The majority of cases are of the so-called “rheumatic” variety, and are attributed to exposure to cold. Others result from fractures implicating the middle fossa of the skull, or are associated with chronic suppuration in the middle ear.
In fractures passing across the petrous temporal, the nerve may be torn at the time of the injury, or may become pressed upon by a traumatic effusion or by callus later, but considering the frequency of these fractures it is comparatively seldom damaged.
Suppurative disease of the middle ear is a more common cause of facial paralysis. The nerve, as it traverses the facial canal (aqueductus Fallopii), may be pressed upon by inflammatory effusions or granulations, or may be destroyed by the suppurative process, particularly in young children, as in them the osseous wall of the aqueduct is very thin. It may also be involved in tuberculous and in malignant disease of the middle ear.
The nerve may be injured also in the course of operations on the mastoid or middle ear, or in the removal of tumours or glands in the parotid region. As the nerve breaks up into numerous branches soon after it leaves the stylo-mastoid foramen, the paralysis may be confined to one or more of its branches.
Temporary paralysis may result from inflammatory conditions such as parotitis, or from blows or pressure over the nerve, for example by the forceps in delivery.
Symptoms.—In complete unilateral facial paralysis (Bell's paralysis) the affected side of the face is expressionless and devoid of voluntary or emotional movement. The muscles are flaccid, the cheek is flattened and smooth, all its folds and wrinkles being obliterated. When the patient speaks or smiles, the face is drawn to the sound side ([Fig. 201]). The eye on the affected side cannot be closed, and on making the attempt the eyeball rolls upwards and outwards. The lower lid droops, the patient cannot wink, and the conjunctiva therefore becomes dry, and is irritated by exposure to cold and dust. The tears run over the cheek. From paralysis of the buccinator muscle there is inability to whistle or to puff out the cheeks and food collects between the cheek and the gums. The orbicularis oris being also paralysed, the patient is unable to show his upper teeth, and the labial consonants are pronounced indistinctly. The sense of taste is often impaired from involvement of the chorda tympani nerve.
Fig. 201.—Patient suffering from left facial Paralysis. Note smoothness of left side of face, imperfect closure of left eye, and deviation of face to right side.
(From a photograph lent by Dr. Edwin Bramwell.)
When the paralysis is bilateral, the symmetrical appearance of the face renders the condition liable to be overlooked.