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