Facial nerve palsy

The facial nerve is the main nerve supplying the structures of the second embryonic branchial arch. It is predominantly an efferent nerve to the muscles of facial expression, digastric muscle and also to many glandular structures. It contains a few afferent fibres which originate in the cells of its genicular ganglion and are concerned with taste.

• face: muscles of facial expression
• ear: nerve to stapedius
• taste: supplies anterior two-thirds of tongue
• tear: parasympathetic fibres to lacrimal glands, also salivary glands

• sarcoidosis
• Guillain-Barre syndrome
• Lyme disease
• bilateral acoustic neuromas (as in neurofibromatosis type 2)
• as Bell's palsy is relatively common it accounts for up to 25% of cases f bilateral palsy, but this represents only 1% of total Bell's palsy cases

Causes of unilateral facial nerve palsy - as above plus

• Bell's palsy
• Ramsay-Hunt syndrome (due to herpes zoster)
• acoustic neuroma
• parotid tumours
• HIV
• multiple sclerosis*
• diabetes mellitus

• stroke|

• upper motor neuron lesion 'spares' upper face i.e. forehead
• lower motor neuron lesion affects all facial muscles

*may also cause an UMN palsy

Path

• Origin: motor- pons, sensory- nervus intermedius
• Pass through the petrous temporal bone into the internal auditory meatus with the vestibulocochlear nerve. Here they combine to become the facial nerve.

• The canal passes superior to the vestibule of the inner ear
• At the medial aspect of the middle ear, it becomes wider and contains the geniculate ganglion.

• 1. greater petrosal nerve
• 2. nerve to stapedius
• 3. chorda tympani

• Passes through the stylomastoid foramen (tympanic cavity anterior and mastoid antrum posteriorly)
• Posterior auricular nerve and branch to posterior belly of digastric and stylohyoid muscle