What is Pleomorphic Adenoma?
Pleomorphic adenoma, often referred to as benign mixed tumors (BMT’s), is the most frequent type of salivary gland tumor. The word ‘benign’ means it’s not cancerous, and ‘mixed’ refers to its origin – it grows from two different types of cells in your salivary glands, specifically epithelial and myoepithelial cells. It’s noteworthy to mention that this type of tumor makes up two-thirds of all salivary gland tumors, making it the most common kind out there.
What Causes Pleomorphic Adenoma?
The exact cause of pleomorphic adenoma, a type of tumor, is unknown. However, its occurrence has been on the rise in the past 15-20 years. This increase is linked to exposure to radiation. Some research suggests that a certain type of virus, known as simian virus (SV40), might contribute to the start or growth of this tumor. Additionally, it’s been observed that prior exposure to radiation in the head and neck areas can increase the risk of developing these types of tumors.
Risk Factors and Frequency for Pleomorphic Adenoma
Pleomorphic adenoma, a common non-cancerous tumor of the salivary gland, makes up 45-75% of all salivary gland tumors. Each year, about two to three and a half of every 100,000 people will be diagnosed with this condition. It can affect people of all age groups, but it’s most prevalent in people who are in their thirties to sixties. Slightly more women than men experience this (a 2:1 ratio). Pleomorphic adenomas are specially common in the parotid gland, which is a major salivary gland. Here’s how this tumor typically distributes among the different salivary glands:
- Parotid gland: 84%
- Submandibular gland: 8%
- Minor salivary glands: 6.5%
Signs and Symptoms of Pleomorphic Adenoma
Pleomorphic adenoma generally appears as a sole, slowly expanding, painless lump. This lump could be present undetected for a long duration. The principal indications of this ailment heavily rely on the size of the lump, its location, and its potential to turn malignant or cancerous. Should the adenoma be located in the parotid gland (the major salivary gland), there might be signs of facial muscle weakness, especially if the lump is big or if it turns cancerous. In some instances, a pleomorphic adenoma in the deep part of the parotid gland might appear as a lump in or around your throat or tonsils, which is often visible or can be felt. If you notice a quick enlargement of this lump, it may signal that it has turned malignant or cancerous.
On the other hand, tumors in smaller salivary glands might lead to a range of symptoms, which depend on the location of the tumor:
- Dysphagia or difficulty swallowing
- Hoarseness
- Dyspnea or difficulty breathing
- Issues with chewing
- Nosebleeds (medically termed as epistaxis)
Testing for Pleomorphic Adenoma
The diagnosis of a medical condition is often made through two methods: collecting and studying tissue samples, and performing imaging studies. Procedures like a fine needle aspiration (FNA), where a thin needle is used to draw out cells from a lump, and core needle biopsy, where a wider needle is used to take a small tissue sample, can be done without requiring an overnight hospital stay. These procedures carry a very low risk of spreading the tumor.
The FNA can help tell if the tumor is cancerous, with about 90% accuracy. A core needle biopsy is slightly more invasive but can provide a more accurate picture of the type of tumor, with an accuracy rate of around 97%. A method called immunohistochemistry may also be used to identify different cell types present in the tissue sample.
If you need a computed tomography or CT scan, a pleomorphic adenoma typically appears as a round mass with clear borders. If the tumor is larger, there may be signs of tissue death, and traces of calcification, or mineral deposits, are common. Smaller tumors might show an intense increase in density sooner, while in larger tumors, the increase in density is less noticeable and delayed.
An MRI is another imaging method used and gives similar results to a CT scan. Smaller lumps can appear well-circumscribed (having clear margins) and uniform, while larger ones appear less uniform.
Different MRI results can indicate different things:
* T1: usually shows low intensity.
* T2: usually shows very high intensity, especially in the myxoid type (a category of tumors), suggesting the presence of surrounding fibrous tissue.
* T1 C+ (Gd): usually shows an even increase in intensity after adding a contrast agent.
* T2 hypointensity or ill-defined margins after contrast administration can be a simple MR imaging test for cancerous parotid tumors (salivary gland tumors), with 70% sensitivity and 73% specificity.
* Post-contrast STIR images can help identify the spread of the tumor along nerve pathways if there is malignant change.
An ultrasound is another imaging technique sometimes used, where pleomorphic adenomas typically appear less dense. Such tumors may show a distinct border, with or without an increase in sound waves (acoustic enhancement) behind the tumor. Ultrasounds can also guide a biopsy or FNA, which are minimally invasive and cost-effective procedures.
Additionally, angiography (DSA), an imaging test that creates pictures of your body’s blood vessels, could also be considered.
Treatment Options for Pleomorphic Adenoma
In the past, a type of procedure known as enucleation was used to treat a condition called pleomorphic adenoma of the parotid gland. This is an issue where a benign (non-cancerous) tumour forms in one of the salivary glands. However, this procedure wasn’t very effective because the tumour frequently came back. Now, doctors prefer to use two different types of procedures: Patey’s operation, which involves removing only a portion of the gland, or parotidectomy, which is removing the whole gland. The latter option is used more often because it’s less likely for the tumor to return. Both procedures require great care to avoid damaging the facial nerve.
For tumors that form in another set of salivary glands, the submandibular glands, a simple excision procedure is conducted. In this procedure, the tumor is cut out, and nearby nerves are carefully preserved. These include the mandibular branch of the trigeminal nerve, the hypoglossal nerve, and the lingual nerve, all of which play important roles in facial sensation and movements.
When dealing with tumors in the minor salivary glands, the surgeon aims to remove the tumor with at least a five millimeter margin of healthy tissue around it. These types of tumors don’t typically spread to the bone, so it isn’t necessary to remove any bone tissue. If the tumor comes back in the same spot, it may be more difficult to treat. In such cases, the options might include just keeping an eye on it through regular check-ups, having another surgery, or using radiation therapy.
It is rare for pleomorphic adenomas to become cancerous, but the risk does go up the longer they’re left untreated. This risk is around 1.5% in the first five years and increases to 9.5% after 15 years. Because of this, doctors usually recommend removing these tumors. Other factors that could increase the risk of the tumor turning into cancer are being older in age, having had radiation therapy, the tumor being large in size, and the tumor having come back after being removed before.
What else can Pleomorphic Adenoma be?
If a person has a pleomorphic adenoma, it can look similar to a number of other conditions. These can include:
- Warthin tumor
- Nodal metastasis in the parotid gland
- Facial nerve schwannomas
- Myoepitheliomas
- Mucoepidermoid carcinoma
- Adenoid cystic carcinoma
- A wide variety of other tumors that aren’t specific to the salivary glands
The most reliable way to tell these conditions apart is through histopathology, which is the study of changes in tissues caused by disease.
