OCSP Classification - 4 Syndromes

1. Total Anterior Circulation Syndrome (TACS)

• All three of the following must be present:
  • Hemiparesis (weakness of one side)
  • Higher cortical dysfunction (dysphasia or visuospatial neglect)
  • Homonymous hemianopia (visual field loss on one side)
• Vascular basis: Proximal Middle Cerebral Artery (MCA) or Internal Carotid Artery (ICA) occlusion - a large vessel stroke
• Imaging: CT shows a large hypodense (dark) area over a whole hemisphere; MRI DWI shows a large bright cortical infarct
• Prognosis: Worst of all four - high mortality and disability

2. Partial Anterior Circulation Syndrome (PACS)

• Either:
  • Isolated higher cortical dysfunction alone, OR
  • Any 2 of 3 features: hemiparesis, higher cortical dysfunction, hemianopia
• Vascular basis: Branch MCA occlusion - smaller, more peripheral vessel
• Imaging: CT/MRI shows a smaller, more focal cortical infarct
• Prognosis: Intermediate - high early recurrence risk

3. Posterior Circulation Syndrome (POCS)

• Features of posterior fossa involvement:
  • Isolated hemianopia (PCA territory)
  • Brainstem syndromes (diplopia, dysarthria, vertigo, crossed signs)
  • Cerebellar syndromes (ataxia, nystagmus)
• Vascular basis: Occlusion of vertebral, basilar, cerebellar, or posterior cerebral artery (PCA)
• Imaging: CT may show a hyperdense basilar artery or cerebellar hypodensity; MRI DWI shows small bright foci in brainstem/cerebellum
• Prognosis: Variable - basilar artery occlusion is catastrophic; isolated POCS can have good recovery

4. Lacunar Syndrome (LACS)

• Small, pure subcortical syndromes - no cortical features, no hemianopia:
  • Pure motor stroke
  • Pure sensory stroke
  • Sensorimotor stroke
  • Ataxic hemiparesis
  • Clumsy hand-dysarthria syndrome
• Vascular basis: Small perforating artery occlusion (lipohyalinosis or microatheroma), usually deep structures (internal capsule, thalamus, basal ganglia, pons)
• Imaging: CT often normal early; MRI DWI shows a small (<1.5 cm) deep bright lesion
• Prognosis: Generally best functional outcome, but recurrence risk if risk factors uncontrolled

Why OCSP Matters Clinically