History
A female patient in her 30s had a significant past medical history of left facial nerve paralysis with partial recovery complicated by synkinesis.
Presentation and Examination
The patient has incompletely recovered Bell's palsy with residual left-sided oral commissure and midface facial paresis. She has been treated with Botox for ocular-oral synkinesis, but still has trouble with facial and smile asymmetry, specifically with reduced left commissure excursion and left upper lip elevation limitation.
We decided she would be an ideal candidate for a left masseter nerve graft transfer to treat her condition.
About Bell’s palsy
Bell's palsy is a neurological disorder that causes weakness or paralysis in the muscles on one side of the face. Patients may experience facial pain, increased sensitivity in their face, a drooping of their eyelid or mouth and difficulty closing their eyelid. Bell’s palsy is one of the most common causes of facial paralysis. Although its origin is idiopathic, it is thought that inflammation of the immune system is a common trigger of the condition.
According to the National Institute of Health, Bell's palsy is estimated to affect about 40,000 people in the United States every year and typically affects patients between 15 and 45 years of age. Patients who are pregnant and obese or those who have diabetes, hypertension or contracted an upper respiratory infection or viral infection are at greater risk for developing this condition.
Treatment
Anatomical identification
I first identified the landmarks and boundaries of the sub-zygomatic triangle and made a left preauricular incision using a 15-blade including a post-tragal component. A skin flap was broadly elevated over the left face. The superficial musculoaponeurotic system (SMAS) was then sharply incised and a SMAS flap was carefully elevated using blunt dissection and limited bipolar cautery. This allowed me and my team to identify the distal branches of the facial nerve.
We identified several midface facial nerve branches. Three parallel buccal nerve branches were dissected and followed distally and proximally. Each individual branch was stimulated with the nerve stimulator, and we examined the facial movement to identify their exact function.
The most inferior buccal branch split into two branches. The lower nerve stimulated the orbicularis oris and the left oral commissure. The middle branch stimulated the zygomaticus muscles with upper lip elevation and some commissure excursion. The superior buccal branch had redundant function as the middle branch.
Nerve transfer
Due to the incomplete nature of her paresis and, in order to avoid post-op weakness, I coapted the common branch prior to its split into the lower and middle buccal branch. This preserved the superior buccal branch with redundant function to maintain her pre-operative movement.
I performed an end-to-side anastomosis in order to add neural input from the masseteric nerve and preserve existing function. This also used the masseteric input from the two branches that were found to most significantly contribute to her areas of concern--specifically commissure excursion and upper lip elevation.
The sub-zygomatic triangle was then explored to identify the masseteric nerve. The nerve was freed from surrounding masseter muscle fibers and followed for length. It was stimulated to confirm the correct nerve with vigorous masseteric muscle contraction. The nerve was cut, tagged and reflected towards the facial nerve anastomosis site.
I then coapted the nerves in order to align the fascicles perfectly. The patient was then closed.
Outcome
About six weeks after surgery, the patient was doing well overall; she no longer had to accentuate the left side of her smile, which she had to do prior to surgery. She still experienced facial pain centered around the face and down her chin, along with some numbness. She experienced a lot of twitching, but did not notice synkinesis on the left side of her face. She also notes that she was able to squeeze her eyes shut a lot more than prior to surgery.
Three months post-surgery, the patient reported her left eye would get considerably smaller when she smiled. We decided to manage this symptom with an additional Botox injection to her upper eyelid. Currently, the patient is doing great overall. We will continue to use routine Botox treatments to treat the patient’s residual symptoms indefinitely.
Analysis
Although relatively common, patients with Bell’s palsy experience functional, aesthetic and psychological disturbance. Symptoms typically resolve themselves with or without treatment over a few weeks and can vary in their intensity with each patient. Although most patients will regain some or all of their facial function within a few weeks, about 20% of patients who develop this condition may experience lasting weakness of the smile and eye.
Should a patient’s symptoms not improve on their own or through steroid treatment, we have 12 months from the onset of the weakness to intervene surgically to perform a masseter nerve transfer. However, surgical intervention after 12 months will not work.
Both hypoglossal and masseteric nerve transfer are currently the most popular cranial nerve transfer techniques for patients with facial paralysis. In this case, I opted to connect the patient’s masseteric nerve with her facial nerve to give it more power and improve her ability to smile.
The masseteric nerve transfer is efficacious and has rare chances for complications. Masseteric nerve transfer was also rated superior by the Sunnybrook Facial Grading System (SFGS), possibly due to consideration of synkinesis. In addition, direct masseteric transfer versus direct hypoglossal transfer was, on average, two months after (although this benefit was lost with an interposition graft).
