What side of facial droop would a right Middle Cerebral Artery (MCA) infarct cause?

Right MCA Infarct Causes Contralateral (Left-Sided) Facial Droop

A right middle cerebral artery (MCA) infarct causes a contralateral (left-sided) facial droop due to damage to the corticobulbar tracts that cross in the brainstem before innervating the facial nerve nucleus. 1

Neuroanatomical Explanation

The facial weakness pattern in MCA infarcts follows specific neuroanatomical principles:

• Corticobulbar Pathway: Motor fibers originating from the primary motor cortex travel through the corona radiata and internal capsule before descending to the brainstem
• Decussation: These fibers cross (decussate) in the brainstem before synapsing with the facial nerve nucleus
• Result: Damage to the right cerebral hemisphere affects the left side of the face

Clinical Presentation of Right MCA Infarct

A right MCA infarct typically presents with:

• Left-sided facial weakness/droop (contralateral to the lesion)
• Left-sided hemiparesis (arm and leg weakness)
• Left-sided sensory deficits
• Left-sided neglect
• Abnormal visual-spatial ability
• Possible right monocular blindness or left homonymous hemianopsia 1

Central vs. Peripheral Facial Palsy

It's important to distinguish central from peripheral facial weakness:

• Central (Upper Motor Neuron) Facial Palsy:

  • Preserves forehead movement (frontalis muscle)
  • Affects primarily the lower face
  • Results from supranuclear lesions (like MCA infarcts)

• Peripheral (Lower Motor Neuron) Facial Palsy:

  • Affects entire hemifacial muscles including forehead
  • Results from facial nerve nucleus or facial nerve lesions 1

Imaging Findings

Early CT signs of right MCA infarction may include:

• Hyperdense MCA sign
• Attenuation of the lentiform nucleus
• Loss of insular ribbon
• Hemispheric sulcus effacement 2

MRI with diffusion-weighted imaging is more sensitive for early detection of acute infarction and can better delineate the extent of the infarct.

Clinical Pearls and Pitfalls

Pearls:

• The presence of forehead sparing (preserved forehead movement) is a key clinical finding that helps distinguish central from peripheral facial palsy
• Right MCA infarcts may also present with left visual field deficits and left-sided neglect

Pitfalls:

• Rare cases of ipsilateral central facial palsy with contralateral hemiparesis have been reported with medullary infarcts, but these are exceptions to the typical pattern 3, 4
• Isolated central facial palsy was traditionally thought to represent a lacunar syndrome, but recent evidence suggests it may actually represent flow-limiting thromboembolic MCA disease in many cases 5

Management Considerations

For patients presenting with facial droop and suspected MCA infarct:

1. Immediate neurological evaluation
2. Emergent neuroimaging (CT/MRI)
3. Assessment for thrombolysis eligibility if within the appropriate time window
4. Monitoring for cerebral edema, especially with large MCA territory infarcts 1

Remember that large right MCA infarcts can develop malignant cerebral edema, requiring close monitoring for signs of increased intracranial pressure and potential consideration of decompressive craniectomy in appropriate cases.