Understanding the origin of benign salivary gland tumors requires knowledge of the embryology and ultrastructure of the normal salivary gland. The major salivary glands originate from ectoderm and begin their development during the sixth week of gestation as solid, ridgelike ingrowths of the oral epithelium.² These ingrowths continue to develop into tubules that later become the ductal system of the salivary glands. In the major salivary glands both serous and mucous cells are arranged into acini that are drained by a series of ducts. An intercalated duct drains into a striated duct, which empties into an excretory duct. Contractile myoepithelial cells surround the acini and intercalated ducts and help in draining saliva through the ductal system (Fig. 87-1). The parotid gland consists of predominately serous acini. The submandibular gland is composed of a mixture of serous and mucinous acini, whereas sublingual gland and minor salivary glands scattered throughout the upper aerodigestive tract contain predominantly mucinous acini.

Figure 87-1. Structural elements of the salivary gland unit.

Histogenesis of Salivary Neoplasms

At least two theories of tumorigenesis have been proposed for salivary gland neoplasms.³ In the multicellular theory, each type of neoplasm is thought to originate from a distinctive cell type within the salivary gland unit. According to this theory, Warthin’s and oncocytic tumors are thought to arise from striated ductal cells, acinic cell tumors from acinar cells, and mixed tumors from intercalated duct and myoepithelial cells.⁴ This theory is supported by the observation that all differentiated salivary cell types retain the ability to undergo mitosis and regenerate.^5,⁶ An alternative theory, the bicellular reserve cell theory, assumes that the origin of the various types of salivary neoplasms can be traced to the basal cells of either the excretory or the intercalated duct. According to this theory, either of these two cells can act as a reserve cell with the potential for differentiation into a variety of epithelial cells.⁷ Hence despite the seeming heterogeneity of salivary tumors, all of them are thought to arise from one of two pluripotential cell populations. In this model, adenomatoid tumors including pleomorphic adenoma and oncocytic tumors are derived from the reserve cell of the intercalated duct, whereas epidermoid tumors, such as squamous cell carcinoma and mucoepidermoid carcinomas, are derived from the reserve cell of the excretory duct.⁸ Some reports provide molecular evidence to support the reserve cell theory of salivary gland tumorigenesis.⁹

Recent efforts to identify biomarkers of salivary neoplasia have focused on methylation patterns. Williams and colleagues ¹⁰ investigated methylations status and protein expression of four tumor suppressor genes (DAPK, MGMT, RARB2, and RASSF1) in the largest cohort study of benign and malignant salivary neoplasms to date. The authors found benign and malignant salivary tumor differed in the frequency and pattern of gene methylation. They postulate methylation may aid in diagnosis and targeted therapy for salivary neoplasms.¹⁰ Maruya and colleagues analyzed the gene expression profile of 18 primary tumors representing the major benign subtypes using a membrane-based DNA microarray platform. Of the 5000 genes arrayed, S-100 beta, galectin-9 isoform, vimentin, and tyrosine kinase receptor were more highly expressed in adenomas than in carcinomas.¹¹

Etiology

The etiology of salivary gland neoplasms, like most other types of tumors, remains unknown. However, there is growing evidence that certain environmental factors such as radiation, viruses, diet, and certain occupational exposures may increase the risk of developing tumors of the salivary glands. In addition to environmental factors, specific genetic abnormalities associated with the development of some types of salivary tumors have recently been well characterized.

Radiation

There is increasing evidence to suggest that exposure to ionizing radiation may increase the risk of developing tumors of the salivary glands. In 1996 the Radiation Epidemiology Branch of the National Cancer Institute published a study on the risk of developing salivary gland tumors among atomic bomb survivors.¹² The study indicated a higher radiation-related risk of developing both benign and malignant salivary gland tumors, as compared with the general population. Dose-response analyses found statistically significant increases in risk with increasing A-bomb dose for both cancer and benign tumors. The risk was higher for malignant tumors, especially mucoepidermoid carcinoma. Among those with benign neoplasms, Warthin’s tumor showed the highest dose-response–related risk.

Radiation therapy to the head and neck, especially if it encompassed the salivary glands, may also be a risk factor in the development of salivary gland tumors.¹³ A recent study found a 4.5-fold increase in the incidence of salivary gland cancer and a 2.6-fold increase of benign tumors among persons exposed to scalp irradiation compared with matched controls.¹⁴ The mean length of latency period until tumor development was 11 years for malignant tumors and 21.5 years for benign. The study also demonstrated a clear dose response effect for cancer and benign tumors, suggesting that ionizing radiation may play an important role in salivary gland tumorigenesis.

Viral

Although Epstein-Barr virus (EBV) has been consistently associated with lymphoepithelial carcinoma of the salivary gland in the Asian population, there is no evidence of a causal role of EBV in other primary salivary gland neoplasms.¹⁵ Pollock and colleagues¹⁶ failed to demonstrate any positive signal by in situ hybridization for EBV RNA in 42 benign salivary gland neoplasms. Other viruses including human papillomavirus, human herpesvirus-8, and cytomegalovirus do not appear to have any etiologic role in salivary gland neoplasms.¹⁷

Other Factors

Although tobacco use was not associated with a higher incidence of malignant salivary neoplasms, Warthin’s tumor is strongly associated with cigarette smoking.¹⁸ Occupational exposure to silica dust was linked to a 2.5-fold increased risk of cancer of the salivary gland.¹⁹ The risk was also elevated among rubber workers exposed to nitrosamines.²⁰ Dietary analyses revealed a possible protective effect for a diet high in polyunsaturated fatty acids.^19,²¹ Similar to breast cancer, women with history of early menarche and nulliparity had an increased risk of cancer of the salivary gland, which may be due to a hormonal effect.²² Whether these occupational, dietary, or hormonal factors have any association with the risk of developing benign tumors of the salivary glands remains unknown.

Genetic Factors

Recent developments in the field of molecular biology and human genomics have shed light on the genetic basis of developing several types of neoplasms including tumors of salivary gland origin. A study of several types of salivary gland tumors using comparative genomic hybridization found specific genetic alterations in different types of salivary gland tumors and involvement of several chromosomes in the alterations.²³ Genetic aberrations associated with the salivary gland neoplasia include allelic loss and point mutation, structural rearrangement of chromosomal units (most commonly translocations), the absence of one chromosome (monosomy), and the presence of an extra chromosome (polysomy). Any of these genetic aberrations may be the only karyotypic anomaly indicating an early event in tumor initiation, or several genetic alterations may coexist, which are more likely to be associated with tumor progression and more aggressive biologic behavior.^9,²⁴

Incidence

Salivary gland tumors are relatively rare and constitute 3% to 4% of all head and neck neoplasms. The majority (70%) of salivary gland tumors arise in the parotid gland (Fig. 87-2). Although the majority of minor salivary gland tumors are malignant, three fourths of parotid tumors are benign (Fig. 87-3). Spiro²⁵ reviewed the Memorial Sloan-Kettering experience with salivary neoplasms over a 35-year period. The distribution of these 2807 patients is shown in Table 87-1. Benign neoplasms constituted 54% (1529 patients) of all tumors. Pleomorphic adenoma (1280 patients) constituted 84% of benign tumors and 45% of all salivary gland neoplasms. Warthin’s tumor was the second most benign tumor and comprised 12% (183 patients) of all benign tumors.

Figure 87-2. The site of origin of salivary neoplasms.

Figure 87-3. The incidence of benign and malignant salivary neoplasms according to the site of origin.

Table 87-1 Distribution of 2807 Salivary Neoplasms

Histology	Number of Patients	Percent
Pleomorphic adenoma	1274	45.4
Warthin’s tumor	183	6.5
Benign cyst	29	1.0
Lymphoepithelial lesion	17	0.6
Oncocytoma	20	0.7
Monomorphic adenoma	6	0.2
Mucoepidermoid carcinoma	439	15.7
Adenoid cystic carcinoma	281	10.0
Adenocarcinoma	225	8.0
Malignant mixed tumor	161	5.7
Acinic cell carcinoma	84	3.0
Epidermoid carcinoma	53	1.9
Other (anaplastic)	35	1.3
Total	2807	100

Patient Evaluation

Clinical Features

Regardless of whether they are benign or malignant, tumors of the parotid gland usually present as a painless swelling. Benign tumors are usually present for a long duration and have a slow growth rate. However, patients may indicate that they incidentally noticed the appearance of a “recent” lump. The acute onset of a painful swelling of the parotid gland usually indicates an inflammatory process. Acute bacterial parotitis is usually diagnosed in association with sialolithiasis of the parotid gland or in patients who are elderly, malnourished, dehydrated, or immunocompromised. Acute viral parotitis is most commonly due to “mumps”; however, other viral infections may present with acute parotid swelling. Sjögren’s syndrome and other forms of autoimmune parotitis usually present with bilateral parotid swelling, although in some patients this may be asymmetric or even unilateral. Obstruction of Stensen’s duct with a stone may lead to an acute painful swelling of the parotid gland. Rapid increase in size of a longstanding mass should raise the suspicion of malignant transformation of a preexisting benign tumor, but it may be due to inflammation or cystic degeneration most commonly associated with Warthin’s tumor. Patients presenting with a mass in the parotid gland should be asked about a history of cancer of the scalp or facial skin. Metastasis to the parotid gland from skin cancer including melanoma may be diagnosed by a careful examination of these areas for evidence of a skin cancer or a scar of previous excision.

On examination, benign tumors of the parotid gland are usually well defined, nontender, and freely mobile. They are commonly located in the “tail” of the parotid gland but may be present anywhere in the superficial or deep lobe. Tumors may originate entirely from the deep lobe (Fig. 87-4) or extend from the superficial to the deep lobe through the relatively narrow stylomandibular tunnel, giving the appearance of a dumbbell tumor (Fig. 87-5). In either case, the tumor may extend to the parapharyngeal space and displace the oropharyngeal wall medially (Fig. 87-6). The presence of facial nerve paresis or paralysis, pain, fixation of the mass to the overlying skin or underlying structures, and associated cervical adenopathy usually indicate the presence of malignancy. It should be noted, however, that these findings usually indicate local or regional extension of the tumor, and the diagnosis of parotid malignancy should not await the development of these signs and symptoms. The possibility of malignancy should be ruled out in patients presenting with any mass in the parotid gland. This will usually require cytologic or histologic evaluation with a fine-needle biopsy, or parotidectomy, respectively.

Figure 87-4. A, Axial and B, coronal diagrams of round tumor passing posterior to stylomandibular ligament to appear as mass in parapharyngeal space. Arrows indicate potential routes of tumor spread.

Figure 87-5. A, Axial and B, coronal diagrams of relationship of dumbbell tumor to stylomandibular ligament. Dumbbell tumor enters parapharyngeal space through stylomandibular membrane between the mandible and the stylomandibular ligament. Arrows indicate potential routes of tumor spread.

Figure 87-6. Pleomorphic adenoma of the deep lobe of a parotid gland, causing medial displacement of the palate and tonsil.

Benign tumors of the submandibular gland are relatively uncommon and usually present as a painless, mobile mass in the submandibular triangle. Involvement of the overlying skin or fixation to the mandible usually indicates local extension of a malignant tumor. Ipsilateral weakness or numbness of the tongue indicates perineural spread of malignancy along the hypoglossal or lingual nerves, respectively. Weakness of the marginal mandibular branch of the facial nerve also indicates perineural extension of a malignant tumor. Enlargement of the submandibular or upper cervical lymph nodes may be due to reactive lymphadenopathy associated with submandibular sialadenitis, but it usually indicates regional metastasis of malignancy in the submandibular gland.

Benign tumors of the minor salivary glands are rare. Most tumors arising from the minor salivary glands are malignant (see Fig. 87-3). However, similar to the major salivary glands, pleomorphic adenoma is the most frequent benign tumor of the minor salivary glands. The clinical presentation depends on the site of origin, and the most common sites include the palate, parapharyngeal space, and the lacrimal gland.

Fine-Needle Aspiration Biopsy

Fine-needle aspiration biopsy (FNAB) has been widely recognized and well established as an accurate technique in the diagnosis of salivary gland neoplasms. Numerous studies have reported an exceptionally high degree of sensitivity, specificity, and predictive value for FNAB. The overall sensitivity ranges from 85.5% to 99%, and the overall specificity ranges from 96.3% to 100%.²⁶^–²⁸ In general, diagnostic accuracy is higher for benign than for malignant salivary gland tumors.^29,³⁰ The accuracy of FNAB, however, depends greatly on the experience of the cytopathologist, as well as the overall volume of patients with salivary neoplasms evaluated in any given institution. The most common source of diagnostic error of FNAB is inadequate sampling.³¹ The use of ultrasound-guided FNAB may be of help in cases in which it is difficult to obtain a representative sample, and it enhances the overall diagnostic accuracy of the technique.^32,³³ Despite its overall high accuracy, several significant but uncommon areas can lead to diagnostic difficulties, with the potential for clinically important diagnostic errors.²⁹ The most frequent problems involve variations in the expected cytology of pleomorphic adenoma. Also, there are several benign-malignant “look-alike” pairs of lesions. The first of these is related to small-cell epithelial neoplasms of low nuclear grade; the most frequent problem is between basal cell adenomas and adenoid cystic carcinoma, particularly the solid (anaplastic) type. The next area contrasts mucoepidermoid carcinoma with its cytologic mimic, benign salivary gland duct obstruction. The final difficulty in salivary gland aspiration contrasts large-cell epithelial lesions of low nuclear grade: oncocytic proliferations and acinic cell carcinoma.³⁴

In addition to being accurate, FNAB is safe, simple to perform, and relatively inexpensive. However, one essential question is worth asking. Is FNAB really necessary in the evaluation of salivary gland masses? Would it change the course of management on the basis of clinical assessment? In an attempt to answer this question, Heller and colleagues ³⁵ performed a study to determine the impact of FNAB on patient management. One hundred patients underwent FNAB of major salivary gland masses. The physician’s initial clinical impression was compared with the FNAB diagnosis and the final diagnosis in each case. Overall, FNAB resulted in a change in the clinical approach to 35% of the patients. Examples of such changes in the planned management included avoiding surgical resection for lymphomas and inflammatory masses and adopting a more conservative approach with benign tumors in elderly and high-surgical-risk patients. FNAB also allows better preoperative counseling of patients regarding the nature of the tumor, the likely extent of resection, management of the facial nerve, and the likelihood of a neck dissection. Such information is not only important in treatment planning but also helps alleviate an already high level of anxiety among patients and their families.

The possibility of tumor seeding is a commonly cited argument against the routine use of FNAB in patients with salivary gland tumors. To address these issues, Mukunyadzi and colleagues ³⁶ recently reviewed 94 resected salivary gland masses for infarction, hemorrhage, and needle track tumor seeding, as well as fibrosis after FNAB. They concluded FNAB with a 25-gauge needle is safe and does not significantly alter the histologic diagnosis because tissue effects did not preclude accurate diagnostic interpretation in any case.³⁶

Imaging

The routine use of imaging in patients with small, well-defined masses of the superficial lobe of the parotid gland is probably not warranted because the results of imaging are not likely to change the treatment plan. However, tumors that present with clinical findings suggestive of malignancy, tumors arising from the deep lobe of the parotid gland or the parapharyngeal space, and, tumors of the submandibular and minor salivary gland should be evaluated with high-resolution imaging. In such cases, imaging provides accurate delineation of the location and extent of tumor, its relation to major neurovascular structures, perineural spread, skull base invasion, and intracranial extension.³⁷

Computed Tomography and Magnetic Resonance Imaging

In evaluating patients with tumors of the salivary glands, both computed tomography (CT) and magnetic resonance imaging (MRI) provide information that is superior to that provided by other imaging techniques or by physical examination.³⁸ The normal parotid gland has a high fat content and is easily visualized on both CT and MRI. Therefore both techniques can demonstrate whether a mass in that region is intraglandular or extraglandular. Generally, neither CT nor MRI provides information regarding the specific histologic diagnosis, except rarely.³⁹ An example of such a rare scenario is with lipoma of the parotid gland (Fig. 87-7). The MRI signal characteristics of parotid masses, however, may be suggestive of certain diagnosis.⁴⁰ For example, if a parotid gland mass is bilateral, it is more likely to be Warthin’s tumor, especially if it does not enhance. Less likely, it could be lymphoepithelial cyst or necrotic lymph node. A unilateral, nonenhancing mass with a high T2 signal is more likely to be a Warthin’s tumor and less likely a necrotic lymph node or first branchial cleft cyst. If the mass is unilateral, shows postcontrast enhancement, has a high T2 signal, and does not invade surrounding tissue planes, it is more likely to be a pleomorphic adenoma (Fig. 87-8). An intermediate to low T2 signal mass, with or without invasion of surrounding tissue planes, is more likely to be a malignant mass such as adenoid cystic or mucoepidermoid carcinoma.⁴¹

Figure 87-7. A 40-year-old male presented with a large, painless, slow-growing parotid mass. Fine-needle aspiration biopsy was indeterminate. A, Lateral view. B, An axial computed tomography (CT) with intravenous contrast demonstrating a large, rounded, well-defined mass with smooth borders in the parotid gland. The mass was nonenhancing and had the same density as the subcutaneous fat. These findings were pathognomonic of parotid lipoma. C, A superficial parotidectomy was performed, and the diagnosis was confirmed.

Figure 87-8. Pleomorphic adenoma of the parotid gland. The mass originated from the deep lobe of the gland and extended to the parapharyngeal space through the stylomandibular tunnel, where it was somewhat constricted, giving the appearance of a dumbbell. Note the medial displacement of the oropharynx. The mass has well-defined borders and does not invade surrounding structures. The mass is isointense on T1-weighted magnetic resonance imaging (MRI) (A) and has a high signal intensity on T2-weighted MRI (B). These signal characteristics are highly suggestive of pleomorphic adenoma.

MRI is also superior to CT in demonstrating the internal architecture of salivary gland tumors in a multiplanar fashion and in delineating the interface between tumor and normal salivary gland.⁴² In contrast to benign tumors, which invariably have well-defined margins (see Fig. 87-8), malignant tumors may exhibit irregular margins (Fig. 87-9). Extension of the tumor beyond the fascial confines of the gland can be adequately seen on both CT and MRI and should raise the suspicion of malignancy.⁴³ Bone destruction of the mandible or skull base is best visualized on CT, whereas bone marrow involvement is better demonstrated on MRI. Both studies can adequately evaluate the neck for metastatic adenopathy. CT has the advantage of being less expensive and more available than MRI.

Figure 87-9. T1-weighted magnetic resonance imaging with gadolinium of a patient with mucoepidermoid carcinoma of the parotid shows the tumor to have irregular border and is indistinct from the normal parotid gland. Note complete encasement, rather than displacement of both the internal (white arrow) and external carotid arteries (black arrow) in both the axial (A) and coronal (B) images.

Although parapharyngeal space masses are well visualized by both techniques, they are better delineated with MRI than CT. This is because of the different signal intensity of tumor, fat, and muscle on MRI. The differential diagnosis of parapharyngeal masses includes deep lobe parotid tumors, minor salivary gland tumors, and neurogenic and vascular tumors. Most salivary tumors have low-to-intermediate T1 signal intensities and intermediate-to-high T2 signal intensities. Deep lobe parotid tumors and minor salivary gland tumors of the parapharyngeal space lie in the prestyloid compartment, anterior to the carotid artery, and displace the parapharyngeal fat medially (Figs. 87-10 and 87-11). Deep lobe tumors are connected to the parotid gland at least in one imaging section, whereas minor salivary gland tumors are completely surrounded by fat (see Fig. 87-11). By contrast, neurogenic tumors and glomus tumors lie in the poststyloid compartment, posterior to the carotid artery, which is displaced anteriorly (Fig. 87-12). Neurogenic tumors usually enhance intensely with gadolinium, whereas glomus tumors have characteristic serpiginous flow voids (salt and pepper appearance) on MRI.

Figure 87-10. Large pleomorphic adenoma of the parotid gland. Axial computed tomography with gadolinium. The tumor involves the superficial and deep lobe of the parotid gland and lies anterior to the styloid process (prestyloid) (white arrowhead). The fat of the parapharyngeal space is displaced medially, and the carotid artery displaced posteriorly. The isthmus of tumor between the superficial and deep components passes through the stylomandibular space and is therefore relatively narrow, giving the appearance of a dumbbell (black arrowheads).

Figure 87-11. In contrast to the dumbbell tumor depicted in Figure 87-10, this pleomorphic adenoma originates entirely from the deep lobe of the parotid gland (black arrow) and lies entirely medial to the stylomandibular tunnel. Pleomorphic adenomas originating from the minor salivary glands of the parapharyngeal space have a similar appearance on high-resolution imaging but are not connected to the parotid gland. Regardless of their origin, salivary gland tumors of the parapharyngeal space will occupy the prestyloid compartment and displace the carotid artery posteriorly (white arrow).

Figure 87-12. On magnetic resonance imaging (MRI), tumors of the poststyloid compartment are usually located behind the carotid artery, displacing it anteriorly (arrow). Glomus tumors have characteristic serpiginous flow voids on MRI, giving a “salt-and-pepper appearance.”

Recently, new MR technologies such as dynamic contrast-enhanced MRI, diffusion-weighted MRI, and proton MR spectroscopy have shown promising results in the differentiation between benign and malignant salivary gland tumors.⁴⁴ Further research with larger-scale studies on these particular MR methods is necessary.

Ultrasonography

Ultrasonography has the advantage of being inexpensive, noninvasive, simple to perform, and is virtually free of complications. It can be used to differentiate solid from cystic masses in the salivary glands, and most salivary gland diseases can be diagnosed sonographically.³² Ultrasound guidance may also enhance the accuracy of FNAB in nonpalpable tumors and in masses with a highly heterogeneous architecture.⁴⁵

Color Doppler Sonography

Color Doppler sonography has been recently used to evaluate the vascular anatomy of the salivary glands. It can distinguish between the physiologic changes that occur during salivary stimulation in normal subjects and the flow alterations that occur in diseased glands.⁴⁶

Positron Emission Tomography

PET scans have not gained wide application in imaging of tumors of the salivary gland for several reasons. First, tumors of the salivary glands have a variable and inconsistent uptake of F-18 fluorodeoxyglucose (FDG), which is the most commonly used radiotracer with PET scans, and therefore FDG PET is unreliable both in tumor detection and in distinguishing benign from malignant salivary tumors.⁴⁷ Second, competing techniques such as CT, MRI, and even clinical examination already have a high degree of accuracy. Third, high-resolution studies such as CT and MRI provide anatomic detail required for treatment planning that is unavailable from FDG PET images. Finally, the high cost of FDG PET prohibits its widespread use. Research is ongoing with PET scans. Uchida and colleagues⁴⁸ recently proposed combining FDG PET with Tc-99m pertechnetate salivary gland scintigraphy for differentiating various parotid gland tumors in patients with nondiagnostic needle aspiration.

Pleomorphic Adenomas

Pleomorphic adenomas, also known as benign mixed tumors, are the most common neoplasms of the salivary gland. The term pleomorphic was chosen to describe these tumors because they possess morphologic diversity with both epithelioid and connective tissue components in various proportions. Although highly debated in the past, most now agree that pleomorphic adenomas originate from an uncommitted reserve cell of the intercalated duct that has the potential to differentiate into epithelial and myoepithelial cells. Pleomorphic adenomas occur most frequently in the major salivary glands but may also arise from the minor salivary glands of the upper respiratory and alimentary tracts. Pleomorphic adenomas constitute approximately 75% of all benign tumors of the major salivary glands.

In the parotid gland, approximately 90% of pleomorphic adenomas originate superficial to the facial nerve. Occasionally, tumors of the superficial lobe extend to the deep lobe medial to the facial nerve. If they extend to the parapharyngeal space through the stylomandibular “tunnel” bounded by the stylomandibular ligament, they may have a narrow isthmus connecting the superficial and deep components, giving the tumor a dumbbell appearance (see Figs. 87-5 and 87-10). Approximately 10% of pleomorphic adenomas originate entirely from the deep lobe and are usually located deep to the stylomandibular ligament. Therefore they have a more rounded appearance on high-resolution imaging (see Figs. 87-4 and 87-11). Pleomorphic adenomas may also arise from minor salivary gland tissue that naturally occurs in the parapharyngeal space. Regardless of their origin, pleomorphic adenomas of the parapharyngeal space occupy the prestyloid compartment (see Figs. 87-10 and 87-11) and, like other parapharyngeal tumors, may displace the oropharynx medially (see Fig. 87-6). Pleomorphic adenomas of the minor salivary glands most commonly occur in the palate (Fig. 87-13).⁴⁹ The second most common site is the upper lip. Despite the abundance of minor salivary glands in the lower lip, pleomorphic adenomas are exceedingly rare in this location. Pleomorphic adenomas are the most common benign tumors of the lacrimal gland (Fig. 87-14).⁵⁰^–⁵²

Figure 87-13. Pleomorphic adenoma of the palate. A, Intraoperative view. B, Tumor specimen.

Figure 87-14. Pleomorphic adenoma of the lacrimal gland.

Clinically, pleomorphic adenomas are characterized as painless, slow-growing masses. Multiple primary pleomorphic adenomas are extremely rare, although reported.⁵³ Pathologically, pleomorphic adenomas are solitary, firm, round tumors. The cut surface is characteristically solid and may be hard, rubbery, or soft in consistency with a whitish gray to pale yellow color. Pleomorphic adenomas of the major salivary glands have a capsule, although varying in thickness and completeness, whereas pleomorphic adenomas of the minor salivary glands are usually nonencapsulated.⁵⁴ On histologic examination, pleomorphic adenomas consist of epithelial components that may take the form of ducts, nests, cords, or solid sheets of cells and myoepithelial cells that appear plasmacytoid or spindled in a fibrocollagenous, myxochondroid, or chondroid background. Myoepithelium in pleomorphic adenoma is considered to be responsible for the development of the characteristic myxoid or chondroid stroma. Variations in the histologic appearance of this tumor type are common and may include squamous metaplasia, calcification, cartilage-appearing tissue, oxyphilic cells, and a palisading appearance of the underlying stroma. Lipomatous⁵⁵ and osseous⁵⁶ changes have been occasionally reported in pleomorphic adenoma.

Histopathologic studies have demonstrated that almost all pleomorphic adenomas have focally thin capsules, and one fourth of pleomorphic adenomas demonstrate satellite nodules or pseudopodia.⁵⁷ Therefore the recommended treatment is surgical excision with a surrounding cuff of normal tissue to prevent recurrence from failure to address these pseudopod-like extensions of tumor.⁵⁸ In patients with tumors of the submandibular gland, the gland is generally removed with careful preservation of the marginal mandibular nerve. Tumors of the parotid gland usually involve removal of the tumor with an adequate margin and facial nerve preservation. Because most of the tumors arise from the superficial lobe, a superficial parotidectomy is often required.

Recurrent pleomorphic adenomas are an uncommon but challenging problem. Frequently, multiple foci of recurrence continue to manifest over several years.⁵⁹ This multicentric pattern is characteristic of recurrent pleomorphic adenomas (Fig. 87-15). Currently, no reliable criteria have been established to predict those tumors with a greater tendency to recur. Surgical excision, however, remains the mainstay of treatment for recurrent pleomorphic adenomas. Patients who have undergone previous surgical excision, especially those with previous parotidectomy, are at increased risk for facial nerve injury, as well as recurrence with revision surgery.^60,⁶¹ Neutron radiotherapy offers excellent local control rates and survival rates in patients with multiple recurrences who are not surgical candidates even in the presence of gross residual disease.⁶²

Figure 87-15. Recurrent pleomorphic adenoma of the right parotid gland. Note the multicentric pattern of recurrence in both the coronal (A) and axial images. B, T1-weighted magnetic resonance (MR) with gadolinium. C, The postoperative axial T1-weighted MR with gadolinium shows complete resection of all recurrent tumors.

Malignant transformation of pleomorphic adenoma is rare and occurs most frequently in patients with long-standing tumors. The risk of malignant transformation in pleomorphic adenoma is 1.5% within the first 5 years of diagnosis but increases to 10% if observed for more than 15 years.⁶³ Cases of benign pleomorphic adenoma metastasizing to cervical lymph nodes have been reported.⁶⁴^–⁶⁶

Basal Cell Adenomas

Most basal cell adenomas occur in the parotid gland and minor salivary glands of the upper lip. As with other benign neoplasms, they present as a slow-growing, asymptomatic mass. Gross pathologic examination reveals a well-circumscribed, solid tumor with a gray-white to pink-brown cut surface. Parotid basal cell adenomas are characteristically encapsulated, whereas those of minor salivary gland origin may lack a capsule.⁶⁷ Histologically, an intact basement membrane helps differentiate basal cell adenomas from pleomorphic adenomas. Four histologic growth patterns have been recognized: solid, trabecular, tubular, and membranous.⁶⁸ Basal cell adenomas may be difficult to distinguish from the solid variety of adenoid cystic carcinomas. Cytologic features that help differentiate basal cell adenomas from adenoid cystic carcinomas include lack of true invasion of surrounding tissues, lack of perineural invasion, a vascular stroma, and a peripheral palisading of the outer layer of basaloid cells. The cell-stroma interface is also useful in distinguishing basal cell adenomas from adenoid cystic carcinomas. In basal cell adenomas the collagenous stroma interdigitates with adjacent cells, whereas in those with adenoid cystic carcinomas the two are separated by a sharp, smooth border. Further, the stroma of basal cell adenomas may contain rare spindle cells or capillaries, but the cylinders of adenoid cystic carcinoma are acellular. The treatment of these benign tumors is surgical excision with a cuff of normal surrounding tissue.

Canalicular Adenomas

Canalicular adenomas are benign neoplasms of predominately oral minor salivary glands, the upper lip being the most common site. They have been reported to account for less than 1% of salivary gland tumors and are rarely reported to be multifocal.⁶⁹ The patient presents with complaint of an asymptomatic, slowly enlarging mass. These tumors may be clinically similar to a mucocele or varix and may be multifocal. Histologically, they are characterized by cells arranged in parallel rows forming ductlike structures—hence the term “canalicular.” Canalicular adenomas may be distinguished from adenoid cystic carcinomas by their well-circumscribed appearance and lack of perineural or soft tissue invasion. Surgical excision is the treatment of choice for canalicular adenomas.

Papillary Cystadenoma Lymphomatosum—Warthin’s Tumors

First described by Aldred Warthin in 1929, Warthin’s tumor is the second most common benign salivary gland neoplasm behind pleomorphic adenoma. Warthin’s tumor is also known as papillary cystadenoma lymphomatosum or adenolymphoma. The term “adenolymphoma” is often confused with malignant lymphoma and therefore the use of this term should be discouraged. Papillary cystadenoma lymphomatosum is an accurate descriptive term but is somewhat cumbersome compared with the most favored term of Warthin’s tumor. Warthin’s tumor accounts for approximately 10% of all parotid tumors and is found almost exclusively in the parotid gland. Warthin’s tumor is associated with a higher male preponderance and is more prevalent in whites than in other racial groups. Bilateral Warthin’s tumors occur in 10% of cases and may be simultaneous. As previously discussed, Warthin’s tumor is associated with cigarette smoking, which may be due to irritation of ductal epithelium by tobacco smoke, which initiates tumorigenesis.¹⁸

Clinically, patients with Warthin’s tumor present with an asymptomatic, slow-growing mass often in the superficial lobe of the parotid gland at the angle of the mandible. However, a few patients will present with swelling, pain, and other inflammatory changes, which may be secondary to an immunologic response of the lymphoid element.

On gross pathologic examination, Warthin’s tumors are usually spheric or ovoid masses that are encapsulated with a smooth or lobulated surface. Papillary cysts are commonly found on sectioning and contain mucoid brown fluid. Solid gray tissue encapsulates white nodules of lymphoid tissue. Microscopically, the combination of papillae of eosinophilic epithelia projecting into cystic spaces and lymphoid matrices is a distinct and pathognomonic histologic feature. The typical cystic lining is arranged in two cell layers of even rows. The apical or luminar tall columnar and basal cuboidal cells contain small dark nuclei and abundant granular pink cytoplasm (oncocytes). The granular eosinophilia of oncocytes is due to abundant mitochondria present in the cytoplasm. Treatment of Warthin’s tumor is surgical excision, usually a parotidectomy with facial nerve preservation. Inadequate excision or tumor multicentricity may explain tumor recurrence.

Oncocytic Papillary Cystadenoma

Oncocytic papillary cystadenoma is an uncommon tumor type to originate in the parotid gland. Most of these tumors occur in the larynx, although they have been described in the nasopharynx, palate, buccal mucosa, and the accessory tear ducts. These tumors have no gender predilection and usually occur in those aged 50 years or older. Patients usually present with a painless mass. Those with laryngeal lesions may present with hoarseness or cough. The minor salivary glands of the false vocal cords and ventricles are common sites of presentation, but this tumor type also may originate from any site in the laryngeal mucosa. Although they are usually solitary tumors, there have been reports of multiple tumors.

On pathologic examination, oncocytic papillary cystadenomas are smooth round cysts that may be pedunculated. Microscopically, these tumors look like Warthin’s tumor, although the lymphoid stroma is absent. Sometimes, these tumors are referred to by some pathologists as “Warthin’s tumor without lymphoid matrix.” Whether these are true tumors has been debated. They may reflect metaplasia or hyperplasia of preexisting salivary gland ducts, but nonetheless, they are treated with surgical excision.

Oncocytoma

Oncocytoma accounts for less than 1% of all salivary gland tumors. They are usually benign tumors that arise most commonly in the parotid gland. These tumors may also originate in the submandibular, sublingual, and minor salivary glands. The cells of origin, oncocytes, are large epithelial cells with granular eosinophilic cytoplasm secondary to mitochondrial hyperplasia. Oncocytes may be found individually or in groups in otherwise normal major or minor salivary glands. They are also found in the pancreas, respiratory tract, thyroid, parathyroid, pituitary, adrenal glands, and kidney, although the majority of tumors occur in the superficial lobe of the parotid gland.

Most patients are in the fifth to sixth decade of life at the time of diagnosis and the gender distribution is almost equal. Oncocytomas are painless, slowly enlarging tumors that show a predilection for technetium-99m-pertechnetate and thus often enhance on radionucleotide scan.

On gross pathologic examination, oncocytomas of the major salivary glands are well circumscribed and encapsulated. Those originating from minor salivary glands have less well-defined borders and are not encapsulated. The surface is pink to rust in color. Microscopically, the tumor has a granular appearance as a result of the abundant, hyperplastic mitochondria. The concentration of mitochondria differentiates oncocytomas from other tumors. A true oncocytoma contains no lymphoid tissue. The extensive lymphoid component that is typical of a Warthin’s tumor is never encountered. Histologically, oncocyte-predominant benign lesions may have a degree of epithelial atypia, squamous metaplasia, or necrosis that may mimic some types of malignant salivary tumors with oncocytic components such as adenoid cystic carcinoma, mucoepidermoid carcinoma, and adenocarcinoma.⁷⁰ Metastatic thyroid carcinoma or renal cell carcinoma with a large number of oncocytes should also be differentiated from oncocytoma.

Oncocytomas originating from minor salivary glands tend to grow in an irregular and locally invasive pattern. They are less predictable than those originating in the parotid glands. Those originating from minor salivary glands in the respiratory tract may invade surrounding cartilage or bone. Although histologically benign, they have a destructive potential. Rarely do they demonstrate features indicative of malignancy such as increased mitoses and perineural or vascular invasion. Detection of cellular proliferation using immunohistochemical staining may be helpful in distinguishing a benign oncocytoma from a malignant oncocytoma.⁷¹ Treatment of benign oncocytomas is surgical excision.

Myoepithelioma

Myoepithelioma originates from contractile myoepithelial cells that lie beneath the ductal and acinar epithelium in the salivary glands. These cells also have been identified in sweat glands and mammary glands. They have the ability to contract, and their pumping action helps expel (or discharge) secretions from the salivary glands. Diagnosing myoepitheliomas by fine-needle aspiration is difficult, and immunohistochemistry with CD 10, SMA, and S-100 markers may aid in diagnosis.⁷² On gross pathology, myoepitheliomas are well demarcated and the external surface is smooth. The cut surface is homogeneous and white. Microscopically, these tumors have a thin capsule, except when they occur in the palate, wherein they lack encapsulation. The cells are benign appearing with rare mitosis and often assume spindle, polygonal, or plasmacytoid features. Clinically, these tumors are difficult to distinguish from pleomorphic adenomas due to their painless, slow-growing nature. There is no gender predilection, and they occur in the major and minor salivary glands. Histologically, they should be differentiated from plasmacytomas and any tumors with spindle cells including neurilemoma, fibroma, meningioma, and leiomyoma. The majority of these tumors behave in a benign manner, although there have been reports of local aggressiveness. The treatment is surgical excision.

Sialadenoma Papilliferum

Sialadenoma papilliferum is a rare, benign salivary gland tumor named after the skin tumor syringocystadenoma papilliferum, which it resembles on gross pathologic and microscopic examination. This tumor is painless and exhibits slow-to-moderate growth. It originates in the major and minor salivary glands, most commonly in men about 60 years of age. Microscopically, the tumor originates from the superficial extralobular salivary gland ducts. The cell of origin is thought to be the pluripotential myoepithelial cell.

Clinically, the differential diagnosis includes other papillary lesions like squamous papilloma, verrucous hyperplasia, or carcinoma. Usually it can be distinguished from other intraoral minor salivary gland tumors because it is exophytic and not a smooth, mucosa-covered mass. The treatment is surgical excision.

Inverted Ductal Papilloma

Inverted ductal papilloma is an inverted papilloma that originates from the excretory ducts of the minor salivary glands. This tumor is a different entity from the inverted oral papilloma, which is endophytic and does not bear any clinical resemblance to inverted ductal papilloma. The few cases that have been reported occur equally in men and women. The lesions are raised but not ulcerated. The preoperative differential diagnosis includes salivary gland tumor, fibroma, and lipoma. Treatment should be conservative, but excision should be complete.

Congenital Lesions

Hemangiomas

Congenital vascular lesions are divided into two groups: hemangiomas and vascular malformations. Juvenile hemangiomas are the most common tumors of infancy, occurring in up to 10% of all births.⁷³ They may be present at birth but commonly appear several days to weeks later. A rapid growth phase occurs around the age of 1 to 6 months, followed by gradual involution over 1 to 12 years. During the growth phase, endothelial cells proliferate rapidly and become flat during involution. Facial infantile hemangiomas occur in two distinct patterns of tissue involvement: a focal type with a tumor-like appearance and a less common diffuse type with a plaquelike appearance. The diffuse lesions are more likely to be complicated by ulceration or airway obstruction and show a strikingly segmental distribution pattern. Focal hemangiomas, in contrast, show a predilection for regions of embryologic fusion.⁷⁴ Hemangiomas are more common in the parotid than in the submandibular gland. Hemangiomas of the parotid area are more often seen in female patients and are usually asymptomatic, unilateral, and compressible masses. The overlying skin may be normal or may be involved. It is not uncommon to see other skin lesions present. On gross pathologic examination, this tumor is dark red, lobulated, and nonencapsulated. Microscopically, these tumors are composed of capillaries lined by proliferative endothelial cells. Blood vessels are uniform in size. Mitoses occur frequently but are not indicators of behavior.⁷⁵

Hemangiomas may become extremely large with complications such as bleeding, heart failure, and even death. Treatment initially should consist of steroids administered 2 to 4 mg/kg per day. If the hemangioma is responsive to steroids, the result is usually immediate and often dramatic. Unfortunately, the response rate to steroids is only 40% to 60%. In such patients, interferon may be useful, but it should be reserved for life-threatening situations because of its toxicity and the necessity to continue the drug for prolonged periods. Surgical excision or various types of laser treatments may be performed for select circumstances.⁷⁶ Hemangiomas usually involute completely, but they may take years and may result in medical or psychological problems for children.⁷⁷

Vascular and Lymphatic Malformations

Vascular malformations are different from hemangiomas of the parotid gland. These vascular malformations are not true neoplasms and are divided into different categories, which are discussed briefly as follows.

Management of Benign Salivary Gland Neoplasms

Management of benign salivary gland tumors has not changed dramatically for years. Management of tumors of the salivary glands requires a detailed understanding of the anatomy and pathologic processes affecting these glands. Benign salivary gland tumors should be excised completely with an adequate margin to avoid local recurrences.⁵⁷ Generally tumors in the parotid gland are removed with an adequate cuff of surrounding normal tissue, and the facial nerve is dissected and carefully preserved. The extent of dissection of the facial nerve and the amount of parotid tissue resection depend on the size, location, and histology of the tumor.⁷⁸

Small adenomas located in the tail of the parotid gland may require only dissection of the lower division of the facial nerve with removal of the tumor and the surrounding parotid tissue, avoiding unnecessary dissection of the upper division.

Larger tumors of the superficial lobe, however, usually require a complete superficial parotidectomy. Deep lobe tumors require a total parotidectomy, with facial nerve preservation. Parapharyngeal tumors are most commonly excised through a cervical-parotid approach and only occasionally in conjunction with a mandibulotomy.⁷⁹

A tumor of the submandibular gland requires submandibular gland resection. If the tumor originates from a minor salivary gland, the tumor and a cuff of normal tissue should be excised. Simple enucleation should be discouraged because of the increased risk of recurrence.⁵⁸ Pediatric hemangiomas will generally involute but may be resected in special cases. Vascular malformations involving the parotid or submandibular glands may require surgical excision.

Parotidectomy (see Key Indicator Video online)

The patient is placed in the supine position, and the head turned to the opposite side. The standard incision is a modified Blair’s incision (Fig. 87-16A). The skin incision is placed in a preauricular crease and extends superiorly to the level of the root of the helix. The incision extends inferiorly around the lobule of ear over the mastoid tip. It then gently curves down along the sternocleidomastoid muscle and then slightly forward in a natural skin crease in the upper neck (see Fig. 87-16A). Alternatively, a “face-lift” incision may be done in selected patients with benign tumors of the lower or mid regions of the parotid gland. The preauricular portion of the incision passes on or just inside the tragal margin. The incision is then carried below the lobule of the ear, turns posteriorly over the mastoid, and then is extended within the hairline (Fig. 87-17A). The face-lift incision is less conspicuous and therefore offers better cosmesis (see Fig. 87-17B).

Figure 87-16. Right superficial parotidectomy. A, Modified Blair’s incision for a right parotidectomy. B, Flap elevation and freeing the tail of the parotid gland. C, Identification of the main trunk of the facial nerve. The facial nerve is usually identified by dissecting the main trunk (white arrow) in the region located between the tragal pointer (white arrowhead) and the attachment of the posterior belly of the digastric muscle (DGM) to the mastoid bone. Unless displaced by tumor, the nerve is usually located approximately 1 to 1.5 cm deep and inferior to the tragal pointer. Dissection of the main trunk then proceeds distally until it branches (double arrow), and then all branches are sequentially and meticulously dissected. D, Complete dissection of all parotid tissue lateral to the facial nerve reveals the main trunk and the complex branching pattern of the facial nerve (pes anserinus). PF, parotid fascia; PM, platysma muscle; PT, parotid tail; SCM, sternocleidomastoid muscle.

Figure 87-17. Modified “face-lift” incision for parotidectomy. A, Unlike the modified Blair’s incision, which has a cervical extension (see Fig. 87-16A), the face-lift incision extends posteriorly and inferiorly along the hairline. B, The hairline portion of the incision is inconspicuous, making this approach more cosmetically pleasing.

To expose the parotid gland, skin flaps are elevated in the plane superficial to the parotid fascia in the preauricular region and in the subplatysmal plane in the cervical portion of the incision (see Fig. 87-16B). The greater auricular nerve and the external jugular vein are identified over the sternocleidomastoid muscle and are divided to free the tail of the parotid gland (see Fig. 87-16B). In some cases the greater auricular nerve can be preserved, but whether this preservation has a significant impact on the patients’ quality of life is debatable (as will be discussed under Complications).^80,⁸¹ The posterior belly of the digastric muscle is exposed proximal to its attachment to the mastoid bone. The fascia between the parotid gland and the cartilaginous external auditory canal is dissected, and the parotid gland is retracted anteriorly. This exposes the tragal pointer. The most common method of identifying the main trunk of the facial nerve is in its course in the region located between the tragal pointer and the attachment of the posterior belly of the digastric muscle to the mastoid bone (see Fig. 87-16C). Unless displaced by tumor, the nerve is usually located approximately 1 to 1.5 cm deep and inferior to the tragal pointer. Another reliable, and perhaps a more constant, landmark to identify the facial nerve is the tympano-mastoid suture line, which could be followed medially to the main trunk of the nerve. The nerve is usually 6 to 8 mm deep to the tympano-mastoid suture line. In certain cases where the tumor is directly overlying the region of the main trunk of the facial nerve, one or more of the peripheral branches of the nerve are identified distally and traced proximally toward the main trunk.⁸² The marginal mandibular branch can be identified below the lower border of the mandible, as it crosses superficial to the facial vessels, in the plane immediately underneath the deep cervical fascia. Alternatively, the buccal branch can be identified underneath the parotido-masseteric fascia, coursing parallel to the parotid duct.

Once the facial nerve is identified, the overlying parotid tissue is meticulously elevated from the nerve with a fine clamp and the bridge of tissue between the blades of the clamp carefully divided. If the main trunk of the nerve is identified first, then the overlying parotid tissue is progressively dissected free of the nerve to the first branching of the nerve, usually into an upper and a lower division (see Fig. 87-16C). Subsequent branching of the nerve (pes anserinus) is sequentially dissected in a similar fashion, until the entire superficial lobe of the parotid gland lying lateral to the facial nerve is delivered (see Fig. 87-16D). This completes a superficial or lateral parotidectomy.

If a total parotidectomy is indicated, the procedure is extended by meticulous dissection of the main trunk and the branches of the facial nerve from the underlying parotid tissue in a gentle and atraumatic fashion. This allows the salivary tissue lying deep to the facial nerve to be delivered while preserving the nerve and its function.

Submandibular Gland Excision

A curvilinear incision is placed, preferably in a natural skin crease, 3 to 4 cm below the lower border of the mandible, overlying the submandibular gland. The incision is carried down through the subcutaneous fat, and the platysma muscle. Great care should be taken to avoid injury of the marginal mandibular nerve. The nerve lies immediately beneath the deep cervical fascia, and can be identified crossing the anterior facial vein. The vein is doubly ligated and transected well below the nerve, and upward retraction of the superior ligature displaces the nerve superiorly and protects it from injury during further dissection (Fig. 87-18A). Superior dissection proceeds by double ligation and transection of the facial artery, which frees the superior attachment of the gland. Anteriorly the vessels to the mylohyoid muscle are divided, and the gland is mobilized posteriorly, exposing the free edge of the mylohyoid muscle. The free (posterior) edge of the mylohyoid muscle is retracted anteriorly, while gentle posterior traction on the gland is maintained. This exposes the deep portion of the gland and its duct, the submandibular ganglion, and the lingual and hypoglossal nerves (see Fig. 87-18B). These structures lie superficial to the hyoglossus muscle. The contribution of the lingual nerve to the submandibular ganglion is transected, and the Warthin’s duct is doubly ligated and divided. This delivers the deep portion of the gland. Care should be taken to avoid injury to the lingual and hypoglossal nerves. Finally the facial artery is divided a second time, and the gland is removed.

Figure 87-18. Excision of the submandibular salivary gland. A, Submandibular incision, made in a natural skin crease 3 to 4 cm inferior to mandible. Marginal mandibular nerve generally lies just superficial to anterior facial vein. B, Mylohyoid is retracted anteriorly and the gland posteriorly. This exposes the lingual nerve, submandibular ganglion, and Wharton’s duct.

Excision of Parapharyngeal Salivary Gland Tumors

Surgical excision of salivary gland tumors within the parapharyngeal space is best done via an external approach.^37,⁷⁹ The incision is that of a parotidectomy with a cervical extension (Fig. 87-19A). If the tumor involves the deep lobe of the parotid gland, a superficial parotidectomy is done first. If the tumor arises from the minor salivary glands of the parapharyngeal space, the inferior division of the facial nerve is identified and carefully preserved (see Fig. 87-19B). Next, the sternocleidomastoid is retracted laterally and the upper neck is dissected to expose the internal jugular vein, external and internal carotid arteries, and the last four (IX, X, XI, and XII) cranial nerves (see Fig. 87-19C). The posterior belly of the digastric and the stylohyoid muscle are identified, divided near their mastoid and styloid attachments, respectively, and retracted medially. This allows further superior exposure of the internal carotid artery, internal jugular vein, and adjacent nerves, as well as visualization of the stylomandibular ligament and the styloid process. The stylomandibular ligament is divided (see Fig. 87-19D), which allows further anterior retraction of the mandible and provides a wide opening into the parapharyngeal space (see Fig. 87-19E). The styloid process may be resected for further exposure and to assist delivery of larger tumors. Through this exposure, the tumor can be easily visualized and safely excised (see Fig. 87-19E and F).

Figure 87-19. Transcervical approach to the right parapharyngeal space. A, Incision for transcervical approach to the parapharyngeal space. The incision can be extended to the submandibular region and can also extend as a lip-splitting incision if a mandibulotomy is necessary for added exposure (dotted line). B, The main trunk of the facial nerve is identified in the same manner as described for superficial parotidectomy. For most benign tumors of the parapharyngeal space, dissection of the facial nerve is limited to the main trunk and the inferior division of the nerve (arrow). Dissection of the upper division is occasionally necessary for adequate exposure and tumor resection. C, Exposure of the neurovascular structures in the upper cervical region. These include the internal jugular vein (IJV), internal carotid artery (ICA), external carotid artery (ECA), and cranial nerves (CN) X, XI, and XII. D, The stylomandibular ligament (white arrow) is seen overlying the curved hemostat. The relationship of the main trunk of the facial nerve (black arrow) and the tragal “pointer” (white arrowhead) is also demonstrated. E, Division of the stylomandibular ligament allows further anterior retraction of the mandible, and resection of the styloid process allows more cephalad exposure of the parapharyngeal space. These maneuvers allow wide access to the parapharyngeal space for adequate tumor (T) exposure. F, Pleomorphic adenoma of the parapharyngeal space. DGM, digastric muscle; SCM, sternocleidomastoid muscle.

In patients with tumors located in the superior aspect of the parapharyngeal space approaching the eustachian tube and skull base, the addition of a mandibulotomy may be necessary.^37,⁸³ The enhanced exposure offered by the mandibulotomy allows the visualization necessary for resection of the tumor with adequate margins. First, a cervical-parotid approach is performed as described in the previous section. If a mandibulotomy is indicated, a preliminary tracheostomy is performed. Next, the cervical portion of the incision is extended through the chin to split the lower lip in the midline (Fig. 87-20A). After dissection of the upper carotid sheath, the mandible is exposed carefully, identifying and preserving the mental nerve (see Fig. 87-20B). A stair-step or “Chevron” osteotomy is outlined either in the midline (median mandibulotomy) or just anterior to the mental foramen (paramedian mandibulotomy) (see Fig. 87-20C). These types of osteotomies are more mechanically stable than a straight-line osteotomy. In order to obtain normal dental occlusion, a metal plate is preregistered and fixed to the mandible before performing the planned osteotomy (see Fig. 87-20D). The osteotomy is performed using a micro-reciprocating saw in order to minimize bony loss at the osteotomy site. A paralingual incision is then made along the floor of the mouth. The mylohyoid muscle is divided while carefully preserving the hypoglossal and lingual nerves. The tongue is retracted medially, and the parapharyngeal and retropharyngeal spaces are opened widely (see Fig. 87-20E). The tumor can now be excised safely and adequately while protecting the critical neurovascular structures of the parapharyngeal space. Closure involves a water-tight intraoral suture line and rigid fixation of the mandibulotomy. A nasogastric tube is inserted for feeding. Within 7 to 10 days most patients will have their tracheostomy decannulated and be able to resume oral feeding.

Figure 87-20. Mandibulotomy approach for excision of tumors in the parapharyngeal space. A, Lip-splitting incision for mandibulotomy. B, Upper cervical dissection and exposure of the mandible with identification and preservation of the mental nerve. C, A “Chevron” osteotomy is outlined anterior to the mental foramen. D, A metal plate is preregistered and fixed to the mandible before the planned osteotomy to avoid postoperative malocclusion. E, After the osteotomy is distracted, dissection is carried along the floor of mouth just lateral to the tongue, providing wider access to the parapharyngeal space.

Complications

Facial Nerve Paresis or Paralysis

Facial nerve dysfunction may result from traction injury to the facial nerve during dissection. Facial nerve monitoring has helped decrease the morbidity of a parotidectomy.⁸⁴ As long as the anatomic integrity of the nerve is preserved, this type of injury usually results in neuropraxia and, therefore, complete recovery is anticipated. The degree of weakness or paralysis may range from minimal partial weakness of one or more branches of the facial nerve to complete paralysis of all branches of the nerve. Recovery of facial nerve function may be prompt and complete within days or may be delayed for several months. In a study of 256 consecutive patients who underwent parotid surgery at the Cleveland Clinic over a period of 15 years, immediate postoperative facial nerve dysfunction was frequently encountered (46%), but permanent dysfunction was uncommon (4%).⁸⁵ The incidence of long-term dysfunction was higher in revision cases and when an extended (total or subtotal) parotidectomy was performed. In order to minimize facial nerve injury, the parotid surgeon should adhere to meticulous dissection and gentle handling of the facial nerve. Excessive traction on the nerve must be avoided, as should overzealous use of the nerve stimulator.

Transection of one or more of the branches of the facial nerve will result in paralysis of the corresponding muscles supplied by the injured nerve. The degree of paralysis may vary and depends on the presence and extent of cross-innervation of the involved muscle groups by the uninjured branches of the facial nerve. Complete transection of the main trunk of the facial nerve results in complete and permanent paralysis of all ipsilateral muscles of facial expression.

If the facial nerve is sacrificed, nerve repair may be done by using either direct neurorrhaphy of the cut edges or a cable graft, depending on the length of the resected segment (see Fig. 87-18). Immediate rehabilitation of the paralyzed face requires diligent eye care to prevent exposure keratitis. This involves liberal use of artificial tears, lubricating ointment, and protection with an appropriate eye dressing and eyewear. A gold weight implant should be used routinely in patients with complete facial paralysis. A temporary tarsorrhaphy may be necessary for patients with lower eyelid ectropion. If the facial nerve is not repaired or grafted, then one or more of the various surgical procedures for static or dynamic rehabilitation of the paralyzed face may be indicated.