Pleomorphic adenoma is the most common type of benign tumor affecting the major salivary glands. Although non-cancerous, this growth carries a measurable risk of becoming malignant over time and requires definitive treatment. Understanding the diagnosis begins with recognizing the tumor’s specific characteristics and its typical location within the head and neck. Grasping the nature of this tumor is the first step toward informed medical management.
What Is a Pleomorphic Adenoma and Where Does It Form?
A pleomorphic adenoma is a slow-growing mass originating from glandular tissue. The term “pleomorphic” refers to the tumor’s mixed cellular composition, containing both epithelial and myoepithelial elements. For this reason, the lesion is also commonly referred to as a benign mixed tumor.
The tumor typically presents as a firm, mobile, and painless lump that may have been present for many years. Approximately 85% of cases are found in the parotid gland, the largest salivary gland located just in front of the ear. The remaining cases are distributed between the submandibular gland and minor salivary glands, such as those found in the palate. While slow growth is a hallmark, any sudden increase in size or the onset of pain requires immediate medical evaluation.
Identifying the Mass: Diagnostic Steps
The diagnostic process aims to confirm the tumor’s identity and map its precise location relative to nearby structures. Imaging modalities like ultrasound are typically the first step, revealing the mass as a well-defined, hypoechoic lesion with characteristic lobulated borders. However, ultrasound alone is insufficient for surgical planning.
More advanced imaging, such as Computed Tomography (CT) or Magnetic Resonance Imaging (MRI), is used to determine the tumor’s size and its proximity to the facial nerve. The facial nerve, which controls all facial expressions, runs directly through the parotid gland, and its exact course relative to the tumor must be known before surgery. Specialized MRI sequences can help surgeons visualize the nerve’s path, often using anatomical landmarks to predict the tumor’s position (superficial versus deep lobe).
A Fine Needle Aspiration (FNA) biopsy is also a standard tool used to sample cells from the mass. This minimally invasive procedure, often performed under ultrasound guidance, provides a pre-operative diagnosis with a high degree of accuracy. Although FNA can suggest the tumor type, the definitive confirmation of a pleomorphic adenoma’s benign nature is only possible after the entire mass is surgically removed and analyzed by a pathologist.
Surgical Management and Removal
Surgical excision is the standard treatment for pleomorphic adenoma due to the risk of malignant transformation if the tumor remains. Historically, simple enucleation (shelling out the tumor) led to unacceptable recurrence rates and is now avoided. The current approach focuses on complete removal with a surrounding cuff of normal glandular tissue to prevent recurrence.
The type of surgical procedure depends on the tumor’s size and location within the parotid gland. For small masses in the superficial lobe, Extracapsular Dissection (ED) or partial superficial parotidectomy may be performed. This technique is associated with fewer temporary complications like facial nerve paresis and Frey’s syndrome. Larger tumors or those located deep to the facial nerve require a Superficial Parotidectomy (SP) or Total Parotidectomy (TP).
Preservation of the facial nerve is the paramount concern during parotid surgery. Surgeons use Intraoperative Facial Nerve Monitoring (IFNM) to electrically stimulate and identify nerve branches, ensuring their protection. Complete removal is necessary because the tumor lacks a true capsule and may have microscopic projections, known as pseudopodia, extending into the surrounding gland. If the capsule is breached or extensions are left behind, the risk of recurrence increases significantly.
Long-Term Monitoring and Potential Risks
Despite successful surgery, patients require long-term follow-up due to the potential for late recurrence and malignant change. With proper surgical technique, the recurrence rate is low, typically ranging from 1% to 5%. Recurrences can develop slowly, often appearing 5 to 15 years after the initial surgery.
Recurrence often manifests as multiple, small nodules in the surgical bed, making subsequent treatment more challenging and increasing the risk of facial nerve injury. The primary long-term risk is malignant transformation into a highly aggressive cancer known as carcinoma ex pleomorphic adenoma (CXPA). This transformation risk increases with the tumor’s duration, particularly for untreated or long-standing tumors.
Prompt treatment reduces both the risk of recurrence and the chance of malignant transformation. Regular post-operative checks, including clinical examination and periodic imaging, are recommended, sometimes for the patient’s lifetime. This vigilance ensures that any new growth is detected early, maintaining the overall positive prognosis most patients enjoy after complete surgical removal.