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Stroke vs Bell's Palsy

Notes

Stroke vs Bell's Palsy

Sections

FACIAL NERVE PALSY: STROKE VS BELL'S PALSY

We use wrinkles and smile to test the facial nerve.

Note that an involuntary smile (aka mimetic or emotional smile) has a different innervation pattern than what is drawn, here, so be careful not to make your patients laugh at this point in the exam.

Relevant anatomy for left facial nerve innervation:

  • The bilateral cerebral hemispheres.
  • The pons.
  • The left facial nucleus:
    • Lower division
    • Upper division.

Circuitry

  • Each cerebral hemisphere projects to the upper division of the left facial nucleus, which innervates the upper face.
  • Only the right hemisphere projects to the lower division, which innervates the lower face.

We'll soon see why the distinction in innervation of the upper and lower divisions of the facial nucleus is key to its role in localization.

Upper motor neuron lesion

Right cerebral hemispheric stroke.

  • Clinical Exam - Facial Palsy.
  • Radiographic Image - Right Hemispheric Stroke.
    • There is loss of right hemispheric innervation to the upper division of the left facial nucleus and the lower division.
    • The left hemisphere (the ipsilateral hemisphere) still innervates the upper division facial nuclear division.
    • As a result, there is still innervation to the the left upper face: there is a normal wrinkle.
    • But there is loss of innervation to the left lower face: there is a loss of facial smile.
    • Thus, in cerebral cortical injury, there is contralateral lower facial weakness with preserved upper facial strength.
  • As a small clinical pearl, when there is facial weakness due to upper motor neuron injury, the palpebral fissure on the paretic side of the face will often be wider than on the normal side of the face because the facial droop will pull down the lower eyelid.

Lower motor neuron lesion

Left Bell's palsy.

  • Clinical Exam - Facial Palsy.
  • Radiographic Image - Facial Neuropathy.
    • Damage to the facial nucleus, itself, causes Bell's palsy.
    • There is preserved bilateral innervation to the upper left facial nuclear division.
    • There is preserved contralateral innervation to the left lower facial division.
    • There is loss of innervation from the upper and lower divisions to the face because of damage to the nerve, itself.
    • Both the left upper face and left lower face are weak.
    • In Bell's palsy, there is paralysis of the complete ipsilateral side of the face.
  • Bell's palsy can occur anywhere along the seventh cranial nerve; therefore, the full clinical presentation of a Bell's palsy depends on where along its course the facial nerve is affected.

In part 2 of this tutorial, we will learn the underlying pathologies of Bell's palsy and why its presentation is so varied.

Clinical Challenge Question

With this tutorial as a background, see if you can answer this clinical challenge question regarding distinguishing stroke from Bell's palsy.