Question #244
Which of the following would aid in the location of a facial nerve lesion?
The location of a lesion along the course of the nerve can be detected by clinical assessment:
- Is there frontal sparing? If the lesion occurs between the motor cortex and brainstem, i.e. an upper motor neuron lesion, the upper facial muscles will be spared since innervation is bilateral. A lower motor neuron will result in weakness of both upper and lower facial muscles.
- Is hearing affected? The facial nerve runs adjacent to the vestibulocochlear nerve to the internal auditory meatus. A lesion along this part of its course may affect both nerves.
- Is the eye dry? The greater petrosal nerve branches off the facial nerve in the facial canal of the petrous part of the temporal bone. This nerve carries pre-ganglionic parasympathetic fibres to the pterygopalatine ganglion where the fibres synapse. Post-ganglionic fibres continue to the lacrimal gland to regulate tear production.
- Is taste altered? The chorda tympani branches from the facial nerve on the posterior wall of the tympanic cavity. It carries taste to the anterior 2/3rds of the tongue and pre-ganglionic parasympathetic fibres to the submandibular ganglion.
- Does the patient suffer from hyperacusis? The nerve to stapedius forms on the posterior wall of the tympanic cavity. It carries fibres from the superior olivary nucleus which controls reflex contraction of stapedius in response to loud noise.
- Are all the muscles of facial expression involved?
- Is the corneal reflex intact? Asking the patient to look up and touching the cornea will result in reflex blinking. The nasociliary branch of the ophthalmic branch of the trigeminal nerve forms the afferent.
