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Crash Course in Reading Neurological Imaging

Jul 27, 2024

Crash Course in Reading Neurological Imaging

Lecturer: Dr. Rybinnik

Objectives

  • Introduction of a case study
  • Approach to reading imaging
  • Review major anatomical landmarks
  • Assess the degree of symmetry or asymmetry on scans
  • Review causes of hyperdensity and hypodensity on CT
  • Concepts of cytotoxic and vasogenic edema
  • Causes of hyper- and hypo-intensity on MRI sequences
  • Patterns and locations of enhancement
  • Summary of key points

Case Study

  • Patient: 73-year-old woman
    • Symptoms: Memory difficulties, lethargy, urinary incontinence, mild left-sided weakness and rigidity
    • Imaging: Head CT done

Steps for Reading Imaging

  1. Identify the scan type: Imaging sequence and slice
  2. Look for symmetry: Identify asymmetry
  3. Identify the lesion: Density and intensity
  4. Use contrast enhancement pattern where useful
  5. Locate the lesion: Extra-axial (outside brain) or intra-axial (in brain parenchyma)
  6. Synthesize data for diagnosis

Anatomical Landmarks (Using Head CT)

  • Head CT without contrast: Most common; useful for vascular imaging and perfusion estimates
  • Typical normal head CT images: Orientation, identifying features ( OMEGA SIGN for central sulcus)
  • MRI T1 sequence: Shows white matter as white and gray matter as gray, similar to pathology

Major Brain Structures

  • Basal ganglia: Lateral ventricle, caudate, thalamus, internal capsule, lentiform nucleus, insular cortex
  • Sylveon fissure: Middle cerebral artery location
  • Midbrain: Central structure with CSF-filled basal cistern
  • Pons: Cerebellar peduncles and cerebellopontine angle
  • Medulla: Adjacent to the cerebellum, resolution better on MRI

Symmetry vs Asymmetry in Imaging

  • Identify the midline using anatomical landmarks
  • Look for asymmetry: Indicate lesion, mass effect, midline shift if present
  • Examples of asymmetry include subdural hematoma, middle cerebral artery stroke, cerebellopontine angle mass (e.g., schwannoma), toxoplasmosis

Understanding Density and Intensity

Hyperdensity on CT

  • Normal: Calcified pineal, calcified choroid plexus, bone
  • Abnormal: Acute hemorrhage, subarachnoid hemorrhage, epidural hemorrhage, subdural hematoma

Hypodensity on CT

  • Chronic damage: Encephalomalacia (stroke), chronic traumatic brain injury
  • Fluid-filled structures: Arachnoid cyst
  • Edema: Acute ischemic stroke, cerebral metastasis

Introducing MRI Sequences

  • T1-weighted: Displays gray and white matter
  • T2-weighted: Highlights fluid
  • FLAIR: Subtracts CSF signal
  • Diffusion-weighted Imaging (DWI) and Apparent Diffusion Coefficient (ADC): Detects ischemia and abscess
  • Gradient-recalled echo (GRE): Sensitive to hemorrhages

Edema Types

  • Cytotoxic edema: Energy failure, ischemia; affects both gray and white matter
  • Vasogenic edema: Failing neurovascular unit integrity; affects white matter, spares gray matter

Hyperintensity on MRI

  • General causes: Edema, neoplasms, abscesses, hydrocephalus, inflammatory lesions, subacute hematoma
  • Early ischemia: DWI/ADC pair used

Vasogenic vs Cytotoxic Edema Examples

  • Fluid bright on T2: Subcortical edema, brain metastasis, hydrocephalus
  • T2/FLAIR limitations: Subcortical vs basal ganglia lesions
  • Vasogenic edema: Tumors, trauma, severe hypertension

MRI Patterns and Locations of Enhancement

  • Dural tail: Meningioma, schwannoma
  • Leptomeningeal: Bacterial, tuberculous, carcinomatous meningitis
  • Subcortical nodular: Metastases, acute MS lesions
  • Ring-enhancing lesions: Abscess, glioblastoma, toxoplasmosis, lymphoma
  • Paraventricular enhancement: Lymphoma
  • Mural nodules: Pyelocytic astrocytoma (children)

Putting It All Together

  1. Start with head CT: Identify landmarks, look for asymmetry or lesions
  2. MRI without contrast: Use sequences like T1, T2, FLAIR, DWI, ADC, GRE
  3. Assess edema type: Vasogenic vs cytotoxic
  4. Check enhancement with contrast: Gadolinium for better detail
  5. Use mnemonics: E.g., "Shine and Shimmer" for enhancement types
  6. Compare with radiologist's report: Practice continually to improve diagnostic skills

Final Takeaways

  • Clinical history is the key to diagnosis
  • Imaging supports differential diagnosis but does not replace clinical judgment
  • Continual practice and review are essential for mastering imaging interpretation

Note: This summary should be used in conjunction with review of actual imaging examples for practical understanding.

Full transcript