Approach to CN5, CN7, CN8 Palsy, CPA syndrome Flashcards
CN 7 - facial nerve functions
- Motor function
- Facial muscles (expression)
- Orbicularis oculi (eyelid closure) - Sensory
- Anterior 2/3 of tongue
- Subjective sensation of the face (objective normal) - Hearing - stapedius muscle - loudness control
- Parasympathetic
- Lacrimal gland
- Salivary gland
CN 7 - facial nerve anatomical course
Origin: pons - motor root and sensory root
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Enters cerebellopontine angle – together with CN8
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Travels through internal auditory meatus and enters facial canal (motor and sensory root merges) to form facial nerve
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Branches:
- Greater petrosal nerve (salivary gland)
- Stapedius nerve (stapedius muscle)
- Chorda tympani (anterior 2/3 tongue)
- Posterior auricular nerve (motor muscles around ear)
- Digastric and stylohyoid muscle
- Main trunk (motor root)
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Motor root continues into parotid gland
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Terminal motor branches:
- Temporal branch
- Zygomatic branch
- Buccal branch
- Marginal mandibular branch
- Cervical branch
CN7 - facial nerve testing (mixed nerve)
- Forehead asymmetry
- Look up, wrinkle forehead
(frontalis weakness in LMNL, spared in UMNL) - Orbicularis oculi weakness
- Squeeze eyes shut, bury eyelashes
- Test power of 1 eye at a time with both index fingers - Facial asymmetry
- Observe for drooping
- Puff cheeks
- Smile, show your lower teeth - platysmal asymmetry - Hyperacusis on affected side - stapedius nerve involvement
(Conversely deafness or tinnitus signify acoustic neuroma or large brainstem lesion) - Completing neurological examination
- Look for cerebellar signs (cerebellopontine angle lesion)
- Long tract signs (pronator drift, motor, sensation, reflexes) - stroke
- CN 5 and 8 involvement (brainstem, CP angle)
- Zosteriform rash (Ramsay Hunt), or erythema migrans (Lyme) - Parotid tumours or surgery - peripheral facial nerve palsy
Wishlist
1. Otoscopy - Ramsay-Hunt syndrome
2. Ophthalmology assessment - exposure keratopathy
3. Taste function testing
4. Hypo or hyperlacrimation
How do you differentiate CN7 UMNL vs LMNL?
CN7 UMNL - frontalis muscle sparing (from bilateral innervation)
CN7 LMNL - affects both upper and lower parts of the face
Caveats:
1. Dense stroke (UMNL) may have whole face weakness mimick Bell’s palsy
2. Limited (incomplete) lower facial fibre Bell’s palsy affecting only lower parts of the face
3. Ongoing regeneration of LMNL CN7 palsy may have forehead sparing
What are the causes of unilateral CN7 UMN palsy?
- Contralateral stroke
(NOT brainstem stroke) - Demyelination - multiple sclerosis
- CNS infection - abscess, encephalitis
What are the causes of unilateral CN7 LMN palsy?
A. Pontine level - CN5/6/7/8, contralat pyramidal weakness, ataxia
1. Pontine infarct (brainstem syndrome)
- Damage to facial nerve nuclei or intrapontine fascicles (LMNL)
B. Cerebellopontine angle - with CN8 defect
4. CP angle tumour - meningioma, acoustic neuroma, parotid gland malignancy, mets
C. Facial canal - unilateral CN7 LMNL palsy
5. Middle ear infection
6. Bell’s palsy (idiopathic) - 95%
7. Tumour deposits
8. Fracture of skull base or facial laceration
9. Carcinomatous basal meningitis
D. Geniculate ganglion - vesicle in auditory canal
10. Ramsay Hunt syndrome
E. Peripheral branches - parotid scar/swelling/pain
11. Parotid gland infection, tumour, surgery
F. Mononeuritis multiplex - DM, PAN, CS, WG, RA, SLE, Sjogren, sarcocidosis, lymphoma, Lyme, leprosy
What are the causes of bilateral CN7 LMNL palsy?
- Guillain-Barre syndrome (GBS)
- Myasthenia gravis (NMJ)
- Myopathies
- Dystrophia myotonica
- Facio-scapulo-humeral dystrophy - Infections
- Lyme disease
- Polio - Sarcoidosis
- Carcinomatous basal meningitis
What are the investigations to evaluate for CN7 palsy?
Usually self limiting, however to offer investigations:
- Blood glucose and HbA1c - Bells palsy a/w DM
- MRI brain suprageniculate hyperintensity on T2, as well as TRO intracranial tumours, stroke
- CRP, ESR, infective serologies
- Anti-ganglioside antibodies (GBS)
- Nerve conduction studies
- Lumbar puncture in multi-CN palsy, mononeuritis multiplex, meningeal infiltration, neurosarcoidosis
- VZV serology/PCR, HIV testing
- EMG - muscle denervation and reinnervation for prognosis
How would you manage CN7 LMN palsy?
- High dose prednisolone
- Oral acyclovir
- Corneal protection - eye lubricants and eye shield
What are the complications of Bell’s palsy?
- Persistent facial weakness
- Corneal abrasion
- Subjective pain and sensory disturbance over facial nerve
- Aberrant re-innervation with crocodile tears (tearing while talking or eating)
- Jaw-eyelid synkinesia
- Hemifacial spasm
Prognosis of Bell’s palsy
- 85% patients improve over 3-4 weeks of onset
- 70% achieve complete recovery
- 15% persistent lesion (aberrant reinnervation)
History taking for facial nerve palsy
- Onset and progression
- Acute: Bell’s palsy, stroke, infection, trauma
- Gradual: neoplasm, inflammation (sarcoidosis), rare infection - Unilateral or bilateral
- Associated symptoms
- Ear pain and vesicles
- Headache
- Dry eyes and pain, foreign body sensation (exposure keratopathy)
- Altered taste of anterior 2/3 of tongue, dry mouth - Other neurological deficits - stroke, GBS, brainstem
- Weakness/numbness elsewhere
- Diplopia
- Dysarthria
- Dysphagia - Systemic symptoms
- Fever
- Rashes - erythema migrans (Lyme)
- Constitutional symptoms
- Arthralgia - Significant past medical history
- DM
- HTN
- Pregnancy, postpartum (Bells)
- Malignancy
- Autoimmune disease
- Immunosuppression
CN 5 - trigeminal nerve (mixed)
- Motor: mastication muscle
- Sensory: face, anterior scalp, oral cavity, nasal cavity - touch, pain, temp, proprioception
Pathway:
1A. Sensory nuclei (pons)
1B. Spinal trigeminal nucleus (pons-medulla to C2/C3)
1C. Mesencephalic nucleus (pons to midbrain)
1D. Motor nucleus (pons)
- Travels through posterior cranial fossa
- Sensory root expands into trigeminal ganglion
- Motor root passes inferior to trigeminal ganglion and joins mandibular V3 division - Trigeminal ganglion divides into:
- V1 (sensory): ophthalmic (exits SOF)
- V2 (sensory): maxillary (exits foramen rotundum)
- V3 (sensorimotor): mandicular (exits foramen ovale)
Deficits:
1. Facial sensation loss
2. Jaw weakness and deviation towards side of lesion
3. Mastication muscle fasciculation/atrophy
4. Absent corneal rreflex
5. Brisk jaw jerk (bilateral UMN), absent jaw jerk (LMN)
Corneal reflex (blink reflex)
Afferent: CN5 (V1) to trigeminal ganglion/sensory nuclei (pons/medulla)
Interneuron: motor nuclei of CN7 bilaterally (for consensual blinking of unstimulated eye)
Efferent: CN7 - orbicularis oculi
Procedure:
1. Touch lateral edge of cornea with sterile cotton wool wisp
(from the side to prevent habituation)
2. Observe for direct and consensual reflex
Abnormalities
1. No blinking when one side stimulated - afferent defect on the same side
2. No blinking at all despite stimulated both side - bilateral CN5 or CN7 lesion, pontine pathology, or coma/brain death
2. Opposite eye blink - efferent defect (CN7) on same side
3. Opposite eye no blink - efferent defect (CN7) on opposite site
Common causes:
1. Vestibular schwannoma (compressing CN5 and CN7 in CP angle)
2. Pontine stroke or tumour
3. Peripheral neuropathy of CN5 or CN7 (GBS)
4. Herpes zoster ophthalmicus
5. Bells’ palsy
6. Coma / brain death (loss of brainstem reflex)
CN 8 - vestibulocochlear nerve (sensory) function
- Cochlear nerve - hearing
- Vestibular nerve - balance
CN 8 course
- Cochlear and vestibular nerves join within distal part of internal auditory meatus (IAM)
1A. Accompanied by CN 7 and labyrinthine artery - Exits IAM and crosses cerebellopontine angle
- Enters brainstem at pontomedullary junction lateral to facial nerve
Causes of CN 8 hearing loss or vertigo
Peripheral
1. Vestibular schwannoma within IAM
2. Vestibular neuronitis - viral
3. Labyrinthitis
4. Meniere’s disease
5. BPPV
6. Ototoxicity
7. Presbycusis and noise induced hearing loss
Central
1. Brainstem stroke
2. Cerebellar stroke
3. Tumour within CPA
4. Multiple sclerosis
Cerebellopontine angle (CPA)
CPA is sharply angulated triangular space where cerebellum folds over pons.
2 CN: CN7 and CN8
1 artery: AICA
1 CN passes superiorly: CN5
Commonest tumours:
1. Vestibular schwannoma (from CN8)
- Think of neurofibromatosis type 2
2. Meningioma
3. Dermoid or epidermal cyst
CPA syndrome
- Ipsilateral hemifacial weakness (LMN)
- Compression of intracranial segment of CN7 - Ipsilateral SNHL, difficulty following conversation (speech discrimination) and tinnitus
- Compression of vestibulocochlear nerve
Additional features:
3. Trigeminal nerve palsy
- Ipsilateral hemifacial sensory loss
- Ipsilateral corneal reflex loss
- Cerebellum syndrome
- Brun’s nystagmus - Abducens nerve palsy
- Ipsilateral eye abduction defect
Brun’s nystagmus
Rare, peculiar variant of bilateral nystagmus
Concomitant ipsilateral cerebellar and vestibular dysfunction
On looking towards side of lesion:
Slow, large amplitude nystagmus
- Cerebellar flocculus dysfunction inability to maintain eccentric horizontal gaze
On looking away from lesion:
Fine, jerky small amplitude nystagmus (vestibular nystagmus)
- Corrective fast saccade away from lesion
Investigations for CPA syndrome
- MRI brain
- Pure tone audiometry and tympanogram
- Genetic testing for NF2
- Slit lamp examination - posterior subcapsular lenticular opacities
