Seventh Cranial Nerve Lesions

Lesions of the Facial nerve may present as:

• Lower motor neuron (LMN) lesions — due to both central and peripheral causes
• Upper motor neuron (UMN) lesions — typically part of a central stroke syndrome

Commonest causes:

• UMN: Cortical stroke
• LMN: Bell’s palsy

Anatomy

Course of the Facial Nerve

• Somatic efferent fibres originate in the facial nucleus (pons)
  • Upper face muscles: bilateral cortical innervation
  • Lower face muscles: contralateral cortical innervation
    → In UMN lesions → forehead spared; in LMN lesions → complete ipsilateral facial paralysis
• Emerges from ventral brainstem (junction of pons and medulla)
  • CN VI emerges medial
  • CN VIII emerges lateral
• Travels in posterior cranial fossa, enters facial canal via internal acoustic meatus with CN VIII + labyrinthine artery
• Facial canal → geniculate ganglion → joined by chorda tympani
• Exits via stylomastoid foramen → passes through parotid gland → divides into terminal branches

Facial Nerve Innervations

Branch location	Branches	Innervation
Facial canal	Greater petrosal nerve	Lacrimal gland, nasal glands, palatal glands
	Nerve to stapedius	Stapedius muscle
	Chorda tympani	Taste (anterior 2/3 tongue), submandibular & sublingual glands
Post-canal, pre-parotid	Nerve to posterior belly of digastric	Digastric muscle
	Branches to auricular muscles, occipitofrontalis	Scalp and ear muscles
	Nerve to stylohyoid muscle	Stylohyoid muscle
Within parotid gland (Mnemonic: Two Zebras Bit My Cake!)	Temporal	Muscles of forehead/scalp
	Zygomatic	Muscles around eye
	Buccal	Upper lip, nose, buccinator
	Mandibular	Lower lip, chin
	Cervical	Platysma

Pathology

Upper Motor Neuron (UMN)

Cause
Cortical strokes (middle cerebral artery territory)

Lower Motor Neuron (LMN)

Site	Cause
Brainstem (pons)	Stroke, demyelination (MS), tumour
Cerebello-pontine angle	Acoustic neuroma, meningioma, meningitis
Middle ear	Infections, tumours (affects chorda tympani)
Trauma	Petrous temporal bone fracture, penetrating nerve trauma
Infections	Bell’s palsy, Ramsay-Hunt syndrome (HZV), tetanus, tick paralysis
Parotid gland	Tumour, abscess, trauma/surgery
Rare mononeuritis	Connective tissue disease, diabetes, alcohol, paraneoplastic, sarcoidosis, HIV

Clinical Assessment

1. Inspect for Facial Asymmetry

Look for:

• Unilateral drooping of mouth
• Unilateral smoothing of forehead wrinkles
• Unilateral loss of nasolabial fold

2. Test Forehead (Frontalis) Muscles

• Ask patient to look upwards → observe forehead wrinkles
• Apply downward pressure to test strength

Finding	Indicates
Forehead movement spared	UMN lesion
Forehead + lower face paralysis	LMN lesion

3. Test Orbicularis Oculi (Eye Muscles)

• Ask patient to close eyes tightly
• Attempt to force open eyes

Finding	Indicates
Eye closure weak + Bell’s phenomenon	LMN lesion

4. Show Teeth

• Ask patient to show teeth
• Compare nasolabial folds

Finding	Indicates
Nasolabial fold loss on same side	LMN lesion
Nasolabial fold loss on opposite side	UMN lesion

5. Check for Vesicular Lesions

• Inspect external ear, auditory canal, palate
• Presence suggests Ramsay-Hunt syndrome

6. Taste Testing (if required)

• Apply one taste stimulus to each side of anterior 2/3 tongue:

Taste	Substance
Sweet	Sugar
Sour	Vinegar
Bitter	Quinine
Salty	Saline

Rinse mouth between tests.

Nerve Conduction Studies

• Can be done for Facial nerve
• Some prognostic value in Bell’s palsy
• Not routinely performed

Investigations

Blood Tests

1. FBC
2. U&Es / glucose
3. CRP
4. ESR
5. Additional tests as indicated (e.g. blood lead levels)

CT Scan / CT Angiogram

• Screening for intracranial mass lesions
• CT angiogram → suspected aneurysm

MRI

• Best for:
  • Mass lesions
  • MS plaques
  • Middle ear pathology
  • Visualisation of the facial nerve

Management

• Directed at the underlying cause

Eye Care

• Major complication of LMN lesion → incomplete eye closure → corneal ulceration risk
• Management:
  • Artificial tear drops
  • Protective eye pads
  • Lateral tarsorrhaphy (in severe cases)

Psychological Support

• May be needed due to the disfiguring nature of the lesion

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Appendix 1

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Appendix 2

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References

Publications

• Brazis PW, Masdeu JC, Biller J. Localization in Clinical Neurology. 8e 2021
• Fuller G. Neurological Examination Made Easy. 6e 2019
• O’Brien M. Aids to the Examination of the Peripheral Nervous System. 6e 2023

FOAMed

• Sanger G. Bell’s Palsy. LITFL
• Cadogan M. Ramsay Hunt syndrome. LITFL
• Coni R. Neuro 101: Cranial Nerves. LITFL
• Nickson C. The Brainstem Rules of Four. LITFL
• Ercleve T. The rule of 4 of the brainstem. LITFL
• Nickson C. Cranial nerve lesions DDx. LITFL