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Basic Interpretation of CT Scan

Hon-Man Liu

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Basic Interpretation of CT Scans

Most of the CT pictures are non-

specific

CT pictures are depending on the

density of the structures.

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Principles of CT Diagnosis

Pre-contrast study

Post-contrast study

Change in adjacent structures

Clinical Information Biological or anatomical

characteristics

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Pre-contrast study of CT

Hypo - density

Comparison with CSF and braintissue

Hyper - density

Comparison with cranium bone Iso - density

As brain parenchyma

Hetero- density

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Hypo-density in CT

Higher than CSF but lower than brain tissue

tumor, abscess, resolving hematoma,

evolution infarct,

protein, blood, debris

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Hypo-density in CT

Higher than CSF but lower than brain tissue

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Hypo-density in CT

Iso-density to CSF

chronic hematoma, chronic infarct,

porencephaly, congenital cyst,

encephalomalacia change

Water-like content

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Hypo-density in CT

Iso-density to CSF

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Hypo-density in CTLower than CSF

fat or cholesterol

congenital tumor: dermoid ,

epidermoid,lipoma,

air

head injury, pneumocephaly

myxoid

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Hypo-density in CT

Lower than CSF

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Hyper-density in CT

Comparison with bone

Iso- or higher than boneossification, calcification, metallic,

iatrogenic, blood pooling

Less than bone but higher than brain tissuehemorrhage, compacted cellularity

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Hyper-density in CT

Iso- or higher than bone

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Hyper-density in CT

Less than bone but higher than brain tissue

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P

ost-contrast CTEnhancement patterns

gyral, ribbon, cortical

soild

rim or ring

mural nodular

linear and dot

heterogenous

no enhancement

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EnhancementP

atterns

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Change in Adjacent Structures in

CT

Edema

Bone

Ventricles, sulci and cistern

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EdemaP

attern in CT Vasogenic edema

tumors, infection, late infarct

along the white matters, finger-like

Interstitial edema

periventricular white matter, ependymitis

granularis

Cytotoxic edema

ischemia or infarct, gray matter

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Vasogenic Edema

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Vasogenic edema

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Cytotoxic Edema

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CAUSES of RAISEDCAUSES of RAISED

INTRACRANIAL PRESSUREINTRACRANIAL PRESSURE

HydrocephalusHydrocephalus Brain edemaBrain edema

S.T.LS.T.L

Tumor,Tumor,Hematoma,Hematoma,

Cyts,Cyts,Infarct.Infarct.

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RAISED INTRACRANIALRAISED INTRACRANIAL

PRESSUREPRESSURE

ICPICP

DAYSDAYS WEEKSWEEKS HOURSHOURS

ConingConingFocal mass effectFocal mass effect CSF spaceCSF space

changechange

hydrocephalushydrocephalusHerniationHerniation

DEATHDEATH

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HerniationHerniation

Subfalcine

Parahippocampus

Central, tonsillar

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SUBFALCINEH

ERNIASUBFALCINEH

ERNIA

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TRANSTENTORIALH

ERNIASTRANSTENTORIALH

ERNIAS

1. PARAHIPPOCAMPAL GYRUS (PHG)HERNIATION

2. CENTRAL/DIENCEPHALICHERNIATION

MAY OCCUR INDEPENDENTLY ORMAY OCCUR INDEPENDENTLY OR

IN COMBINATIONIN COMBINATION

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PARAHIPPOCAMPAL GYRUSPARAHIPPOCAMPAL GYRUS

(PH

G)H

ERNIATION(PH

G)H

ERNIATION

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COMPLICATIONS of PHGCOMPLICATIONS of PHG

HERNIATIONHERNIATION

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COMPLICATIONS of PHGCOMPLICATIONS of PHG

HERNIATIONHERNIATION

PCA ossculsion

3rd nerve palsy

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CENTRALH

ERNIATIONCENTRALH

ERNIATION

MAMILLARYMAMILLARY BODYBODY

PONSPONS

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CENTRAL HERNIATIONCENTRAL HERNIATION

NORMALNORMAL HERNIAHERNIA

AP

diameter> trans

diameter

AP

diameter

=/< trans

diameter

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SECONDARY BRAINSECONDARY BRAIN

STEMSTEM

HAEMORRHAGESHAEMORRHAGES

Duret hemorrahge

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CEREBELLAR TONSILAR HERNAITIONCEREBELLAR TONSILAR HERNAITION

CONINGCONING

OROR

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Bone Change in CT

Foramen

internal auditory canal, foramen ovale,

orbital fissures

Cranium bone

hyperostosis

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CSF Spaces Change in CT

Widening or obliterated

Sensitive to mass effect

Proportional or in-proportional

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Ischemia: gray matter

increased water -- density --

density closed to whitematter -- loss of the

differentiation between the

lentiform nucleus and

internal capsule

CT of Cerebral Ischemia

(lentiform nucleus sign)

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CT of Cerebral Ischemia

(Insular ribbon sign)Ischemia -- cytotoxic

edema -- cellular

swelling -- mass

effect -- straightening

the normal wavinginsular ribbon

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CT of Cerebral Ischemia

(Hyper-dense vascular sign)

Ischemia -- blood

stasis in greatvessel such as M1 -

- blood clot -- high

density

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Biological and AnatomicalCharacteristics

Hemangioblastomahemoglobin, hematocrit, erythropoietin

Craniopharyngioma

anterior 3rd ventricle to nasopharynx

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Clinical Information in CT

Acute, progressive or stationary

Timingimportant in ischemic disease

previous history of irradiation or

operation