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What is a facial paralysis?
Facial paralysis is a loss of facial expression due paralysis of muscles indispensable for mimic functions, such as wrinkling of the forehead, eye closure, and smiling. Movement of each side of the face is commanded by a separate nerve originating at the brain stem. The left branch of this facial nerve innervates the left side of the face. Analogously, the right branch innervates the right side. This nerve's anatomical projection from the brain passes through the ear region and subsequently splits into five different bundles in the soft tissues in front of the ear. These branches innervate separate regions of the face, such as the forehead, the eye, the upper lip, the corner of the mouth, and the lower lip and neck. To some extent, these branches do overlap adjacent regions of the face.
What are the causes of facial paralysis?
There are several causes of facial paralysis. Depending on the nature of its cause, the paralysis can be partial or total (involving the entire hemi face). In addition, it can be localized to one or both sides of the face. The most frequent causes found are congenital (developmental), after brain surgery (such as acoustic neurinoma), traumatic such as a skull base fracture, infectious or due to Bell's paralysis, or due parotid gland pathology. Exceptionally no cause can be found.
What are the complaints?
The nature of the complains depend on the cause, the severity, and the duration of the paralysis. Usually, young patients do not complain of asymmetry at rest due to skin elasticity at the affected side. These patients mainly complain of facial asymmetry during smiling. Sometimes, the paralyzed eye is irritated due to dryness as a consequence of insufficient or inadequate eye closure. With increasing age, and also in older patients, asymmetry of the face at rest becomes an additional complaint: the corner of the mouth droops resulting in drawling during drinking; the lower eyelid lacks sufficient support, which will additionally impede with the eye closure; the brow drops, which may hinder eye sight.
Treatment will focus on the following aspects: restoration of symmetry at rest (facial tone); restoration of a symmetrical smile; and finally, restoration of eye closure. Which techniques are most appropriate to achieve a particular goal depends on the nature of the cause and the duration of the paralysis.
- Duration of the paralysis between 9 and 12 months in patients younger than 65 years of age
If the face nerve is simply disrupted through its anatomical course in the face, the nerve can be directly repaired by means of re-approximation. This type of lesion is usually caused by a direct trauma to the nerve. The sooner the nerve is being repaired, the more favorable the final outcome will be.
If the nerve is disrupted with additional loss of nerve tissue, the nervedefect needs to be bridged by means of a nerve graft. A sensible nerve of the leg (sural nerve graft) is mostly used for that purpose, which means that some loss of sensation at the outer side of the foot does occur after the operation. In general, the shorter the duration of the lesion, the better the final outcome will be.
If the defect of the facial nerve is too large to be bridged by a nerve graft, as the facial nerve disappears within the skull behind the ear, other techniques have to be used. In these cases, the undamaged peripheral facial nerve can be operatively connected to part of another nerve innervating the tongue, resulting in the restoration of facial tone due to the natural tongue contraction at rest. Restoration of a smile is achieved through a nerve graft between the healthy facial nerve and the paralyzed muscles responsible for smiling. Eye closure will be separately addressed in the next section.
- Duration of the paralysis between 9 and 12 months in patients older than 65 years of age
Depending upon the biological age of the patient, the capability of nerve regeneration can be insufficient in older patients, even if the paralysis initiated within one year. Due to lack of skin elasticity asymmetry at rest, drooping during drinking and lack of lower eyelid support will be a functional issue. Static suspension of the corner of the mouth by means of insertion of tendineous tissue is needed to relief these complaints. If motion is desired, the large jaw closure muscle (m. temporalis) can be used to make the corner of the mouth movable. The patient will learn to smile postoperatively by means of teeth biting. Regrettably, spontaneous smiling will not be possible. Sometimes an additional brow suspension is needed.
- Duration of the paralysis longer than 12 months, in patients younger than 65 years of age
In these cases, muscle damage is evidently present in the face, which results from the long-lasting lack of nerve supply. Consequently, both nerve as well as muscle tissue need to be replaced in order to restore the smiling mechanism. For that purpose, muscle tissue plus its innervating nerve from the upper leg needs to be transplanted to the face with a microscopical repair of the nerve as well as the blood vessels. In the operation the nerve is approximated through the upper lip towards parts of the healthy facial nerve of the other side of the face. Smiling with the normal side is therefore accompanied by a simultaneous (smiling) movement of the transplanted muscle.
- Duration of the paralysis longer than 12 months, in patients older than 65 years of age
Mostly, these patients will be treated by means of a static procedure. Sometimes a temporalis muscle transposition is carried out to allow for at least some movement (see group 2 above)
Correction of eye closure
In young patients it is possible to restore eye closure by means of transposition of part of the temporalis muscle, which will be guided beneath the skin around the eye. Patients will have to learn to bite in order to close their eye. After some practice, eye closure will become possible without this intentional and conscious action.
In older patients, learning abilities necessary for this technique are usually insufficient. Hence, in these patients a golden weight is inserted in their upper eyelid. That weight will cause the eye to close except when it is voluntarily opened, since the eye opening mechanism is still intact in patients suffering from facial paralysis. Finally, lower lid support by means of a tendon graft is sometimes needed to obtain full closure.
The most important complication: bleeding or infection are seldom seen. Free tissue transfer bears the risk of thrombus formation at the anastomosis side; surgical re-exploration with removal of the thrombus is only possible within the first hours of thrombus formation. Irreversible thrombus formation with complete flap loss is seen in 3-5%.
The fact that in some techniques the healthy side is used to command the paralyzed side, will result in a more balanced face due to weakening of the healthy side.
In exceptional cases, due to an unknown reason, nerve regeneration will be insufficient to obtain a satisfactory result. Additional corrections may be needed in these cases.
What else should you know?
None of these techniques will automatically lead to a 100% recovery of the facial nerve injury. Independent of the patient's age and of the cause of the injury, some differences as compared to the healthy side, will remain visible after the surgical intervention.