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Dr lokesh kumar meenaDept of Radiodiagnosis
MGIMS, Sevagram
About this presentationThis presentation will give you a systematic approach
to head CTBy the end you should be familiar with normal
anatomy and be able to identify classic abnormalities on CT
You can test your knowledge with the short cases at the end
Types of head CT’sNon-contrast
ContrastIV contrast is given to better evaluate:
Vascular structures Tumors Sites of infection
Relative contraindications: Allergy, renal failure
Common Indications for Head CTCranial-facial traumaAcute strokeSuspected subarachnoid or intracranial hemorrhageEvaluation of headacheEvaluation of sensory or motor function lossEvaluation of sinus cavities
CT basicsBefore we begin, there are key concepts you should
be familiar with:
Hounsfield unitsWindowing & levelingPlanes
What’s a Hounsfield Unit?Named after the inventor of CTCT scanners record the attenuation (brightness) of each
pixel in Hounsfield Units (HU)This number represents the relative density of the
scanned substanceRanges from -1000 to +1000
Hounsfield Unit (HU)Different substances have different relative densities and
thus, different Hounsfield units
Air: -1000 HU Fat: -50 HU Water: 0 HU Soft tissue: +40 HU Blood: +40-80 HU Stones: +100 to +400 HU Bone: +1000 HU
Therefore, if you’re not sure what you’re looking at, measure its Hounsfield Unit!
How to measure HUIn EFILM, you can
measure the HU using the oval ROI tool:
On the right, you can see sample measurements of different structures
Note how bone, CSF, brain tissue, and air all have different mean HUs
WindowingThe human eye can only perceive ~ 16 shades of
gray
The CT scanner records levels of gray far beyond what the eye can see
Therefore, to interpret images, we have to limit the number of Hounsfield units shown (windowing)
The computer then converts this set range of HU into shades of gray we can see
Windows & levelsWindow width:
The range of HU of all tissues of interestTissues in this range will be displayed in various shades
of grayTissues with HU outside the range are displayed as
black or white Window level:
The central HU of all the numbers in the window width
Windowing
+400+400
+300+300
+200+200
+100+100
00
-100-100
-200-200
-300-300
-400-400
Wide Wide WindowWindow
Narrow Narrow WindowWindow
Hounsfield UnitsHounsfield Units
Window examplesIn head CT, 3 windows are commonly used
BRAINBRAIN window windowW:80 L:40W:80 L:40
BONEBONE window windowW:2500 L:480W:2500 L:480
SUBDURALSUBDURAL window windowW:350 L:90W:350 L:90
Plane
Transaxial plane used most often for head CT’s
Coronal plane good for evaluation of
pituitary/sella and sinusesSaggital plane
rarely used (more common in MRI)
Plane refers to how the picture slices are orientatedPlane refers to how the picture slices are orientated
Plane examples
AxialAxial plane plane CoronalCoronal plane plane Saggital Saggital planeplane
IdentificationNow we can begin our basic approach to the head CT
Start with the easy stuff:PATIENT NAME (make sure you have the right patient !!)
MEDICAL RECORD # (MRN)AGEDATE OF EXAM
Previous studiesAlways check for any previous scans for comparison
Findings can be very subtle A good way to spot them is to look for changes between
the current and previous scansEven old chest and abdominal films can give you clues to
possible brain pathology ie. Brain mets from lung cancer
Study parametersMake note of the study technique:
Anatomic region of scan: head, neck, spineSlice thickness (mm)Window level & widthPlane: Transaxial, coronal, saggitalUse of contrast?
Look for the Circle of Willis. It will be enhanced on studies using contrast
Image analysisNow that you have noted all the basic information
about the scan, it’s time to look at the scan itselfUse a systematic order & approach to what you look
atUse the same approach for all scans to ensure that you
don’t miss anything
Regions to inspectWe will start from the inside and move outwards:
1.1. Midline structures & Midline structures & symmetrysymmetry
2.2. VentriclesVentricles3.3. CisternsCisterns4.4. Brain parenchymaBrain parenchyma
5.5. SulciSulci6.6. SinusesSinuses7.7. BonesBones8.8. Skin/soft tissueSkin/soft tissue
1. Midline structures
Falx Cerebri
Identify:Identify:
Pineal gland Pineal gland (usually calcified)(usually calcified)
Great vein of Galen Great vein of Galen
FornixFornix
Midline shiftEvaluate for midline shift:
Find a slice where the 2 Find a slice where the 2 lateral ventricles are lateral ventricles are prominentprominent
Draw a vertical line down Draw a vertical line down the middle joining the falx the middle joining the falx cerebri anteriorly & cerebri anteriorly & posteriorlyposteriorly
The septum The septum between the between the lateral ventricles lateral ventricles should should not deviatenot deviate more than 5mm more than 5mm from the midlinefrom the midline
Midline shift examples
A right-sided abscess is causing a A right-sided abscess is causing a midline shift to the leftmidline shift to the left
A left-sided tumor is causing a A left-sided tumor is causing a midline shift to the rightmidline shift to the right
L LR R
2. Ventricles
Lateral ventricles x 2
Third ventricleThird ventricle
Fourth ventricleFourth ventricle
Identify:Identify:
Cerebral aqueductCerebral aqueduct
VentriclesEvaluate for any changes in
SymmetrySizeShapeDensity
A displaced ventricle is often the product of mass effect or atrophy
VentriclesCommon pathology:
HydrocephalusHydrocephalus
Intra-ventricular HemorrhageIntra-ventricular Hemorrhage
Mass effectMass effect AtrophyAtrophy
3. Cisterns Identify:Identify:
Supracellar cisternSupracellar cistern Ambient cisternAmbient cistern Prepontine cisternPrepontine cistern
Cisterna magnaCisterna magna
CisternsEvaluate for any changes in
SymmetrySizeDensity
Cisterns often contain blood with subarachnoid hemorrhage
Cisterns can fill with pus in the setting of meningitis
4. Brain parenchyma – LobesFirst, identify the major lobes:
Temporal lobeTemporal lobe
Occipital lobeOccipital lobe
Frontal lobeFrontal lobe
Parietal lobeParietal lobe
Brain Parenchyma - BrainstemThen identify:
PonsPons
CerebellumCerebellum
MidbrainMidbrain
MedullaMedulla
Brain parenchyma – Deep structuresLastly, identify the deep structures:
ThalamusThalamus Lentiform NucleusLentiform Nucleus
CaudateCaudate
Corpus CallosumCorpus Callosum
Internal capsuleInternal capsule External capsuleExternal capsule
Parenchymal massesLook for mass lesions
AbscessAbscess
NeoplasmNeoplasm
Note how the tumor becomes bright with contrast
Also note the surrounding dark area of edemaNote the ring enhancing lesion consistent
with that of an abscess
Acute Infarct
The middle cerebral artery (MCA)becomes hyperdense due to occlusion
The usual border between grey and white The usual border between grey and white matter is matter is lostlost due to vasogenic edema due to vasogenic edema
Hyperdense MCA signHyperdense MCA sign
Look for signs of Look for signs of acuteacute infarction infarction Loss of gray-white Loss of gray-white
differentiationdifferentiation
Click meClick me to see to see Click meClick me to to seesee
Chronic Infarct Then, look for signs of Then, look for signs of chronicchronic infarction: infarction:
Mild midline shift to the right due to atrophy
Retractment of parenchyma from skull due to atrophy
Focal area of hypodensity
Infarction locations
Microangiopathic changeYou may encounter the term
“microangiopathic change” in reports and wonder what it is
Microangiopathic change refers to age-related white matter ischemia due to microvessel disease
Very commonly seen in the elderly
Its clinical significance is still not known
Microangiopathic change
Normal
Types of HematomaLook for evidence of a bleed:
Subdural HematomaDue to tear of bridging veinsLook for crescentic shape along brain surfaceCrosses suture lines
Epidural HematomaDue to rupture of middle meningeal arteryAssociated with skull fracturesLook for biconvex, lenticular shapeDoes not cross suture lines
Subdural vs. Epidural
Note the cresentic shape
SUBDURALSUBDURAL EPIDURALEPIDURAL
Note the lenticular shapeNote the lenticular shape
Subarachnoid HemorrhageLook for a subarachnoid hemorrhageDue to aneurysm rupture, trauma, or AVMBlood in the subarachnoid space and/or ventriclesBlood can often first be seen in the inter-peduncular cistern
Blood in subarachnoid
space
Blood in sulci
Blood in ventricle
(Normal)
Intraparenchymal HemorrhageLook for intraparenchymal
hemorrhage:blood (acute, subacute, or
chronic) located in brain parenchyma
surrounding area of edema may also be seen
Usually caused by hypertension
Hemorrhage timelineIf you see a bleed, try to assess if its new or old:
ACUTE bleed (< 3 days)Hyperdense (80-100 HU) relative to brainCaused by protein-Hb componentCan be hard to spot if hemoglobin is low (<80)
SUBACUTE bleed (3-14 days)Hyperdense, isodense, or hypodense relative to brainDensity loss starts from periphery and goes to centre
CHRONIC bleed (>2 weeks)Hypodense (<40 HU) relative to brain
Density of blood over time in a subdural hematoma
Acute Acute (<3 days)(<3 days)
Sub-acuteSub-acute (3-14 days)(3-14 days)
Chronic Chronic (>14 days)(>14 days)
Hyperdense blood
Isodense blood
Hypodense blood
5. SulciIdentify:
Central sulcusCentral sulcus Precentral Precentral
sulcussulcus
SulciSulci Sylvian fissuresSylvian fissures
Postcentral sulcusPostcentral sulcus
SulciRemember that sulci will become deeper and more prominent
with ageLook for blood in the sulci & Sylvian Fissure which are
indications of a sub-arachnoid bleed
Acute blood in Sylvian fissure
Acute blood in sulci
6. SinusesSwitch to Bone Window to better evaluate the sinusesIdentify:
Ethmoid SinusEthmoid Sinus
Sphenoid SinusSphenoid Sinus
Superior Saggital SinusSuperior Saggital Sinus Frontal SinusFrontal Sinus
Maxillary SinusMaxillary Sinus
SinusesEvaluate for any sinusitis:
fluid in sinusesfluid in sinuses(notice the air/fluid level)(notice the air/fluid level)
normalsinusitis
SinusesAlso look for any:
Mucosal thickeningBlood in sinuses (especially with history of trauma)
Polyps or mucous retention cysts
7. BoneStay on the Bone Window and look at the bones nowIdentify:
SkullSkull
SuturesSutures
Mastoid air cellsMastoid air cells
BoneEvaluate for any:
FracturesFractures Surgical changes Surgical changes
(ie. craniotomies)(ie. craniotomies)
8. Skin & Soft tissueEvaluate for any:
Surgical changesSurgical changes
Sub-galeal hematomaSub-galeal hematoma Foreign bodyForeign body
Thank you……………
RecapBegin with the basic identificationRemember to check for previous scansCheck the techniqueLook at each region of the brain systematically
We started from the middle and worked out:
1.1. Midline structuresMidline structures2.2. VentriclesVentricles3.3. CisternsCisterns4.4. Brain parenchymaBrain parenchyma
5.5. SulciSulci6.6. SinusesSinuses7.7. BonesBones8.8. Skin/soft tissueSkin/soft tissue
RecapIn each area, identify the major anatomyThen look for findingsBelow is a list of important things not to miss:
Midline: midline shiftVentricles: blood and mass effectCisterns: blood and pusParenchyma: signs of ischemia and/or bleedingSulci: for bloodSinuses: signs of sinusitisBones: fracturesSoft tissue: hematoma
RecapRemember to use the same approach every time so
that you don’t miss anything!
Try out the cases in the next slides to test your knowledge
Case #1Mr A is an 80 y/o female presenting with:
Expressive aphasia/apraxia Mild right facial droopAtrial fibrillation
A non-contrast CT scan of her brain is performed
Your analysisWhat are your findings?What is your impression?What would be your top diagnosis?
Normal
Case #1 - AnswerMr A had an infarction of her Left
Parietal LobeThe location is consistent with
MCA infarctionThe cause was emboli related to
her atrial fibrillation
Case #2Mr. B is a 56 y/o male presenting with:
A sudden onset 10/10 headache while running Photophobia, nausea & vomitingNo history of trauma or LOCOtherwise well
A non-contrast CT scan of his brain is performed
Your analysisWhat are your findings?What is your impression?What would be your top diagnosis?Is this pathology acute, subacute, or chronic
Case #2 - AnswerMr. B had a large subarachnoid
hemorrhageThe bleed was acuteThis was caused by rupture of an
ACA aneurysm He was admitted to ICU where
his condition deteriorated rapidly
He passed away shortly after admission
Case #3Mr C is a 66 y/o female who slipped down the stairs
yesterday and hit the back of her head. She presents with
Generalized left sided weaknessLight headache
A non-contrast CT scan of her brain is performed
R L
Your analysisWhat are your findings?What is your impression?What would be your top diagnosis?Is this pathology acute, subacute, or chronic
Case #3 - AnswerMr C had a large right-
sided subdural hematoma The hematoma is acuteThis was caused by
rupture of bridging veins when she hit her head
A craniotomy was performed and the bleed was drained
Bonus caseMr. X is a 80 y/o male presenting with:
3 month history of deliriumRecent fall from bedLarge scalp lacerationNo focal neurological findings
An non-contrast CT scan of his brain is performed
Subdural
Look closely at the midline structuresHint?
AnalysisCan you spot the abnormalities?What is your impression?What would be your top diagnosis?
Bonus case - Answer Mr. X had a tiny right-sided Mr. X had a tiny right-sided
subdural hematoma subdural hematoma Blood is seen along the left Blood is seen along the left
subdural space as well as in the subdural space as well as in the falx cerebri anteriorly (arrows)falx cerebri anteriorly (arrows)
The hematoma is The hematoma is acuteacute Because of its small size, no Because of its small size, no
immediate treatment was immediate treatment was requiredrequired
Follow-up CT scans showed Follow-up CT scans showed resolution of the subdural resolution of the subdural hematoma hematoma
Normal scan for comparisonNormal scan for comparison