Facial Nerve

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facial nerve palsy
facial nerve palsy

Facial nerve palsy is the name given to the medical condition where the muscles to one side of the face become weak and partially or completely paralysed. This name may give rise to some confusion as, although the words facial and nerve are self-explanatory, the word palsy can have different meanings. It is widely used to describe uncontrollable movements such as tremors or shaking of parts of the body or even the whole body but, in this instance, its meaning specifically refers to the lack of movement or paralysis of certain muscles.

The word palsy is regarded as being a spelling variation of the 13th-century English word parlesie which was derived from the old French word paralisie. This, in turn, had its roots in the Latin word paralysis which, as will come as no surprise, means paralysis. There are many different nerves serving the skull but this condition is due to problems affecting a specific nerve, along with its branches. This nerve is officially known as the peripheral 7th cranial nerve and is often simply referred to as cranial nerve VII or CN VII.

Facial Nerve Anatomy

In order to better understand the nature and causes of facial nerve palsy, it is worthwhile to consider the anatomy of the facial nerve including its location and functions. This nerve, known as cranial nerve 7 (CN VII), is the seventh paired cranial nerve and it is mainly a motor nerve. It has some sensory functions however including the sense of taste for the front two thirds of the tongue and it is also described as being “parasympathetic” innervating various glands of the head and neck. Its course is very complex and it has many branches. Its path runs partly within the cranium and partly without. It arises at the pons which is part of the brain stem and at this point consists of two separate roots, a large motor root, and smaller sensory root. These root nerves extend to an internal opening in the bones of the skull known as the acoustic meatus and pass through into the facial canal passing very close to the inner ear. At this point, the two roots fuse to form the facial nerve and this is the location of a nerve ganglion.

Facial nerve anatomy
Facial nerve anatomy

Whilst still within the bones of the cranium, three nerve branches lead from the facial nerve these being the greater petrosal nerve, which innervates several glands, the stapedius nerve, leading to the stapedius muscle in the middle ear and the chorda tympani responsible for the sense of taste on the tongue.

The facial nerve then exits the cranium via the stylomastoid foramen, just to the rear of the styloid process of the temporal bone. The nerve then runs forwards just in front of the lower part of the outer ear. Here there are three nerve branches these being the posterior auricular, responsible for the innervation of the muscles near to the ear, the nerve to the digastric muscle and the nerve to the stylohyoid muscle. From this point on, the nerve has purely motor functions and is referred to as the motor root of the facial nerve. It then passes into the parotid gland where it splits into a further five branches. It should be noted that it plays no part in the innervation of the parotid gland. The five nerve branches then lead to various facial muscles, the individual nerves being the temporal, zygomatic, buccal, marginal mandibular and cervical. It can be seen that such a complex pathway of nerves may affect many different areas and any problems may affect different parts depending on the precise location of the problem.

Symptoms of Facial Nerve Palsy

Facial nerve palsy is most commonly caused by the malfunction of the 7th cranial nerve and, as this nerve has several branches each controlling different parts of the face, different symptoms may be observed. It is almost always a unilateral condition affecting only one side of the face and the most obvious symptom is the weakness of some of the facial muscles usually leading to some degree of paralysis which may be partial or total. This results in the characteristic twisted visage as the muscles on the opposite side continue to contract and move as usual. This may at first be mistaken for symptoms of a stroke which often also results in unilateral facial paralysis but this can easily be discounted by a closer examination of the symptoms. In cases of stroke or tumour, the central facial nerve is affected meaning that only the lower part of the face is paralysed.

Stroke victims are almost always able to fully close their eyes and wrinkle their brows but those suffering from facial nerve palsy are often unable to perform these functions. In addition to enabling the more obvious motor functions of facial muscles, the 7th cranial nerve also controls the tear glands, salivary glands and the sense of taste. The middle ear is also involved, specifically the muscular control of the eardrum. An episode of facial nerve palsy is therefore likely to result in paralysis of one side of the face including the inability to move the forehead, difficulty or the complete inability to close one eye, the eye tending to turn upwards as closure is attempted, loss of control of the salivary and tear glands, possibly resulting in some degree of drooling and tearing, a loss of the sense of taste on the front two thirds of the tongue on the affected side only and interference with hearing on one side which may manifest itself as deafness, tinnitus, or frequently as excessive loudness (hyperacusis).

Facial Nerve Palsy vs. Bell’s Palsy

One of the most commonly encountered forms of facial nerve palsy is frequently referred to as Bell’s palsy (also Bell palsy or Bell’s disease). It was named after the eminent 19th century Scottish surgeon who studied this condition and the way in which the nervous system was involved. Although this term is now less frequently used in medical circles, it remains well known and there may be a tendency for the two names to be regarded as synonymous but this is not strictly correct. Bell’s palsy is always an acute condition which manifests itself quickly, the symptoms appearing in a matter of a few hours. It is also usually described as being idiopathic, meaning that there is no known cause, but in truth of course there is a cause but it may not be easily determined. Many cases of facial nerve palsy closely fit these parameters but some others may be more chronic in nature with symptoms appearing and worsening over a more prolonged period.

What Causes Facial Nerve Palsy?

Despite often being described as an idiopathic condition, it is known that most cases of facial nerve palsy are due to inflammation of the 7th cranial nerve. This inflammation usually arises from a viral infection or an autoimmune disorder. Many common viruses have been implicated with one study suggesting that herpes simplex (the common cold sore virus) is a major cause but conflicting studies have suggested that herpes zoster (the chickenpox virus) is more likely to be the causative agent. Other viruses which have been shown to cause the condition include: mumps virus, rubella (German measles) virus, influenza B virus, Epstein-Barr virus, coxsackievirus, adenovirus and cytomegalovirus. There are other known causes of facial nerve palsy and a physician will consider the nature of the symptoms along with the clinical history of the patient in determining whether further tests are needed. Some non-viral causes of this condition include: traumatic injury to the nerve, Petrons bone fracture, middle ear or mastoid infection, chronic meningitis, diabetes, tumours or carcinomatous/leukaemic nerve invasion. Other conditions which can give rise to similar symptoms include sarcoidosis and Lyme disease.

How is Facial Nerve Palsy Diagnosed?

In most cases where the onset of the condition is rapid and there are no other suspected causes of these symptoms, diagnosis is usually based purely on the presence of typical symptoms. Where there is an indication that this condition may be non-viral in origin, the physician may require further tests. Blood tests will be required if Lyme disease is suspected and an X-ray will be needed in cases of suspected sarcoidosis. If a tumour is considered as a possibility, a CT scan is likely to be required.

Facial Nerve Palsy Treatment

In all cases of facial nerve palsy, expert medical attention is required. The methods of treatment are dictated by the cause of the condition, if known. Primary bacterial infections such as those of the middle ear or meninges may respond well to a course of antibiotics but the more common viral infections can prove to be more difficult to identify and treat effectively. Antiviral drugs may be used but their effectiveness may be questionable. Where tests have established other primary causes, these must be addressed first. The use of anti-inflammatory drugs is usually recommended and in some cases, corticosteroids can be useful in speeding the recovery process. The paralysis of the eyelids and possible involvement of the tear glands can result in potentially damaging dry eyes which must be addressed usually by the administration of suitable eye drops and it is sometimes necessary to physically keep the eyelid closed for periods using tape or an eye patch.

Facial Nerve Palsy Prognosis

Facial nerve palsy is a frightening condition which usually occurs without warning, although in some cases it may be preceded by a pain behind the ear, and the symptoms develop rapidly with the appearance of causing life-changing paralysis. Whilst there is no denying the seriousness of this condition, the good news is that the vast majority of patients go on to make a full and complete recovery within the course of a few months. Depending on the severity of the symptoms and whether permanent nerve damage has occurred, there may be some future loss of function but this is usually relatively minor in nature. During the healing process, the nerves can form abnormal connections resulting in unexpected muscle responses and movements. The tear glands and salivary glands have, on occasion, been found to share an empathy resulting in the production of tears when eating. In most cases, there is no reason to expect any recurrence of a facial nerve palsy episode unless there is a family history of such events.

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