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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
Brian A. Stettler, MD, FACEP
Objectives
• 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
Brian A. Stettler, MD, FACEP
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
Brian A. Stettler, MD, FACEP
ED Presentation
PMHx: DM, HTN, CAD
Meds: Atenolol, HCTZ, ASA, Insulin
All: NKDA
SocHx: 1PPD, Occasional Etoh, denies drugs
ROS: mild anorexia, weight loss approx 5 lbs
over past month, o/w neg
Brian A. Stettler, MD, FACEP
ED Presentation
PE: 176/94, 65, 16, 98.8, 93% RA
Gen: alert and conversive, sl uncomfortable
appearing
HEENT: WNL
Pulm: sl wheezes, otherwise WNL
CV: WNL
Neuro: strength 4/5 throughout, gait unsteady
without overt ataxia, no deficits to cranial nerves
Brian A. Stettler, MD, FACEP
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?
Brian A. Stettler, MD, FACEP
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
Brian A. Stettler, MD, FACEP
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
Brian A. Stettler, MD, FACEP
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
Brian A. Stettler, MD, FACEP
Head CT Interpretation
• Scout, assessment for adequacy
• Quick look
• Detailed look (force yourself)
– Extra-axial blood – Vessel density
– Mass effect – Bone windows
– Ischemia – Extras (sinuses, mastoids)
– Ventricles – Compare to old
Brian A. Stettler, MD, FACEP
Head CT Interpretation
• Look at the scout
• Adequate study?
– Minimize motion
– Subject to artifact from metal
Brian A. Stettler, MD, FACEP
Head CT Interpretation
• Quick look
– Get the gestalt
– Assess for gross
abnormalities
Brian A. Stettler, MD, FACEP
Head CT Interpretation
• Extra-axial hemorrhage
– Epidural hematoma
– Subdural hematoma
– Subarachnoid hemorrhage
• Intracerebral hemorrhage
• Intraventricular hemorrhage
Brian A. Stettler, MD, FACEP
Epidural Hematoma
• “Lens” shaped
• Does not cross suture
lines
• Typically acute or
hyperacute
• Frequently associated
with mass effect
Brian A. Stettler, MD, FACEP
Subdural Hematoma
• Located along Acute
calvarium, falx,
tentorium
• Crosses suture lines,
usually spreads more
extensively than
epidural
Brian A. Stettler, MD, FACEP
Subdural Hematoma
• Can be acute, Subacute
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
Brian A. Stettler, MD, FACEP
Subdural Hematoma
Chronic
• 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
Brian A. Stettler, MD, FACEP
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
Brian A. Stettler, MD, FACEP
Subarachnoid Hemorrhage
• Source:
– Post-traumatic
– Aneurysmal
– AVM
– Other
• Hounsfield units
– Blood is 50-100 (80)
Brian A. Stettler, MD, FACEP
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
Brian A. Stettler, MD, FACEP
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
Brian A. Stettler, MD, FACEP
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
Brian A. Stettler, MD, FACEP
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
Brian A. Stettler, MD, FACEP
Herniation
• 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
Brian A. Stettler, MD, FACEP
Tying it Together
• Spontaneous ICH
• Supratentorial (L
basal ganglia)
• Approx 45cc
• 8mm of midline
shift
• Evidence of uncal
herniation
Brian A. Stettler, MD, FACEP
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
Brian A. Stettler, MD, FACEP
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
Brian A. Stettler, MD, FACEP
Ischemia
• 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
Brian A. Stettler, MD, FACEP
Ischemia
• ASPECTS
– Larger areas of grey-white
changes on initial CT have worse
outcomes
– Score < 7 had OR 82 for worse
functional outcome
Barber, Lancet 2000
Brian A. Stettler, MD, FACEP
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
Brian A. Stettler, MD, FACEP
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
Brian A. Stettler, MD, FACEP
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
Brian A. Stettler, MD, FACEP
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
Brian A. Stettler, MD, FACEP
Questions?
Brian A. Stettler, MD, FACEP
