What is nerve transplant and cross-face nerve graft surgery?
Nerve transplant are surgeries where nerves are transferred form one body site to another in order to substitute a particular function. Generally, we prefer using sensory nerves to bring back movement, because loss of sensation at the donor site is much easier for patients to live with. In facial paralysis surgery, patients may need a nerve transplant if a piece of the facial nerve was removed during cancer or tumor surgery. The transplanted nerve serves as a cable or conduit for the neurons or nerve cells to re-grow, thus regaining function.
A special kind of nerve transplant is called a cross-face nerve graft. This nerve transplant allows surgeons to use a facial nerve on the normal side to power facial movement on the paralyzed side. Usually a nerve is borrowed from a different side of the body and tunneled across the face connecting the normal facial nerve to the paralyzed nerve. This cross wiring allows patients to move their paralyzed side using their unaffected facial nerve. The resulting facial movement is very natural, but may not be very powerful, because we are limited by the size and caliber of a smile branch that could be borrowed without affecting the smile on the normal side.
Furthermore, patients with paralysis for more than 2 years may no longer have functional facial muscles, because the muscles waste away if they are not used. In addition, smile muscles may be removed during cancer surgery. In those circumstances, patients do need both a nerve transplant and a muscle transplant in order to restore their natural smile. Usually nerve transplant or cross-face graft surgery is performed first, allowing 6-12 months for the nerves to grow across the face. Your surgeon will test the readiness of the nerve for muscle transplant by tapping on the skin in a location where it was placed, which is called the โTineal signโ. Tapping the nerve will produce โpins and needlesโ sensation signalling that the nerve is ready to receive the muscle transplant. The muscle from the inner thigh, called gracilis muscle can be used to replace missing or wasted smile muscles. During the second stage surgery, the muscle is brought from the inner thigh and shaped into a smile muscle. Gracilis transfer is free flap surgery, meaning that the muscle is brought up with its own artery, vein and nerve like a transplant. It is then connected to the cross-face nerve graft performed 6-12 month prior and the arteries and veins in the neck under a microscope. The muscle transplant then slowly learns movement from the nerve transplant over additional 8-12 months with guidance from our facial physiotherapist.
When do I need nerve transplant and cross-face nerve surgery?
Patients with flaccid facial paralysis of less than 2 years in duration may benefit from cross-face nerve graft. If paralysis has been present for over 2 years patients often need both a cross-face nerve graft and a muscle transplant from their inner thigh.
During cancer surgery of the parotid gland or tumor removal operations a segment of the facial nerve may have to be removed with the tumor or cancer. These patients will need substitute nerve transplants during their cancer removal operation in order to maintain facial movement. If a nerve transplant is performed for a missing piece of the facial nerve, it generally takes 6-12 months for the nerves to regrow. Time to being able to smile again can be reduced to 3-4 months if masseter to facial nerve transfer done concurrently.
How do I prepare for nerve transplant and cross-face nerve surgery?
Prior to cross-face nerve graft surgery, your surgeon may get an electromyography (EMG) study of your facial muscles to determine if you are a candidate for a nerve transplant. Donor nerve options will be discussed in detail. Generally, for a nerve transplant to go across the face, an adequate length of the nerve is required. Most common donor nerve is sural nerve. It is a long nerve in your lower leg that provides sensation to the outer edge of the foot. Using that nerve would give you a permanent patch of numbness in a small area of your outer foot and ankle. The benefit is return of movement to the paralyzed face, so most patients do not mind a small area that loses sensation. An alternative donor nerve is medial antebrachial cutaneous nerve, which is taken from an inner aspect of the upper arm. If used, patients will permanently lose sensation in the inner forearm. Greater auricular nerve which provides sensation to the earlobe is generally not long enough to tunnel across the face, but it could be used as a connector or a โcable graftโ if a segment of the facial nerve is missing.
What happens during nerve transplant and cross-face nerve surgery?
Patients are taken in to the operating room and surgery is performed under general anesthesia. Facial nerve monitoring system to carefully monitor the facial nerve to ensure its integrity. Facial monitoring is used to identify and confirm functions of each facial nerve branches. There is significant variability in number and pattern of branching of nerves responsible for facial expressions including smile and frown.
In a cross-face nerve transplant surgery, the good side of the face with a fully functional nerve is explored and multiple smile branches are identified with nerve monitoring and anatomical landmarks. The incision is made in natural facial grooves, similar to a facelift incision. There are usually multiple smile branches, so a surgeon can use one of them to power the other side of the face. Using a smile branch on a good side can temporarily weaken the normal side of smile, but full strength is usually regained in 3-6 months post-surgery.
If sural nerve is used from the leg, there will be a small incision on the outer ankle. A special camera called an endoscope is used to identify and isolate the nerve. Sutures and tapes are placed on the incision and the ankle is wrapped with a special tensor bandage to minimize swelling. The outer aspect of the ankle will remain numb, but there will be no consequences in terms of movement. This nerve is most commonly used for cross-face nerve transplant surgery because it has ideal length to be tunneled across the face.
If medial antebrachial cutaneous nerve is used, a long incision (similar to an arm lift) will be placed in the inner aspect of the upper arm. The will be a loss in sensation in the inner forearm which most patients donโt mind as the goal is to regain facial movement. The arm movement is not affected by the use of this nerve.
If greater auricular nerve is uses as a nerve transplant, permanent loss of sensation to the ear lobe is expected. It can be bothersome to persons who wear earrings, as they will need to look in the mirror to put them on because earlobe sensation is lost. Greater auricular nerve is not long enough for cross-face nerve transplants, but it can be used as a connector or a โcable graftโ if a segment of the facial nerve is missing.
The nerves are hand stitched together under a high-powered microscope using sutures smaller than the size of human hair. Special nerve sheaths are also placed on suture connections in order to facilitate nerve growth. The nerves do not function right away, but the surgery creates new pathways or conduits for nerves to grow.
What are the risks of nerve transplant and cross-face nerve surgery?
The general risks of any facial surgery include scarring, bleeding, bruising, infection, fluid or saliva collections under the skin, injury to nerves, donor site issues, numbness, the need for additional surgery, hair loss, chronic pain, numbness, temporary or permanent loss of facial movement on the functional side effects of general anesthesia. Preparing for surgery and following your surgeonโs instructions are useful to help minimize risks.