How to Read a Head CT Dr Mohamed El Safwany. MD. 1.

How to Read a Head CT

Dr Mohamed El Safwany. MD. 1

Intended learning outcome• The student should learn at the end of this lecture interpretation of CT

Brain.

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 acton the CT without specialist assistance.

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Head CT

“Blood Can Be Very Bad”4

Blood Can Be Very Bad

•Blood•Cisterns •Brain •Ventricles•Bone 5

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

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

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 ScanCT Scan

CT ScanCT Scan

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22ndnd Key Level Sagittal View Key Level Sagittal View2nd Key Level

Circummesencephalic Cistern

Cisterns at Cerebral Peduncles Cisterns at Cerebral Peduncles LevelLevel

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CT ScanCT Scan

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CT ScanCT Scan

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33rdrd Key Level Sagittal View Key Level Sagittal View

Circummesencephalic Cistern

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Cisterns at High Mid-Brain LevelCisterns at High Mid-Brain Level

CT ScanCT Scan

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. 24

Andrew D. Perron, MD, FACEP25

1 day 1 day 1 year 1 year 2 years 2 years

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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BB is for Blood is for Blood

• Blood becomes hypodense at approximately 2 weeks.

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•Blood becomes isodense at approximately 1 week.

• Acute blood is bright white on CT (once it clots).


• Blood becomes hypodense at approximately 2 weeks. 28

• Blood becomes isodense at approximately 1 week.



• Blood becomes hypodense at approximately 2 weeks. 29

• Blood becomes isodense at approximately 1 week.


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CT ScansCT Scans

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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Subarachnoid Hemorrhage

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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

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CT ScanCT Scan

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CT ScanCT Scan

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Intraventricular/Intraparenchymal Hemorrhage

CT ScanCT Scan

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C is for CISTERNS

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

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((BBlood lood CCan an BBe e VVery ery BBad)ad)

Circummesencephalic

Cisterns• 2 Key questions to answer regarding cisterns:

• Is there blood?• Are the cisterns open?

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B is for BRAIN

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((BBlood lood CCan an BBe e VVery ery BBad)ad)

TumorTumor

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AtrophyAtrophy

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AbscessAbscess

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Hemorrhagic ContusionHemorrhagic Contusion

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Mass EffectMass Effect

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Intracranial AirIntracranial Air

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Intracranial AirIntracranial Air

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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.

Text Book• David Sutton’s Radiology• Clark’s Radiographic positioning and techniques

Assignment• Two students will be selected for assignment.

Question• Define differences between subdural and epidural hematoma?

• Thank You

How to Read a Head CT Dr Mohamed El Safwany. MD. 1.

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