Page 342 - Medicine and Surgery

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338 Chapter 7: Nervous system

the medial wall of the middle ear. Here the sensory nerve Management
cell bodies cause a swelling called the geniculate ganglion If the patient is unable to close their eye completely, ar-
and give off the nerve to stapedius and chorda tympani tificial tears should be used and the eye taped shut at
(taste and lacrimation) before exiting the skull through night to prevent corneal ulceration. The evidence for
the stylomastoid foramen. steroid treatment is weak but may have an effect if given
Each facial nucleus supplying the forehead muscle within a day of onset. In cases that do not resolve tars-
(frontalis) receives some innervation from each hemi- orrhaphy (suturing of upper to lower lid, laterally) may
sphere, so that unilateral upper motor neurone lesions be necessary. Cosmetic surgery and/or reinnervation us-
cause sparing of the forehead, whereas unilateral lower ing a lingual nerve transfer for example, can be used for
motor neurone lesions cause forehead involvement. chronic cases.

Function
Prognosis
Muscles of facial expression and taste of the anterior two
A significant proportion do not completely resolve and
third of the tongue.
it occasionally recurs.
Specific causes
Lower motor neurone (all of one half of the face af- Vestibulocochlear nerve (VIII) lesion

fected) – Bell’s palsy, herpes zoster, polio, otitis media,
Anatomy
skull fracture, parotid tumours.
th
The VIII nerve carries sensory information from the
Upper motor neurone (forehead spared) – stroke, tu-

cochlear and vestibular apparatus. The auditory fibres
mours.
arise from the cochlea and pass to the pontine auditory
nucleus. These then project to the temporal lobes. The
Clinical features
vestibular nerves arise from the semicircular canals and
The features of facial nerve palsy depend on the level
pass to the vestibular nuclei in the pons, and the cerebel-
of the lesion. If both lacrimation and taste are unim-
lum.
paired, the lesion is below the stylomastoid foramen.
Hyperacusis (hearing sounds louder than normal) sug-
gests a lesion proximal to the stapedial branch. Function
Hearing (cochlear nerve) and movement/position of
head in space, for balance and head–eye coordination
Bell’s palsy
(vestibular nerve).
Definition
Idiopathic weakness of the muscles of facial expression.
Specific causes
M´ eni` ere’s disease, acoustic neuroma, lead, aminoglyco-
Clinical features sides, furosemide, Paget’s disease, herpes zoster.
Spontaneous unilateral weakness of the muscles of facial
expression. As it is a lower motor neurone deficit, the
forehead is affected and the eye may not be able to close Clinical features
Sensorineural deafness, tinnitus, vertigo, nystagmus.
completely. It usually begins to improve spontaneously
after about 10 days, but may take months to recover
completely.
Glossopharyngeal (IX) and vagus (X)
lesions
Investigations
Electrophysiological tests may help to predict outcome: Anatomy
lack of evoked potential after 3 weeks has a poor prog- Nerve fibres arise from nuclei in the medulla to form
nosis. these two nerves, which pass out via the jugular foramen.