Lesions

Localizing CNS Lesions

Localizing CNS lesions involves matching the patient's symptoms to specific brain and spinal cord anatomy. This process can be broken down into simple steps:

Step 1: Is the lesion in the Brain or Spinal Cord?

  • Both arms and legs involved? Likely brain or cervical spinal cord.

  • Only legs involved? Likely thoracic or lumbar spinal cord.

  • Face + arm/leg affected? Likely brain (above spinal cord level).

Step 2: If it's in the Brain, which part?

  • Cortex lesions: Affect higher functions (speech, personality).

  • Brainstem lesions: Affect cranial nerves + long tracts (motor/sensory).

  • Cerebellar lesions: Cause uncoordinated movements.

Step 3: If it's in the Spinal Cord, which level?

  • Spinal cord lesions cause bilateral symptoms below the level of injury.

  • One side weak, other side sensory loss? → Brown-Séquard Syndrome (hemisection of spinal cord).

Step 4: Is the lesion Upper or Lower Motor Neuron (UMN vs. LMN)?

  • Brain & Spinal Cord: Present UMN signs (e.g., stroke, MS, spinal cord injury).

  • Peripheral Nerves: Present LMN signs (e.g., Guillain-Barré, polio, nerve trauma).

Final Step: Special Patterns of Localization

  1. One-sided face + one-sided arm/leg weakness (opposite side) → Brainstem lesion.

  2. Sudden complete paralysis on one side → Stroke (cerebral lesion, opposite side).

  3. Weakness in both legs with bladder issues → Spinal cord lesion (thoracic or lumbar).

  4. Weakness + sensory loss on different sides → Brainstem or spinal cord (Brown-Séquard Syndrome).

Quick Clinical Examples

  • 60-year-old: Right arm + leg weakness, difficulty speaking? → Left cerebral stroke (dominant hemisphere).

  • 25-year-old: Sudden vision loss + leg weakness? → Multiple sclerosis (demyelination in brain + spinal cord).

  • 40-year-old: Both legs weak, no arm involvement, recent back trauma? → Spinal cord lesion (thoracic level).

Brain Lesion Localization

Step 1: Is it the Brain or Spinal Cord?

Before localizing, verify it's in the brain.

Brain Lesion Signs:

  • Face involvement (facial weakness, difficulty speaking).

  • Hemiparesis (suggests brain lesion on opposite side).

  • Higher cognitive dysfunction (memory loss, confusion, speech difficulty).

Spinal Cord Lesion Signs:

  • No face involvement (arms/legs affected, face normal).

  • Bilateral symptoms (both sides affected).

  • Loss of sensation below a certain level on the body.

Step 2: Which Part of the Brain?

The brain consists of four major regions where lesions can occur.

Step 3: Localizing Within the Cerebrum (Cortex & Subcortex)

Localization Tricks:

  • Weakness or sensory loss? → Opposite side lesion (due to crossover of pathways).

  • Speech difficulty? → Left hemisphere lesion (if right-handed).

  • Vision problems? → Occipital lobe or optic pathway affected.

Step 4: Localizing Within the Brainstem

The brainstem controls vital functions.

Brainstem Lesion Clues:

  • Face symptoms on one side, body symptoms on the other → "Crossed signs" (brainstem lesion).

  • Double vision, difficulty swallowing, dizziness → Cranial nerve involvement.

  • Loss of consciousness or irregular breathing → Severe brainstem damage.

Step 5: Localizing Cerebellar Lesions

  • Cerebellum: Coordinates balance.

Cerebellar Lesion Clues:

  • Ataxia (unsteady walking).

  • Intention tremor (tremor when reaching, not at rest).

  • Vertigo & dizziness.

  • Trick: Affects the same side (ipsilateral).

Step 6: Localizing Basal Ganglia Lesions

  • Basal ganglia: Controls movement.

Basal Ganglia Lesion Clues:

  • Tremors, rigidity, slow movement (Parkinson's-like).

  • Involuntary movements (Huntington's disease).

  • Trick: Parkinson's → Dopamine loss; Huntington's → Excessive movements.

Final Step: Putting It All Together

  1. 60-year-old: Sudden left-sided weakness, difficulty speaking? → Right frontal lobe (stroke).

  2. 45-year-old: Double vision, right-sided facial droop, left arm/leg weakness? → Right brainstem (pons).

  3. 30-year-old: Shaking hands and unsteady walking? → Cerebellum lesions.

  4. 55-year-old: Slow movements, resting tremor, rigidity? → Basal ganglia lesions (Parkinson's disease).

How to Localize Spinal Cord Lesions

Step 1: Confirm It’s a Spinal Cord Lesion

Spinal Cord Lesion Clues:

  • Bilateral symptoms.

  • Weakness and sensory loss below a specific level.

  • Bladder and bowel dysfunction (especially with thoracic/lumbar lesions).

  • Hyperreflexia (UMN signs) below lesion.

Not a spinal cord lesion if:

  • Face affected → Think brain.

  • Weakness/sensory loss in one limb → Think peripheral nerve.

  • Flaccid paralysis with no hyperreflexia → Think LMN disorder.

Step 2: Determine the Level of the Spinal Cord Lesion

Localization Tricks:

  • Arm + leg weakness → Cervical lesion.

  • Leg weakness only → Thoracic or lumbar lesion.

  • Bladder/bowel + perineal numbness → Sacral lesion.

Step 3: Determine the Type of Spinal Cord Syndrome

  1. Complete Cord Lesion: Paralysis, sensory loss below lesion, bladder dysfunction.

  2. Hemicord Syndrome (Brown-Séquard Syndrome): Half of spinal cord affected.

    • Same side: Weakness + loss of touch.

    • Opposite side: Loss of pain & temperature.

  3. Central Cord Syndrome: Arms > legs weakness (cape-like distribution). Loss of pain/temperature over shoulders/arms.

  4. Posterior Cord Syndrome: Loss of vibration & proprioception, no motor weakness.

  5. Anterior Cord Syndrome: Complete paralysis, that spares touch/proprioception.

  6. Cauda Equina vs. Conus Medullaris Syndrome: Distinguishing features based on pain and bladder dysfunction.

Step 4: Identify UMN vs. LMN Signs

  • Spinal cord lesions typically show UMN signs.

  • Cauda equina lesions present LMN signs.

Final Step: Case-Based Practice

  1. 25-year-old: Right-sided weakness & left-sided pain/temp loss? → Right spinal cord hemisection.

  2. 50-year-old: Complete paralysis below chest but can still feel vibration? → Anterior cord syndrome.

  3. 30-year-old: Severe low back pain, asymmetric leg weakness, bladder dysfunction? → Cauda equina syndrome.

Summary of Key Localization Points

  • Quadriparesis → Cervical lesion.

  • Paraparesis → Thoracic or lumbar lesion.

  • Bladder/bowel dysfunction → Thoracic/lumbar/sacral lesion.

  • "Crossed signs" → Brown-Séquard Syndrome.

  • Cape-like pain/temp loss → Central Cord Syndrome.

Brain & Spinal Cord Lesion Etiologies

  1. Vascular Causes: Stroke, venous thrombosis.

  2. Infectious Causes: TB, syphilis, viral, fungal infections.

  3. Autoimmune/Inflammatory: MS, autoimmune encephalitis.

  4. Neoplastic Causes: Primary/secondary tumors.

  5. Traumatic Causes: Head/spinal injuries.

  6. Toxic & Metabolic: Vitamin deficiencies, hypoxia, toxins.

  7. Degenerative: Alzheimer's, ALS.

  8. Congenital/Genetic: Spina bifida.

Most Commonly Asked Questions During Rotations

  1. Most common brain lesions? → Stroke (ischemic > hemorrhagic).

  2. Differentiate infections vs. autoimmune causes? → Symptoms, CSF changes.

  3. Preferred imaging modality? → MRI with contrast.

  4. Common infections in immunocompromised? → Cryptococcus, toxoplasmosis.

  5. MS hallmark on MRI? → Periventricular white matter lesions.

  6. Spinal cord infarction presentation? → Sudden weakness, dysfunction.

  7. Most common spinal cord tumor? → Meningioma, ependymoma.

  8. Vitamin deficiency causing degeneration? → Vitamin B12 deficiency.