Can a left posterior communicating artery (PCOM) problem cause right-sided facial weakness?

Left Posterior Communicating Artery Problems Can Cause Right-Sided Facial Weakness

Yes, a left posterior communicating artery (PCOM) problem can cause right-sided facial weakness due to its role in the cerebral circulation affecting contralateral brain structures that control facial movement.

Anatomical Basis and Mechanism

The posterior communicating artery is a critical component of the circle of Willis that connects the internal carotid artery with the posterior cerebral artery. When a left PCOM is affected:

• It can compromise blood flow to structures in the left cerebral hemisphere
• This affects areas supplied by the middle cerebral artery (MCA) territory on the left side
• Since motor pathways cross in the brainstem, left hemisphere ischemia results in right-sided weakness, including facial weakness 1

According to the AHA/ASA guidelines, ischemia or infarction in the distribution of the left internal carotid artery or middle cerebral artery typically causes right-sided weakness, right-sided paresthesia or sensory loss, and aphasia 1.

Clinical Presentation

When a left PCOM problem occurs, the following clinical manifestations may appear:

• Right-sided facial weakness (item 4 on the NIH Stroke Scale)
• Right-sided limb weakness (arm and/or leg)
• Possible aphasia if language centers are affected
• Potential sensory deficits on the right side 1

The NIH Stroke Scale specifically evaluates facial movement with scores ranging from 0 (normal) to 3 (complete unilateral palsy), making it a key component in stroke assessment 1.

Diagnostic Considerations

When evaluating a patient with right-sided facial weakness potentially caused by a left PCOM problem:

1. Brain imaging (CT or MRI) is essential to identify ischemic changes
2. Vascular imaging (CTA, MRA, or conventional angiography) to evaluate the PCOM
3. Assessment of other neurological deficits using standardized scales like NIHSS 1

It's important to note that PCOM occlusion can sometimes mimic aneurysmal pathology on imaging, as reported in case studies 2. This highlights the importance of careful radiological interpretation.

Differential Diagnosis

Other conditions that can cause right-sided facial weakness include:

• Other stroke locations affecting the facial motor cortex or pathways
• Bell's palsy (though this typically affects the ipsilateral face)
• Primary angiitis of the central nervous system (as seen in case reports with similar presentations) 3
• Posterior communicating artery aneurysms (which can cause cranial nerve deficits) 4, 5

Management Implications

For patients with facial weakness due to PCOM problems:

1. Acute management follows standard stroke protocols:

   • Evaluation for thrombolysis if within time window
   • Blood pressure management (keeping systolic <185 mmHg if thrombolysis is planned) 1
   • Assessment for large vessel occlusion that might benefit from endovascular therapy

2. Secondary prevention based on stroke etiology:

   • Antiplatelet therapy (typically aspirin with or without clopidogrel)
   • Management of vascular risk factors
   • Consideration of surgical or endovascular interventions if indicated 1

Conclusion

The anatomical arrangement of the cerebral circulation and the crossing of motor pathways explains why a left PCOM problem can manifest as right-sided facial weakness. This follows the general principle that cerebrovascular events affecting one hemisphere typically cause motor and sensory deficits on the contralateral side of the body.