Facial Nerve: Central vs Peripheral Palsy

Facial weakness is one of the most common findings in clinical neurology, and one of the most useful for localization. The simple but critical distinction is central (supranuclear) vs peripheral (nuclear or infranuclear) facial palsy — a distinction that hinges on whether the upper face is involved. Beyond that, the precise anatomy of the facial nerve from cortex to muscle allows further localization based on associated findings: hearing, taste, hyperacusis, tearing, and sensory loss. This page covers central vs peripheral facial palsy, the syndromes that arise at each segment of the facial nerve, and the differential diagnosis of acute and chronic facial weakness.

Anatomy of the Facial Nerve (CN VII)

Functions

• Motor: muscles of facial expression, stapedius (middle ear), stylohyoid, posterior digastric.
• Parasympathetic (nervus intermedius): submandibular and sublingual salivary glands (via chorda tympani → submandibular ganglion); lacrimal gland (via greater petrosal nerve → pterygopalatine ganglion).
• Sensory: taste from anterior two-thirds of tongue (via chorda tympani); small area of skin around external ear.

Course

1. Cortical origin: motor cortex face area projects via corticobulbar fibers.
2. Corticobulbar projection: to facial nucleus in pontine tegmentum. Critical distinction: the upper face (forehead, eye closure) receives bilateral cortical innervation; the lower face receives only contralateral cortical innervation. This asymmetry explains the upper-face sparing of central facial palsy.
3. Facial nucleus: in caudal pons.
4. Fascicle: loops around the abducens nucleus (forming the facial colliculus on the floor of the fourth ventricle) before exiting at the cerebellopontine angle.
5. Cerebellopontine angle (CPA): emerges with CN VIII.
6. Internal auditory canal (IAC): travels with CN VIII.
7. Facial canal (temporal bone): branches off at:
   • Greater petrosal nerve: parasympathetic to lacrimal gland.
   • Nerve to stapedius: dampens loud sounds.
   • Chorda tympani: taste from anterior 2/3 of tongue + parasympathetic to submandibular/sublingual glands.
8. Stylomastoid foramen: exits temporal bone.
9. Parotid gland: divides into terminal branches (temporal, zygomatic, buccal, marginal mandibular, cervical).

Central (Supranuclear) Facial Palsy

Lesion of the corticobulbar tract above the facial nucleus. Result:

• Weakness of lower face only (mouth, perioral muscles) on the contralateral side.
• Forehead, eye closure are spared (bilateral cortical innervation).
• Often accompanied by other cortical or subcortical signs: hemiparesis, aphasia, neglect, etc.

Causes: stroke (cortical or subcortical), tumor, abscess, demyelination. Most commonly stroke in the territory of the MCA affecting the face area of motor cortex or the corticobulbar fibers in the corona radiata or internal capsule.

One important caveat: emotional facial movements may be preserved or even exaggerated on the affected side, because they are mediated by separate pathways (anterior cingulate / supplementary motor area) that descend through different white matter — sometimes producing “emotional facial paresis” in the opposite direction (preserved voluntary movement with loss of emotional facial movement) from anterior cingulate or pontine lesions.

Peripheral (Nuclear or Infranuclear) Facial Palsy

Lesion of the facial nucleus or the facial nerve. Result:

• Weakness of BOTH upper and lower face on the ipsilateral side.
• Forehead does NOT wrinkle, eye cannot close completely.
• Drooping of the corner of the mouth, loss of nasolabial fold.
• Inability to whistle, retain food on the affected side.
• Tearing may run down (Bell tearing).
• Bell phenomenon: when attempting to close the eye, the eye rolls upward (normal protective movement).

Localizing Peripheral Facial Lesions by Associated Findings

Because the facial nerve gives off branches as it travels through the temporal bone, the combination of findings narrows the location precisely:

Bell Palsy

The most common cause of peripheral facial palsy. Idiopathic, acute, often complete unilateral lower motor neuron facial palsy.

Features

• Onset over hours to 1-2 days; full development within 72 hours.
• Often preceded by ear pain or pain around the mastoid.
• Sometimes hyperacusis (stapedius involvement).
• Sometimes loss of taste (chorda tympani).
• Reduced tearing on the affected side (greater petrosal involvement).
• Often a viral prodrome (HSV reactivation hypothesized as a key mechanism).

Diagnosis

Clinical — exclusion of other causes by examination and history. Imaging not routinely required for typical Bell palsy. Indications for imaging: progressive over weeks, recurrent, no recovery after 3 months, atypical features (bilateral, multiple cranial nerves, signs of central involvement).

Treatment

• Oral steroids (prednisone 60 mg daily for 5-7 days, tapered) within 72 hours of onset — improves recovery.
• Antivirals (acyclovir or valacyclovir) — modestly added benefit, especially for severe cases.
• Eye protection: artificial tears, lubricating ointment at night, taping the eye closed during sleep. Critical to prevent corneal abrasion.
• Facial physical therapy: helpful for recovery and prevention of synkinesis (cross-wiring during regeneration).

Prognosis

• Most patients (70-80%) recover fully within weeks to months.
• Worse prognosis: complete paralysis at onset, age over 60, no recovery by 3 weeks, hyperacusis, taste loss.
• Synkinesis (involuntary facial movements during voluntary movements — for example, eye closure with smiling) is a common late complication.

Ramsay Hunt Syndrome

Facial palsy from herpes zoster reactivation in the geniculate ganglion. Features:

• Acute facial palsy.
• Vesicles in the external ear, mastoid area, soft palate, anterior 2/3 of tongue.
• Often more painful than Bell palsy.
• Frequently accompanied by hearing loss and vertigo (CN VIII involvement in adjacent IAC).
• Worse prognosis than Bell palsy.

Treatment: oral acyclovir or valacyclovir + oral steroids. Look for and treat any visible zoster lesions.

Other Causes of Facial Palsy

Acute / Subacute

• Lyme disease: bilateral or unilateral facial palsy, sometimes with other features of early Lyme. In endemic areas, especially in children, Lyme is a common cause. Treat with antibiotics; steroids alone may be insufficient.
• Sarcoidosis: bilateral facial palsy classic (Heerfordt syndrome: facial palsy + parotitis + uveitis + fever).
• Otitis media / mastoiditis: middle ear infection can extend into the facial canal — facial palsy in a child with ear pain warrants urgent ENT evaluation.
• HIV seroconversion: can present with facial palsy.
• Guillain-Barré syndrome: often bilateral facial weakness with limb weakness.
• Trauma: temporal bone fracture damaging facial nerve.

Subacute / Chronic / Progressive

• Vestibular schwannoma (acoustic neuroma): hearing loss + tinnitus + facial palsy (usually late) + sometimes facial twitching.
• Cholesteatoma: middle ear erosion into facial nerve canal.
• Parotid tumor: can involve terminal branches.
• Neoplastic infiltration: schwannoma, neurofibromatosis, meningioma, perineural spread of skin cancer (especially squamous cell).
• Melkersson-Rosenthal syndrome: recurrent facial palsy + facial swelling + fissured tongue.
• Möbius syndrome: congenital bilateral facial palsy + bilateral CN VI palsy.

Bilateral Facial Palsy

Always more concerning than unilateral. Causes:

• Lyme disease (especially in endemic areas).
• Sarcoidosis.
• Guillain-Barré syndrome.
• HIV seroconversion.
• Lymphoma, leukemia.
• Möbius syndrome (congenital).
• Bilateral Bell palsy (rare, simultaneous or sequential).

Distinguishing Central from Peripheral Facial Palsy

The single most useful distinguishing feature: forehead and eye closure.

Examination Workflow

1. Inspect the face at rest: asymmetry, ptosis, mouth droop, loss of nasolabial fold, eye position.
2. Test each muscle group: raise eyebrows (frontalis), close eyes tightly (orbicularis oculi), smile (zygomaticus), purse lips (orbicularis oris), puff out cheeks, show teeth, look downward and crease forehead.
3. Compare upper vs lower face: critical to distinguish central from peripheral.
4. Test Bell phenomenon: eye rolls up when closing.
5. Examine the ear: look for vesicles (Ramsay Hunt), erythema, mass, cholesteatoma.
6. Test hearing: side comparison, Weber and Rinne if abnormal.
7. Ask about taste: anterior 2/3 of tongue (CN VII), posterior 1/3 (CN IX).
8. Ask about hyperacusis (sounds seeming abnormally loud).
9. Look for other cranial nerve involvement: CN VIII (vestibular), CN V (corneal reflex).
10. Examine for other neurologic signs: long tract findings, ataxia, sensory loss.

Workup for Atypical or Persistent Facial Palsy

• MRI brain and CN VII with gadolinium.
• Lyme serology in endemic areas.
• Chest imaging for sarcoidosis.
• HIV test.
• ESR, CRP for inflammation.
• CSF analysis if multiple cranial nerves, GBS suspicion, malignancy.
• Electromyography of the facial nerve and electroneurography (ENoG) for prognostic information.

🔍 Did You Know?

The key bedside distinction between central and peripheral facial palsy hinges on the anatomical fact that the upper face receives bilateral cortical innervation while the lower face receives predominantly contralateral cortical innervation. This was first systematically described in the 19th century and remains one of the most useful single-question localization tests in neurology. The clinical consequence: a cortical or subcortical lesion (stroke, MS plaque, tumor) damages the corticobulbar fibers to the contralateral lower face only — sparing the upper face on both sides — producing a contralateral lower facial droop with intact forehead wrinkling and eye closure. A facial nucleus or facial nerve lesion (Bell palsy, vestibular schwannoma, temporal bone fracture) damages ALL the motor output to one side of the face, producing complete weakness of both upper and lower face on the ipsilateral side. Asking the patient to raise the eyebrows and close the eyes tightly distinguishes the two patterns in seconds — preserved forehead means central; weak forehead means peripheral. This simple test can prevent misdiagnosing Bell palsy as a stroke (and unnecessary thrombolytic exposure) or missing a stroke as Bell palsy (and missing the window for stroke intervention).

Pitfalls and Pearls

• Central facial palsy spares the forehead and eye closure; the lower face droops.
• Peripheral facial palsy affects all the face on one side — forehead and eye too.
• Bell palsy: rapid-onset peripheral facial palsy; oral steroids within 72 hours improve recovery.
• Eye protection in peripheral facial palsy is essential: artificial tears, ointment, tape at night. Corneal abrasion is a preventable complication.
• Ramsay Hunt syndrome: facial palsy + vesicles in ear/mouth; treat with steroids + antivirals.
• Bilateral facial palsy is concerning: think Lyme, sarcoid, GBS, HIV, tumor.
• Lyme facial palsy in endemic areas: especially in children — treat with antibiotics, not just steroids.
• Sarcoidosis: bilateral facial palsy + parotitis + uveitis = Heerfordt syndrome.
• Vestibular schwannoma: hearing loss + tinnitus first; facial palsy usually late.
• Progressive or non-recovering facial palsy: image for tumor or other cause.
• Synkinesis after Bell palsy: involuntary movements during voluntary expression — treat with facial PT and selective botulinum toxin.
• Brainstem lesions: peripheral facial palsy + other crossed signs (Millard-Gubler, eight-and-a-half).
• Otologic causes (otitis, cholesteatoma) — facial palsy with ear findings → urgent ENT.
• Emotional facial paresis: weak emotional but intact voluntary movement — anterior cingulate or pontine lesion.

References

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2. Tiemstra JD, Khatkhate N. Bell’s palsy: diagnosis and management. Am Fam Physician. 2007;76(7):997-1002.
3. Sullivan FM, Swan IR, Donnan PT, et al. Early treatment with prednisolone or acyclovir in Bell’s palsy. N Engl J Med. 2007;357(16):1598-1607.
4. Gronseth GS, Paduga R. Evidence-based guideline update: steroids and antivirals for Bell palsy. Neurology. 2012;79(22):2209-2213.
5. Ropper AH, Samuels MA, Klein JP, Prasad S. Adams and Victor’s Principles of Neurology. 11th ed. McGraw-Hill; 2019.