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Pleomorphic adenoma

What Is It, Causes, Signs, Symptoms, and More

Author:Lily Guo

Editors:Alyssa Haag,Józia McGowan, DO

Illustrator:Jessica Reynolds

Copyeditor:Sadia Zaman, MBBS, BSc


What is pleomorphic adenoma?

Pleomorphic adenomas are the most common tumors of the salivary glands. They are often referred to as benign mixed tumors since they originate from both epithelial cells, or cells that come from the surface of the body, and myoepithelial cells, or contractile cells that exist within glands to aid with secretion. Pleomorphic adenomas constitute up to two-thirds of all benign tumors of the salivary glands. 

The salivary glands can be divided into major salivary glands (parotid, submandibular, and sublingual glands) and minor salivary glands (labial and buccal gland, glossopalatine gland, and palatine and lingual glands). Their purpose is to produce saliva which aids in digestion, keeps the mouth moist, and supports healthy teeth. While pleomorphic adenomas typically develop in the parotid gland or the largest salivary gland located in front of the ears, they can also arise in the submandibular gland, located below the jaw; and the sublingual glands, located under the tongue

What causes pleomorphic adenoma?

The causes of pleomorphic adenoma are still unknown. Those who are 30-40 years of age and who have a history of repeated head and neck radiation are at higher risk of developing pleomorphic adenoma. The incidence is also twice as likely in individuals assigned female at birth than it is in individuals assigned male at birth. Other risk factors include smoking, alcohol misuse, diets rich in cholesterol, and certain occupations (e.g., rubber manufacturing, asbestos mining, and plumbing). 

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What are the signs and symptoms of pleomorphic adenoma?

The signs and symptoms of pleomorphic adenoma typically include the growth of a smooth, painless mass on one side of the face that gradually enlarges over time. It typically begins as a painless lump at the back of the jaw, just below the earlobe. As the adenoma swells, it can affect the facial nerve and make it difficult for an individual to move one side of their face. Over time, hearing impairment, difficulty chewing, difficulty swallowing, and muscle weakness of the face can occur. Depending on the size of the tumor, the person may have a hard time opening the mouth widely. 

Of note, there are many other noncancerous conditions that can lead to a swollen salivary gland, such as an infection or a stone in the salivary duct. Unlike a benign adenoma, these conditions would present with pain. A clinician should be consulted if the individual’s symptoms are persistent. 

How is pleomorphic adenoma diagnosed?

Pleomorphic adenomas can be suspected with the help of physical examination. Individuals with salivary gland swelling will typically receive a full head and neck evaluation and the physician may ask about associated symptoms, such as numbness, prickling, or burning sensations of the face.  

Imaging, including ultrasound scans, computed tomography (CT), magnetic resonance imaging (MRI), and nuclear magnetic resonance (NMR), can be conducted to further evaluate the potential diagnosis. On all of the aforementioned modalities, the tumors typically appear as round masses with well-defined borders.

If the clinician is concerned about the possibility of a pleomorphic adenoma after imaging and physical exam, a biopsy can be performed to confirm the diagnosis. The clinician examining the tissue may observe both the epithelial and myoepithelial cells and assess if the specimen is surrounded by a fibrous capsule. This can help differentiate a pleomorphic adenoma from another tumor, which can be either malignant or benign. 

How is pleomorphic adenoma treated?

Treatment of pleomorphic adenoma is aimed at completely removing the mass in order to prevent reoccurence. In doing so, it is important to prioritize preserving any nearby anatomical structures. In about 5% of cases where the benign tumor is not completely removed, the tumor can undergo malignant transformation and become a malignant (i.e., cancerous) carcinoma. This risk of malignant transformation heightens with increased duration of the tumor and increased age of the individual. While surgical resection usually cures the individual, there is a risk of recurrence of parotid tumors if the adenoma is not completely removed. If the tumor is poorly encapsulated, the entire parotid gland may be removed in a procedure known as a total parotidectomy. For tumors that cannot be surgically removed due to their size and location, radiation therapy is typically used. Radiation can also be used in conjunction with surgery, if there is worry that the tumor has a chance of growing back post-surgery. 

What are the most important facts to know about pleomorphic adenoma?

Pleomorphic adenomas are the most common tumor that can arise in the salivary glands. In 70% of cases, the pleomorphic adenoma is found in the parotid gland. It is commonly a benign tumor that is slow growing and does not spread to surrounding tissue. Overall, pleomorphic adenomas constitute less than 3% of head and neck tumors. They are of mixed tissue origin, derived from both epithelial cells and myoepithelial cells. While causes are largely unknown, some risk factors include being female, smoking, and excess alcohol consumption. As the adenoma grows, symptoms like immobility of one side of the face, trouble chewing, and trouble swallowing may arise. Diagnosis of pleomorphic adenomas involve physical examination, imaging, and biopsy. To distinguish a pleomorphic adenoma from other conditions that may present with similar symptoms, the pathology seen on biopsy is important and can also distinguish from other types of tumors. Treatment can consist of full surgical resection and radiation, if necessary.

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Related links

Anatomy of the salivary glands
Anatomy of the oral cavity
Oral Cancer
Warthin Tumor

Resources for research and reference

Alves, F. A., Perez, D. E., Almeida, O. P., Lopes, M. A., & Kowalski, L. P. (2002). Pleomorphic adenoma of the submandibular gland: clinicopathological and immunohistochemical features of 60 cases in Brazil. Archives of otolaryngology--head & neck surgery, 128(12), 1400–1403. DOI: 10.1001/archotol.128.12.1400

Bokhari M. R., Greene J. Pleomorphic Adenoma. [2020, July 10]. In: StatPearls [Internet]. Retrieved November 16, 2021 from: https://www.ncbi.nlm.nih.gov/books/NBK430829/

Center for Advanced Parotid & Facial Nerve Surgery. (2021). Parotid Tumors & Pleomorphic Adenoma. In Center for Advanced Parotid & Facial Nerve Surgery. Retrieved November 16, 2021 from: https://www.parotidsurgerymd.com/education/articles/salivary-gland-tumor/

Fondazione CNAO. (2021). Pleomorphic Adenomas. In CNAO. Retrieved November 16, 2021 from: https://fondazionecnao.it/en/pathologies-than-can-be-treated/pleomorphic-adenomas

Gaillard, F., Saber, M. (2021). Pleomorphic adenoma of the salivary glands. In Radiopaedia.org. Retrieved November 16, 2021 from: https://radiopaedia.org/articles/1893

Mayo Foundation for Medical Education and Research. (2020, July 30). Salivary gland tumors. In Mayo Clinic. Retrieved November 16, 2021 from: https://www.mayoclinic.org/diseases-conditions/salivary-gland-cancer/symptoms-causes/syc-20354151

Memorial Sloan Kettering Cancer Center. (2021). Radiation therapy for salivary gland cancer. In Memorial Sloan Kettering Cancer Center. Retrieved November 16, 2021 from: https://www.mskcc.org/cancer-care/types/salivary-gland/salivary-gland-cancer-treatment/radiation-therapy-salivary-gland