Superficial Parotidectomy
Pavel Dulguerov
INTRODUCTION
Pathologic swellings of the parotid gland are the main indication for parotidectomy. Swellings of the parotid gland may be divided into two broad categories: diffuse and localized. Diffuse swellings usually represent inflammation of the parotid gland and/or infections that are generally treated with medication or sometimes sialendoscopy. Localized swellings represent tumors in the parotid gland or cyst-like conditions (Table 25.1), and their treatment consists of some form of parotidectomy.
Both benign and malignant tumors occur in the parotid gland. The majority (˜80%) of parotid tumors are benign, and the most common tumor of the parotid gland is pleomorphic adenoma. This peculiar benign tumor tends to recur if not completely excised and may degenerate with time into its malignant form, carcinoma ex pleomorphic adenoma. Surgery for recurrent pleomorphic adenoma is associated with a higher incidence of complications, in particular, facial paralysis.
The goals of parotid surgery are:
Prevention of recurrence, which requires a complete removal of the tumor, ideally with a cuff of normal parotid tissue and without tumor seeding by spillage
Protection and preservation of the facial nerve unless the nerve is directly involved by a neoplasm (almost always malignant)
Prevention of Frey syndrome
Prevention of other complications, such as salivary gland fistula, hematoma, wound infection, and anesthesia of the skin
Optimal cosmetic results
To achieve these goals, the parotid surgeon should have extensive knowledge of parotid pathology, including the exact clinical significance of each parotid tumor (Table 25.1) and intimate knowledge of the anatomy of the facial nerve.
Relevant Anatomy
In addition to the parotid gland, the parotid space contains (a) arteries (the external carotid and its terminal branches, superficial temporal and internal maxillary); (b) veins (the retromandibular or retrofacial, which is generally (in 71%) posterior to the branches of the facial nerve); (c) lymphatic vessels and lymph nodes draining the scalp and face and contained within the gland because these structures develop before the gland is completely surrounded by fascia; and (d) nerves (the facial, the greater auricular, and the auriculotemporal).
Fascias
The fascia in the neck is divided into a superficial and a deep layer. The superficial fascia is usually a thin connective tissue layer under the dermis, and, as a rule, vessels and nerves are located deep to it. The superficial
cervical fascia covers the superficial aspect of the platysma muscle and splits to also cover its deep surface. It is attached to overlying skin with thin fibrous septa and continues on the face and scalp to extend all the way to the vertex where it covers the epicranius muscle.
cervical fascia covers the superficial aspect of the platysma muscle and splits to also cover its deep surface. It is attached to overlying skin with thin fibrous septa and continues on the face and scalp to extend all the way to the vertex where it covers the epicranius muscle.
TABLE 25.1 Etiology of Parotid Masses and a Concise Summary of Treatment | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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 FIGURE 25.1 Anatomical cross section showing the fascial layers lateral to the parotid gland. M, mandible and masseter muscle; P, parotid gland; S, submandibular gland; SCM, sternocleidomastoid; SF, superficial fascia; T, temporalis muscle; Z, zygomatic bone. The discussion is centered about the fascia layers included in the fascia marked by ?. It should contain the SMAS, which is the facial extension of the platysma and its fascia, and the facial extension of the deep cervical fascia. Whether this fascial layer can be divided into two layers, with a separate parotid fascia, is debatable. The superficial fascia below the epidermis is clearly seen. |
The recognition of the superficial musculoaponeurotic system (SMAS) and its importance in face-lift surgery added to the controversy about the exact composition of the fascia overlying the parotid gland (Fig. 25.1). While it is now accepted that the SMAS layer is a continuation of the superficial fascia-platysma layer in the neck, it is unclear (1) whether there is a distinct superficial fascial layer lateral to the SMAS, (2) whether the parotid fascia is a separate layer deep to the SMAS, and (3) whether the deep cervical fascia participates in the lateral parotid coverage. The SMAS is a thick solid layer below the subcutaneous adipose tissue from which fibrous septa extend laterally to the skin, interpreted by some as a separate fascia; a distinct parotid fascia is present covering the gland, but it is extremely thin. In addition, significant individual variation is present in the thickness of these different layers.
Facial Nerve
The facial nerve, after exiting the stylomastoid foramen, is almost immediately surrounded by the parotid gland. The nerve enters the parotid space between the digastric and stylohyoid muscle. The nerve is lateral (more superficial) to the styloid process and to the most superior extension of the posterior belly of the digastric muscle. The point of entry of the facial nerve into the parotid gland has been described along a line uniting the tip of the tragus to the angle of the jaw. Within the parotid gland, the facial nerve takes an upward and medianward concave course. It is in close relation to the stylomastoid artery, which arises from the occipital or post-auricular branches of the external carotid artery and is responsible for vascularization of the mastoid segment of the facial nerve. The distance between the main trunk of the facial nerve and the closest point of the digastric muscle was found to be 9 ± 2.7 mm, and the depth of the trunk of the facial nerve from the skin surface was measured in cadavers as 20.1 ± 3.1 mm.
The facial nerve always branches within the parotid gland into two main divisions: the temporofacial and cervicofacial divisions. Several generalizations can be made about the intraparotid anatomy of the facial nerve (Fig. 25.2):
The buccal ramus can originate from either the temporofacial or the cervicofacial division.
Branches located at the extremities of the nerve distribution receive fewer anastomosis with other branches.
The majority of anastomosis occurs between the buccal and zygomatic divisions, forming the so-called plexus.
The number of anastomosis decreases in caudal branches, with the marginal mandibular branch receiving anastomosis in only 6.3%.
There is no anastomosis between the cervical and other branches.
The anastomosis is more extensive when the buccal branch arises from the cervicofacial division.
 FIGURE 25.2 Branching patterns of the extratemporal facial nerve. The data were obtained from the dissection of 350 cervicofacial halves. The division patterns of the facial nerve are classified in types (I to VI), and the relative frequency of each type is marked. Type I: no anastomosis between facial branches. Type II: numerous anastomosis between zygomatic and buccal branches (parastenon anastomosis, zygomatic loop). Type III: single anastomosis between zygomatic and buccal branch, located distal anterior to the parotid tissue. Type IV: anastomosis between temporal and zygomatic branches and extensive anastomosis between zygomatic and buccal branches. Type V: combination of type II and III with extensive anastomosis between zygomatic and buccal branches. Type VI: plexiform anastomosis between temporal, zygomatic, buccal, and marginal mandibular rami. Type VII: double main facial trunk (3%). (Reprinted from Davis RA, Anson BJ, Budinger JM, et al. Surgical anatomy of the facial nerve and parotid gland based upon a study of 350 cervicofacial halves. Surg Gynecol Obstet 1956;102:385-412.) |
Anterior to the parotid gland, the facial nerve branches are covered by the SMAS and the masseteric fascia. Further nerve divisions are observed as branches approach the muscle they innervate, always on the deep aspect of the muscle.
Parotid Lobes
The parotid gland was viewed as having two lobes, where “the facial nerve is like the meat of the sandwich,” and this concept helped devising partial parotid resections, such as superficial parotidectomy. While this lobe concept was abandoned, the facio-venous plane is an important concept in parotid surgery. It is important to realize that neither is this plane strictly vertical, nor is the same amount of parotid tissue found superficial to the facial nerve: In the superior portion of the gland, the temporal and zygomatic branches of the facial nerve are more superficial than the facial nerve branches in the inferior portion of the parotid. In addition, as the plane of the facial nerve is followed anteriorly, it becomes more superficial, with less parotid tissue covering the nerve.
Parotidectomy Classification
Surgical resection of the parotid gland includes some form of parotidectomy. Because of the great confusion about the various naming in parotid surgery, The European Salivary Gland Society (ESGS) recently organized a classification of parotidectomies: the gland is divided in five levels (Fig. 25.3) and the operation termed according to the level removed. The classical superficial parotidectomy corresponds to the removal of levels I and II; it is thus called parotidectomy I-II.
 FIGURE 25.3 ESGS division of the parotid gland in five levels. The division in five levels: I (lateral superior), II (lateral inferior), III (deep inferior), IV (deep superior), and V (accessory). The superior level is the area corresponding to the branch of the temporofacial nerve and the inferior level the area of the cervicofacial branch. (Modified from Quer M, Pujol A, Leon X, et al. Parotidectomies in benign parotid tumours: “Sant Pau” surgical extension classification. Acta Otorrinolaringol Esp 2010;61:1-5.) |
HISTORY
Most patients who are candidates for parotidectomy present with the history of a slow-growing painless mass in the parotid gland and no other associated symptoms. While a complete medical history is necessary prior to ordering further tests, it will most often remain unremarkable.
A patient with such a slow-growing mass in the parotid gland will typically have a pleomorphic adenoma. If a heavy smoking history is present or if bilateral parotid masses are present, Warthins tumor is a likely diagnosis. A malignant tumor will be suggested by a constellation of symptoms including a rapidly growing mass, pain, facial weakness, infiltration of the skin, and cervical lymphadenopathy. The history of treatment for skin cancer should make one suspicious of a metastatic cancer to a peri- or intraparotid lymph node.
Obstruction of the duct with secondary infections usually presents with pain that typically increases during meals and could thus be differentiated from a parotid tumor by history.
PHYSICAL EXAMINATION
A careful examination of the head and neck is necessary, starting with inspection of the parotid region, looking for the location of the mass or skin erosion. Thorough evaluation of the skin of the pinna, preauricular and malar area, forehead, and scalp is mandatory to look for a previously treated or undiagnosed primary cancer of the skin. Otoscopy should be performed, again looking for skin lesions but also for infiltration of the skin of the external auditory meatus from an adjacent parotid tumor. Ipsilateral and contralateral facial nerve function should be evaluated with a standardized grading system. I prefer the regional modification of the House-Brackmann scale because the global scale gives little information about individual branches.
After inspection, palpation of the gland and the mass is carried out assessing its size, consistency, mobility, and location. Intraoral examination should investigate the palate and lateral pharynx for asymmetry suggesting parapharyngeal extension. The neck is then palpated to detect a lymphadenopathy.
INDICATIONS
The treatment of most localized masses in the parotid gland is surgical excision, and only rarely could any form of medical therapy be curative or observation recommended.
CONTRAINDICATIONS
The general teaching is that any mass in the parotid gland should be excised to provide a final diagnosis and usually definitive treatment. There are several exceptions to this attitude:
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