Can left facial numbness be caused by a right posterior cerebral artery (PCA) stroke?

Left Facial Numbness and Right PCA Stroke

Left facial numbness is not typically caused by a right posterior cerebral artery (PCA) stroke, as the PCA territory does not include the primary sensory pathways for facial sensation.

Anatomical Considerations

PCA Territory and Symptoms

• The posterior cerebral artery primarily supplies:
  • Occipital lobe (visual cortex)
  • Medial and inferior temporal lobe
  • Thalamus (in some cases)
  • Parts of the midbrain 1

Typical PCA Stroke Manifestations

• Visual field defects (homonymous hemianopia) are the most common symptom (87% of patients) 2
• Other common symptoms include:
  • Memory impairment (particularly with dominant hemisphere involvement)
  • Visual hallucinations
  • Sensory deficits (typically affecting the contralateral body, not isolated to face) 3, 4

Facial Sensory Pathways

Facial sensation is primarily mediated through:

1. The trigeminal nerve (cranial nerve V)
2. Central pathways that ascend through the brainstem
3. Thalamic relay to the primary sensory cortex in the parietal lobe

These pathways are predominantly in the territory of the:

• Middle cerebral artery (MCA) for cortical representation
• Vertebrobasilar system for brainstem components 1

Differential Diagnosis for Left Facial Numbness

More likely causes of isolated facial numbness include:

1. Carotid artery disease: Facial numbness can be a symptom of carotid artery dissection 5
2. Anterior circulation stroke: MCA territory strokes more commonly affect facial sensation 1
3. Brainstem lesions: Affecting the trigeminal nucleus or pathways
4. Peripheral causes: Trigeminal neuropathy, Bell's palsy, or other cranial neuropathies

Special Considerations

In rare anatomical variants where:

• The PCA originates from the internal carotid artery (fetal PCA)
• There is extensive involvement of the thalamus
• The stroke extends to involve adjacent vascular territories

In these cases, a right PCA stroke might contribute to left-sided sensory symptoms, but isolated facial numbness would still be unusual 1.

Clinical Approach

When evaluating a patient with left facial numbness:

1. Consider more common etiologies first (anterior circulation or brainstem)

2. Perform a complete neurological examination looking for associated symptoms:

   • Visual field defects (suggesting PCA involvement)
   • Other sensory or motor deficits
   • Speech or language disturbances (suggesting MCA involvement)

3. Obtain appropriate neuroimaging:

   • MRI/MRA or CT/CTA to visualize both anterior and posterior circulation 1
   • Include imaging of the neck vessels if carotid dissection is suspected

Conclusion

While a right PCA stroke can cause various neurological symptoms, isolated left facial numbness is not a typical manifestation. When encountering facial numbness, clinicians should consider more common etiologies in the anterior circulation or peripheral nervous system before attributing it to a PCA stroke.