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The facial dissection commences on the unparalyzed side. The entire side of the face and upper neck are infiltrated with 1 to 200,000 adrenalin and saline. Local anesthesia is not used because facial nerve branches must be stimulated to analyze nerve branch function. The incision for the facial dissection depends upon the age of the patient. In young people, the incision starts in the anterior temple area much like a facelift incision and extends down along the preauricular region, behind the tragus, and down to 2 cm below the angle of the mandible, in a Risdon extension to permit exposure of the marginal mandibular nerve. In older individuals with redundant tissue, the incision is the classical facelift incision carried out in the postauricular region and extending posteriorly, paralleling the hairline back to the midline of the back of the neck. The facial dissection is carried out in a subcutaneous plane up to the nasolabial folds. Branches of the facial nerve are dissected out in the fatty areolar tissue anterior to the parotid gland. The mandibular branch of the facial nerve is isolated as it crosses superficial to the facial vessels and traces proximally to entrap as many branches as possible. The objective is to try to denervate the marginal mandibular branches of the normal side because this overactivity is a major contributor to lower lip asymmetry. Working superiorly, the next donor branch is isolated in the area to the upper lip and nasolabial fold. Again, the objective is to share some of the nerve supply to this relatively hyperactive area of the normal side. Usually, two large branches are isolated to this area, and it is our custom now to take the larger of these two as the donor nerve. These two nerve sources are usually sufficient to neurotize the sural crossfacial nerve graft. A tunnel is created subcutaneously across the lower lip to the region of the nasolabial fold on the paralyzed side. The premarked nasolabial fold on the paralyzed side is then incised to communicate with this subcutaneous tunnel. The dissection is extended superiorly and laterally so that the tunnel for the facial nerve graft extends to the preauricular area on the paralyzed side. A short skin incision is made in front of the tragus to recoil and secure the end of the nerve graft. The leg team has harvested the sural nerve through either multiple step-by-step ladder incisions or one continuous stocking-seam incision, depending on the age and sex of the patient. The stocking-seam incision permits one to mobilize the sural nerve under direct vision without trauma to the nerve by traction. Multiple small step-like incisions produce less scarring and are used in children and women for cosmetic reasons. An external vein stripper or Anderl nerve stripper facilitates the nerve dissection, but one must be careful not to put undue traction on the sural nerve itself. Tunneling from one incision to the other from above and from below with blunt scissors makes the nerve extraction less traumatic. Sharp strippers are to be avoided because they can transect or injure the nerve graft.
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The sural nerve graft harvested by the leg team is then brought into position and easily passed through the subcutaneous tunnel and across the lower lip to the nasolabial area and then to the preauricular area. The graft is placed in a reversed fashion, anastomosing the distal end of the grafts to the donor branches to prevent axonal escape. One wants all axons entering the graft to exit into the recipient muscle placed in the second stage. In contradistinction, when doing a facial-nerve-to-facial-nerve "Smith-Andrel" procedure, the nerve is placed in its normal anatomic direction. Axons escaping in branches may innervate more facial muscles. The microscope is brought into position and, under high magnification, using 11.0 nylon sutures, the sural nerve graft is split into two bundles, one to the marginal mandibular and the second to the zygomatic donor branch. Great care is taken to produce an absolutely anatomic alignment of the fascicular bundles of the donor nerves and the recipient crossfacial sural nerve to prevent extra fascicular "axonal escape."44 This meticulous nerve repair is one of the most challenging of all microsurgery procedures. Once these neural anastomoses have been performed, the cheek flap is replaced and the wound closed on the normal side. If the patient is an older individual, a simultaneous facelift is accomplished.
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