Mnemonic for Brainstem Lesions

Introduction

• Brainstem lesions are uncommon compared to MCA, ACA, and PCA strokes.
• Important for students, especially those in clinical practice without frequent exposure to neurological cases, to understand brainstem lesions.

Brainstem Anatomy

• 3 parts of the brainstem:
  • Midbrain
  • Pons
  • Medulla
• Supplied by posterior circulation of the circle of Willis.
• Necessary to know the location of ascending/descending tracts, cranial nerve nuclei, and basal ganglia.

Key Components

• Cranial Nerves Distribution:
  • Midbrain: CN 3, 4
  • Pons: CN 5-8
  • Medulla: CN 9-12
• Tracts:
  • Corticospinal (motor)
  • DCML (dorsal column-medial lemniscus)
  • Spinothalamic (pain & temperature)
• Sympathetic Fibers: Knockout leads to Horner's syndrome.
• Cerebellar Peduncles: Knockout can cause ataxia.
• Substantia Nigra: Part of the basal ganglia involved in movement initiation, its damage leads to bradykinesia (Parkinson's).

Circulation

• Posterior Circulation:
  • Vertebral arteries give off posterior inferior cerebellar arteries (PICA) and anterior spinal artery.
  • Basilar artery supplies the medial pons.
  • Posterior cerebral artery (PCA) supplies the midbrain and occipital lobe.

Mnemonic for Lesions

• Medial Cranial Nerves: 3, 4, 6, 12 (divisible by 12, paired nerves).
• Lateral Cranial Nerves: 5, 7, 8, 9, 10.

Syndromes

Medial Medullary Syndrome

• Vessel: Anterior spinal artery.
• Lesions:
  • Corticospinal: Contralateral hemiparalysis.
  • DCML: Contralateral loss of fine touch/vibratory sensation.
  • CN 12: Ipsilateral tongue paralysis (tongue deviation towards lesion side).

Lateral Medullary Syndrome (Wallenberg Syndrome)

• Vessel: PICA.
• Lesions:
  • CN 5, 8, 9, 10: Loss of gag reflex, vertigo, vomiting, nystagmus, facial numbness.
  • Sympathetic tract: Horner's syndrome.
  • Spinothalamic: Contralateral loss of pain/temperature sensation.

Lateral Pontine Syndrome

• Key Features:
  • Medial cerebellar peduncle: Ataxia.
  • CN 7: Ipsilateral facial droop.
  • CN 8: Vertigo, vomiting, nystagmus, hearing deficit.
  • CN 5: Facial paralysis, difficulty chewing.

Weber's Syndrome

• Vessel: Paramedian branches of PCA.
• Lesions:
  • CN 3, 4: Oculomotor palsy (down and out eye).
  • Corticospinal: Contralateral spastic hemiplegia.
  • Corticobulbar: Contralateral lower facial weakness.
  • Substantia nigra: Contralateral parkinsonism.

Cerebellopontine Angle Syndrome

• Cause: Not a stroke, typically due to acoustic neuroma or meningioma.
• Lesions:
  • CN 5, 8: Tinnitus, hearing loss, jaw muscle weakness.
  • Cerebellar signs: Ataxia.
  • Possible non-communicating hydrocephalus due to 4th ventricle obstruction.

Conclusion

• Knowing the diagram of cranial nerves, circulation, and tracts helps in diagnosing and understanding these syndromes.
• Understanding the mnemonics and conditions associated with brainstem lesions is vital for medical exams and practice.