Salivary gland hyperplasia is hyperplasia of the terminal duct of salivary glands.

There are two types:

- Acinar adenomatoid hyperplasia

- Ductal adenomatoid hyperplasia

Salivary gland aplasia (also termed salivary gland agenesis) is the congenital absence of salivary glands. Usually the term relates to the absence of some or all of the major salivary glands.

It is a rare condition, and most known cases have been in association with syndromes of the ectodermal tissues, particularly the lacrimal apparatus. Example syndromes which have been reported with salivary gland aplasia include hereditary ectodermal dysplasia, mandibulofacial dysostosis and hemifacial microsomia.

The main significance of the condition is a lack of saliva, causing xerostomia (dry mouth), with accompanying susceptibility to dental caries (tooth decay), infections of the mouth, and upper respiratory tract infections (e.g., candidiasis, ascending sialadenitis, laryngitis and pharyngitis). Patients with salivary gland aplasia typically require regular application of topical fluoride to prevent tooth decay.

An "accessory salivary gland" is ectopic salivary gland tissue with a salivary gland duct system. The most common location of accessory salivary gland tissue is an extra major salivary gland in front of the parotid gland. It is typically about 3 cm or less in size, and drains into the parotid duct via a single tributary. Accessory parotid tissue is found in 21-56% of adults. Any disease process which affects the salivary glands, including cancer, may also occur within an accessory salivary gland tissue.

Ectopic salivary gland tissue which is located in sites other than the normal location is variously described as aberrant, accessory, ectopic, heterotopic or salivary gland choristoma.

Congenital disorders of the salivary glands are rare, but may include:

- Aplasia

- Atresia

- Ectopic salivary gland tissue

- Stafne defect - an uncommon condition which some consider to be an anatomic variant rather than a true disease. It is thought to be created by an ectopic portion of salivary gland tissue which causes the bone of the mandible to remodel around the tissue, creating an apparent cyst like radiolucent area on radiographs. Classically, this lesion is discovered as a chance finding, since it causes no symptoms. It appears below the inferior alveolar nerve canal in the posterior region of the mandible.

Salivary gland diseases (SGD) are multiple and varied in cause.

There are 3 paired major salivary glands in humans (the parotid gland, the submandibular gland, and the sublingual gland), as well as about 800-1000 minor salivary glands in the oral mucosa of the mouth. The parotid gland is located in front of the ear, and it secretes its mostly serous saliva via the parotid duct (Stenson duct) into the mouth, usually opening roughly opposite the maxillary second molar. The submandibular gland is located medial to the angle of the mandible, and it drains its mixture of serous and mucous saliva via the submandibular duct (Wharton duct) into the mouth, usually opening in a punctum located in the floor of mouth. The sublingual gland is located below the tongue, in the floor of the mouth. It drains its mostly mucous saliva into the mouth via about 8-20 ducts which open along the plica sublingualis (a fold of tissue under the tongue).

The function of the salivary glands is to secrete saliva, which has a lubricating function, which protects the oral mucosa of the mouth during eating and speaking. Saliva also contains digestive enzymes (e.g. salivary amylase) and has antimicrobial action and acts as a buffer. Persons with reduced salivary flow or hyposalivation often suffer from dry mouth or xerostomia, which can result in severe dental caries (tooth decay) as a result of the loss of the protective effects of saliva.

Various examples of disorders affecting the salivary glands are listed below. Some are more common than others, and they are considered according to a surgical sieve, but this list is not exhaustive. Sialadenitis is inflammation of a salivary gland, usually caused by infections, although there are other less common causes of inflammation such as irradiation, allergic reactions or trauma.

Sclerosing polycystic adenosis is a rare, reactive inflammatory condition of the salivary glands. It may be mistaken for salivary gland neoplasia. It does not seem to be a fatal disease.

Blepharophyma is chronic swelling of eyelids, mainly due to sebaceous gland hyperplasia.

Salivary gland tumours usually present as a lump or swelling in the affected gland which may or may not have been present for a long time. The lump may be accompanied by symptoms of duct blockage (e.g. xerostomia). Usually, in their early stages it is not possible to distinguish a benign tumour from a malignant one. One of the key differentiating symptoms of a malignant growth is nerve involvement. For example signs of facial nerve damage (e.g facial palsy) are associated with malignant parotid tumours. Facial pain, and paraesthesia are also very often associated with a malignant tumours. Other red flag symptoms which may suggest malignancy and warrant further investigation are fixation of the lump to the overlying skin, ulceration and induration of the mucosa.

The inflammatory lesions in Küttner's tumor may occur on one side (unilateral) or both sides (bilateral), predominantly involving the submandibular gland, but is also known to occur in other major and minor salivary glands, including the parotid gland.

Overall, salivary gland tumors are relatively rare, with approximately 2.5–3 cases per 100,000 people per year seen in the Western world; however, salivary gland malignancies account for 3–5% of all head and neck cancers. However, salivary tumors show a great deal of morphological diversity, as well as variations in the nature of the lesion (malignant vs. benign): approximately 20% to 25% of parotid tumors, 35% to 40% of submandibular tumors, and more than 90% of sublingual gland tumors are malignant. This situation underscores the diagnostic challenges in respect of Küttner's tumor; despite being benign, this condition mimics the clinical appearance of malignancy in the salivary gland.

The swollen masses of Küttner's tumor are generally painful, and patients are advised surgical resection (known as 'sialadenectomy') of a part or whole of the glandular tissue upon suspicion of possible malignancy. It is only upon post-surgical histopathology of the excised mass that the diagnosis of Küttner's tumor is definitively made.

Salivary gland hypoplasia is relative underdevelopment of the Salivary glands. Salivary gland hypoplasia tends to produce xerostomia (dry mouth), with all the associated problems this brings.

It is a rare condition, which may occur as a congenital abnormality or result from lack of neuromuscular stimulation.

It may be associated with Melkersson–Rosenthal syndrome, and hereditary ectodermal dysplasia.

Little is known about the total incidence of salivary gland tumours as most benign tumours go unrecorded in national cancer registries. The majority of salivary tumours are benign (65-70%). Within the parotid gland 75 - 80% of tumours are benign. Around 50% of the tumours found in the submandibular glands are benign. Sublingual gland tumours are very rare but if present, they are most likely to be malignant.

In the United States, salivary gland cancers are uncommon with an incidence rate of 1.7 in 100000 between 2009 and 2013.

The treatment is simple excision and exclusion of a malignant neoplasm.

Sebaceous lymphadenoma is a tissue diagnosis, e.g. salivary gland biopsy.

It may be confused with a number of benign and malignant neoplasms, including Warthin tumour, mucoepidermoid carcinoma and sebaceous lymphadenocarcinoma.

Hyperplasia is considered to be a physiological (normal) response to a specific stimulus, and the cells of a hyperplastic growth remain subject to normal regulatory control mechanisms. However, hyperplasia can also occur as a pathological response, if an excess of hormone or growth factor is responsible for the stimuli. Similarly to physiological hyperplasia, cells that undergo pathologic hyperplasia are controlled by growth hormones, and cease to proliferate if such stimuli are removed. This differs from neoplasia (the process underlying cancer and benign tumors), in which genetically abnormal cells manage to proliferate in a non-physiological manner which is unresponsive to normal stimuli. That being said, the effects caused by pathologic hyperplasia can provide a suitable foundation from which neoplastic cells may develop.

Hyperplasia (from ancient Greek ὑπέρ "huper", "over" + πλάσις "plasis", "formation"), or hypergenesis, is an increase in the amount of organic tissue that results from cell proliferation. It may lead to the gross enlargement of an organ and the term is sometimes confused with benign neoplasia or benign tumor.

Hyperplasia is a common preneoplastic response to stimulus. Microscopically, cells resemble normal cells but are increased in numbers. Sometimes cells may also be increased in size (hypertrophy). Hyperplasia is different from hypertrophy in that the adaptive cell change in hypertrophy is an increase in the "size" of cells, whereas hyperplasia involves an increase in the "number" of cells.

The histopathological features that characterize Küttner's tumor include:

- Heavy infiltration of the glandular tissue by lymphocytes (predominantly activated B-cells and helper T-cells) as well as plasma cells (collectively known as 'Lymphoplasmacytic Infiltrate').

- Presence of reactive lymphoid follicles in the infiltrate, marked by a lack of atypical lymphoid cells (this is in sharp contrast to the presentations in lymphoma).

- Atrophy and loss of acini (groups of secretory cells found in the salivary glands).

- Encasement of the glandular ducts in thick fibrous tissues, as a result of chronic presence of inflammatory infiltrate in that area - a condition known as periductal fibrosis.

- Eventual periductal and interlobular (inside the gland) sclerosis (replacement of regular tissue with hard connective tissue).

An adenoma of a parathyroid gland may secrete inappropriately high amounts of parathyroid hormone and thereby cause primary hyperparathyroidism.

See Hepatocellular adenoma. Hepatic adenomas are a rare benign tumour of the liver, which may present with hepatomegaly or other symptoms.

Epithelial-myoepithelial carcinoma, abbreviated EMCa, is a rare malignant tumour that typically arises in a salivary gland and consists of both an epithelial and myoepithelial component. They are predominantly found in the parotid gland

and represent approximately 1% of salivary gland tumours.

Hyperparathyroidism is present in ≥ 90% of patients. Asymptomatic hypercalcemia is the most common manifestation: about 25% of patients have evidence of nephrolithiasis or nephrocalcinosis. In contrast to sporadic cases of hyperparathyroidism, diffuse hyperplasia or multiple adenomas are more common than solitary adenomas.

Salivary gland oncocytomas are most common in ages 70–80, females, the parotid gland (85–90%), and are firm, slowly growing, painless masses of less than 4 cm. They may be bilateral.

EMCas are diagnosed by examination of tissue, e.g. a biopsy.

Its appearance is very similar to adenomyoepithelioma of the breast, which may be the same tumour at a different anatomical site.

The histologic differential diagnosis includes adenoid cystic carcinoma and pleomorphic adenoma.

Presents as painless, slow-growing mass that is firm or hard. Most appear clinically as mixed tumors.

An oncocytoma is a tumor made up of oncocytes, epithelial cells characterized by an excessive amount of mitochondria, resulting in an abundant acidophilic, granular cytoplasm. The cells and the tumor that they compose are often benign but sometimes may be premalignant or malignant.