(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”)

Andrew D. Perron, MD, FACEP EM Residency Program Director Department of Emergency Medicine Maine Medical Center Portland, ME Andrew D. Perron, MD, FACEP 2 54 54 1

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

Head CT “Blood Can Be Very Bad”

Blood Can Be Very Bad Blood Cisterns Brain Ventricles Bone

Blood Can Be Very Bad Blood Cisterns Brain Ventricles Bone

Blood Can Be Very Bad Blood Cisterns Brain Ventricles Bone

Blood Can Be Very Bad Blood Cisterns Brain Ventricles Bone

Blood Can Be Very Bad Blood Cisterns Brain Ventricles Bone

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

2 Sheet Head CT

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

CT Scan

CT Scan

Sagittal View C Circummesencephalic Cistern

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

Cisterns

CT Scan

Brainstem Lateral View

2nd Key Level Sagittal View Circummesencephalic Cistern

Cisterns at Cerebral Peduncles Level

CT Scan

Suprasellar Cistern

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

CT Scan

3rd Key Level Sagittal View Circummesencephalic Cistern

Cisterns at High Mid-Brain Level

CT Scan

Ventricles

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 Scan

CT Scans 37 Andrew D. Perron, MD, FACEP

A Few Kid-Specific Thoughts

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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Trauma Pictures

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 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 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.

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.

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.

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

CT 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.

CT Scan 50 Andrew D. Perron, MD, FACEP

Subarachnoid Hemorrhage

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 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 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 55 Andrew D. Perron, MD, FACEP

CT Scan 56 Andrew D. Perron, MD, FACEP

Intraventricular/ Intraparenchymal Hemorrhage

CT Scan 58 Andrew D. Perron, MD, FACEP

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

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 66 Andrew D. Perron, MD, FACEP

Atrophy 67 Andrew D. Perron, MD, FACEP

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

Abscess 69 Andrew D. Perron, MD, FACEP

Hemorrhagic Contusion 70 Andrew D. Perron, MD, FACEP

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Mass Effect 72 Andrew D. Perron, MD, FACEP

Stroke 73 Andrew D. Perron, MD, FACEP

Intracranial Air

Intracranial Air 75 Andrew D. Perron, MD, FACEP

Intracranial Air 76 Andrew D. Perron, MD, FACEP

V is for VENTRICLES (Blood Can Be Very Bad)

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Ex-Vacuo Phenomenon 80 Andrew D. Perron, MD, FACEP

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BONE 84 Andrew D. Perron, MD, FACEP

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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.

RIP

www.ferne.org ferne@ferne.org Andrew D. Perron, MD, FACEP Questions www.ferne.org ferne@ferne.org Andrew D. Perron, MD, FACEP perroa@mmc.org (207) 662-7015 ferne_acep_2005_peds_perron_ich_bcbvb_fshow.ppt 4/13/2017 9:09 PM 54 1 54