2nd Key Level Sagittal View
2nd Key Level
Circummesencephalic Cistern
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Cisterns at Cerebral Peduncles Level
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CT Scan
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Suprasellar Cistern
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CT Diagnostics

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

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CT Scan
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3rd Key Level Sagittal View
Circummesencephalic Cistern
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Cisterns at High Mid-Brain Level
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CT Scan
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Ventricles
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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 ccs.
• Adult CSF production is approx. 500-700 ccs per
  day.

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CT Scan
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CT Scans
Andrew D. Perron, MD, FACEP
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A Few Kid-Specific Thoughts
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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.

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1 day 1 year 2 years
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Trauma Pictures
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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?

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CT Diagnostics

• At what point does blood become isodense with
  brain?
• About 48 hours
• About 1 week
• About 2 weeks
• After 1 month

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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.

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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.

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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.

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Epidural Hematoma

• Lens shaped
• Does not cross sutures
• Classically described with injury to middle
  meningeal artery
• Low mortality if treated prior to unconsciousness
  
• (

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CT Scans
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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.

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CT Scan
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Subarachnoid Hemorrhage
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Subarachnoid Hemorrhage

• Blood in the cisterns/cortical gyral surface
• Aneurysms responsible for 75-80 of SAH
• AVMs responsible for 4-5
• Vasculitis accounts for small proportion (
• No cause is found in 10-15
• 20 will have associated acute hydrocephalus

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CT Diagnostics

• What is the sensitivity of CT for SAH?
• 100
• 95
• 80
• DependsI need a lot more information to answer.

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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.

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CT Scan
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CT Scan
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Intraventricular/Intraparenchymal Hemorrhage
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CT Scan
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C is for CISTERNS
(Blood Can Be Very Bad)

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

Circummesencephalic
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Cisterns

• 2 Key questions to answer regarding cisterns
• Is there blood?
• Are the cisterns open?

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B is for BRAIN
(Blood Can Be Very Bad)
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Tumor
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Atrophy
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CT Diagnostics

• What percentage of mass lesions will require IV
  contrast to be identified?
• 100
• 50
• 30-40
• 10-20

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Abscess
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Hemorrhagic Contusion
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Mass Effect
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Stroke
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Intracranial Air
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Intracranial Air
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Intracranial Air
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V is for VENTRICLES
(Blood Can Be Very Bad)
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Ex-Vacuo Phenomenon
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BONE
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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.
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RIP
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Questions
www.ferne.orgferne_at_ferne.orgAndrew D. Perron,
MD, FACEP perroa_at_mmc.org(207) 662-7015
ferne_acep_2005_peds_perron_ich_bcbvb_fshow.ppt 7/
2/2009 1219 PM