Since Scaramella’s report in 1971, cross-facial nerve graft has been considered the treatment of choice for patients with facial nerve damage at the proximal stump level [2, 3]. Traditionally, long skin incisions and wide dissections were required for skin flap elevation and to locate specific branches of the facial nerves in this technique. In our cases, however, a cross-facial nerve graft was successfully performed via an intraoral mucosal incision and dissection without wide elevation of the facial skin. This per-oral approach was advantageous over the conventional extraoral approaches for several reasons.
First, the presence of a stable anatomic landmark, the parotid papilla, aids in locating the parotid duct, which is closely associated with the course of the facial nerve’s buccal branch. There have been numerous studies on anatomic markers associated with the paths of the facial nerves and their branches. The facial nerve divides into five branches within the parotid gland, and the buccal branch courses along the parotid duct between superficial and deep fascia in the masseter muscle region. Pogrel et al. reported that the distance between the parotid duct and the buccal branch of the facial nerve measured approximately 5.43 ± 3.65 mm . Son et al. reported that the distance was about 2.54 ± 1.48 mm . The parotid duct arises from the anterior aspect of the parotid gland and passes anteriorly in the masseter muscle region with a close proximity to the buccal branch of the facial nerve. At the anterior border of the masseter muscle, the duct turns medially through the buccal fat pad and buccinator muscle to its associated oral mucosa papillae [5, 6]. It is therefore possible, with sufficient anatomic knowledge and clinical experience, to locate the buccal branch of the facial nerve through intraoral incision and dissection along the parotid duct from the parotid papilla.
Second, the invasive extraoral approach that consists of skin flap elevation and wide dissection to the anterior border of the parotid gland is unnecessary. Wilhelmi et al. reported that the mean distance between the anterior border of the parotid gland and tragus was 38.8 mm . Therefore, a flap over 40 mm in length needs to be elevated from the preauricular incision line to find the buccal branch. However, with an intraoral approach, the range of dissection and depth of the elevated flap were no more than 20 mm from the incision line made just anterior to the parotid papilla. In addition to reduced morbidity from a smaller incision and less dissection, scar on the facial skin can also be avoided through the intraoral approach.
Finally, the intraoral approach required a shorter operation time. As mentioned above, because of a reduced dissection and smaller flap size, along with relatively convenient upper vestibular tunneling, the procedure allows for an easier, faster surgery. The presence of reliable anatomical structures—the parotid papillae and parotid duct—also helps reduce operation time.