Facial Nerve Paralysis
Facial nerve is a long paired nerve belonging among the cranial nerves. Anatomically, it is considered as the seventh cranial nerve and thus it is marked by Roman number VII. Its brain centre (also paired) is located in the brain cortex and out of there, the signals are transmitted into neural nuclei located in the brainstem. The nerve anatomically penetrates the temporal bone and through a little hole it gets into the facial are, where it innervates facial muscles. Hence, a facial nerve allows the expression of the corresponding face including the movement of the mouth and closing of the eye. Some of the facial nerve fibers also lead information about taste from the tongue.
Facial nerve palsy has two main forms – central and peripheral. Central form occurs due to disorders of the brain cortex or nerve fibers within the brain. Peripheral form occurs due to pathology of the nucleus or the peripheral nerve. During the way through the central nervous system (i.e. through brain), the nerve fibers cross and this means that right-sided damage causes symptoms on the left face and vice versa. To make it more complicated, some of the nerve fibers controlling the eye closure is supplied with both nuclei of the facial nerve and this ensures muscles of both eyes to be controlled by both sides of brain cortex.
This above mentioned complex explanation can be simplified so that the central damage of the unilateral brain cortex affects the opposite facial nerve, but its function is partially substituted by fiber that go to both facial nerves. The peripheral palsy damages the whole facial nerve, thus causing paralysis of the face on the same side.
The condition causes partial paralysis on the opposite side of the face. The patient can not close the mouth and suffers from dropped mouth corner. The inability to fully close the mouth causes saliva to leak out an impaired ability to articulate. The ability to close eye on the affected side is maintained (replaced by nerve fibers from the second brain center).
In this case there is a disruption in nerve nucleus in the brainstem or in the peripheral facial nerve. The result is a total loss of nerve function on the appropriate side of the face. The patient loses mimics in the half of the face; he is unable to fully close both the mouth and the eye (technically it is known as lagophthalmos).
Scheme - Peripheral facial nerve paralysis
Note: The disruption of the nerve also causes loss of taste sensation of two thirds of the half of the tongue. However, other parts of the tongue function normally and therefore; the taste disorder is usually not perceived by the patient.
This is the most common cause of central paralysis of the facial nerve. The cortical center or brain neural fibers may be directly damaged by the stroke and this leads to the neurological symptoms. In addition, a larger stroke may cause other symptoms including impaired speech, impaired consciousness, impaired swallowing, muscle paralysis of other parts of the body, etc.
Facial nerve palsy typically accompanies the herpesvirus infections. The paralysis occurs suddenly and unexpectedly. Similarly, middle ear infections may be also associated with a disorder of the facial nerve. Infectious damage of the peripheral nerve results in peripheral type of the palsy.
Cold environment affecting the facial nerve such as when riding a motorcycle in cold weather may be associated with temporary loss of the peripheral nerve functions. The result is a paralysis of the peripheral type, which has fortunately a tendency to spontaneously disappear after a short time.
Traumatic injury to the nerve occurring anywhere in its course may result in impaired function of the peripheral type.
Malignant and benign tumors occurring anywhere in the vicinity of the facial nerve may compress it, or directly injure it. Again, we find signs of peripheral paralysis.
Facial nerve passes through the parotid gland and there is a risk of its damage during local operations (for example in operations of parotid gland tumors). The damage has a character of the peripheral palsy.
When there is suspected paralysis of the facial nerve, the patient should be examined by a neurologist. Besides physical examination, it is advisable to use some imaging methods to exclude organic diseases such as computed tomography or magnetic resonance imaging.
The treatment is usually not very effective. The patients are usually administered some vitamins, but their effect is at least controversial. In case of a suspected herpesvirus infection, the patient may be given some antiviral drugs. When the nerve is compressed, local surgery is performed. Much attention is paid to eye affection in the peripheral form. The inability to close the eye may cause permanent corneal contact with the surrounding environment. The cornea may be repeatedly damage and this can result in loss of vision. Special moistening solutions and night ointments must be regularly applied locally to prevent the eye from drying. If there is no hope of improvement, the eye may be closed by a surgical procedure. The effect is similar- loss of vision in the affected eye – but the patient at least avoids repeated inflammations and eye tissue damage.