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Head CT Interpretation in the ED: The Complete Primer. Brian A. Stettler, MD Assistant Professor Department of Emergency Medicine University of Cincinnati. Objectives. Discuss the utility of Head CT Discuss what Head CT will miss Review basic interpretation of the Head CT

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Head ct interpretation in the ed the complete primer

Head CT Interpretation in the ED: The Complete Primer

Brian A. Stettler, MD

Assistant Professor

Department of Emergency Medicine

University of Cincinnati


  • Discuss the utility of Head CT

  • Discuss what Head CT will miss

  • Review basic interpretation of the Head CT

  • Discuss a few specific disease processes

Clinical history
Clinical History

CC: Headache and weakness

HPI: 67 year old female with several months of dull headaches relieved by Tylenol and subjective “dizziness” without falls. Symptoms worsened today about 2 hours ago and she now complains she cannot walk secondary to dizziness

Ed presentation
ED Presentation


Meds: Atenolol, HCTZ, ASA, Insulin


SocHx: 1PPD, Occasional Etoh, denies drugs

ROS: mild anorexia, weight loss approx 5 lbs over past month, o/w neg

Ed presentation1
ED Presentation

PE: 176/94, 65, 16, 98.8, 93% RA

Gen: alert and conversive, sl uncomfortable appearing


Pulm: sl wheezes, otherwise WNL


Neuro: strength 4/5 throughout, gait unsteady without overt ataxia, no deficits to cranial nerves

Points of discussion
Points of Discussion

  • In addition to other labs, a non-contrast head CT is ordered

    • How is this study interpreted?

    • What findings affect the treatment of the patient?

    • What findings portend a bad outcome for the patient?

Non contrast head ct
Non-contrast Head CT

  • The most common neuroimaging tool employed in the ED

    • Performed in seconds, usually read in minutes

    • No IV access required

    • Available 24 hours/day in most EDs

    • No real contraindications

    • Good sensitivity and specificity for many disease processes

Non contrast head ct1
Non-contrast Head CT

  • Benefits:

    • Gold standard in assessment for acute hemorrhage

    • Very good at documenting mass effect and herniation

    • Will visualize acute ischemia, neoplasm, localized intracranial infection

    • Good at visualizing skull fracture

Non contrast head ct2
Non-contrast Head CT

  • Drawbacks

    • Poor at visualizing disease in the posterior cranial fossa, especially ischemia

    • Poor at diagnosing intracranial mass that does not have significant mass effect

    • Sensitivity is not high enough to completely eliminate SAH

    • Will miss delayed disease, such as delayed SDH

Head ct interpretation
Head CT Interpretation

  • Scout, assessment for adequacy

  • Quick look

  • Detailed look (force yourself)

    • Extra-axial blood

    • Mass effect

    • Ischemia

    • Ventricles

  • Vessel density

  • Bone windows

  • Extras (sinuses, mastoids)

  • Compare to old

Head ct interpretation1
Head CT Interpretation

  • Look at the scout

  • Adequate study?

    • Minimize motion

    • Subject to artifact from metal

Head ct interpretation2
Head CT Interpretation

  • Quick look

    • Get the gestalt

    • Assess for gross abnormalities

Head ct interpretation3
Head CT Interpretation

  • Extra-axial hemorrhage

    • Epidural hematoma

    • Subdural hematoma

    • Subarachnoid hemorrhage

  • Intracerebral hemorrhage

  • Intraventricular hemorrhage

Epidural hematoma
Epidural Hematoma

  • “Lens” shaped

  • Does not cross suture lines

  • Typically acute or hyperacute

  • Frequently associated with mass effect

Subdural hematoma
Subdural Hematoma

  • Located along calvarium, falx, tentorium

  • Crosses suture lines, usually spreads more extensively than epidural


Subdural hematoma1
Subdural Hematoma

  • Can be acute, subacute, or chronic

    • Density on CT helps to age hematoma

    • Can frequently be a mix of ages

  • Can have mass effect that ranges from none to severe


Subdural hematoma2
Subdural Hematoma


  • Not all SDH are bright white

  • MUST follow gyri/sulci to edge of calvarium on every cut

  • Falx may be calcified but should be thin

Osborn, Diagnostic Imaging Brain 2004

Subarachnoid hemorrhage
Subarachnoid Hemorrhage

  • Can be present in cisterns, around gyri and sulci

  • Almost always acute

  • Sensitivity of NCHT

    • Not well known or agreed upon

    • Probably in the high 90’s early

    • Decreases as time progresses from onset of symptoms

Subarachnoid hemorrhage1
Subarachnoid Hemorrhage

  • Source:

    • Post-traumatic

    • Aneurysmal

    • AVM

    • Other

  • Hounsfield units

    • Blood is 50-100 (80)

Intracerebral hemorrhage
Intracerebral Hemorrhage

  • Location can be anywhere in the parenchyma

  • Can be caused by hypertension, AVM, amyloid

  • Typically present with headache, focal neurologic findings, AMS, N/V

Intracerebral hemorrhage1
Intracerebral hemorrhage

  • CT findings that affect outcome

    • Volume of hemorrhage

    • Location of hemorrhage (supra vs infratentorial)

    • Presence of intraventricular hemorrhage

  • Also describe:

    • Presence of midline shift

    • Presence of herniation

    • Presence of hydrocephalus

Volume of hemorrhage
Volume of Hemorrhage

  • (A x B x C)/2

  • A and B are perpendicular dimensions in the slice that shows the maximal amount of hemorrhage

  • C is the total number of slices that show hemorrhage x the slice thickness

  • Ex: 4cm x 5.5 cm by (8 x 5mm slices)/2

    • 4 x 5.5 x 4/2 = 45cc

Mass effect and midline shift
Mass Effect and Midline Shift

  • Mass effect can be local or generalized

  • When generalized, typically seen as shift of the midline structures away from the area of mass effect

  • Midline shift

    • Use drawing tools to draw line down center of skull

    • Measure from midline structure (pineal gland, falx, septum pellucidum) to line drawn


  • Herniation is an ominous sign on CT

  • Types

    • Uncal (3rd nerve palsy – the “blown pupil”)

    • Transtentorial

    • Sub-falcine

    • Tonsillar

  • Look for structures where they should not be

Tying it together
Tying it Together

  • Spontaneous ICH

  • Supratentorial (L basal ganglia)

  • Approx 45cc

  • 8mm of midline shift

  • Evidence of uncal herniation

Trauma contusions
Trauma - Contusions

  • Patchy hemorrhage contained to the superficial grey matter

  • Frequently associated with local edema

  • Caused by brain impact to bone

  • Locations most commonly temporal lobes and frontal, but can occur anywhere

Trauma contusions1
Trauma - Contusions

  • Contusions frequently evolve from small petechiae to large areas of edema and hemorrhage over the course of 1-2 days

Osborn, Diagnostic Imaging Brain 2004


  • Very early CT typically negative

  • Early findings

    • Loss of grey-white differentiation

      • Insular “ribbon”

      • Basal ganglia/internal capsule

    • Effacement of ventricles and local mass effect

    • Hyperdense artery



    • Larger areas of grey-white changes on initial CT have worse outcomes

    • Score < 7 had OR 82 for worse functional outcome

Barber, Lancet 2000

Being thorough
Being Thorough

  • Use bone windows on every trauma

  • Don’t forget the extras

    • Sinuses, mastoid air cells

    • Air where it shouldn’t be

    • Orbits

    • Old infarcts

  • If abnormal, look for an old CT

Case follow up
Case Follow-up

  • Pt’s CT showed a small, ill-defined parenchymal hemorrhage

  • Follow-up MRI showed multiple enhancing lesions suspicious for mets

  • Pt undergoing treatment for metastatic lung CA

Head ct conclusions
Head CT - Conclusions

  • Scan early and often

  • Beware the lurking slit subdural

  • Contusions can be tiny – at first

  • Ischemia can be subtle

  • You still can’t completely trust the negative SAH CT

  • Negative early doesn’t always mean negative late – and vice versa

Head ct conclusions1
Head CT - Conclusions

  • Useful imaging screening tool for many life-threatening neurologic processes

  • May miss early findings in hemorrhage or ischemia

  • Interpretation must be done thoroughly

    • The same way every time

    • Assess not only primary pathology, but factors contributing to outcome