Surgical Details of Parotidectomy
The parotid gland is divided into lateral and medial lobes. Most tumors occur in the lateral lobe which is described below. However, tumors can occur in the medial lobe with definitive treatment requiring total parotidectomy. This is accomplished by first performing a lateral lobectomy to identify the facial nerve before the dissection to remove the medial lobe is initiated.
Tumors (benign) – the most common indication for parotidectomy or removal of the tumor are benign mixed tissue tumors that originate in the lateral lobe of the parotid. Definitive treatment is wide resection (removal) with a surrounding margin of normal tissue to decrease the likelihood of local recurrence. For these tumors, the facial nerve and its branches are generally not surgically removed.
Tumors (malignant) – While not common, malignant tumors of the parotid gland do exist. Definitive treatment is total parotidectomy with wide excision with inclusion of the facial nerve and its branches if they are involved.
Metastatic disease – Surgical treatment of malignancies (particularly melanoma) located on the face usually includes sentinel lymph node mapping with the typical drainage basin surveyed including the parotid gland. Presence of a positive node or signal in the parotid necessitates at least a partial parotidectomy and resection of the gland.
Preoperative Workup and Preparation
The most important task to be accomplished preoperatively before parotidectomy is thorough counseling of the patient about the risks and consequences of injury to the facial nerve. All facial hair should be removed the morning of surgery.
The patient is placed supine (face up) and the head is turned away from the side of the lesion, with the head being placed in slight extension. The head of the operating room table is elevated slightly to reduce venous pressure in the parotid gland and surrounding tissues.
The incision for parotidectomy is made from the area immediately in front of the ear, traces the trajectory of the lower ear lobe , passes over the mastoid process, and then descends 2 cm below the angle of the mandible into the superior cervical crease. Care must be taken so that the skin that is pulled toward the side the head is turned is not incised in such a manner that the incision lies over the mandible when the head is straightened.
Surgical Details of the Procedure
1. In parotidectomy, the dissection is begun to expose the main trunk of the facial nerve.
2. Sharp dissection is used to incise the subcutaneous tissue.
3. The anterior border of the sternocleidomastoid, the greater auricular nerve, and the posterior facial vein with the overlying marginal mandibular branch of the facial nerve are all identified.
4. Dissection in parotidectomy is done in a manner to avoid the above identified structures until the capsule of the parotid is identified.
5. The capsule of the parotid is then dissected free from the anterior border of the sternocleidomastoid.
6. Most surgeons then doubly ligate the posterior facial vein with 2-0 silk ties and transsect this with care taken to avoid injury to the adjoining nerves.
7. The dissection is then continued inferiorly and posteriorly to the external auditory canal.
8. The sternocleidomastoid is then retracted posteriorly and the parotid gland anteriorly.
9. The posterior belly of the digastric muscle is then identified along with the membranous portion of the external auditory canal.
10. The facial nerve is then identified lying anterior to the digastric muscle pushing up into the surgical field and inferior to the above membrane approximately 5 mm.
11. If the position of the tumor makes the visualization of the facial nerve difficult, the dissection can be completed in a distal to proximal fashion.
12. If a distal to proximal dissection strategy is performed care must be taken to identify and void injury to the buccal branch, which lies immediately superior to Stensen’s duct.
13. Once the facial nerve has been tentatively identified, confirmation is done by using gentle mechanical stimulation or a Farradic stimulation to produce the appropriate muscle contraction.
14. If facial nerve is not identified by the above anatomic guides, a search for the posterior auricular artery is made that most usually lies just lateral to the main trunk of the facial nerve.
15. The gland is then separated from the nerve and its’ branches through blunt dissection using a fine-tipped hemostat and scissors in lieu of Bovie cautery.
16. Some surgeons performing parotidectomyuse gentle retraction of the gland by grasping the parenchyma with forceps or a hemostat and pulling it upwards.
17. The dissection is usually down in a superior to inferior fashion to take advantage of normal tissue and tissue planes, as most tumors are located in the inferior part of the gland.
18. Some bleeding is unavoidable and is controlled with carefully applied low voltage electrocoagulation (i.e., fine-tipped Bovie cautery) and fine silk sutures.
19. The lateral branch of Stensen’s duct is then located and ligated with fine silk ties (e.g., 3-0) and divided with a scissors.
20. Care must be taken in parotidectomy to not injure or ligate the medial branch or main trunk of Stensen’s duct as this will result in medial lobe atrophy.
21. Once the portion of the lateral lobe that contains the tumor and a margin of normal surrounding gland has been completely dissected free, the parenchyma is transected.
22. The isthmus and remaining medial lobe should be carefully inspected for bleeding and the wound is thoroughly irrigated.
23. A small closed-suction Silastic catheter (i.e., small Jackson Pratt drain) is then placed over the remaining 20% of the parotid gland with a small stab wound brought through the skin posterior to the face.
24. The subcutaneous tissues are approximated using interrupted dissolvable sutures.
25. The skin is closed after parotidectomy using a running dissolvable subcuticular stitch such as 4-0 Monocryl.
25. Adhesive skin strips are placed on the wound edges.
Temporary paralysis of the facial muscles is not uncommon in parotidecomy and should clear by seven days. Sensory disturbances may be more lasting and include permanent numbness, particularly if the greater auricular nerve has been transected.
Unfortunately, permanent paralysis can occur after parotidectomy. Division of the marginal mandibular branch off the cervical segment of the facial nerve results in permanent paralysis as this branch lacks cross-anastomoses. The temporal branch also lacks significant cross-anastomoses and has poor regenerative ability. Significant injury to this nerve results in loss of function to the frontalis muscle (inability to raise eyebrows.)