Neurologic Lesion Localization

Aka: Neurologic Lesion Localization, Localization of Neurologic Deficit

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II. Causes: Peripheral Nerve

  1. See Peripheral Neuropathy
  2. Dermatome Distribution of sensory changes
    1. Pain in Dermatomal Distribution suggests peripheral cause
    2. Contrast with higher lesions which follow non-dermatomal loss of Sensation
  3. Lower Motor Neuron Lesion (LMN)
    1. LMN findings include Flaccid Paralysis, muscular atrophy, Fasciculations and hyporeflexia
    2. Contrast with Upper Motor Neuron Lesions (UMN) with overall Muscle group weakness, spasticity and hyperreflexia

III. Causes: Spinal Cord

  1. See Spinal Cord Syndrome
  2. Difference in Sensation loss may identify lesion level
    1. Pain and Temperature sense (Spinothalamic Tract) crosses to contralateral side within 1-2 levels
    2. Conscious proprioception (Posterior Columns) crosses to contralateral side at the Medulla
    3. Unconscious proprioception (Spinocerebellar Tract) never crosses (remains ipsilateral)

IV. Causes: Brainstem

  1. See Brainstem
  2. Cranial Nerve deficits indicate lesions in the peripheral Cranial Nerve, the Brainstem or above
  3. Multiple Cranial Nerve deficits suggest a Brainstem lesion (see Cranial Nerve Nucleus)
    1. Peripheral Cranial Nerve deficit may also cause this (e.g. Cavernous Sinus contains CN 3, CN 4, CN 5, CN 6)
    2. Bilateral Cerebral Hemisphere or Internal Capsule lesions may also cause multiple Cranial Nerve deficits
  4. Cranial Nerve lesions contralateral to extremity deficits suggests a Brainstem lesion
    1. Lesion must be above the spinal cord to affect Cranial Nerves
    2. Cerebral Hemisphere lesions will affect the same contralateral side for both Cranial Nerve and extremity
    3. Extremity motor and sensory central innervation crosses in the Medulla
    4. Cranial Nerve central innervation crosses above their nucleus level

V. Causes: Cerebellum

  1. See Cerebellum
  2. See Cerebellar Function Test
  3. Incoordinated INTENTIONAL movement
  4. Ataxia
    1. See Acute Cerebellar Ataxia
    2. See Cerebellar Gait
  5. Altered Posture and gait
    1. Patient falls on the same side as a CNS Lesion
  6. Incoordinated movement
    1. Dysmetria (overshooting on Finger-Nose-Finger Test)
    2. Dysdiadochokinesia (difficult Rapid Alternating Movements)
    3. Scanning speech (irregularly spaced sounds, words, phrases)
  7. Tremor
    1. See Cerebellar Tremor
    2. Intention Tremor (during purposeful movement)
  8. Nystagmus

VI. Causes: Basal Ganglia

  1. See Basal Ganglia
  2. See Movement Disorder
  3. Incoordinated UNINTENTIONAL movement
  4. Parkinsonism (Basal Ganglia and Substantia Nigra degeneration)
    1. Associated with rigid slow movements, resting Tremor, shuffling gait, mask-like facies
  5. Athetosis
    1. Slow, writhing movements (esp. hand, wrist)
  6. Chorea (e.g. Huntington's Chorea, Sydenham's Chorea)
    1. Sudden, jerky movements
  7. Hemiballismus
    1. Sudden, incoordinated flailing of an extremity

VII. Causes: Cerebral Hemispheres - Frontal Lobe

  1. See Frontal Lobe
  2. Hemiparesis (Brodmann Area 4) with or without spasticity and hyperreflexia (Brodmann Area 6)
  3. Gait disturbance
  4. Generalized Seizures or Focal Seizures
  5. Expressive Aphasia (Brodmann Area 44, 45)
  6. Behavior and Personality change (lesions anterior to the Primary Motor Area, Brodmann Area 4)
    1. Judgment and abstract thinking affected
    2. Affects Instrumental Activities of Daily Living
    3. May present with concerns for Dementia

VIII. Causes: Cerebral Hemispheres - Parietal Lobe

  1. See Parietal Lobe
  2. Receptive Aphasia (Brodmann Area 39)
  3. Sensory loss (Brodmann Area 3,1,2 and Area S2 following Homunculus distribution)
  4. Spatial Disorientation (Brodmann Area 5, 7)
  5. Hemianopia (loss of half of Visual Field in each eye)
  6. Agnosia of tactile Sensation and proprioception (Brodmann Area 40, dominant hemisphere)
  7. Apraxia (difficulty with skilled movement) and altered left-right discrimination (Brodmann Area 40)

IX. Causes: Cerebral Hemispheres - Temporal Lobe

  1. See Temporal Lobe
  2. Complex Partial Seizures or Generalized Seizures
  3. Quadrantanopia (Vision Loss or anopia in a Visual Field quadrant)
  4. Behavioral alterations
  5. Memory Loss (esp. visual memories)
  6. Receptive Aphasia (dominant hemisphere, Brodmann Area 22)

X. Causes: Cerebral Hemispheres - Occipital Lobe

  1. See Occipital Lobe
  2. Contralateral Hemianopia

XI. References

  1. Goldberg (2014) Clinical Physiology, Medmaster, Miami, p. 108

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