Pleomorphic Adenoma: Clinical Features, Diagnosis, and Treatment
Pleomorphic adenoma is the most common benign salivary gland tumor and represents a true neoplasm. Although benign, it is locally persistent and will continue to grow—or recur—if not completely excised. Importantly, pleomorphic adenomas do not metastasize, but incomplete removal can lead to recurrence and, in rare cases, malignant transformation over time.
A thorough understanding of its clinical presentation, differential diagnosis, and appropriate surgical management is essential for optimal outcomes.
Clinical Presentation of Pleomorphic Adenoma
Pleomorphic adenomas most commonly arise in the parotid gland and the minor salivary glands of the oral cavity. In adults, approximately 75% of parotid gland tumors are pleomorphic adenomas, while about 5% are Warthin tumors. Among minor salivary gland tumors, pleomorphic adenomas account for approximately 45% of cases.
When occurring in the oral cavity, the posterior hard palate and anterior soft palate junction is the most common site of involvement.
The two most frequent clinical presentations include a painless, firm mass in the superficial lobe of the parotid gland and a painless, firm mass in the posterior palatal mucosa.
Parotid Gland Presentation
Approximately 80% of pleomorphic adenomas of the parotid gland develop in the superficial lobe. These tumors typically present as a freely movable, firm, slow-growing mass. Pain is uncommon, and facial nerve dysfunction is notably absent, which helps distinguish pleomorphic adenomas from malignant parotid tumors.
Occasionally, patients may report minor fluctuation in size, but rapid growth, pain, or facial nerve paresis should raise concern for malignancy.
Minor Palatal Salivary Gland Presentation
When pleomorphic adenomas arise in the palatal mucosa, they present as a firm, painless mass with intact overlying mucosa. The lesion often appears fixed to the palate. This apparent fixation is not due to bony invasion, as pleomorphic adenomas do not invade bone, but rather results from the inelastic nature of palatal mucosa being stretched over the expanding tumor.
Over time, pressure from the mass may cause a cupped-out resorption of underlying bone, which is a remodeling phenomenon rather than true invasion.
If the overlying mucosa is ulcerated and the ulceration cannot be explained by trauma or biopsy, the lesion should be considered malignant until proven otherwise.
Incidence and Demographics
Pleomorphic adenomas can occur at any age but are most commonly diagnosed between the ages of 30 and 50 years. There is a slight female predominance. The slow-growing nature of the tumor often leads to delayed presentation, with patients noticing a mass for months or even years before evaluation.
Differential Diagnosis
Parotid Gland Masses
The differential diagnosis for a firm parotid mass includes both benign and malignant conditions. Benign considerations include Warthin tumor, particularly in older men, and basal cell adenoma, which has a predilection for the parotid gland.
Malignant salivary gland tumors that must be considered include mucoepidermoid carcinoma, adenoid cystic carcinoma, and acinic cell carcinoma. Non-salivary gland neoplasms such as hemangiomas, lymphangiomas, lipomas, and lymphomas involving intraparotid lymph nodes may also present similarly.
Palatal Mucosal Masses
For a firm palatal mass with intact epithelium, the differential diagnosis primarily includes other minor salivary gland tumors. In order of likelihood, these include adenoid cystic carcinoma, mucoepidermoid carcinoma, and polymorphous low-grade adenocarcinoma.
Benign lesions such as canalicular adenoma should also be considered. Additionally, non-salivary tumors such as non-Hodgkin lymphoma and neurofibroma may mimic this presentation.
Treatment of Pleomorphic Adenoma
Parotid Gland Lesions
For pleomorphic adenomas involving the parotid gland, the specific location within the superficial lobe should be carefully evaluated. The recommended treatment is superficial parotidectomy, which serves as both the diagnostic biopsy and definitive treatment.
Incisional biopsy of a parotid mass is contraindicated, as tumor spillage through the biopsy tract significantly increases the risk of recurrence.
Palatal Lesions
For pleomorphic adenomas of the palate, surgical excision with 1-cm clinical margins is recommended. The excision should include the overlying surface epithelium and underlying periosteum. Removal or curettage of palatal bone is not required, as the periosteum serves as an effective anatomical barrier and the tumor does not invade bone.
Complete excision is critical to prevent recurrence.
Prognosis
When completely excised, pleomorphic adenomas have an excellent prognosis. Recurrence is most commonly associated with incomplete removal or capsular violation. Long-term follow-up is recommended due to the potential for late recurrence.
Conclusion
Pleomorphic adenoma is the most common benign salivary gland neoplasm and frequently affects the parotid gland and palatal minor salivary glands. While benign, it requires careful evaluation and complete surgical excision to prevent recurrence. Understanding its characteristic clinical presentation, differential diagnosis, and proper surgical management allows for predictable outcomes and long-term disease control.
