Presentation on theme: "(or “How I learned to stop worrying and love computed tomography”)"— Presentation transcript:
1(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”)
2Andrew D. Perron, MD, FACEP EM Residency Program DirectorDepartment of Emergency MedicineMaine Medical CenterPortland, MEAndrew D. Perron, MD, FACEP254541
3Head CTHas 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.
4Head CTMost 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 cranialCT interpretation.
5Head CTIn 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.
6Head CTThe intent of this session is to introduce a similar systematic method of cranial CT interpretation, based on the mnemonic…
8Blood Can Be Very BadBloodCisternsBrainVentriclesBone
9Blood Can Be Very BadBloodCisternsBrainVentriclesBone
10Blood Can Be Very BadBloodCisternsBrainVentriclesBone
11Blood Can Be Very BadBloodCisternsBrainVentriclesBone
12Blood Can Be Very BadBloodCisternsBrainVentriclesBone
13CT Scan BasicsA 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.
14CT Scan Basics The denser the object, the whiter it is on CT Bone is most dense = Hounsfield U.Air is the least dense = H Hounsfield U.
15CT Scan Basics: Windowing Focuses the spectrum of gray-scale used on a particular image.
35CSF ProductionProduced in choroid plexus in the lateral ventricles Foramen of Monroe IIIrd Ventricle Acqueduct of Sylvius IVth Ventricle Lushka/Magendie0.5-1 cc/minAdult CSF volume is approx. 150 cc’s.Adult CSF production is approx cc’s per day.
39A 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-developedTerm Infant (36-41 weeks):Small, slit-like lateral ventriclesContinued white-matter prominenceMore prominent sulcal patternTemporal horns unlikely to be seen1st & 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.
42B is for Blood 1st decision: Is blood present? 2nd decision: If so, where is it?3rd decision: If so, what effect is it having?
43CT Diagnostics At what point does blood become isodense with brain? About 48 hoursAbout 1 weekAbout 2 weeksAfter 1 month
44B 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.
45B 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.
46B 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.
47Epidural Hematoma Lens shaped Does not cross sutures Classically described with injury to middle meningeal arteryLow mortality if treated prior to unconsciousness( < 20%)
49Subdural 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.
52Subarachnoid Hemorrhage Blood in the cisterns/cortical gyral surfaceAneurysms responsible for 75-80% of SAHAVM’s responsible for 4-5%Vasculitis accounts for small proportion (<1%)No cause is found in 10-15%20% will have associated acute hydrocephalus
53CT Diagnostics What is the sensitivity of CT for SAH? 100% 95% 80% Depends…I need a lot more information to answer.
54CT Scan Sensitivity for SAH 98-99% at 0-12 hours90-95% at 24 hours80% at 3 days50% at 1 week30% at 2 weeksDepends on generation of scanner and who is reading scan and how much blood there is.
89Blood Can Be Very BadIf 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.