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Tumors of the Salivary Glands

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Salivary gland anatomy: parotid, submandibular, sublingual, and minor salivary glands

The major salivary glands are shown here.

The major salivary glands are shown here.

The salivary glands produce saliva and have potential to develop a variety of benign or malignant tumors. There are three paired major salivary glands (parotid, submandibular, and sublingual) that deliver saliva to the oral cavity through ducts. The mouth also has hundreds of minor salivary glands dispersed throughout the lining of the oral cavity and throat.

evaluation of salivary gland tumors

A growth in a salivary gland is usually noticed by a patient or their physician, though occasionally a cancer in the salivary gland will have spread to a lymph node in the neck that may be identified first. A head and neck surgeon will obtain a history, perform a physical exam, and then, if indicated, may perform or arrange a biopsy, often a needle biopsy of the mass (with or without ultrasound imaging) and/or obtain cross sectional imaging (such as a CT scan or MRI).

common types of salivary gland tumors

Salivary glands have many different types of cells, each specialized to perform a certain task. Each of the cell types is thought to have potential to develop into a specific type of tumor, and thus, there are several different types of tumors that can arise in a salivary gland. Identification of the tumor type is done with a biopsy, and the advantage of knowing the tumor type is that it allows reasonable prediction of the behavior of the tumor and the best strategy for treatment.

The most common benign salivary gland tumors include:

  • Pleomorphic adenoma: Overall the most common type of salivary gland tumor, this benign neoplasm typically grows indefinitely. If neglected over years or decades, a pleomorphic adenoma does have the potential to transform into a cancer (called “carcinoma ex-pleomorphic adenoma), which, becomes more aggressive in growth and can spread to other parts of the body.

  • Warthin's tumor (papillary cystadenoma lymphomatosum): Warthin’s tumor, also known as cystadenoma lymphomatosum, is a benign salivary gland tumor usually found in the parotid gland, and it is not unusual for people to have this this type of tumor on each side. Tobacco smoking is a significant risk factor for the development of a Warthin’s tumor.

  • Myoepithelioma: Benign myoepithelioma are treated with simple excision. They are less prone to recurrence than pleomorphic adenoma. It is rare for a myoepithelioma to be malignant.

  • Basal cell adenoma: Treatment is by surgical excision with a margin of healthy tissue. Although the recurrence rate is high, the prognosis is generally good.

  • Oncocytoma: The salivary gland oncocytoma, also known as an oxyphilic adenoma is a well-circumscribed, benign neoplastic growth. It comprises about 1% of all salivary gland tumors. Salivary gland oncocytomas are most common in ages 70–80, females, the parotid gland (85–90%), and are firm, slowly growing, painless masses of less than 4 cm diameter.

The most common malignant (cancerous) salivary gland tumors include:

  • Mucoepidermoid carcinoma is the most common type of minor salivary gland malignancy in adults, but is also found in the major salivary glands as well as in other organs, such as bronchi (lower windpipes), lacrimal sac (tear duct), and thyroid gland. Generally, there is a good prognosis for low-grade tumors, and a poor prognosis for high-grade tumors, however recent research have found reoccurring low grade tumors also have a poor prognosis. Surgery is the recommended treatment for localized resectable disease. When the tumor is incompletely resected (positive margins) post-operative radiotherapy gives local control comparable to a complete resection (clear margins). Sometimes when surgery is not possible due to extent of disease or if a patient is too frail for surgery, or declines surgery, palliative radiotherapy may be helpful.

  • Acinic cell carcinoma is a malignant tumor representing 2% of all salivary tumors. 90% of the time found in the parotid gland, 10% intraorally on buccal mucosa (cheek lining) or palate. The disease presents as a slow growing mass, associated with pain or tenderness in 50% of the cases. Prognosis is good for acinic cell carcinoma of the parotid gland, with five-year survival rates approaching 90%, and 20-year survival exceeding 50%. Patients with acinic cell carcinomas with high grade transformation have significantly worse survival. Acinic cell carcinoma is known for its potential to spread to the lungs and grow there so slowly that detection may occur decades after the salivary gland primary tumor has been treated.

  • Polymorphous low-grade adenocarcinoma (PLGA) is an uncommon, asymptomatic, slow-growing malignant salivary gland tumor. It is most commonly found in the minor salivary glands of the palate. PLGAs are treated with wide local surgical excision and long-term follow-up. There is a recurrence rate of 14%

  • Adenoid cystic carcinoma is a rare type of cancer that can exist in many different body sites. This tumor most often occurs in the salivary glands, but it can also be found in many other anatomic sites, including the trachea, and the paranasal sinuses. It is the third-most common malignant salivary gland tumor overall. It represents 28% of malignant submandibular gland tumors, making it the single most common malignant salivary gland tumor in this region. Patients may survive for years with metastases because this tumor is generally well-differentiated and slow growing. In a 1999 study of a cohort of 160 ACC patients, disease-specific survival was 89% at 5 years, but only 40% at 15 years, reflecting deaths from late-occurring metastatic disease.

  • Epithelial-myoepithelial carcinoma (EMCa) is a rare malignant tumour that typically arises in a salivary gland and consists of both an epithelial and myoepithelial component. They are predominantly found in the parotid gland and represent approximately 1% of salivary gland tumors.

  • Carcinoma ex pleomorphic adenoma  is a type of cancer typically found in the parotid gland. It arises from the benign tumour pleomorphic adenoma. Its prognosis depends on the stage. Early tumours have essentially a benign behavior. The signs and symptoms are similar to other malignant salivary gland tumors; however, it may have been preceded by an appreciable mass that was long-standing (typically for greater than a decade) and did not appear to be growing. Findings that suggest transformation of pleomorphic adenoma into a malignant salivary gland tumor include rapid growth, facial weakness (due to facial nerve compression or invasion), pain, skin ulceration, fixation of the mastoid tip and parasthesias (e.g., numbness or tingling on the nearby skin).

removal of the parotid gland (parotidectomy)

Surgery to remove the parotid gland (parotidectomy) may be undertaken to diagnose or treat a tumor. The incision tends to heal nicely (as it is basically the same incision used for a facelift). Since the facial nerve runs through the parotid gland, every effort is made to identify and protect the main nerve and all of its branches as they make their way to muscles of the face. A separate nerve that provides sensation to the skin of around the outer ear is often unable to be spared, leading to numbness of that patch of skin which gradually becomes less noticeable over time. On occasion, a phenomenon known as “gustatory sweating” or Frye’s syndrome can set in after parotidectomy. This is when situations in which one would normally salivate (before or during a meal) can cause sweating of the skin over the operated parotid gland, and is due to the microscopic nerves that relay the need for salivation from the brain to the parotid gland loose their target with parotidectomy and with time and nerve healing, they grow right into the sweat glands of the skin. If this occurs, it sets in some months after surgery and often resolves spontaneously a year or two later. In the meantime, avoiding a sweaty cheek during a meal is most effectively and economically treated by applying a clear antiperspirant deodorant to the skin. Botox injections are also effective and last about three months at a time. A similar phenomenon can occur with the tear gland on that side of the face, called “Crocodile tear syndrome,” in which the healing nerves find their way to the lacrimal gland and the eye waters before or during a meal. Less commonly, pain syndromes can occur after parotidectomy. The “first bite syndrome” is when the first bite of food, especially if it is tart, can cause a spasm of pain in the cheek. This too is often temporary, resolving over months or years, and is best treated by starting a meal with something bland or a sip of water before eating anything tart. Much less commonly, a deeper pain can arise in the surgical site on occasion, but this problem is uncommon unless the tumor surgery involved extensive dissection into an area called the parapharyngeal space.

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