CT brain interpretation

Mnemonic

Blood Can Be Very Bad

• Blood
• Cisterns
• Brain
• Ventricles
• Bone

Blood

• Questions
  • Is blood present?
  • If so, where is it?
  • If so, what effect is it having?
• Physiology
  • Acute blood is bright white (once it clots)
  • Blood becomes isodense at 1wk (exact time depends on size of clot)
  • Blood becomes hypodense at 2wks (exact time depends on size of clot)
• Findings
  • Epidural Hematoma (blood problem)
    • Lens shaped
    • Does not cross sutures
    • Classically described with injury to middle meningeal artery
    • Low mortality if treated prior to unconsciousness (<20% morbidity/mortality)
  • Subdural (brain problem)
    • Sickle shaped
    • Crosses sutures but not midline
    • Marker for severe head injury (mortality approaches 80%)
      • Small amount of bleed can be associated with major shift (secondary to brain injury/oozing)
  • SAH
    • Blood in the cisterns/cortical gyral surface/interhemispheric fissure
      • Suprasellar cistern is first place see SAH (location adjacent to circle of willis)
    • Aneurysm: 80%
    • AVM: 5%
  • Intraventricular/Intraparenchymal Hemorrhage
    • Typically obvious findings
    • Unimportant if intraventricular ruptured into parenchyma or vice-versa

Cisterns

• 4 key cisterns:
  • Circummesencephalic
    • First cistern to show increased ICP (squished shut)
  • Suprasellar
  • Quadrigeminal
    • "W" shaped
    • Second cistern to show increased ICP
  • Sylvian
    • May see isloated distal MCA bleed
• 2 questions:
  • Is there blood?
  • Are the cisterns open?

Brain

• Compare side to side
• Look for grey-white differentiation
  • Grey is denser so appears lighter on CT
• Look at gyral pattern all the way around (gyri effacement indicator of increased ICP)
• Findings
  • Tumor
    • May see increased hypodensity (edema)
    • 80% visisble without contrast
  • Atrophy
  • Abscess
  • Hemorrhagic contusion
  • Mass effect
  • Stroke
  • Intracranial air (skull fracture)
  • Hyperdense middle cerebral artery or basilar artery sign
    • Suggests thrombosis of vessel
  • Suggestive of Cerebral venous thrombosis :
    • Empty delta sign: dense triangle in superior sagittal sinus
    • Cord sign: hyperattenuated, homogenous linear or round foci in cerebral sinus
    • Vein Sign: hypoattenuated foci in the deep vein

Ventricles

• Check all 4 for size and for hemorrhage
  • Temporal tips (comma-shaped) of lateral ventricle first place to show hydrocephalus
  • If enlarged must differentiate between hydrocephalus from increased pressure versus atrophy:
    • Are the gyri effaced? If yes suggestive of increased pressure

Bone

• Inspect petrous ridges for skull base fracture
• Look at mastoid air cells full of fluid (blood) for indirect evidence of fracture

See Also

• Head CT (Clinical Decision Rules)
• CT Before Lumbar Puncture
• Intracerebral Hemorrhage (ICH)
• X-ray interpretation (main)

References

• Blood Can Be Very Bad: CT Interpretation Course Guide
• www.uic.edu/com/ferne/pdf/acep2005_spring/perron_acep2005_spring_bcbvb_course.pdf

Authors

Ross Donaldson