Introduction to CT Head

Purpose of the Talk

• Aimed at new radiology residents and generalists (e.g., emergency medicine, internal medicine).
• Goal: Build a strong foundational understanding of CT scans of the head.

Overview

• Watch the first talk in the series: "A Practical Introduction to CT" for foundational concepts.
• Review key concepts and relevant anatomy.
• Introduce a conceptual approach to CT scans.
• Discuss the importance of windowing in CT analysis.
• Learn through case repetition.
• Final segment for those interested in a more comprehensive approach.

Key Concepts

Radiographic Densities

• Hounsfield Units Scale:
  • Water: 0 HU
  • Air: -1000 HU
  • Cortical bone/metal: ~1000 HU
  • Soft tissue: ~50 HU (approx.)
  • Fat: ~-100 HU (approx.)
  • CSF: ~15 HU (close to water)
  • Gray matter: ~40 HU
  • White matter: ~25 HU
  • Acutely clotted blood: ~+80 HU
• Principle: CSF is low density, gray matter is more dense than white matter, and acutely clotted blood is denser than brain tissue.

Basic Anatomy of the Brain

• Important structures to identify:
  • Cortex: Gray matter.
  • Deep gray matter structures: Caudate, putamen, globus pallidus, thalamus.
  • White matter structures: Internal and external capsules, corona radiata.
  • Cerebellum: Located inferiorly with vermis and cerebellar tonsils.
  • Brainstem: Midbrain, pons, medulla (recognized by shapes).

CSF System

• Ventricular System: Lateral ventricles, third ventricle, fourth ventricle.
• CSF flow: Choroid plexus → Lateral ventricles → Foramen of Monro → Third ventricle → Cerebral aqueduct → Fourth ventricle.
• Blockage can cause ventricular dilation.

Basal Cisterns

• Important CSF pools at the base of the brain, e.g., pre pontine, subarachnoid, and super cellar cistern.

Approach to CT Head

• Conceptual Approach:
  1. Initial Scroll: Look for anything significant.
  2. Mass Effect: Check for midline shifts, herniations.
  3. Look for Blood: Identify hyper densities indicating bleeds.
  4. Stroke signs: Loss of gray-white differentiation, hyperdense vessels.
  5. Soft tissues and bones: Check for fractures.

Key Findings Search Order

1. Mass Effect and Herniation:
   • Look for signs of herniation and midline shift.
   • Types of herniation: Subfalcine, uncal, tonsillar.
2. Bleeds:
   • Epidural, subdural, subarachnoid, intracerebral hemorrhages.
3. Strokes:
   • Hyperdense vessel sign, loss of gray-white differentiation.
4. Windowing:
   • Adjust window settings to better visualize pathologies.

Practical Tips

• Windowing is crucial: Helps distinguish between subtle differences in density.
  • Blood Window: Enhances visibility of clots against bone.
  • Stroke Window: Improves assessment of gray-white differentiation.

Conclusion

• The talk provided a framework for assessing CT scans of the head, emphasizing the importance of recognizing major pathologies and utilizing windowing techniques.
• For future radiologists: Enhance knowledge of anatomy, blood densities, and details about herniation and stroke evaluation.