Overview of Facial Nerve Repair
Facial paralysis can significantly affect a person’s life. It can cause problems with basic functions like closing the eye, breathing through the nose, or even talking and eating properly. It also affects a person’s ability to show emotion through smiling and can make the face look uneven when at rest. This condition can be particularly difficult for young women and can even lead to depression. Facial paralysis can be caused by various conditions, such as Bell’s palsy, Lyme disease, tumors, bone fractures around the ear, among other factors.
This summary will focus on facial paralysis that results from an injury that cuts or damages the facial nerve. When this occurs, doctors tend to prefer a surgical repair immediately. If the nerves cannot be joined without causing tension, a cable graft interposition might be needed. This surgical procedure involves using nerves from the ear or leg to replace the damaged ones. The success of nerve repair differs widely, with some studies showing a success rate between 5% to 86%. But, sometimes, instant nerve repair isn’t achievable, depending on where the nerve injury is located or if the injury is not immediately detected.
If the nerve injury is left unattended for some time, risks may arise, such as injury to other facial structures during surgery. Methods like grafting from another site have potential risks at the donor site too. All these methods require time for the facial function recovery. No matter the chosen treatment, it’s crucial to know that it will take time to regain function and facial aesthetics after facial nerve injury.
Due to the complexity of this kind of treatment, a team approach is often utilized. It’s best for the medical team to include a surgeon who specializes in nerve damage, an eye doctor (ophthalmologist), and physical and speech therapists. Combining these specialists’ skills ensures that the patient receives comprehensive care for their facial paralysis.
Anatomy and Physiology of Facial Nerve Repair
The facial nerve, also known as the seventh cranial nerve, begins deep in the brain at a part called the pons. It crosses over to a narrow, curved area in the brain, before entering a tiny tunnel in the inner ear next to the cochlear nerve and two vestibular nerves. This part within the tiny tunnel in the bone near the ear is about 8-10 mm long. The facial nerve is positioned at the front and top quadrant of the inner ear’s canal, while the cochlear nerve, responsible for our sense of hearing, is slightly below it at the front. The two vestibular nerves, responsible for our balance, are situated at the back quadrants – one at the top and one at the bottom.
The facial nerve then takes a turn towards the front into a small labyrinth-like passage about 4 mm long, ending at an area called the geniculate ganglion. This part of the nerve is vulnerable to pressure or impingement that can be caused by fractures or swelling within the nerve. From there, the nerve loops back, gives off a larger branch and continues its path within the temporal bone, an area of the skull near the ear which is also called Fallopian canal. The narrowest – and most susceptible to obstruction – part of this canal is the labyrinth segment, with a diameter of only 0.7 mm.
After exiting the Fallopian canal, the facial nerve extends for about 9-10 mm going towards the back through the middle ear, moving above a part called the stapes footplate. This part of the facial nerve can be damaged by conditions affecting the middle ear, such as infections or a cholesteatoma, which a kind of skin cyst that can develop in the middle ear. This risk is especially high if the bone surrounding the Fallopian canal is not intact. At the mastoid cavity, an area of the temporal bone near the ear, the nerve turns downward through a space 11-12 mm long. Here, the nerve fibres start to separate and organize, getting ready to split in the parotid gland at an area called the pes anserinus. The facial nerve then controls the muscles of the upper, middle and lower face, and neck.
Within the mastoid, a specific branch of the facial nerve called the chorda tympani turns upward and exits the temporal bone to reach the oral cavity. This nerve carries the sensation of taste from the front two-thirds of the tongue.
Outside the temporal bone, the facial nerve travels approximately 14 mm before splitting into five main branches: the frontal, zygomatic, buccal, marginal mandibular, and cervical. But the exact pattern of these branches can vary, with six different possibilities described in the 1950s by Davis and colleagues. Despite this variability, certain surface landmarks – like the line of Pitanguy and point of Zuker – allow for the reliable identification of the main extra-temporal facial nerve branches. These branches provide different kinds of movements for the face, helping us blink, smile, frown, and make other expressions.
The facial nerve branches also pass through the parotid gland (one of our salivary glands), separating the gland into a superficial and deep part. These branches leave the gland at its front edge and run beneath a layer of fibrous tissue in the cheek known as the superficial musculoaponeurotic system (SMAS). Eventually, they provide the nerve supply to numerous muscles of facial expression, except for three muscles which get nerve supply from their superficial surfaces.
The SMAS layer, which is just above the parotid gland, extends upwards to the cheekbone and beyond, where it is connected with the temporoparietal fascia (a layer of tissue between the skin and underlying muscle). Going downwards, SMAS is continuous with a muscle in the neck, the platysma. Towards the front, it joins with the muscles responsible for our facial expressions.
Why do People Need Facial Nerve Repair
If you’ve experienced a serious facial nerve injury, which is classified as a Sunderland Class V injury, surgery may be required to repair the damage. This can happen if the main trunk or a branch of your facial nerve is injured. If the doctors can see the injury during another operation, they may decide to fix it right away. The best option is to repair the nerve as soon as possible, but sometimes the injury might not appear until after the surgery is over.
Nerve damage may cause paralysis, which might show up immediately after waking up from anesthesia or take some time. If the paralysis takes some time to appear, then the nerve isn’t fully broken and won’t need to be repaired or transferred. But if the paralysis appears immediately after waking and wasn’t noticed during surgery, a test called an ENoG may be used 3 to 5 days later. If this test shows that the nerve strength has dropped by more than 90% compared to the normal side, repair or transfer might be necessary.
The same process can be used to decide whether a surgery for facial nerve injuries is needed, particularly in the case of lacerations due to traumas. If injuries happen to the nerve near the corner of your eye, surgery won’t be needed as these nerve branches are small and usually recover on their own.
If repair or grafting is to be tried, both ends of the nerve should be healthy. If the injury happens very near to the brain or involves the central nervous system––like in the case of a brainstem tumor–– nerve transfer techniques would be the best choice. When doing nerve repair or transfer, the muscle it connects to should remain healthy for the duration of the surgery procedure. Muscles usually start to atrophy and become fibrotic (or harden) after 12-18 months without nerve supply, but nerve repair or transfer can be successful if performed within six months.
Nerve cells regenerate at around 1 millimeter per day but this can be affected by age, nutritional status, and general health. Therefore, the repair site to muscle distance can give an approximate time-frame for the nerve to reach the muscle. However, immediate repair at the time of injury is the best approach. There are reports of better facial movement in patients who received immediate facial nerve repair compared to patients whose repair was delayed.
A view inside the muscle tissue (EMG) should be done to confirm that the muscle is still healthy and capable of movement if nerve repair or transfer is planned for six or more months after injury. If the EMG shows multiple nerve signals, surgery should be postponed to see if the nerve can recover itself.
Also, doctors typically follow a process for selecting treatment options for patients with facial nerve trauma:
If the two ends of the cut nerve can reach each other without tension, your doctors would connect them directly.
If the nerve ends are within 6mm of each other without tension, they would use a nerve connector to bring them together.
If the cut nerve ends are far apart and can’t reach each other without tension, a nerve graft from another body part (usually the ear or the leg nerve) would be used. This is done ideally within a year from when paralysis began.
If more than half of the nerve diameter is disrupted, like when injury happens because of a drill during a ear bone surgery, the injured part should be removed and the healthy nerve ends connected, if possible. If needed, a nerve graft could be used.
In total, the method and timing of restoring facial nerve function should be guided by many factors and the situation of each patient.
When a Person Should Avoid Facial Nerve Repair
Facial nerve repair is a delicate procedure, and there’s a lot of factors to consider before a doctor can recommend it. Here are some reasons why a doctor might choose not to do facial nerve repair:
If a person has some paralysis or delayed paralysis in the face, they might not need the repair at all. That’s because the nerve is still in one piece and it might be able to fix itself without surgery. Also, if the nerve damage is near a point called the lateral canthus (which is the outer corner of the eye), the surgery would be difficult to perform. Plus, there’s typically enough nerve connections in that spot, so the function of the face may just return on its own.
Sometimes a test called an EMG (which is short for electromyography) is done before surgery. This test measures the electrical activity of muscles. If there is no electrical activity found, it suggests the junctions where nerves connect to muscles have decayed, possibly with fibrosis (which means the muscle has turned into scar tissue). It also suggests that the muscle may not be able to accept nerve signals anymore. Along the same lines, if a person doesn’t have certain facial muscles due to a birth defect, surgery, or trauma, there wouldn’t be any muscles to re-connect the nerves to.
Another reason to avoid the surgery is if a person has advanced cancer or another disease that might reduce their lifespan. The surgery has a risk involved and if a person may not live long enough to see the benefits, it may not be worth it. In case of cancer, the surgery should wait until after all of the cancer has been removed. Finally, if a person cannot respond or has serious memory loss issues, they wouldn’t be able to do the facial exercises needed after the surgery. This reduces the benefits of the surgery.
One other thing to consider: if a person has difficulty swallowing (which is called dysphagia), a type of nerve repair called hypoglossal nerve transfer isn’t a good choice. This surgery could make their swallowing issues worse, especially if the patient is older.
Equipment used for Facial Nerve Repair
To fix a damaged facial nerve, your doctor will use particular medical tools. The main ones are:
- A special microscope made for surgery. This isn’t always needed if they’re only connecting the nerve ends (neurorrhaphy).
- Microsurgical instruments like tiny forceps, scissors (straight and curved), and a tool to help with stitching called a non-locking micro needle driver.
- Very thin nylon stitches with a type of needle known as TG 160-4.
- Weck cell spears, absorbent pointed tools used to soak up tiny amounts of blood or other fluids.
- A Goodhill suction tip, which is a tool to suck away any unwanted liquids.
- Extra tiny forceps that help control bleeding during surgery.
- A collagen wrap or another kind of casing for the nerve, like a vein graft, which replaces the damaged section.
- Small, straight scissors like Iris or tenotomy scissors, used for precise cutting.
- Retractors, like those named Senn, Ragnell, Cummings, or Lone Star. These help keep the wound open during surgery.
- Fibrin glue, a special surgical glue that helps stop bleeding and can help wounds heal faster.
- A nerve stimulator that checks if the nerves are working properly during surgery.
Your doctor may also need to use other tools for different parts of the procedure. For example, they might need different types of special scissors like Metzenbaum, Gorney-Freeman, or Reynolds tenotomy scissors. Other items may include clamps, instruments that help to separate tissue layers delicately, like petit point Crile clamps, fine right-angle clamps, and forceps like DeBakey or Gerald.
Who is needed to perform Facial Nerve Repair?
A nerve repair procedure, often called nerve coaptation, is typically done by a specialized doctor like a facial plastic surgeon, neurosurgeon, head and neck surgeon, or plastic surgeon. This could be the main doctor who accidentally injured the facial nerve during a previous operation, or it could be a consultant who is specifically skilled in nerve repairs. If the facial nerve deep inside the mastoid process (part of the skull bone near your ear) needs to be reached, a special type of ear doctor, like an otolaryngologist or otologist, will perform a procedure called mastoidectomy to access it.
Besides the doctor doing the operation, a circulating nurse and a surgical technologist will also be there to assist. In some cases, a surgical first assistant may also be needed. An anesthesiologist, who is a doctor specializing in controlling pain during operations, is vital. This professional will ensure that the anesthesia is strong enough to prevent any movement from you during the surgery, without having to use long-lasting paralytics that might interfere with the ability to stimulate the nerve during the operation.
Preparing for Facial Nerve Repair
When you’re about to undergo facial reinnervation (a procedure to restore movement to a paralyzed face), it’s important to understand that this process can take several months before any visible progress is noticed. To enhance the results of the procedure, you would often need some facial physical therapy sessions after the surgery. There might also be some additional minor treatments, such as injections, to help speed up the recovery.
If you need a donor graft (a piece of nerve tissue that is moved from one part of your body to another), be aware that this might lead to a temporary feeling of numbness in the area where the graft was taken. This area will be prepared at the same time as the face for the surgery. The sural nerve (from the leg) and the greater auricular nerve (from the ear) are the usual choices for grafting. Sometimes, while one team of doctors is working on making your facial nerve ready, another team might be preparing the donor graft to save time.
There are some specific considerations for facial reinnervation procedures. Your eyes need to be protected during the procedure, this is typically done with a special dressing or temporary stitches. The side of your face that’s paralyzed will be clearly marked to avoid any confusion during the surgery. One way of doing this is by writing ‘P’ on the affected cheek and ‘NP’ on the unaffected one.
While you are under anesthesia, the breathing tube that’s placed in your mouth will be positioned in such a way that it doesn’t affect the lower part of your face. There’s a special requirement for anesthesia depending on the type of surgery: If the procedure is a nerve repair within 72 hours after an injury or a nerve transfer at any time, long-lasting anesthetics will be avoided, allowing the use of a nerve stimulator during the operation.
Lastly, you might receive preoperative injections containing a medication called epinephrine. This medication helps control bleeding without affecting the nerve stimulation response, which is crucial for the success of the surgery. The concentration of this medication is carefully prepared to ensure its effectiveness.
How is Facial Nerve Repair performed
Direct end-to-end coaptation is a procedure often used to treat damage to the facial nerve as soon as possible after the injury occurs. Essentially, it connects the two ends of the injured nerve together, which is why it’s called “end-to-end”. This method is usually chosen because it improves the outcome or results of the treatment.
When the nerve is injured, the most effective treatment is to repair it as soon as possible. This is most likely to occur if the injury happened during a medical procedure. If the repair cannot be done right away, ideally it should be carried out within 72 hours. This timing is important because it allows the doctors to use a tool called an “intraoperative stimulator”, which helps identify the damaged part of the nerve.
To locate the injured nerve, doctors trace the facial nerve from the main trunk, which is typically hidden beneath a small vein and small fat pad. The doctor may also locate the nerve through a cut on the face, or via a surgical incision, usually a “modified Blair” or “parotidectomy” incision.
Once the injured parts of the nerve have been found, the doctors remove the damaged part and any scar tissue around it before proceeding with the repair. The repair process involves stitching the cut ends of the nerve together using very small sutures. This part of the procedure is usually done under a microscope to ensure precision. The stitches are done carefully to avoid putting too much pressure on the nerve. Sometimes, the doctors may use a special glue made from fibrin, a protein that helps in the clotting of blood, to join the nerve ends together.
If the nerve damage is too significant and the ends of the nerve cannot be stitched together directly, the doctors have a few options. They might use a nerve sheath, essentially a protective tissue, connecting the nerve ends and leaving a small gap between them. They can also use a graft, which means they take nerve tissue from another part of your body and use it to bridge the gap between the two nerve ends. However, grafting is generally avoided whenever possible, because it can potentially result in more loss of nerve function.
In summary, direct end-to-end coaptation is a process to repair facial nerve injury by rejoining the cut ends of the nerve. If direct joining is not possible, doctors might use a nerve sheath or a graft as the intermediary. The method chosen depends on the severity of the injury and the doctor’s judgement.
Possible Complications of Facial Nerve Repair
When getting surgery to repair or transfer nerves, there is the risk that the nerves may not regain their normal function. Several things increase this risk, such as if the paralysis has been going on for over 6 to 12 months before the surgery, or if the person is elderly or in poor health. Also, each time a nerve is stitched back together, there is a chance for loss of nerve fibers, which can lower the chance of successful recovery. Neither radiotherapy after surgery nor chemotherapy seem to affect the outcome of nerve repair surgeries.
When the facial nerve is fixed or another nerve is grafted to the main trunk of the facial nerve, the result might be synkinesis or unwanted muscle movements. This is not a complication per se but can interfere with voluntary movements like smiling, leading to uneven facial appearances and lowering the quality of life despite other improvements. It is thought that synkinesis is mainly caused by nerves reconnecting wrongly to different muscle junctions after injury.
Apart from this, nerve fibers that connect to multiple muscle junctions can cause uncoordinated movements and lead to increased resting tone of the muscles. Injections of botulinum toxin and exercises to help with facial physical coordination are the main treatment options for such uncoordinated movements. Surgical options like removing only the problematic part of the nerve or muscle have also been performed successfully. There is the possibility of avoiding synkinesis or reducing it by reconnecting the branches of the facial nerve properly.
There’s also a risk particularly in surgery performed more than 72 hours after injury, of reconnecting to the wrong branch of the nerve. While the misplaced connection might not result in completely different movements, it might distort facial expressions like smiles. Surgeons aim to reinnervate the muscles of the face whenever possible. But if the results of the nerve transfer are not perfect, causing persistent synkinesis, or if the paralysis has been ongoing for more than a year to a year and a half, separate muscle transfers might be performed instead of nerve repair or transfer.
When a healthy nerve is tapped to graft or transfer, there is the risk of what is known as donor site morbidity. Common side-effects include numbness at the source site of the graft, and rare chances of developing painful neuromas or nerve tumors. These can be removed and the cut nerve end can be buried into muscle. Sacrificing a motor nerve involves a greater risk. But generally, the loss of the masseteric nerve, which results in some loss of facial volume due to muscle atrophy, is well tolerated and there are minimal issues. Rarely, there might be a weakening of the smile on the healthy side of the face.
There is the highest risk for donor site morbidity with the hypoglossal-facial nerve transfer, which could potentially lead to swallowing and speaking difficulties due to tongue weakness. Transferring an entire hypoglossal nerve results in good facial outcomes because of its high axon count, but the side-effects can be severe. Sacrificing only part of the hypoglossal nerve reduces side-effects dramatically but can compromise the results due to a reduced number of nerve fibers transferred into the facial nerve.
What Else Should I Know About Facial Nerve Repair?
Facial paralysis, which affects your ability to move the muscles on your face, can greatly impact your quality of life both socially and functionally. However, it can be treated through surgical procedures like facial nerve repair and transfer. These treatments aim to restore the natural movements of your facial muscles and generally have a good balance of benefits versus risks as they usually lead to minor complications.
These procedures tend to work best with younger, healthy individuals where the damage to the facial nerves is located towards the end (distal) of the facial nerve. It is also important that these surgeries are performed swiftly especially in cases such as facial cuts or injuries caused inadvertently during medical procedures (iatrogenic injuries).
However, older individuals, those who are not in good health, or those with long-standing (chronic) facial paralysis might not see as successful outcomes. For instance, conditions like advanced parotid malignancies (advanced cancer of a type of salivary gland) and recurrent cholesteatomas (benign, but destructive, growths of the skin of the ear) may not respond as well to such treatments. On the other hand, patients with benign (non-cancerous) slow-growing tumors or injuries respond better to the treatment.
With these procedures, the initial signs of regaining nerve control over facial muscles can typically be expected within 2 to 12 months following the surgery.
