Introduction

The ophthalmic (V1) branch innervates the following areas:

• Scalp
• Forehead
• Upper eyelid
• Eyeball
• Nose
• Frontal sinuses
• Parts of the meninges

Maxillary (V2) branch of CN V

The maxillary (V2) branch supplies the following areas:

• Lower eyelid and cheek
• Upper lip
• Nasal mucosa
• Palate
• Roof of the pharynx
• Maxillary, ethmoid and sphenoid sinuses

The mandibular (V3) branch supplies the following areas:

• Lower lip
• Teeth and gums
• Chin and jaw
• Part of the external ear and meninges

It supplies touch and position fibres, and pain and temperature fibres to the mouth, but has no involvement in taste, which is supplied by facial and glossopharyngeal nerves.

The mandibular branch also provides a motor supply to the muscles of mastication:

• Masseter
• Temporalis
• Medial and lateral pterygoids

It also supplies four other muscles:

• Tensor veli palatini
• Mylohyoid
• Anterior belly of digastric
• Tensor tympani

V1 traverses the superior orbital fissure, V2 traverses the foramen rotundum and V3 traverses the foramen ovale.

These branches converge at the trigeminal ganglion in Meckel’s cave, just lateral to the sphenoid bone.

V2 and V3 travel along the skull base to reach the ganglion, whereas V1 traverses the lateral aspect of the cavernous sinus.

From the ganglion, CN V enters the pons.

The three dermatomes have very little overlap. Therefore, there is a well-defined edge if a deficit is present.

The terminal branches of the trigeminal nerve are useful landmarks to allow for nerve blocks of the face.

Terminal V1 exits via the supraorbital foramen which can be palpated as the notch in the supraorbital ridge. Local anaesthetic can be directly injected here.

Terminal V2 Infraorbital nerve exits via the infraorbital foramen just below the eye. This can be accessed via an intraoral approach with injection anterior to the 2nd premolar.

Terminal V3 is the inferior alveolar nerve which can be accessed intra-orally via injection at the coronoid notch, and the mental nerve with can be accessed via injection anterior to the lower 2nd premolar

Sensory:

• Facial sensation in the areas innervated by the three divisions of the trigeminal nerve
• Corneal reflex

Motor:

• Masseter/Temporalis/medial pterygoid- clench your teeth
• Lateral pterygoid- open your mouth and stop me from closing it
• Pterygoids- move your jaw from side to side

Depending on the site of trauma, patients presenting with a CN V palsy will either need a CT head scan or facial x-rays (OPG or facial views).

CT head may diagnose basal skull fracture or, if not visible on CT, diagnosis may need to be based on clinical findings of basal skull fracture.

When there is no history of trauma, a CT head is needed to exclude tumours of the maxillary antrum and nasopharyngeal cancers.

Tumours such as carcinoma of the maxillary antrum and nasopharynx can cause V3 damage.

Trigeminal neuralgia is a sensory disorder characterised by severe shooting pains in the distribution of the nerve. It usually involves V2 or V3.

Cavernous sinus pathology will produce a deficit in V1.

All three branches have bilateral cortical representation, so a unilateral central lesion, for example a stroke, does not usually produce a deficit.

Other central causes of facial sensory loss are:

• Multiple sclerosis
• Brain tumours (posterior or middle fossa)
• Syringobulbia

Such pathologies are often associated with other cranial nerve deficits, as their nuclei lie adjacent within the pons.

Fractures of the middle third of the face can damage V2.

Trauma to the mandible can damage V3 causing the jaw to deviate to the paralysed side when open.

V3 can be damaged following anaesthetic block of the inferior alveolar nerve.

Basal skull fractures have been occasionally reported as the cause of CN V nerve injury.