Head CT: The Basics
Stephen Magill
Radiology Rotation
August, 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)
Bone
Contrast
Acute Blood
Soft Tissue:
– Gray matter
– White matter
• Dark (Low Density)
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:
A
Basilar
Cistern
B
Ventricle Size
Make sure no hydrocephalus
- Evans ratio (A/B) < 0.3
Also check temporal horns
Cisterns
Should be plenty of CSF
(Black space)
No blood/compression
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:
OUT
IN
•
•
•
•
•
Location (Cause)
Epidural
Between Skull and Dura (Trauma)
Subdural
Between Dura and Arachnoid (Trauma)
Subarachnoid (SAH)
Cisterns or Sulci (Trauma, Aneurysm rupture)
Intraventricular (IVH)
Ventricles (Trauma, HTN hemorrhage)
Intraparaenchymal (IPH) Brain Tissue (Tra./Tmor, HTN hem)
Locations of blood around/in the brain
Locations of blood around/in the brain
IPH
Examples of bleeding in different locations
EDH
Blood spread
limited by
suture lines
Midline shift
IPH
SAH filling sulci
SDH
Blood crosses
suture lines
Calcified choroid
Plexus (normal)
IVH
Saatman et al (2008) J Neurotrauma
Examples of bleeding in different locations
IVH
Examples of bleeding in different locations
SAH in the basilar cistern
and extending out into the
fissures
A classic CT after rupture
of 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
Midline shift
Surrounding
soft tissue edema
(dark areas)
IPH
“This is a non-contrast, axial head CT showing…
…a large left-sided intraparenchymal hemorrhage with surrounding
edema and significant midline shift”
Case example
Midline shift
Surrounding
soft tissue edema
(dark areas)
IPH
“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”
Case example
More caudal slice of previous axial head CT
Herniating Uncus
Notice the lack
of space where
the basilar cistern
should be; it is
filled with brainstem
Inferior portion
of IPH
“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.”
Case Example
• Taken to OR for clot evacuation
• Post op-head CT shows…
Case Example
Pneumocephalus
Markedly improved
midline shift
Some new IVH
Drain
Residual IPH
• 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 postoperative finding
Case Example
Basilar cistern
is now open and
decompressed
• Decompression allows improvement in herniation
• Basilar cistern now wide open
• Neurological exam improved post-operatively
Improvement in
herniation
Pneumocephalus
where inferior portion
of IPH was located
The End