ct brain - basics dr mohamed el safwany, md.. intended learning outcome the student should learn at...
TRANSCRIPT
HOUNSFIELD UNITS
• Numeric information in each pixel of ct image
• Related to composition & nature of tissue• Represent the density of tissue• Also called as CT NUMBER
air --- 1000fat ---70Pure water 0Csf +8White matter +30Gray matter +45blood +70Bone/cacification +1000
CT /MRI
• CT PICTUREI. WHITE MATTER IS
DARKER THAN GREY MATTER SINCE LIPID CONTAINING MATERIAL IS RADIOLUCENT
I. CSF IS BLACK
• MR PICTURE GREY GREY
MATTERMATTERT1WIDARK
T2WI
BRIGHT
WHITE WHITE MATTRMATTR
BRIGHT DARK
CSFCSF GREY TO DARK
WHITE
Step wise approach
1. Ventricles/ cisterns2. Cortex3. Deep gray matter4. Focal lesions5. Bone6. Extracranial soft tissue7. Para nasal sinuses
COMMON SECTIONSAXIAL SECTIONS CORONAL SECTIONS SAGITTAL SECTIONS
POSTERIOR FOSSA CUTS-ABOVE THE FORAMEN MAGNUM LEVEL
-LEVEL OF THE FOURTH VENTRICLE
-ABOVE THE FOURTH VENTRICULAR LEVEL
- TENTORIAL
SUPRATENTORIAL CUTS
-THIRD VENTRICULAR LEVEL
-LOW VENTRICULAR LEVEL
-ABOVE THE VENTRICULAR LEVEL
-FRONTAL HORN LEVEL
-THIRD VENTRICULAR LEVEL
-MID VENTRICULAR LEVEL
-OCCIPITAL HORN LEVEL
-MID SAGITTAL LEVEL
-PARASAGITTAL LEVEL THROUGH THE LATERAL VENTRICULAR BODY
-LATERAL ORBITAL LEVEL
Cerebral Arterial Territory• MCA-most of lateral hemisphere, Basal
ganglia, insula, • ACA-Inferomedial basal ganglia,ventromedial
frontal lobes, anterior 2/3rd medial cerebral hemispheres, 1 cm supero medial brain convexity
• PCA-Thalami, midbrain, posterior 1/3of medial hemisphere, occipital lobe, postero medial temporal lobe
• AICA- inferolateral part of pons, middle cerebellar peduncle, floccular region, anterior petrosal surface of cerebellar hemisphere
• PICA-posteroinferior surface of cerebellar hemisphere , ipsilateral part of inferior vermis,
• Superior cerebellar artery-superior aspect of cerebellar hemisphere (tentorial surface), ipsilateral superior vermis, largest part of deep white matter including dentate nucleus, pons
Cerebral ischemia
• Significantly diminished blood supply to all parts(global ischemia) or selected areas(regional or focal ischemia) of the brain
• Focal ischemia- cerebral infarction• Global ischemia-hypoxic ischemic
encephalopathy(HIE),hypotensive cerebral infarction
Goal of imaging• Exclude hemorrhage
• Identify the presence of an underlying structural lesion such as tumour , vascular malformation ,subdual hematoma that can mimic stroke
• Identify stenosis or occlusion of major extra- and intracranial arteries
• Differentiate between irreversibly affected brain tissue and reversibly impaired tissue (dead tissue versus tissue at risk)
•
Infarct vs pneumbra
• In the central core of the infarct, the severity In the central core of the infarct, the severity of hypoperfusion results in irreversible of hypoperfusion results in irreversible cellular damage . cellular damage .
• Around this core, there is a region of decreased flow Around this core, there is a region of decreased flow in which either:in which either:– The critical flow threshold for cell death The critical flow threshold for cell death
has not reached has not reached – Or the duration of ischemia has been Or the duration of ischemia has been
insufficient to cause irreversible damage. insufficient to cause irreversible damage.
• Hyper acute infarct(<12 hours)Hyper acute infarct(<12 hours)• Acute infarct(12 - 48 hours)Acute infarct(12 - 48 hours)• Subacute infarct(2 - 14 days)Subacute infarct(2 - 14 days)• Chronic infarct(>2 weeks)Chronic infarct(>2 weeks)• Old infarct(>2 monthsOld infarct(>2 months)
CT-Hyperacute infarct
• Hyperdense MCA sign-acute intraluminal thrombus
• Attenuation of lentiform nulei• Dot sign-occluded MCA branch in sylvian
fissure• Insular ribbon sign –grey white interface
loss along the lateral insula
CT- Acute infarct• Low density basal ganglia• Sulcal effacement• Wedge shaphed parenchymal hypo density
area that involves both grey and white matter • Increasing mass effect• Hemorrhagic transformation may occur -15
to 45% ( basal ganglia and cortex common site) in 24 to 48 hours
CT-chronic infarct
• Plain ct • Focal, well-delineated low-attenuation areas
in affected vascular distribution• sulci become prominent; ipsilateral ventricle
enlarges• Dystrophic Ca++ may occur in infarcted brain
but is very rare• CECT: No enhancement
INFARCT / TUMOUR
• CLINICAL HISTROY• DISTRIBUTION• SHAPES• GRAY / WHITE INVOLVEMENT• ADVANCED IMAGING
VENOUS INFARCT
• HISTROY• BEYOND VASCULAR DISTRIBUTION• HAEMORRHAGIC INFARCT• THORMBUS IN VENOUS SINUSES• SYMMETRICAL LOW ATTENUATION IN DEEP
GRAY MATTER - DEEP CEREBRAL VEIN THORMBUS
EDEMA/ INFARCT
• INFARCT TYPICAL VASCULAR DISTRIBUTION
GRAY MATTER INVOLVEMENT• EDEMA NOT CONFINED TO VASCULAR DISTRIBUTION MOSTLY INVOLVES WHITE MATTER