Tumors are the most common indication for surgical exploration of the parotid gland. Most are benign mixed tumors that arise in the lateral lobe and are treated with wide excision, including a margin of normal tissue to prevent local recurrence. Exploration of the parotid area must include careful identification of the facial nerve and its branches, thus avoiding the major complication of facial nerve palsy. Malignant tumors are also seen and require a wide excision, which may include all or a portion of the facial nerve if it is involved. Lesions of the medial lobe may necessitate a total parotidectomy; a superficial parotidectomy is carried out first to identify and preserve the facial nerve before the medial lobe is explored.
It is essential that all patients undergoing parotid surgery be made aware of the possible loss of facial nerve function, with its resultant functional and cosmetic consequences. Men should shave themselves early on the morning of surgery; the hair about the ear may be cleared by the surgeon before draping.
Oral endotracheal anesthesia with a flexible coupling is utilized so that the anesthesiologist may be located at the patient's side, thus giving the surgeon adequate room. A short-acting muscle relaxant should be used for the endotracheal intubation. This allows the surgeon to identify motor nerves by direct stimulation (gentle pinch) during the dissection.
The patient is positioned on his or her back, and the face is turned to the side opposite the lesion. The head and neck are placed in slight extension, and the head of the table is elevated to reduce venous pressure in the head and neck.
After appropriate skin preparation with detergents and antiseptic solutions, sterile towel drapes are positioned to allow visualization of the entire ipsilateral side of the face.
The incision is carried in the crease immediately in front of the ear, around the lobule and up in the postauricular fold (Figure 1). It then curves posteriorly over the mastoid process and swings smoothly down into the superior cervical crease. The superior cervical crease is located approximately 2 cm below the angle of the mandible. It should be remembered that with the patient's neck extended and head turned to the side, the facial skin is pulled down onto the neck, and the incision should be made low enough that when the patient's head is returned to normal position, the incision does not lie along the body of the mandible. No incisions are made on the cheek itself. The cervical-facial skin flap is then elevated with sharp dissection to expose adequately the area of the tumor. This elevation takes place to the anterior border of the masseter muscle. A traction suture may be placed through the earlobe to hold this out of the operator's visual field (Figure 2). The masseteric parotid fascia has then been exposed, and the parotid gland can be seen within its capsule, bounded superiorly by the cartilages of the ear, posteriorly by the sternocleidomastoid muscle, and medially by the digastric and stylohyoid muscles.
The surgeon must understand clearly the surgical anatomy of the facial nerve. The main trunk of the facial nerve emerges from the stylomastoid foramen. It courses anteriorly and slightly inferiorly between the mastoid process and the membranous portion of the external auditory canal. The main trunk of the nerve usually bifurcates into the temporofacial and cervicofacial divisions after it enters the gland, but occasionally this occurs before entrance. The parotid gland is commonly described as being divided into superficial and deep lobes, the nerve passing between the two. These lobes are not anatomically distinct, because the separation is defined by the location of the nerve, which actually passes directly through the glandular parenchyma. The cervicofacial division bifurcates into the small platysmal or cervical branch and the marginal mandibular branch at the inferior margin of the gland. The latter courses within the platysma muscle just inferior to the horizontal ramus of the mandible, where it innervates the lower lip. Whereas most other branches of the facial nerve have numerous cross-anastomoses, the marginal mandibular branch has none; therefore division of this branch will always result in paralysis of half of the lower lip. Identification of the marginal mandibular branch before the main nerve trunk is defined is facilitated by the fact that 97 percent of the time it lies superficial to the posterior facial vein.
The buccal zygomatic division emerges from the anterior margin of the gland with numerous filamentous branches that innervate the muscles of facial expression, including the periorbital muscles and circumoral muscles of the upper lip. The temporal branch runs superiorly and innervates the frontal muscles. This branch has poor regenerative potential and no cross-anastomosis; injury to it will lead to permanent paralysis of the frontalis muscle.
The safest way of identifying the facial nerve is to locate and expose the main trunk. The anterior border of the sternocleidomastoid muscle is identified, as are the posterior facial vein and the greater auricular nerve, in the inferior portion of the incision (Figures 2 and 3). The capsule of the parotid gland then is mobilized from the anterior border of the sternocleidomastoid muscle, and dissection is carried down in an area inferior and posterior to the cartilaginous external auditory canal.
Several landmarks are utilized here in the search for the main trunk of the facial nerve. The sternocleidomastoid muscle is retracted posteriorly and the parotid gland anteriorly. The posterior belly of the digastric can be visualized as it pushes up into its groove (Figure 4), and the nerve lies anterior to this. The membranous portion of the canal is the superior landmark, and the nerve lies approximately 5 mm from the tip of this cartilage. By using these landmarks as well as a Faradic stimulator or gentle mechanical stimulation with forceps, the surgeon safely can locate the main trunk of the nerve (Figure 5). If mechanical stimulation is used, the instruments must not be clamped firmly on the tissue as a form of testing, but rather the tissue should be pinched gently as the muscles of the face are observed for motion. If an electrical nerve stimulator is used, it must be tested regularly to be certain that it is functioning in each test situation. A final landmark is a branch of the postauricular artery just lateral to the main trunk of the facial nerve. If the position or bulk of the tumor makes exposure of the main trunk of the facial nerve difficult, it may be identified distally. As indicated previously, the marginal mandibular branch lies superficial to the posterior facial vein in most circumstances. The buccal branch lies immediately superior to Stensen's duct, and identification of this duct will lead the operator to the buccal branch of the nerve. Dissection from distal to proximal must be carried out carefully, because the junction of other branches of the nerve may not be seen as easily as divisions of the nerve when the dissection is carried out in the opposite direction.
Numerous methods have been described for freeing the gland from the nerve. The safest dissection technique is the hemostat-scissors dissection. By dissecting bluntly with a fine hemostat and then cutting only the tissue exposed in the open jaws, the surgeon can protect the nerve (Figure 6). The gland may be elevated by clamping the tissue or by the use of holding sutures, and the two major divisions of the facial nerve are identified. Dissection may proceed anteriorly along any or all of the major divisions, depending upon the tumor's position. Since the majority of tumors occur in the lower portion of the lateral lobe, the upper segment of the gland is usually mobilized first (Figure 7). A moderate amount of bleeding may be expected, but this will be controllable with finger pressure, electrocoagulation, or fine ligatures. Once the tumor has been freed from the facial nerve, Stensen's duct will appear in the midanterior portion of the gland (Figure 8). Only the lateral lobe tributary is ligated, because medial lobe atrophy will occur if the main duct is tied. After removal of the lateral lobe, the isthmus and the medial lobe remain deep to the facial nerve; they will appear as small islands of parotid tissue and should represent only 20 percent of the total parotid gland. The lobe may be transected when the tumor and a surrounding portion of normal tissue have been completely separated from the facial nerve.
The wound is thoroughly irrigated and meticulous hemostasis obtained. A small perforated closed-suction Silastic catheter may be brought up through a stab wound and attached to a suction apparatus. The subcutaneous tissue is approximated with fine absorbable sutures followed by adhesive skin strips.
Temporary paresis from traction on the facial nerve may occur and usually clears in a few days to a week. If the greater auricular nerve has been divided in the course of the procedure, anesthesia in its distribution will be permanent.