We have both major and minor salivary glands secreting saliva into the mouth. The minor salivary glands are many, about 8000, and are single salivary units which open directly into the mouth, mostly situated on the inside lips, cheeks, hard and soft palates. We call the major ones major because they are both bigger than the minor ones and made up of many salivary units which collect saliva into ducts which then open into the mouth. We have three pairs of these, the parotid gland in front of the ear, submandibular gland under the jaw and sublingual gland under the tongue.
The minor salivary glands and submandibular glands are largely responsible for the saliva in our mouth at rest, when we are not eating. The parotid gland works mostly when we eat and makes a different consistency of saliva than the submandibular glands.
Saliva helps to protect our teeth and prepare the food for chewing and swallowing. It also gets the digestive enzymes going. Like anything in the body we don’t realise how important it is until we lose it.
Problems with the salivary glands are usually divided into inflammatory and neoplastic causes, though rarely there are developmental issues also. The most common acute inflammatory causes are a viral but sometimes bacterial infection, duct obstruction from scarring or stones, and immune mediated inflammation. Chronic inflammatory causes are usually immune mediated or auto-immune.
80% of tumours occur in the parotid gland, 80% of these are benign and 80% are pleomorphic adenomas. They present as painless slow growing masses and have the potential for malignant transformation the bigger they get and the longer they are there. We almost always recommend excision of salivary neoplasms.
Tumours of the other major and minor salivary glands have about a 50% chance of being malignant and should always be removed. The more anterior the tumour is in the palate, the more likely it is to be malignant.
Initial investigations for suspected tumours usually include an ultrasound for the submandibular and parotid masses and a CT scan or MRI for the mouth masses. MRI is the best scan for salivary neoplasms. We like fine needle aspiration biopsies (FNAB) to exclude lymphomas and help for better pre-operative counselling.
Major salivary gland surgery is essentially nerve surgery, meaning the most critical aspect of the operation is identifying and preserving cranial nerves. Obviously we need to get the whole tumour out without compromising the capsule, but it is damage to nerves that causes morbidity. This is another area where the skill and training of the surgeon comes into play. The most important nerve for the parotid gland is the facial nerve; for the submandibular gland it is the marginal mandibular branch of the facial nerve as well as the lingual and hypoglossal nerves; and for the sublingual gland it is the lingual nerve.
Ranula is an interesting problem where saliva leaks into the surrounding tissue though tears in the duct system and looks like a cyst under the tongue. The cyst can expand into the neck. It is not a true cyst and treatment involves removal of the sublingual gland through the mouth and not removal of just the ‘cyst’ in the mouth or neck.
For major gland duct obstruction, removal of the gland is the definitive cure, but depending on the size of the stone or severity of the scarring, sialoendoscopy can be considered. This involves placement of a small camera into the natural opening of the affected gland’s duct to both diagnose and treat duct obstruction. This is done under general anaesthetic with very low risk, but definitive cure is less likely as it doesn’t eliminate the possibility of recurrence. It does however avoid the excision of the gland.
Lack of saliva can be related to side effects of medicines or radiation treatment for cancer of the mouth and throat. Excess saliva is usually related to the mouth’s inability to deal with the normal saliva properly such as with poor muscle tone or movement for any number of reasons.