approach to head ct

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