Andrew D. Perron, MD, FACEP 1 How to Read a Head CT (or “How I learned to stop worrying and love computed tomography”)

1Andrew D. Perron, MD, FACEP

How to Read a Head CTHow to Read a Head CT

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

Andrew D. Perron, MD, FACEPAndrew D. Perron, MD, FACEP

EM Residency Program DirectorEM Residency Program Director

Department of Emergency MedicineDepartment of Emergency MedicineMaine Medical CenterMaine Medical Center

Portland, MEPortland, ME

Andrew D. Perron, MD, FACEP2


Head CTHead 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.


Head CTHead 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 CTHead 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 CTHead CT

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


Head CTHead CT

“Blood Can Be Very Bad”


BBlood lood CCan an BBe e VVery ery BBadad

• Blood

• Cisterns

• Brain

• Ventricles

• Bone



• Blood

• Cisterns

• Brain

• Ventricles

• Bone



• Blood

• Cisterns

• Brain

• Ventricles

• Bone



• Blood

• Cisterns

• Brain

• Ventricles

• Bone



• Blood

• Cisterns

• Brain

• Ventricles

• Bone


CT Scan BasicsCT 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 BasicsCT 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: WindowingCT Scan Basics: Windowing

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

2 Sheet Head CT


•Brainstem•Cerebellum•Skull Base

–Clinoids–Petrosal bone–Sphenoid bone–Sella turcica–Sinuses

Posterior FossaPosterior Fossa


CT ScanCT Scan

CT ScanCT Scan

Sagittal ViewSagittal View

C Circummesencephalic Cistern


CT DiagnosticsCT Diagnostics

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

A. Lateral Ventricles

B. IVth ventricle

C. Basilar Cisterns

D. Gyral pattern


CisternsCisterns


CT ScanCT Scan


Brainstem Lateral ViewBrainstem Lateral View


2nd Key Level22ndnd Key Level Sagittal View Key Level Sagittal View

Circummesencephalic Cistern


Cisterns at Cerebral Peduncles Cisterns at Cerebral Peduncles LevelLevel


CT ScanCT Scan


Suprasellar CisternSuprasellar Cistern



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

A. IIIrd ventricle

B. IVth ventricle

C. Temporal horns of lateral ventricles


CT ScanCT Scan


33rdrd Key Level Sagittal View Key Level Sagittal View

Circummesencephalic Cistern


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

CT ScanCT Scan


VentriclesVentricles


CSF ProductionCSF 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 ScansCT Scans



A Few Kid-Specific ThoughtsA Few Kid-Specific Thoughts


A Few Kid-Specific ThoughtsA Few Kid-Specific Thoughts• Premature Infants (30-34 weeks):

Larger sylvian, basilar (circummesencephalic) cisterns.Larger subarachnoid spacesThin cerebral cortex (Gray matter)Prominent white matter (with higher water content)Limited cortical gyral patternVentricles are variable: slit-like to well-developed

• Term Infant (36-41 weeks):Small, slit-like lateral ventriclesContinued white-matter prominenceMore prominent sulcal patternTemporal 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.


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

Trauma PicturesTrauma Pictures


BB is for Blood is for Blood

• 1st decision: Is blood present?

• 2nd decision: If so, where is it?

• 3rd decision: If so, what effect is it having?



At what point does blood become isodense with brain?

A. About 48 hours

B. About 1 week

C. About 2 weeks

D. After 1 month



• Blood becomes hypodense at approximately 2 weeks.

•Blood becomes isodense at approximately 1 week.

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




• Blood becomes isodense at approximately 1 week.





• Blood becomes isodense at approximately 1 week.



Epidural HematomaEpidural Hematoma

• Lens shaped

• Does not cross sutures

• Classically described with injury to middle meningeal artery

• Low mortality if treated prior to unconsciousness

( < 20%)


CT ScansCT Scans


Subdural HematomaSubdural 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 Scan CT Scan



Subarachnoid HemorrhageSubarachnoid Hemorrhage


Subarachnoid HemorrhageSubarachnoid 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



What is the sensitivity of CT for SAH?

A. 100%

B. 95%

C. 80%

D. Depends…I need a lot more information to answer.


• 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 Scan Sensitivity for SAHCT Scan Sensitivity for SAH

Andrew D. Perron, MD, FACEP

CT ScanCT Scan

55

CT ScanCT Scan



Intraventricular/Intraventricular/Intraparenchymal HemorrhageIntraparenchymal Hemorrhage

CT ScanCT Scan



CC is for CISTERNS is for CISTERNS

• 4 key cisterns– Circummesencephalic

– Suprasellar

– Quadrigeminal

– Sylvian

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

Circummesencephalic


CisternsCisterns• 2 Key questions to answer regarding

cisterns:– Is there blood?

– Are the cisterns open?





BB is for is for BBRAINRAIN((BBlood lood CCan an BBe e VVery ery BBad)ad)


TumorTumor


AtrophyAtrophy




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

A. 100%

B. 50%

C. 30-40%

D. 10-20%

AbscessAbscess


Hemorrhagic ContusionHemorrhagic Contusion



Mass EffectMass Effect


StrokeStroke



Intracranial AirIntracranial Air






VV is for is for VVENTRICLESENTRICLES((BBlood lood CCan an BBe e VVery ery BBad)ad)



Ex-Vacuo PhenomenonEx-Vacuo Phenomenon





BONEBONE







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.

Blood Can Be Very Bad

RIPRIP


QuestionsQuestions

ferne_acep_2005_peds_perron_ich_bcbvb_fshow.ppt 04/18/23 13:13

[email protected]@ferne.org

Andrew D. Perron, MD, FACEPAndrew D. Perron, MD, FACEP

[email protected](207) 662-7015207) 662-7015

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Andrew D. Perron, MD, FACEP 1 How to Read a Head CT (or “How I learned to stop worrying and love computed tomography”)