Benign Parotid Tumors 

Updated: May 18, 2017
  • Author: Sanford Dubner, MD; Chief Editor: Deepak Narayan, MD, FRCS  more...
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Significance

Salivary gland disorders are not a major public health problem in the Western world. Neoplasms of the salivary glands account for fewer than 3% of tumors in the US and only 6% of head and neck neoplasms.

Salivary gland tumors in children are uncommon, but the frequency of malignant tumors is higher in children than in adults. (For more information, see Medscape Reference article Malignant Parotid Tumors.) All masses in children require thorough diagnostic evaluation. Benign masses of the parotid gland in children may be due to vasoformative abnormalities, cysts, inflammatory processes, or neoplasms. The most common intraparotid mass is the benign lymph node, as a significant number of lymph nodes are present in the parotid. The most common benign tumor in children is the hemangioma. Of the benign epithelial tumors, the mixed tumor (pleomorphic adenoma) is the most common.

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Anatomy

The parotid gland is the largest of the major salivary glands. It arises as an epithelial proliferation from the lining of the oral cavity at 5 weeks postovulation. It lies in the preauricular region deep to the skin and subcutaneous tissue. The facial nerve (cranial nerve VII) divides the gland into the larger superficial and smaller deep component. Though these are commonly referred to as the superficial and deep lobes, they are not true lobes.

The parotid duct (Stensen duct) courses from the anterior border of the parotid gland below the zygoma, crosses the masseter muscle and the buccal fat pad, and turns deep to penetrate the buccinator muscle, finally opening intraorally at a papilla opposite the second upper molar. The duct varies in length from 4.0-7.0 cm. The parotid tail extends inferiorly into the neck as low as the sternocleidomastoid muscle. Acinar cells of the parotid gland are primarily secretory and produce thin, watery saliva devoid of mucous.

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Incidence and Etiology

Approximately 2500 new cases of salivary gland neoplasms are diagnosed each year. Parotid neoplasms account for 80% of salivary neoplasms. Of parotid masses, 75% are neoplastic; the remaining 25% are nonneoplastic infiltrative processes, such as cysts and inflammation. Of parotid neoplasms, 70-80% are benign. Except for Warthin tumors, benign tumors of the parotid gland are more likely to occur in women than in men. The median age for occurrence of these tumors is in the fifth decade of life. Parotid tumors occur most commonly in Caucasians. The etiology of these tumors is unknown, but the possibility of an adenoma gene currently is under investigation for its involvement in the development of pleomorphic adenomas. The most common benign parotid tumor in children is the mixed tumor.

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History and Physical Examination

A thorough history and physical examination is important in the workup of parotid masses. The major goal in the evaluation is to determine or exclude the diagnosis of malignancy. History often is the most useful tool in distinguishing inflammatory from neoplastic masses.

Characteristics of inflammatory conditions are sudden onset, pain, and systemic infection. The most common presentation is that of an asymptomatic mass (81%) noted incidentally while washing or shaving the face. [1] Pain (12%) or facial nerve paralysis (7%) is less frequent. Facial nerve paralysis is more commonly due to malignancy in the presence of a parotid mass, but most facial nerve paralysis is due to Bell palsy. Parotid masses occur most commonly in the lower pole, or tail, and in the superficial lobe of the gland.

Physical examination most often reveals a mobile nontender mass that is firm and solitary. Evaluate the possibility of a deep tumor by intraoral examination, with attention directed to the tonsillar fossa and soft palate. Inspect the Stensen duct for the character of the salivary flow (clarity, consistency, purulence) and notation of redness, bulging, and irritation of the ductal orifice as part of the physical examination. Evaluate the skin, oral cavity, oropharynx, and neck for possible primary lesions or nodal disease.

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Diagnosis

Laboratory studies

Hematologic and serologic tests are of little importance in the workup of salivary gland tumors.

Radiologic studies

Radiologic studies are involved minimally in the workup of an asymptomatic mass.

  • Plain radiography findings can help the clinician exclude calculi.
  • Sialography is rarely used. When used, it helps the clinician delineate disorders of ductal function or anatomy.
  • CT scan is almost 100% sensitive in detecting a salivary gland mass, but it cannot help the clinician differentiate between a benign and a malignant mass. It is most helpful in specifying the size and anatomic extent of a tumor.
  • MRI is superior in demonstrating benign tumors of the parotid gland because of its greater contrast than CT scan.
  • Positron emission tomography (PET) scans may be of value in assessing malignant tumors, with attention to metastatic adenopathy and distant metastases.

Ultrasonography

A study by Rong et al identified differences between the ultrasonographic characteristics of Warthin tumors and those of pleomorphic adenomas, including with regard to shape, vascularity, and the prevalence of cystic areas. The study involved 93 Warthin tumors (61 patients) and 77 pleomorphic adenomas (70 patients), with lobulated lesions representing 38.7% of Warthin tumors and 63.6% of pleomorphic adenomas. Grade 2 or 3 vascularity was identified in the majority of Warthin tumors (73.1%), while grade 0 or 1 vascularity was present in most of the pleomorphic adenomas (77.9%); vessel distribution also varied significantly between the two types of tumors. In addition, cystic areas were identified in 45.2% of the Warthin tumors but in only 20.8% of the pleomorphic adenomas. [2]

Biopsy

Fine-needle aspiration may be a valuable pretreatment diagnostic test. Its overall accuracy is greater than 96%, with a sensitivity for benign tumors of 88-98% and a specificity of 94%. Its sensitivity for detecting malignant tumors ranges from 58-96%, and its specificity is 71-88%. Frozen sections are 93% accurate when performed at surgery, but their use is controversial, since diagnosis depends on the experience of the pathologist with regard to salivary gland tumors.

The standard biopsy approach is a superficial parotidectomy with preservation of the facial nerve. For 80-90% of parotid neoplasms, this procedure is both diagnostic and therapeutic. For this reason, preoperative fine-needle aspiration biopsy is recommended, since it can change the clinical approach in up to 35% of patients. [3] Lymph nodes can be enucleated, [4] as can Warthin tumors, and sialadenitis does not require surgical intervention in most cases.

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Classification

Table 1. Classification of Benign Primary Epithelial Salivary Gland Tumors (Open Table in a new window)

Mixed tumor (pleomorphic adenoma)
Warthin tumor (papillary cystadenoma lymphomatosum)
Oncocytoma
Monomorphic tumors
Sebaceous tumors
Benign lymphoepithelial lesion
Papillary ductal adenoma (papilloma)
Unclassified

 

Benign pleomorphic adenoma or benign mixed tumor

See the list below:

  • Most common parotid neoplasm (80%) [5]
  • Proliferation of epithelial and myoepithelial cells of the ducts and an increase in stromal components
  • Slow growing, lobular, and not well encapsulated
  • Recurrence rate of 1-5% with appropriate excision (parotidectomy)
  • Recurrence possibly secondary to capsular disruption during surgery
  • Malignant degeneration occurring in 2-10% of adenomas observed for long periods, with carcinoma ex-pleomorphic adenoma occurring most frequently as adenocarcinoma

Warthin tumor (papillary cystadenoma lymphomatosum or adenolymphoma)

See the list below:

  • Second most common benign parotid tumor (5%)
  • Most common bilateral benign neoplasm of the parotid
  • Marked male as compared to female predominance
  • Occurs later in life (sixth and seventh decades)
  • Presents as a lymphocytic infiltrate and cystic epithelial proliferation
  • May represent heterotopic salivary gland epithelial tissue trapped within intraparotid lymph nodes
  • Incidence of bilaterality and multicentricity of 10%
  • Malignant transformation rare (almost unheard of)

Oncocytoma

See the list below:

  • Accounts for 1% of salivary gland tumors
  • Composed of large oxyphilic cells (oncocytes)
  • May be multiple

Monomorphic tumors

See the list below:

  • Rare, usually epithelial in origin
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Treatment & Management

Published in 2016, national multidisciplinary guidelines from the United Kingdom on the management of salivary gland tumors included a recommendation that benign parotid tumors undergo complete excision, a strategy that, according to the guidelines, leads to good cure rates. [6]

Superficial parotidectomy is the treatment of choice for most benign tumors in the superficial lobe. Make every effort to preserve the facial nerve. In order to preserve the facial nerve, it is important to try to determine the proximity of the nerve to the capsule of the tumor prior to surgery. Results of a retrospective review showed that malignant tumors were likely to have a positive facial nerve margin. [7]

Avoid enucleation (except for Warthin tumors and lymph nodes), since it greatly increases the likelihood of recurrence (up to 80%) and nerve damage. Deep lobe tumors demand total parotidectomy with preservation of the facial nerve. For recurrences, postoperative radiotherapy may be administered, with local control rates exceeding 95%.

A study by Cristofaro et al suggested that extracapsular dissection may be superior to superficial parotidectomy in the treatment of pleomorphic adenoma, with extracapsular dissection leading to fewer side effects. The study involved 198 patients with pleomorphic adenomas of the parotid gland, including 153 patients who underwent extracapsular dissection (mean follow-up 61.02 months) and 45 who underwent superficial parotidectomy (mean follow-up 66.4 months). The investigators found that although both techniques were comparably effective, superficial parotidectomy was associated with a significantly greater rate of transient facial nerve injury and facial paralysis than was the other procedure. [8]

Surgical incision

Parotidectomy incision should allow for adequate exposure and the most aesthetic result. The incision begins anterior to the superior root of the helix and descends anterior to the tragus. It then is directed behind the lobule of the pinna and can be carried down anteriorly onto the neck as dictated by the need for exposure.

If a large soft tissue defect is created by the excision of the parotid tumor, numerous autologous or allograft tissues (ie, dermal grafts, fascial grafts, fat grafts, AlloDerm) or synthetic substances may be used for filling these defects. Try to preserve a layer of tissue (the parotid fascia or SMAS layer) if it does not compromise the capsule of the tumor. This preservation is important so that a layer of tissue interposes between the cut salivary tissue and the skin. This has been shown to reduce the incidence of Frey syndrome (gustatory sweating).

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Complications

Parotidectomy can be performed with little morbidity and no mortality. Most serious complications result from damage to the facial nerve (either temporary or permanent paralysis). Injury to the greater auricular nerve results in hypesthesia of the ear. A slight loss of fullness and an increased prominence of the angle of the mandible may occur after superficial parotidectomy. Uncommon sequelae include salivary fistula, seroma, hematoma, and infection.

Frey (auriculotemporal) syndrome results from aberrant regeneration of auriculotemporal nerve fibers to sweat glands in the skin. The result is sweating on the affected side of the face during mastication. The incidence of this complication is variable, depending upon whether the examiner performs a starch-iodine test. Its incidence may be decreased by interposing a layer of tissue (either preserving the SMAS layer and replacing it on the surface of the parotid gland before closing the incision or placing a layer of allograft in a similar position).

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