basic interpretation of ct scan - national...
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Basic Interpretation of CT Scan
Hon-Man Liu廖漢文
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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 brain tissue
• Hyper - densityComparison with cranium bone
• Iso - densityAs 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 CTHigher 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 CTIso-density to CSF
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Hypo-density in CT
Lower than CSF• fat or cholesterol
congenital tumor: dermoid , epidermoid,lipoma,
• airhead injury, pneumocephaly
• myxoid
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Hypo-density in CTLower than CSF
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Hyper-density in CT
Comparison with bone• Iso- or higher than bone
ossification, calcification, metallic, iatrogenic, blood pooling
• Less than bone but higher than brain tissuehemorrhage, compacted cellularity
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Hyper-density in CTIso- or higher than bone
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Hyper-density in CT Less than bone but higher than brain tissue
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Post-contrast CTEnhancement patterns
• gyral, ribbon, cortical• soild• rim or ring• mural nodular• linear and dot• heterogenous• no enhancement
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Enhancement Patterns
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Change in Adjacent Structures in CT
• Edema• Bone• Ventricles, sulci and cistern
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Edema Pattern in CT• Vasogenic edema
tumors, infection, late infarctalong the white matters, finger-like
• Interstitial edemaperiventricular white matter, ependymitisgranularis
• Cytotoxic edemaischemia 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 RAISED CAUSES of RAISED INTRACRANIAL PRESSUREINTRACRANIAL PRESSURE
HydrocephalusHydrocephalus Brain Brain edemaedema
S.T.LS.T.LTumorTumor,,
HematomaHematoma,,CytsCyts,,
InfarctInfarct……..
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RAISED INTRACRANIAL RAISED INTRACRANIAL PRESSUREPRESSURE
ICPICP
DAYSDAYS WEEKSWEEKS HOURSHOURS
ConingConingFocal mass effectFocal mass effect CSF space CSF space
changechangehydrocephalushydrocephalus
HerniationHerniation
DEATHDEATH
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HerniationHerniation
Subfalcine
Parahippocampus
Central, tonsillar
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SUBFALCINE HERNIASUBFALCINE HERNIA
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TRANSTENTORIAL HERNIASTRANSTENTORIAL HERNIAS
1. PARAHIPPOCAMPAL GYRUS (PHG) HERNIATION
2. CENTRAL/DIENCEPHALIC HERNIATION
MAY OCCUR INDEPENDENTLY OR MAY OCCUR INDEPENDENTLY OR IN COMBINATIONIN COMBINATION
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PARAHIPPOCAMPAL GYRUS PARAHIPPOCAMPAL GYRUS (PHG) HERNIATION(PHG) HERNIATION
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COMPLICATIONS of PHG COMPLICATIONS of PHG HERNIATIONHERNIATION
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COMPLICATIONS of PHG COMPLICATIONS of PHG HERNIATIONHERNIATION
PCA ossculsion
3rd nerve palsy
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CENTRAL HERNIATIONCENTRAL HERNIATION
MAMILLARYMAMILLARY BODYBODYPONSPONS
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CENTRAL HERNIATIONCENTRAL HERNIATION
NORMALNORMAL HERNIAHERNIA
AP diameter > trans diameter
AP diameter =/< trans diameter
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SECONDARY BRAIN SECONDARY BRAIN STEM STEM
HAEMORRHAGESHAEMORRHAGES
Duret hemorrahge
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CEREBELLAR TONSILAR HERNAITIONCEREBELLAR TONSILAR HERNAITION
CONINGCONING
OROR
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Bone Change in CT
• Forameninternal auditory canal, foramen ovale, orbital fissures
• Cranium bonehyperostosis
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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 white matter -- 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 -- cytotoxicedema -- cellular swelling -- mass effect -- straightening the normal waving insular ribbon
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CT of Cerebral Ischemia(Hyper-dense vascular sign)
• Ischemia -- blood stasis in great vessel such as M1 -- blood clot -- high density
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Biological and Anatomical Characteristics
• Hemangioblastomahemoglobin, hematocrit, erythropoietin
• Craniopharyngiomaanterior 3rd ventricle to nasopharynx
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Clinical Information in CT
• Acute, progressive or stationary• Timing
important in ischemic disease• previous history of irradiation or
operation