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Head CT: The BasicsStephen MagillRadiology RotationAugust, 2012
Computed Tomography: Intro
• Uses X-Rays (radiation) to create cross sectional images (tomographs) through the human body
• Findings are always described based in relative “densities” (vs MRI “intensity”)
CT: Relative Density
• Bright (High Density)
• Dark (Low Density)
Bone
Contrast
Acute Blood
Soft Tissue:– Gray matter– White matter
Water
Fat
Air
How To Describe A Head CT
• Always start with this sentence:
• “This is a
[non-contrast vs contrast enhanced]
[axial vs sagittal vs coronal]
head CT showing…”
Normal Axial Head CT
TOP (Superior)
BOTTOM (Inferior)
Important Places to look:
Ventricle SizeMake sure no hydrocephalus - Evans ratio (A/B) < 0.3Also check temporal horns
CisternsShould be plenty of CSF(Black space)No blood/compression
BasilarCistern
A
B
Lesion Location: Intra- vs Extraparenchymal
• Intraparenchymal:– Located within brain tissue
• Extraparenchymal:– Located within the bony casing of CNS– BUT outside the brain tissue itself
Lesion Location: Extraparenchymal
• Two examples of meningioma– Extraparenchymal tumor (not in the brain tissue)– The tumor is slow growing which is reflected in by the mild
displacement of the other brain structures; acute extraparenchymal lesions (bleeds) will cause marked displacement or herniation
Lesion Location: Intraparenchymal
• Two examples of glioblastoma– Intraparenchymal tumor (within the brain tissue)– Dark regions (gray arrow) within the tumor are necrotic cavities
Head CT in Acute Situation
• Anytime someone has head trauma with altered mental status they should have a head CT
• You are looking for acute blood, which is bright
• All MD’s should know what acute blood looks like and be able to describe its general location:
• Epidural• Subdural• Subarachnoid (SAH)• Intraventricular (IVH)• Intraparaenchymal (IPH)
Location (Cause)
Between Skull and Dura (Trauma)
Between Dura and Arachnoid (Trauma)
Cisterns or Sulci (Trauma, Aneurysm rupture)
Ventricles (Trauma, HTN hemorrhage)
Brain Tissue (Tra./Tmor, HTN hem)
OUT
IN
Locations of blood around/in the brain
Locations of blood around/in the brain
IPH
Examples of bleeding in different locations
IPH
Midline shift
Saatman et al (2008) J Neurotrauma
SAH filling sulci
EDHBlood spread
limited by suture lines
IVH
Calcified choroidPlexus (normal)
SDHBlood crosses
suture lines
Examples of bleeding in different locations
IVH
Examples of bleeding in different locations
SAH in the basilar cisternand extending out into thefissures
A classic CT after ruptureof a Circle of Willis aneurysm
So called “Star of Death”
Case example
• 68 y/o female brought in by ambulance to ED after rapid mental status deterioration
• Obtunded on exam• BP: 210/106• Considering hypertensive hemorrhage• Head CT shows…
Case example
What do you see?
Try to describe it as you would present it.
Case example
“This is a non-contrast, axial head CT showing…
…a large left-sided intraparenchymal hemorrhage with surrounding edema and significant midline shift”
IPH
Surroundingsoft tissue edema(dark areas)
Midline shift
Case example
“This is a non-contrast, axial head CT showing…
…a large left-sided intraparenchymal hemorrhage with surrounding edema and 2.2 cm of midline shift”
IPH
Surroundingsoft tissue edema(dark areas)
Midline shift
Case example
“This is a non-contrast, axial head CT showing…
…a large left-sided intraparenchymal hemorrhage with surrounding edema and 2.1 cm of midline shift. There is also left sided uncal herniation and compression of the basilar cistern due to likely brainstem herniation.”
Inferior portionof IPH
Herniating Uncus
More caudal slice of previous axial head CT
Case Example
• Taken to OR for clot evacuation
• Post op-head CT shows…
Case Example
• Removal of the majority of the clot and improvement in midline shift. Also notice the drain that is left in place.
• Pneumocephalus (air in the head) is also present, a normal post-operative finding
Residual IPH
DrainMarkedly improved
midline shift
Some new IVH
Pneumocephalus
Case Example
• Decompression allows improvement in herniation• Basilar cistern now wide open
• Neurological exam improved post-operatively
Pneumocephaluswhere inferior portionof IPH was located
Improvement in herniation
Basilar cisternis now open and
decompressed
The End