Fifth Cranial Nerve Lesions

The trigeminal nerve supplies

• Sensory innervation to:
  • Face
  • Teeth
  • Nasal cavity
• Motor supply to:
  • Muscles of mastication
  • Tensor veli palatini
  • Tensor tympani

The commonest lesions of the trigeminal nerve include:

• Herpes zoster infection
• Multiple sclerosis (MS)
• Trigeminal neuralgia

Other lesions of the trigeminal nerve are relatively uncommon.

Variable facial numbness may be seen with presentations of MS.

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Anatomy

Course of the Trigeminal Nerve

• Motor origin: Trigeminal motor nucleus, pons
• Sensory nuclei: Trigeminal sensory nucleus (pons and extends through brainstem)
• Emerges from the ventral pons via:
  • Large sensory root
  • Smaller motor root
• Enters middle cranial fossa
• Sensory root forms trigeminal (Gasserian) ganglion at apex of petrous temporal bone
• From this ganglion arise 3 major branches:

Branch	Foramina	Innervation type
Ophthalmic	Superior orbital fissure	Sensory only
Maxillary	Foramen rotundum	Sensory only
Mandibular	Foramen ovale	Sensory + Motor

Trigeminal Nerve Innervations

1. Ophthalmic Branch (V1)

Branch	Supplies
Lacrimal nerve	Upper lateral eyelid (sensory), parasympathetic fibres pass to lacrimal gland
Nasociliary nerve	Ciliary ganglion, long ciliary nerve, posterior & anterior ethmoidal nerves, infratrochlear nerve
Frontal nerve	Supratrochlear & supraorbital nerves

2. Maxillary Branch (V2)

Branch	Supplies
Meningeal branches	Middle cranial fossa
Pterygopalatine ganglion branches	Lacrimal gland, palate, nasal cavity
Posterior superior alveolar nerve	Maxillary molars
Zygomatic nerve → zygomaticotemporal & zygomaticofacial	Lateral face, parasympathetics to lacrimal gland
Middle & anterior superior alveolar nerves	Maxillary teeth
Infraorbital nerve	Lower eyelid, cheek, upper lip

3. Mandibular Branch (V3)

Branch	Supplies
Meningeal branch	Dura mater
Nerve to medial pterygoid	Medial pterygoid, tensor veli palatini, tensor tympani
Nerve to masseter, temporalis, lateral pterygoid	Muscles of mastication
Buccal nerve	Cheek mucosa (sensory)
Auriculotemporal nerve	Auricle, outer tympanic membrane, temporal region, TMJ, carries parasympathetics to parotid
Lingual nerve	Anterior 2/3 tongue (general sensation), floor of mouth; taste via chorda tympani
Inferior alveolar nerve → nerve to mylohyoid, mental nerve	Lower teeth, mylohyoid, anterior digastric, chin skin

Pathology

Central Lesions

Cause
Vascular lesions
Tumours
Demyelination (MS)
Syringobulbia

Peripheral Lesions

Cause
Space-occupying lesions (tumours, aneurysms) in middle cranial fossa
Cavernous sinus lesions (thrombosis, tumour, aneurysm) → can involve CN III, IV, VI
Skull base trauma (middle cranial fossa fractures)
Mononeuritis (rare) → diabetes, connective tissue disease, alcohol, paraneoplastic, sarcoidosis, HIV

Clinical Assessment

1. Corneal Reflex

• Stimulus: Cotton bud to cornea
• Normal: Bilateral blinking
• Afferent limb: Ophthalmic branch of CN V
• Efferent limb: Facial nerve (CN VII) → orbicularis oculi

Finding	Indicates
No blink, no sensation	Ophthalmic nerve lesion
Blink in contralateral eye only	Ipsilateral facial nerve palsy

2. Facial Sensation

• Test each division (V1, V2, V3)
• Compare sides
• Pain: sterile needle or blunt stick
• Light touch: cotton wool
• Temperature: if syringobulbia suspected

3. Motor Function

• Inspect for temporal/masseter wasting
• Clench teeth → palpate masseters
• Open mouth against resistance → pterygoid function
  • Jaw deviates to weak side if V3 lesion

4. Jaw Jerk Reflex

• Mouth slightly open → tap examiner’s finger on symphysis menti
• Normal: slight closure or no response
• Hyperactive: UMN lesion (e.g. pseudobulbar palsy)

Summary of Clinical Patterns

Pattern	Likely lesion site
Loss of all 3 divisions	Central lesion or trigeminal ganglion
Loss of single division	Peripheral lesion post-ganglion
Dissociated pain/touch loss	Brainstem or cervical cord lesion

Investigations

Blood Tests

1. FBC
2. U&Es / glucose
3. CRP
4. ESR

CT Scan / CT Angiogram

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

MRI

• Best modality for trigeminal nerve lesions
  • Intracranial / intraorbital pathology
  • Demyelination (MS)
  • Tumours
  • Brainstem lesions

Management

• Directed at the underlying cause
  • Tumour → Neurosurgery
  • MS → Neurology
  • Neuralgia → Medical therapy
  • Infection → ID / Neurology
  • Trauma → Neurosurgery

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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

• 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. Third Cranial Nerve Lesions. LITFL
• Nickson C. Cranial nerve lesions DDx. LITFL