Salivary Glands
Figure 1. Salivary Glands
Salivary glands are responsible for producing saliva, which keeps the mouth moist, aids in swallowing and digestion, and helps fight infection. The glands are divided into the major and minor glands. There are three pairs of major salivary glands: the parotid glands (side of face/jaw), the submandibular glands (just below the jaw), and the sublingual glands (in the floor of the mouth). There are also nearly 1,000 tiny minor salivary glands found throughout the head and neck area (Figure 1).
The Parotid gland is located in a very crucial location on the side of the face. The facial nerve (the nerve that controls the movement of facial musculature thus giving us our facial expressions) pierces the gland from behind, just underneath the ear; it travels through the whole gland, thus dividing the gland into the superficial and deep lobes, and then enters the face and its muscles (Figure 2). Any surgery on this gland must consider this intricate anatomy and protect it. There are also several lymph nodes within the Parotid gland itself that may give rise to tumors such as lymphoma or can be destination for cancers spreading from other areas. (for example, skin of scalp).
The submandibular gland produces more saliva than the other glands; it sits just deep to the jaw at the midpoint between the chin and the angle of the jaw. Several important nerves are located in close proximity of the gland, including: (1) the marginal mandibular nerve that moves the lower lip (2) the hypoglossal nerve that moves half the tongue (3) the lingual nerve that is in charge of taste and sensation of the tongue. The surgical anatomy of these nerves are very complex but quite consistent in expert hands. There are also several lymph nodes around this gland that, at times, may be involved with tumors and will need to be removed.
Risk Factors
The most well known cause is exposure to radiation, either in the environment or as treatment for a cancer of the head and neck area. Exposure to sawdust and chemicals used in the leather industry, pesticides, and industrial solvents may increase the risk of a type of salivary gland cancer that occurs in the nose and sinuses. Salivary gland cancer is considered to be very rare, but when present, they are usually aggressive.
Symptoms and Diagnosis
A painless mass is the most common initial finding. Facial paralysis and pain are some of the symptoms of a parotid tumor that occur in more advanced lesions. Growth rate can be quite variable. A fine needle biopsy is then performed to determine whether the lesion is benign or malignant. MRI scan of the face & neck with contrast is most helpful in assessing the size and extent of the tumor (Figure 3 & 4). The decision to get other studies including CT scans and PET scans will be dependent on the particular type and extent of tumor.
Figure 3. MRI –
Left Parotid Tumor
Figure 4. MRI – Left
Submandibular Tumor
Benign Tumors
80% of tumors in the parotid glands are benign, while only 50% are benign in the submandibular gland, less than 35% in the minor salivary glands. Benign tumors include Pleomorphic adenoma, and Warhtin’s tumor. Both have a tendency to continue to and possibly the surrounding nerves. They require close monitoring and ideally need to be surgically removed since as they get larger the risk of injury to the nerves gets larger. Overall, pheomorphic adenoma is the most common salivary gland tumor (Graph 1); additionally, if left for an extended period of time, pleomorphic adenomas have the potential of transforming into a more aggressive cancer called Carcinoma ex-Pleomorphic, which is extremely destructive and has a poor cure rate.
| SALIVARY GLAND |
IINCIDENCE OF
TUMORS |
CHANCE OF
MALIGNANCY |
| Parotid |
80% |
20% |
| Submandibular |
15% |
50% |
| Sublingual/Minor |
5% |
65% |
Malignant tumors
- Mucoepidermoid Carcinoma is the most common malignancy in the parotid gland. It can be low grade, which is slow growing, and relatively less aggressive, which makes it easily treatable through a complete surgical excision. The high grade variant is very aggressive and requires immediate attention. The treatment of choice is complete surgical excision with an adequate margin of tissue (meaning the tumor and a rim of normal tissue measuring close to half an inch around the tumor), and if possible sparing the surrounding nerves if possible (however, often times the proximity of the tumor to the nerve does not allow the nerve to be preserved while achieving a complete tumor resection). Most often this is followed by post-operative radiation therapy.
- Acinic Cell Carcinoma or Oncocytic Carcinoma is the only salivary malignancy that has the potential of occurring on both sides. This tumor tends to also be relatively less aggressive than other salivary cancers and has lower potential for spread, as such if the diagnosis is made early and the tumor is surgically removed completely the chance of cure is high.
- Adenoid cystic Carcinoma is the most common cancer in the submandibular, sublingual, and minor salivary glands. It is an aggressive cancer that has a relatively high incidence of recurrence (return of tumor) after treatment and a relatively high incidence of distant metastases (spread to other parts of the body). It also tends to spread along nerves (peri-neural invasion) or through the bloodstream. It only spreads to the lymph nodes in about 5% to 10% of cases. The most common place of metastases (spreading) is the lung. As such this tumor needs to be treated very aggressively when diagnosed before it has the opportunity to spread elsewhere, and to decrease the chance of its return. Surgery is indicated in all cases except those patients who are physically healthy enough to undergo surgery, or in the very advanced cases. At the Center our team of experts immediately evaluate the patient and decide on the most appropriate surgical course and if necessary reconstructive option.Post-operative radiation therapy is indicated in most cases; neutron beam radiation therapy has been reported to have the best outcomes in treating this particular type of tumor, however, radiation alone is not enough to achieve cure in most cases. Another unusual fact about this cancer is that even after the tumor has recurred or spread, patients may still have long survival period. So treatment of this particular type of tumor is challenging and must be performed by head and neck surgeons, oncologists, and radiation oncologists quite familiar with the character of this tumor.
- Squamous Cell Carcinoma rarely originates in the saliva glands; most often squamous cell cancers spread to the parotid gland from skin cancers in the temple, scalp, ear and cheek areas. Treatment involves not only removing the parotid gland but also investigating the site of origin of this particular tumor and treating the primary site as well. Without a careful assessment of the site where this tumor may have originated from, the treatment will be incomplete. Often times a neck dissection (removal of lymph nodes in the neck area) needs to be done to assure complete removal of microscopic cancer cells that may have spread to the lymph nodes of the neck.
- Carcinoma Ex-Pleomorphic Adenoma is a cancer that arises from a pleomorphic adenoma that has not been removed for years and years. This is a particularly aggressive tumor that does not respond well to chemotherapy or radiation therapy. The treatment of choice remains radical surgical excision. The telltale sign of this tumor is having a lump in saliva gland for years and years followed by a sudden rapid growth. These tumors need to be addressed immediately without any delay.
- Other less common tumors include Adenocarcinoma, Polymorphous low-grade adenocarcinoma, Oncocytic carcinoma (malignant oncocytoma), Clear cell carcinoma, Epithelial-myoepithelial carcinoma of intercalated ducts, Undifferentiated carcinoma, and Lymphomas.All these malignancies need to be treated immediately as the risk damage to the surrounding nerves (specifically the facial nerve) increases with advancement of the tumor. In all the mentioned cancers, except lymphoma, the treatment involves surgery. Radiation and chemotherapy is used in special circumstances.
