What is Benign Salivary Gland Tumors?
Salivary gland tumors can develop in different areas of the salivary glands. These include the parotid, submandibular, sublingual gland, and other smaller glands located in the upper part of the throat that help with digestion. Out of all these tumors, 80% are harmless but can vary in their chances of recurring or becoming cancerous. That’s why it’s crucial get the right diagnosis to determine the best treatment. In 2017, the World Health Organization (WHO) listed 11 different types of non-cancerous salivary gland tumors.
The most common harmless types are pleomorphic adenoma (PA), Warthin’s tumor (WT), and myoepithelioma (MYO). Other less common types include lymphadenoma (LA), sebaceous adenoma (SA), oncocytoma (OC), cystadenoma, sialadenoma papilliferum (SP), ductal papilloma (which can be intraductal or inverted), canalicular adenoma (CA), and basal cell adenoma (BCA).
What Causes Benign Salivary Gland Tumors?
We don’t completely understand why benign salivary tumors form, but research suggests that they might be linked to factors like radiation, smoking, physical injury, viruses, and genetics. Some studies have found a connection between salivary gland tumors and exposure to radiation in the past. In fact, roughly half of the tumors that are caused by radiation end up being a specific type of tumor called a pleomorphic adenoma.
Even though consuming tobacco and alcohol doesn’t seem to increase the risk of some types of salivary tumors, research showed a strong link between a type of tumor called Warthin’s tumor and smoking tobacco. There is also evidence that the development of a tumor type called lymphadenoma might involve the activity of a certain type of immune cell called IgG4-positive plasma cells.
A growth inside a duct, called a ductal papilloma (intraductal type), could be linked to oral injuries. These are frequently found on the lower lip, the base of the mouth, the palate, and the tongue. Another variety known as ductal papilloma (inverted type) could be related to certain types of the Human Papillomavirus (HPV), specifically types 6 and 11, along with oral injuries.
There’s a type of genetic change known as a chromosomal translocation, which involves the swapping of parts of two chromosomes, specifically, parts 8q12 and 12q13-15. These changes can activate two specific genes, PLGA1 and HMGA2. These genes are usually activated in two common types of tumors found in the salivary glands, called pleomorphic adenomas and carcinoma ex-pleomorphic adenomas.
Risk Factors and Frequency for Benign Salivary Gland Tumors
Salivary gland tumors tend to occur more frequently in women, with very few cases observed in children, accounting for less than 5% of all cases. These types of tumors typically favor benign and vascular forms. There are different types of salivary glands where these tumors can be found:
- The parotid gland is the most common location, housing 60-75% of all salivary gland tumors. Of all parotid tumors, around 85% are found in the superficial lobe, 11% in the deep lobe, and 1% in the accessory lobe. Common benign tumors in this gland include pleomorphic adenoma, Warthin’s tumor, Basal cell adenoma, Myoepithelioma, and Oncocytoma.
- The submandibular gland is host to about 10 to 15% of all salivary gland tumors. The most common benign tumor in this gland is a pleomorphic adenoma.
- Minor salivary glands account for 9.5% to 14.7% of all salivary gland tumors, usually affecting the palate equally between benign and malignant forms. Common benign tumors in these glands include pleomorphic adenoma, cystadenoma, and canalicular adenoma.
- In rare sublingual gland tumors, the most typical benign type is pleomorphic adenoma.
Pleomorphic adenoma is seen quite frequently in salivary gland tumors, resulting in 60 to 70% of all benign cases. It is more likely to occur in females between their 3rd to 5th decade of life and is most commonly found in the parotid gland.
There are other types of salivary gland tumors such as Warthin tumor (favoring males), Myoepithelioma, Lymphadenoma, Sebaceous adenoma, Oncocytoma, Cystadenoma, Sialadenoma papilliferum, Ductal papilloma (both Intraductal and Inverted types), Canalicular adenoma, and Basal cell adenoma. Each type has specific characteristics regarding location, gender predisposition, and age group most affected.
Signs and Symptoms of Benign Salivary Gland Tumors
People who have tumors in their saliva glands often have a history of a painless, noticeable lump. It’s important to ask these patients a wide range of questions about their symptoms and medical history. This might include asking about any pain, when the lump first appeared, how quickly it grew, difficulty swallowing, and any facial weakness. Past medical procedures, family history of cancer, and risk factors should also be considered – including smoking, exposure to past radiation, and workplace hazards.
When doing a physical check, a focused exam of the head and neck is necessary. Both harmless and harmful tumors can appear as painless, immovable lumps. Lumps of the parotid gland are most commonly found in the superficial lobe. Deep parotid lobe tumors often don’t show symptoms but can cause narrowing of the throat, disturbed sleep due to irregular breathing, or shortness of breath from exertion. Tumors of the submandibular gland present as swelling of the whole gland, and sublingual tumors result in generalized swelling under the tongue. Feeling the salivary lumps with both hands can help determine the size and movement of the tumor.
Different types of tumors present in unique ways:
- A pleomorphic adenoma appears as a painless, slow-growing, lump with clear boundaries. As the tumor grows, the skin above may change and develop bumps.
- Warthin’s tumor is a painless, cyst-like, squeezable, contained lump, often found at the end of the parotid. Check both sides as it can present with lumps on each side.
- Myoepithelial tumors are well-encapsulated tumors often found in the parotid.
- Sialadenoma papilleferum appears as a painless lump that grows outward, most often seen on the hard roof of the mouth (80%). It’s sometimes mistaken for a squamous cell papilloma, verrucous carcinoma, or warty dyskeratoma.
- Ductal papilloma (intraductal type) may present as a single-cell cyst-like, well-circumscribed, and encapsulated lesion in the parotid gland or on the lower lip, floor of mouth, palate, and tongue.
- Ductal papilloma (inverted type) may appear as a well-circumscribed but unencapsulated lump growing inward at the meeting point of the salivary gland and the surrounding oral mucosa.
Testing for Benign Salivary Gland Tumors
You may undergo several tests if your doctor wants to study superficial tumors in more detail:
Ultrasound: This first-step technique is non-invasive and helps in identifying where the tumor is, telling apart solid masses from fluid-filled sacs, and assisting with fine-needle aspiration biopsy—a procedure where a thin needle is inserted into a lump to extract a sample for testing.
Computerized Tomography (CT): Regular CT scans and MRI (Magnetic Resonance Imaging) share comparable sensitivity and specificity in establishing tumor location, edge, and the extent to which it has spread. Although CT scans don’t capture soft tissue details as well as MRI, they’re better for identifying if the tumor has affected the edge of the jawbone earlier.
Magnetic Resonance Imaging (MRI): If the tumor is in the deep lobe of the parotid gland (located in front of your ears), sublingual gland (under the tongue), or in the minor salivary glands, MRI can determine how far it has extended, its exact position, and how it is related to the facial nerve, which would be essential for surgical planning. MRI contains a feature that measures the movement of water in the tissue, which can be useful, especially in the case of pleomorphic adenoma (PA), a benign salivary gland tumor.
Positron Emission Tomography (PET): A PET scan might provide more accurate images of the tumor’s spread and whether cancer has spread to other parts of the body compared to a regular CT scan. However, it might not tell apart benign and malignant tumors because both pleomorphic adenoma and Warthin’s tumor (another type of benign salivary gland tumor) show high levels of sugar intake.
Biopsy: Despite the utility of imaging, it cannot definitively distinguish between benign and malignant lesions. Hence, taking a sample of your tissue for examination is crucial for forming a treatment plan. In this regard, two common procedures are fine needle aspiration (FNA) and core needle biopsy (CNB). FNA uses a thin needle to extract cells from the lump and has a good accuracy rate; however, it cannot always determine the specific type and grade of a malignant tumor. On the other hand, CNB helps obtain a larger tissue sample, enabling better understanding of tumor grading. Though, it brings more discomfort, requires local anesthesia, and has more risk such as possible injury to facial nerve and hematoma formation (a swelling of clotted blood).
Treatment Options for Benign Salivary Gland Tumors
The most effective way to treat non-cancerous salivary gland tumors is through complete surgical removal, making sure to take out all of the tumor and a little bit of the healthy tissue around it. Radiotherapy and medication typically aren’t used to treat these kinds of tumors. However, in some cases where the tumor has come back, affects the facial nerve extensively, or the patient cannot undergo surgery, radiotherapy might be used to help control the disease.
Performing surgery multiple times can increase the risk of spreading the tumor and damaging the facial nerve. The facial nerve controls the muscles of the face; damage to this nerve can cause weakness or paralysis of the facial muscles.
What else can Benign Salivary Gland Tumors be?
There are various medical concerns that might be the cause of certain symptoms. Some of these are:
- Malignant salivary gland tumors (such as mucoepidermoid carcinoma, adenoid cystic adenoma, acinic cell carcinoma, adenocarcinoma, salivary duct carcinoma, carcinoma ex pleomorphic adenoma, squamous cell carcinoma)
- Intra-parotid lymphadenopathy – enlarged lymph nodes within the parotid gland
- Neuroma of the facial nerve – a benign growth of nerve tissue
- Lymphoma – a type of blood cancer
- Paraganglioma – a rare type of tumor that arises from cells associated with the peripheral nervous system
- Developmental cyst – sacs filled with fluid that occur within the body
- Plunging ranula – a mucus-filled swelling in the neck
- Granulomatous disease (such as sarcoidosis, tuberculosis)- disorders characterised by the formation of granulomas, which are collections of immune cells that form at sites of inflammation or injury
- Sialadenitis – inflammation of salivary glands
- Sialoliths – stones in the salivary glands
- Mucocele – a type of cysts caused by a blocked salivary gland
- Hemangioma – a benign tumor made up of blood vessels.
Surgical Treatment of Benign Salivary Gland Tumors
The top choice of treatment for non-cancerous tumors found in salivary glands is usually surgical removal. However, a procedure called enucleation, which is the removal of the eye, is not generally recommended due to a high chance of the tumor returning.
For lesions in a section of the parotid gland – one of your salivary glands, situated close to your ear – the recommended treatment might be superficial parotidectomy. This surgery involves removing the superficial (outer) part of the gland. If the tumor is large, deep, or has started to spread, a total parotidectomy may be necessary. This involves removing the entire gland but preserving the facial nerve to minimize side effects.
A side effect of this kind of surgery can be greater than necessary removal of parotid tissue that results in the loss of function of the gland, damage of the facial nerve leading to paralysis, as well as changes to the contour of the face. To provide a better quality of life post-surgery, and reduce the complications, gland-preserving surgery is another approach. This is only recommended for non-cancerous tumors. The partial superficial parotidectomy is another alternative, where only a normal size margin of parotid tissue around the tumor is removed, and the facial nerve is only worked on close to the tumor.
Extracapsular dissection (ECD) is an even more conservative approach that only removes the tumor and its immediate pseudocapsule, or fake outer shell. This surgery usually does not involve dealing with the branches of the facial nerve. Overall, this technique can result in fewer complications, especially with respect to scarring, compared to the superficial parotidectomy.
When dealing with non-cancerous tumors found in the submandibular glands – another set of salivary glands, under your mouth – the common treatment is removal of the entire gland. This, however, might reduce resting saliva production. Recent studies have found that patients treated with partial sialoadenectomy, a gland-preserving surgery for the submandibular gland, had higher post-surgery saliva rates and less facial deformity. Keep in mind that patients with malignant tumors and tumors within the gland are not suitable for this type of surgery because of the risk of damage to the remaining parts of the gland.
For non-cancerous tumors of minor salivary glands located in the palate, the recommended treatment is a wide local excision – a procedure where the tumor, along with some of the tissue around it, is removed carefully. The bone of the palate that is exposed is usually left to heal naturally or it can be resected and replaced with a soft tissue flap.
What to expect with Benign Salivary Gland Tumors
The outcome of benign salivary gland tumors can vary a lot based on the many different types of tumors, each with their own rates of recurrence and chance of becoming malignant.
A recurrence rate of 1% to 5% has been reported for Pleomorphic Adenoma, a common type of salivary gland tumor, 7-10 years after initial treatment. This can be due to incomplete removal, rupture of the capsule, or other reasons. “Metastasizing” Pleomorphic Adenoma, where the tumor spreads to other parts of the body, is rare. This can develop in the bone, lung and lymph nodes, liver, and skin, even without any signs of spreading on a histology exam. Patients with this condition have a survival rate of 58% after five years. The World Health Organization reports that 40% of patients die with the disease, 47% live free of disease, and 13% live with it. A malignant transformation known as ‘Carcinoma ex-pleomorphic adenoma’ can also occur in 2% to 15% of cases.
Warthin’s tumor, another type of salivary gland tumor, has a recurrence rate of 7% to 12% due to incomplete surgical removal among other reasons. It can rarely become malignant and develop into several types of carcinomas. Warthin’s tumor may be associated with certain types of lymphomas, a kind of blood cancer.
Myoepithelioma, a rare type of salivary gland tumor, rarely recurs and malignant transformation is also extremely rare. Lymphadenoma, a tumor of the lymph gland, rarely recurs. There have been a few reported cases of it transforming into another type of cancer called sebaceous carcinoma.
Sebaceous adenoma, which forms from oil-producing glands, does not recur after surgical removal. Oncocytoma, which forms from cells of gland and other organs, can recur if not fully removed, but transformation into a malignant form is not reported.
Cystadenoma does not recur after full removal, but few cases have reported transformation into a malignant form. Sialadenoma papilliferum and ductal papilloma rarely recur and there are few cases of them becoming malignant.
Canalicular adenoma has a recurrence rate of 3%, with no reports of malignant transformation. Membranous BCA has a recurrence rate of 25%, it can transform into basal cell adenosarcoma or adenoid cystic carcinoma in up to 4.3% of cases. Other rare transformations are also possible.
Possible Complications When Diagnosed with Benign Salivary Gland Tumors
The standard treatment for all salivary gland tumors is surgery. However, this can cause a reduction in functioning tissue and saliva production, leading to dry mouth, tooth decay, bad breath, gum disease, and oral infections. Facial nerve damage (palsy) after removing the parotid gland is a potential side effect, with temporary paralysis reported in 10-65% of cases and permanent paralysis in less than 5%. Frey syndrome is another common issue following this surgery, with occurrence rates varying between 2% to 80% due to factors like time since surgery and different monitoring protocols used by surgeons.
Treatments for Frey syndrome include:
- Antiperspirant ointment
- Botulinum toxin A injections
- Barrier flaps like the superficial musculoaponeurotic system flap, temporoparietal flap, sternocleidomastoid flap, anterolateral thigh flap, or thick skin flap
Additional complications from the surgery may include accumulation of saliva in a cavity (sialocele), abnormal passage from an abscess, cavity, or hollow organ to the body surface (salivary fistula), painful lumps of nerves (neuromas) of the great auricular nerve, or numb skin in front of the ear.
Patients undergoing surgery to remove the submandibular gland could also face possible nerve damage to the tongue, or the lower edge of the facial nerve.
Radiation treatment, which is another treatment, can lead to complications such as hearing loss, chronic ear infections, ear pain, skin redness, mouth inflammation, difficulty swallowing, taste changes, oral dryness, fibrosis of soft tissue, bone death due to irradiation (osteoradionecrosis), and radiation-induced cancer. Studies have found that approximately 36% of patients developed hearing loss of 10dB and higher at 4kHz. However, complications like mandibular osteoradionecrosis and radiation-induced cancer are rare, and are seen in less than 2% and 1% of patients respectively, after 10 to 25 years.
Preventing Benign Salivary Gland Tumors
Explaining salivary tumors to patients can be complicated due to the varied types and treatment methods needed. Patients and their families should be given information about the various treatment options available, including surgery, radiation therapy if needed, and regular long-term check-ups to monitor for any returning tumors. Doctors will also discuss potential risks and side effects tied to each treatment, and assess any other existing health conditions of the patient to determine if surgery is suitable for them.
It’s very important to remember that even after treatment for non-cancerous salivary tumors, regular, long-term follow-up visits with your doctor are crucial. These tumors can return, and some types may even become cancerous over time. Therefore, it’s vital to continue with your routine check-ups, even after initial treatment has been completed.
